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Evaluating methods for quality of laser shock processing
Optik - International Journal for Light and Electron Optics 200 (2020) 162940
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Original research article
Evaluating methods for quality of laser shock processing ⁎
Jiajun Wua,b,c, Jibin Zhaoa,b, Hongchao Qiaoa,b, , Yinuo Zhanga,b,c, Xianliang Hua,b,c, Yongfei Yua,b,d
T
a
Shenyang Institute of Automation, Chinese Academy of Sciences, Shenyang 110016, Liaoning, China Institutes for Robotics and Intelligent Manufacturing, Chinese Academy of Sciences, Shenyang 110016, Liaoning, China University of Chinese Academy of Sciences, Beijing 100049, China d Northeastern University, Shenyang 110819, Liaoning, China b c
A R T IC LE I N F O
ABS TRA CT
Keywords: Laser shock processing Surface modification Development status Evaluating methods
Laser shock processing is an advanced surface modification technology that can effectively enhance the mechanical properties of alloy and metallic materials, such as micro-hardness, fatigue resistance and corrosion resistance, by using laser-induced plasma shock waves, and it has a wide applications in the field of aerospace industry. In this work, the development of laser shock processing is introduced briefly, the research of evaluating methods for quality of laser shock processing is summarized emphatically, and the study necessary of online measuring methods for quality of laser shock processing is indicated.
1. Introduction With the development of high-end equipment such as aerospace, nuclear power, high-iron, ships and weapon, etc. The requirements of comprehensive properties for it’s part is getting higher and higher, which require not only high geometric accuracy, but also high service performance [1,2]. In order to improve the fatigue performance and mechanical properties of alloys and metallic materials, surface hardening technologies have been widely used in industrial community without changing the performance of matrix materials [3,4]. However, the traditional surface hardening technologies such as peening [5], rolling [6] and low plasticity burnishing [7], etc, which are gradually unable to meet the requirements of production and processing for high performance materials, because the depth of the residual compressive stress layer introduced on the surface of alloys and metallic materials with the treatment of traditional surface hardening technologies can only reach 75–250 μm at most. Laser shock processing (LSP) [8,9] is an advanced surface modification technology, which can introduce residual compressive stress layer with the depth of over 1 mm, at the same time, the surface specifications of materials (such as surface roughness, surface microhardness, residual stress distribution and deformation amount of parts,etc.) can be controlled accurately due to the process parameters (such as laser energy, pulse width and path trajectory, etc.) can be set accurately. So LSP can solve these difficult problems of traditional surface hardening technologies [10]. With the rapid development of both laser equipment and laser shock processing theories, LSP becomes more and more mature gradually and plays irreplaceable roles in many industries fields. However, about the research of evaluating methods for quality of LSP, which lack of systematic theoretical summaries. In order to deepen people’s overall understanding of both LSP and the evaluating methods for quality of LSP, in this work, the development of LSP is introduced briefly, the research of evaluating methods for quality of LSP is summarized emphatically, and the study necessary of online measuring methods for quality of LSP is indicated.
⁎
Corresponding author at: Shenyang Institute of Automation, Chinese Academy of Sciences, Shenyang 110016, Liaoning, China. E-mail addresses: [email protected] (J. Wu), [email protected] (J. Zhao), [email protected] (H. Qiao).
https://doi.org/10.1016/j.ijleo.2019.162940 Received 20 March 2019; Received in revised form 4 June 2019; Accepted 11 June 2019 0030-4026/ © 2019 Published by Elsevier GmbH.
Optik - International Journal for Light and Electron Optics 200 (2020) 162940
J. Wu, et al.
2. The development of laser shock processing The conception of LSP can be traced back to the 1960s, but the real research of LSP was started in 1970s, and it received widespread attention and rapid development after the 1990s. After decades of rapid development, LSP is becoming more and more mature, and it has widely used in aerospace, defence and military, nuclear power, weapons, automobiles and many other fields. The phenomenon of laser-induced shock waves was first discovered by an American scientist White R M [11] in the early 1960s, which can produce plastic deformation in the surface of metallic material [12]. Fairand et al. first used high power pulsed laserinduced shock waves to change the microstructure and mechanical properties of 7075 aluminum alloy in 1972 at Battlle Memorial Institute with the support of the National Science Foundation of the United States, and the research results showed that the yield strength of 7075 aluminum alloy is increased by 30% with the LSP treatment, which show a great development prospects of LSP [13]. Subsequently, more and more systematic researches about LSP were studied around the world. Among them, the researches of Fabbro et al. [14–17] are the most prominent. Since 1987, with the support of French Automobile Industry Association, Fabbro et al. mainly conducted systematic studies on the mechanism and model of laser induced plasma shock wave [14,15] and the changes of material properties with LSP treatment [16,15–17], etc. With the rapid development of laser equipment especially the high-energy nanosecond pulse lasers, LSP is attracting comprehensive attentions of more and more researchers in the field of surface modification. However, according to the existing public reports, only the United States have achieved the large-scale engineering applications of LSP [18]. 3. Evaluating methods for quality of laser shock processing After the treatment of LSP, the hardness, fatigue life, fatigue strength, wear resistance, corrosion resistance, surface roughness and fracture resistance of metallic materials can be increased significantly due to the changes of microstructure and the presence of compressive residual stresses in metallic materials [19,20]. Therefore, the evaluating methods for quality of LSP can be analyzed and summarized from the four aspects of hardness, residual stress, surface roughness and microstructure (show in Fig. 1 for details), where residual stress is the most important parameter to evaluate the quality of LSP [21,22], which should be analyzed and summarized emphatically (see Section 4 for detail). 3.1. Hardness Hardness, as an important property of material to resist deformation, which determines many technological applications [23]. The hardness of materials can be improved by the treatment of LSP due to high density arrays of dislocations [24]. For polycrystalline metals, the relationship between the strength of metallic materials and the dislocation density can be described by the Taylor equation [25].
ΔH = Kh MαGb ρ
(1)
Where, △H, M, G, b, α, Kh and ρ are the strength of metallic materials, Taylor factor, shear modulus of metallic materials, Burgers vector magnitude, constant, the slope of the Hall–Petch plot [26] and dislocation density, respectively. Generally, the hardness of alloys and metallic materials are proportional to the strength of alloys and metallic materials [27]. So the changes of strength of alloys and metallic materials can reflect the changes of hardness of alloys and metallic materials. The hardness is found to increase with the increasing of dislocation density. And the increasing amount of hardness with the treatment of LSP are depended by the conditions of LSP [28]. Zhang et al. investigated the effect of the LSP treatment on micro-hardness of Ti-6Al-4V alloy [29] (shown in Fig. 2 for details), and research results showed that the micro-hardness of the as-received Ti-6Al-4V alloy can be improved through LSP, which is attributed to the high-density dislocation near the surface of the specimen after LSP. At the same time, the LSP treatments with one single laser shock and two successive laser shocks respectively provide a 22.2% and 41.7% increase in the fatigue strength as
Fig. 1. Evaluating methods for quality of LSP. 2
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Fig. 2. Micro-hardness profiles at the surfaces of two specimens of Ti-6Al-4V alloy shocked with different shocks [29].
compared with the as-received specimens [29]. Hardness is an important indices to evaluate the ability of resist residual deformation and anti-destruction of alloys and metallic materials [30]. So the quality of LSP can be indirectly evaluated by testing the hardness of materials, this method has the advantages of simple convenient and practical. 3.2. Surface roughness Surface roughness is a critical parameter to characterize the surface state of materials and evaluate the manufacturing process, which has an important influence on the fatigue performance and mechanical properties of alloys and metallic materials [31,32]. The surface characteristics of materials can be described by the statistical data of surface roughness, which can achieve the purpose of characterizing the surface integrity of the material and evaluating the quality of LSP [33] Gill et al. studied the effect of LSP treatment on the IN718 SPF superalloy [34], and the surface profiles of IN718 SPF samples with and without LSP treatment were obtained by optical interferometer test. Their experiment results (shown in Fig. 3 for details) tell us that the roughness of materials will be increased with the treatment of LSP, which directly reflect the strong plastic deformation of the alloy surface. However, LSP has obvious advantages in maintaining the smooth surface morphology of alloys and metallic materials compared to these traditional surface hardening techniques [35]. MONTROSS et al. investigated the effects of shot peening and LSP on the A356 aluminum alloy and 7075 aluminum alloy [36], and results showed that the surface roughness of A356 aluminum alloy and 7075 aluminum alloy with the treatment of shot peening are 5.8 μm and 5.7 μm, respectively, while the surface roughness of A356 aluminum alloy and 7075 aluminum alloy with the treatment of LSP are 1.1 μm and 1.3 μm, respectively. The greater the surface roughness of materials, the deeper the shock crater. The residual compressive stress of materials and the fatigue life of materials will be decreased, which will lead to the problem of stress concentration caused by the deep shock crater [37]. As for aero-engine blades, steam turbine blades and other structures, low surface roughness can reduce the air resistance and enable the structural components can meet the requirements of gas dynamics better [38]. 3.3. Microstructure In general, the macroscopic properties of materials are closely related to the microstructure of materials. At the same time, the microstructure of the materials, which determine the service performance, application range, and service life of materials [39,40]. With the effects of laser induced plasma shock wave, the strain rate of material surface can be reached over 107s−1, the surface structure will be changed, the dislocation density will be increased and various sub-structures even nano-crystallization will be
Fig. 3. Surface profiles of IN718 SPF samples with and without LSP treatment [34]. 3
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Fig. 4. Schematic diagram of compressive residual stresses induced by LSP [46].
formed, which can significantly improve the mechanical properties of materials [41,42]. Tedan et al. investigated the effect of LSP on the dislocation transitions and grain refinement of Al-Mg-Si alloy [43], and proposed the grain refinement mechanism of LSP processed 6082-T651 Al alloy. In comparison with the untreated specimen, the dislocation density after LSP was found to be increased by a factor of 2.45, with various dislocation structures as an effect of severe plastic deformation due to plasma generation and the propagation of the dominant shock waves during LSP treatment. At the same time, the accumulation of dislocation structures contributes to the formation of the ultra-fine and even nano-sized grains. Zhang et al. found that the grain of magnesium alloys can be refined by the treatment of LSP, and the refining lever of magnesium alloys is increased with the LSP times [44]. 3.4. Residual stress LSP is an advanced surface modification technology based on the laser induced plasma shock waves. In the irradiation process between metallic material with laser radiation, when the laser power density is over 1 GW/cm2, it generates, through the expansion of a high-temperature, high-pressure surface plasma, a high-intensity laser-induced plasma shock wave which induces plastic strain in the near surface of metallic materials [45]. The schematic diagram of compressive residual stresses induced by LSP is shown in Fig. 4. When the shock wave is applied to the surface of metal material, the uniaxial stress will be generated along the propogation direction of shock wave, which will lead to plastically strained (Fig. 4a). After the action of shock wave, the volume of plastically strained is restricted and counteracted by the surrounding material, which will lead to biaxial compressive residual stresses on a plane parallel to the surface (Fig. 4b) [46]. The residual compressive stress in the surface layer of materials after the treatment of LSP, which has a significant effect on the fatigue resistance of materials and is a key factor in improving the fatigue life of materials [47]. Therefor, the residual stress of materials are usually used to evaluate the quality of LSP. The measurement of residual stress has two categories: offline measuring methods and online measuring methods. At present, the most common measuring methods of residual stress test are offline measuring methods, which have become very mature. But the offline measuring methods of residual stress are inefficient and unable to change the process in time. In order to achieve large-scale industrial application of LSP, it is necessary to develop the online measuring methods of residual stress to evaluate the quality of LSP [4]. 4. Measurements of residual stress Residual stress is widely used to evaluate the quality of LSP, measurement of the residual stress can be carried out by both offline methods and online methods. 4.1. Offline measurements There are several offline measuring methods of residual stress to evaluate the quality of LSP such as hole-drilling method, X-ray stress measurement, ultrasonic method, neutron diffraction and the velocity interferometer system for any reflector (VISAR), etc. Where the hole-drilling method and X-ray stress measurement are most commonly used. 4.1.1. Hole-drilling method The hole-drilling method, also known as little hole method or hole-drilling strain-gage method, was first proposed by Mathar in 1934 [48]. With decades of development, the American Society for Testing Materials (ASTM) issued the standard ASTM E 837 (Test Method for Determining Residual Stresses by the Hole-Drilling Strain Gage Method) in 1981, which was identified as the measuring method of residual stress [49]. 4
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Fig. 5. Measuring principle of hole-drilling method [52].
The hole-drilling method is one of the most commonly used methods for measuring residual stresses at the present stage, which is based on the fact that the residual stresses can be calculated from the measurement of surface strains which result when stresses are relieved by a hole. The measuring principle of hole-drilling method is shown in Fig. 5. The basic process of this method is to drill a small hole with a diameter of 1–4 mm in the center of the special strain gauge garland at first, then need to measure the released strain, the residual stress originally present at the hole position can be finally calculated based on these strain values [50]. The equations for calculating the residual stress are as follows [51]:
σ1 =
E E (ε1 + ε2) − ⋅ (ε1 − ε2 )2 + (2ε2 − ε1 − ε3 )2 4A 4B
(2)
σ2 =
E E (ε1 + ε3) − ⋅ (ε1 − ε3 )2 + (2ε2 − ε1 − ε3 )2 4A 4B
(3)
tan 2θ =
2ε2 − ε1 − ε3 ε3 − ε1
(4)
Where ε1, ε2 and ε3 are the residual strains measured by the sensitive gates R1, R2 and R3, respectively. σ1 and σ2 are the residual principal stress. θ is the angle between the direction of the residual principal stress σ1 and the sensitive gates R1. E is the longitudinal elastic modulus (Young’s modulus). A and B are the stress release factors, which can be derived by the elastic theory or determined by test methods using standard test samples. The hole-drilling method is a powerful technique for measuring the residual stress of materials after the treatment of LSP with the advantages of simple principle, easy to operate and economical, etc. However, the method is a destructive measure method, it is easy to cause the material damage during the process of drilling, which will affect the effects of measuring. At the same time, the method also has the limitation of low strain resolution. 4.1.2. X-ray stress measurement X-ray stress measurement is a nondestructive measure method based on the Bragg’s law [53] and the elastic theory [54], which utilizes the effect of variation of the crystal lattice interplanar distance on X-ray diffraction angle. The effect of variation of the crystal lattice interplanar distance on X-ray diffraction angle is shown in Fig. 6. The crystal grains of polycrystalline metals that have experience no residual stress are composed of atoms in their thermal positions froming highly ordered planes that consitute the
Fig. 6. Effect of variation of the crystal lattice interplanar distance on X-ray diffraction angle. 5
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Fig. 7. The principle of X-ray residual stress measurement.
crystal lattice. When a stress (external force) is applied, the force is distributed among the crystal grains, the result is that the crystal lattice’s interplanar distances are increased or decreased depending on the direction and angle of the stress with respect to the crystal planes [55]. In X-ray stress measurement, residual stress is determined by measuring this variation of the lattice interplaner distance and the elastic constants of the metal. The principle of X-ray residual stress measurement is shown in Fig. 7, wherein Fig. 7(a) and (b) are the sin2ѱ method and the cosα method, respectively. The lattice interplanar distance increases or X-ray tube decreases depending on the direction and angle of lattice planes with respect to the direction of the stress [56]. In the sin2ψ method, the variation of the lattice interplaner distance is detected by changing the angle of incident X-rays (ψ0). In the standard X-ray stress measurement, using 7 different directions (angles) of an incident X-ray beam is recommended. The angles of incident X-rays and the detector for detecting diffracted X-rays have to be changed by tilting them around the X-ray irradiation spot. The basic thinking of the sin2ψ method is: the macroscopic strain ε which corresponding to the residual stress σ is taken as the statistical result of the lattice strain εj in the corresponding region, and the residual stress can be calculated by measuring the lattice strain, which according to the principle of X-ray diffraction [57]. the residual stress can be calculated by the following equation [58]:
σφ =
1 1 s 2 2
⋅
{hkl} ∂εφΨ
∂ sin2 Ψ
(5)
{hkl} Where σφ is the stress in the specified direction of the Φ angle, εφΨ is the strain of the normal (hkl) plane spacing in the direction of
1
the Φ angle and the Ψ angle, and the 2 s2 is the X-ray elastic coefficient. In the sin2ψ method, the angles of incident X-rays and the detector for detecting diffracted X-rays have to be changed by tilting them around the X-ray irradiation spot. To achieve the acurracy in operation during the measurement, the surface region of the material that irradiated by X-rays should be in a plane stress state, which require the measure system needs high stablity and tight tolerences when setting up and during the measurement process. The cosα method is an another important method for residual stress measurement, the X-rays are 360°-omnidirectionally diffracted from the sample’s polycrystalline structure around the path of incident X-rays and are detected immediately by the 2 dimensional detector. The residual stress is determined from the change to the diffraction angle due to the effect of residual stress on the interplanar distances within the grain’s crystal structure. In this method, the measure system should have the ability to detector the complete Debye-Scherrer ring in a single exposure. According to the measure message of Debye-Scherrer ring (shown in Fig. 8), the surface residual stress can be calculated by following equation [59–62].
εα =
σx 2 2(1 + ν ) [n1 − ν (n 22 + n32)] + [n 22 − ν (n32 + n12)] + τxy n1 n2 E E
σx = −
E 1 1 ∂εα1 ⎤ ⋅ ⋅ ⋅⎡ 1 + ν sin 2η sin 2Ψ0 ⎣ ∂ cos α ⎦
(6)
(7)
Where εα is the strain, σx is the residual stress, n1, n2, n3 are the orientation cosine, respectively. E is Young’s modulus, ν is the poisson's ratio. Defining
n1 = cos η sin ψ0 cos ϕ0 − sin η cos ψ0 cos ϕ0 cos α − sin η sin ϕ0 sin α
(8)
n2 = cos η sin ψ0 sin ϕ0 − sin η cos ψ0 sin ϕ0 cos α + sin η cos ϕ0 sin α
(9)
6
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Fig. 8. The distortion of Debye-Scherrer ring collected by area detector [62].
n3 = cos η cos ψ0 + sin η sin ψ0 cos α
(10)
1 [(εα − επ + α ) + (ε−α − επ − α )] 2
(11)
a1 =
The principle of cosα method tell us that the residual stress is determined by the Debye-Scherrer ring, due to there are more measuring point in the ring, so the cosα method is more reliable than the sin2ѱ method [62]. The effects of LSP treatment on the residual stress, three-point bending fatigue performance of Ti–6Al–4V alloy were studied by Zhang et al. [29]. The residual stresses at the surface and subsurface of the laser-peened specimens were determined by applying Xray stress measurement technique. Their experiment results (shown in the Fig. 9 for details) showed that the surface residual compressive stress and the fatigue life of samples are increased significantly by the treatment of LSP. 4.2. Online measurements LSP is one of the most important surface modification techniques and LSP is regarded as a competitively alternative technology, which has obtained practical industrial applications in more and more fields [63]. In order to realize the large scale application of LSP, it is very necessary to develop the non-destructive online measuring method of LSP [64]. 4.2.1. Natural frequency method The natural frequency method for quality control measuring of LSP of samples by analysis the change value of a certain stage (or multi-stage) natural frequency shifts during LSP was first proposed by the US General Electric Company in the form of patent [65]. During the treatment of LSP, the residual compressive stress will be introduced into the alloys or metallic materials, while the natural frequency of alloys or metallic materials will be changed [66]. The natural frequency experiment of turbine blades in LSP was studied
Fig. 9. Effect of laser shock peening on Ti-6Al-4V alloy [29]. 7
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Fig. 10. Effect of laser power density on plasma acoustic wave signal amplitude at different distances in air [4].
by Yang et al. [67–69], they analyzed the variation of the natural frequency and the relationship between the residual stress at LSP point and the variation of the natural frequency, their experiment results showed that both the natural frequency (first-order & second-order) and the surface compressive residual stress of the turbine blades are found to increase similarly with the increasing of laser pulse energy, the residual stress is positively correlated with the variation value of first-order natural frequency. 4.2.2. Plasma acoustic wave signal amplitude method In the process of LSP, the plasma shock wave will propagate inside the materials, which cause high strain dynamic response of the material and produce plastic deformation. So the plasma shock wave is the directed power to realize the materials’ strengthening and determine the quality of LSP [4,70]. At the same time, the plasma shock wave will propagates in the air as the form of plasma acoustic wave. The plasma acoustic wave contain much important information about LSP, which can reflect the parameter variation characteristic in the process of LSP comprehensively [4,70,71]. So the real-time online measurements for the quality of LSP can be realized by the analysis and extraction of plasma acoustic wave [4,64]. Li et al. at Air Force Engineering University (China) studied the effect of laser power density on plasma acoustic wave signal amplitude at different distances in air by the plasma acoustic wave characteristic test and analysis experiment [4]. The experiment results is showed in Fig. 10. The plasma acoustic wave signal amplitude at different distances in air are increased with the laser power density, and their growth trend are very similar, and the difference in signal amplitude of the plasma acoustic wave at the same distance, which reflected the energy at the plasma explosion moment [4]. In the process of LSP treatment on alloys or metallic materials, with the increase of the energy of shock wave, the plastic deformation of alloys or metallic materials will become more obvious, then the residual compressive stress of alloys or metallic materials will be increased, which means that the effect of LSP become better, and will significantly improve the fatigue life of alloys or metallic materials. 5. Conclusion (1) After the treatment of LSP, the hardness, surface roughness, microstruture and residual stress of alloys and metallic materials are changed to a certain extent, which play important roles in the quality of LSP. (2) The evaluating methods for quality of LSP can be analyzed and summarized from the four aspects: hardness, residual stress, surface roughness and microstructure, where residual stress is the most important parameter to evaluate the quality of LSP. (3) With the repaid development of LSP, the existing offline evaluating methods have gradually failed to satisfy the production requirements of LSP, so it is necessary to study online evaluating methods for quality of LSP. Declaration of Competing Interest The authors declare no competing financial interests. Acknowledgements This work were co-supported by the NSFC-Liaoning Province United Foundation (U1608259), National Natural Science Foundation of China (51501219), National Key Development Program of China (2016YFB1192704) and National Key Technology Research and Development Program of the Ministry of Science and Technology of China (2015BAF08B01-01). References [1] H.C. Qiao, Y. Gao, J.B. Zhao, et al., Research process of laser peening technology, Chin. J. Nonferrous Met. 25 (7) (2015) 1744–1755. [2] Y. Gao, S. Tse, D. Zhang, et al., Experimental validation of the dynamic models of a high performance workpiece table under preloaded Hertzian contact, J.
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[3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53]
Mater. Process. Technol. 129 (1) (2002) 485–489. B.S. Xu, Nano Surface Engineering, Chemical Industry Press, Beijing, 2004. Y.H. Li, Theory and Technology of Laser Shock Processing, Science Press, Beijing, 2013. Kobayashi, Matsui, Murakami, Mechanism of creation of compressive residual stress by shot peening, Int. J. Fatigue 20 (5) (1998) 351–357. D.E. Mello, J.D.B. Goncalves, et al., Influence of surface texturing and hard chromium coating on the wear of steels used in cold rolling mill rolls, Wear 302 (1-2) (2013) 1295–1309. M.R.S. John, P. Suresh, D. Raguraman, et al., Surface characteristics of low plasticity burnishing for different materials using lathe, Arab. J. Sci. Eng. 39 (4) (2014) 3209–3216. J.J. Wu, J.B. Zhao, H.C. Qiao, et al., The application status and development of laser shock processing, Opto-Electron. Eng. 45 (2) (2018) 170690. P. Peyre, R. Fabbro, P. Merrien, et al., Laser shock processing of aluminium alloys. Application to high cycle fatigue behaviour, Mater. Sci. Eng. A 210 (1–2) (1996) 102–113. U. Trdan, M. Skarba, J. Grum, Laser shock peening effect on the dislocation transitions and grain refinement of Al–Mg–Si alloy, Mater. Charact. 97 (2014) 57–68. R.M. White, Elastic wave generation by electron bombardment or electromagnetic wave absorption, J. Appl. Phys. 34 (7) (1963) 2123–2124. Y.K. Zhang, J.Z. Lu, K.Y. Luo, General Introduction// Laser Shock Processing of FCC Metals, Springer Berlin, Heidelberg, 2013, pp. 1–14. B.P. Fairand, B.A. Wilcox, W.J. Gallagher, et al., Laser shock-induced microstructural and mechanical property changes in 7075 aluminum, J. Appl. Phys. 43 (9) (1972) 3893–3895. R. Fabbro, J. Fournier, P. Ballard, et al., Physical study of laser-produced plasma in confined geometry, J. Appl. Phys. 68 (2) (1990) 775–784. L. Tollier, R. Fabbro, E. Bartnicki, Study of the laser-driven spallation process by the velocity interferometer system for any reflector interferometry technique. I. Laser-shock characterization, J. Appl. Phys. 83 (3) (1998) 1224–1230. P. Peyre, R. Fabbro, L. Berthe, et al., Laser shock processing of materials, physical processes involved and examples of applications, J. Laser Appl. 8 (3) (2012) 135–141. Peyre, Berthe, Scherpereel, et al., Laser-shock processing of aluminium-coated 55C1 steel in water-confinement regime, characterization and application to highcycle fatigue behaviour, J. Mater. Sci. 33 (6) (1998) 1421–1429. G.X. Lu, T. Jin, Y.Z. Zhou, et al., Research progress of applications of laser shock processing on superalloys, Chin. J. Nonferrous Met. 28 (9) (2018) 1755–1764. Y.Q. Li, W.F. He, X.F. Nie, et al., Laser shock peening of GH4133 nickel-based superalloy, Rare Met. Mater. Eng. 44 (6) (2015) 1517–1521. Y. Lu, J.B. Zhao, H.C. Qiao, et al., Strengthening mechanism of TC17 titanium alloy warm laser shock peening, Surf. Technol. 47 (2) (2018) 1–7. T. Takata, M. Enoki, P. Chivavibul, et al., Acoustic emission monitoring of laser shock peening by detection of underwater acoustic wave, Mater. Trans. 57 (5) (2016) 674–680. B. Ahmad, M.E. Fitzpatrick, Analysis of residual stresses in laser-shock-peened and shot-peened marine steel welds, Metall. Mater. Trans. A 48 (2) (2017) 759–770. A.R. Oganov, A.O. Lyakhov, Towards the theory of hardness of materials, J. Superhard Mater. 32 (3) (2010) 143–147. P. Merrien, Laser shock processing of aluminium alloys. Application to high cycle fatigue behaviour, Mater. Sci. Eng. A 210 (1–2) (1996) 102–113. H. Luong, M.R. Hill, The effects of laser peening on high-cycle fatigue in 7085-T7651 aluminum alloy, Mater. Sci. Eng. A 477 (1) (2008) 208–216. C.S. Pande, K.P. Cooper, Nanomechanics of Hall–Petch relationship in nanocrystalline materials, Prog. Mater. Sci. 54 (6) (2009) 689–706. A.I. Slutsker, A.B. Sinani, V.I. Betekhtin, et al., Hardness of microporous SiC ceramics, Tech. Phys. 53 (12) (2008) 1591–1596. N.G. Guo, X.M. Luo, Y.Q. Hua, The effects of laser shock processing on microstructure and properties of metal, Mater. Sci. Eng. R Rep. 20 (6) (2006) 10–13. X.C. Zhang, Y.K. Zhang, J.Z. Lu, et al., Improvement of fatigue life of Ti–6Al–4V alloy by laser shock peening, Mater. Sci. Eng.: A (Structural Materials: Properties, Microstructure and Processing) 527 (15) (2010) 3411–3415. Iman Hejazi, Seyyed Ehsan Mirsalehi, Mechanical and metallurgical characterization of AA6061 friction stir welded joints using microhardness map, Trans. Nonferrous Met. Soc. China 26 (9) (2016) 2313–2319. Charles S. Montross, T. Wei, et al., Laser shock processing and its effects on microstructure and properties of metal alloys: a review, Int. J. Fatigue 24 (10) (2002) 1021–1036. R. Zhu, Y.K. Zhang, G.F. Su, et al., Finite element analysis of surface roughness generated by multiple laser shock peening, Rare Met. Mater. Eng. 47 (1) (2018) 33–38. C. Ye, S. Suslov, B.J. Kim, et al., Fatigue performance improvement in AISI 4140 steel by dynamic strain aging and dynamic precipitation during warm laser shock peening, Acta Mater. 59 (3) (2011) 1014–1025. A. Gill, A. Telang, S.R. Mannava, et al., Comparison of mechanisms of advanced mechanical surface treatments in nickel-based superalloy, Mater. Sci. Eng. A 576 (8) (2013) 346–355. G.X. Lu, Effect of Laser Shock on Surface Topography, Microstructure and Mechanical Behaviors of Superalloys, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, 2017. Charles S. Montross, T. Wei, et al., Laser shock processing and its effects on microstructure and properties of metal alloys: a review, Int. J. Fatigue 24 (10) (2002) 1021–1036. Y.D. Chen, J.Z. Pan, P.T. Liu, et al., Effects of surface roughness on bending fatigue properties of motor train unit wheel steel, Surf. Technol. 46 (2) (2017) 172–177. W.L. Yuan, Gas Dynamics, Science Press, Beijing, 2013. B. Zhou, T. Zhang, F. Lin, et al., Microstructures and mechanical properties of Ti6Al4V and 316L stainless steel impeller body made by electron beam selective melting, Rare Met. Mater. Eng. 47 (1) (2018) 175–180. D.E.R. Brockmann, T.E.M. Staab, F.G. Raether, The influence of sintering additives on the microstructure and material properties of silicon nitride ceramics investigated by advanced simulation tools, Phys. Status Solidi 214 (2017) 1600634. S. Amini, M. Dadkhah, R. Teimouri, Study on laser shock penning of Incoloy 800 super alloy, Opt. – Int. J. Light Electron. Opt. 140 (2017) 308–316. Y.E. Chang, Sergey Suslov, et al., Bimodal nanocrystallization of NiTi shape memory alloy by laser shock peening and post-deformation annealing, Acta Mater. 59 (19) (2011) 7219–7227. U. Trdan, M. Skarba, J. Grum, Laser shock peening effect on the dislocation transitions and grain refinement of Al–Mg–Si alloy, Mater. Charact. 97 (2014) 57–68. Y.K. Zhang, J. You, J.Z. Lu, et al., Effects of laser shock processing on stress corrosion cracking susceptibility of AZ31B magnesium alloy, Surf. Coat. Technol. 204 (24) (2010) 3947–3953. Peyre, Berthe, Scherpereel, et al., Laser-shock processing of aluminium-coated 55C1 steel in water-confinement regime, characterization and application to highcycle fatigue behaviour, J. Mater. Sci. 33 (6) (1998) 1421–1429. P. Peyre, R. Fabbro, Laser shock processing: a review of the physics and applications, Opt. Quantum Electron. 27 (12) (1995) 1213–1229. M.M. Quazi, M.A. Fazal, A.S.M.A. Haseeb, et al., Laser-based surface modifications of aluminum and its alloys, Crit. Rev. Solid State Mater. Sci. 41 (2) (2016) 106–131. J. Mathar, Determination of inherent stresses by measuring deformations of drilled holes, Tech. Rep. Arch. Image Library 56 (4) (1934) 249–254. Beghini, Bertini, Raffaelli, Numerical analysis of plasticity effects in the hole-drilling residual stress measurement, J. Test. Eval. 22 (6) (1994) 522–529. Y.Y. Santana, J.G.L. Barbera-Sosa, M.H. Staia, et al., Measurement of residual stress in thermal spray coatings by the incremental hole drilling method, Surf. Coat. Technol. 201 (5) (2006) 2092–2098. Y. Zhang, Y.P. Zhao, An effective method of determining the residual stress gradients in a micro-cantilever, Microsyst. Technol. 12 (4) (2006) 357–364. B.S. Yin, H.P. Zhao, X.H. Wang, Basic knowledge of residual stress determination—lecture No.7 residual stress determination by mechanical method, Phys. Test. Chem. Anal. (Part A: Physical Testing) 43 (12) (2007) 50–54. S. Hannusch, M. Stockmann, J. Ihlemann, Experimental method for residual stress analysis with fibre Bragg grating sensors, Mater. Today Proc. 3 (4) (2016) 979–982.
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J. Wu, et al.
[54] M.W. Lu, X.F. Luo, Foundation of Elasticity Theory, Tsinghua University Press, Beijing, 1990. [55] H. Suzuki, K. Akita, H. Misawa, X-ray stress measurement method for single crystal with unknown stress-free lattice parameter, J. Appl. Phys. 42 (5A) (2003) 2876–2880. [56] K.M. Lü, Basic knowledge of residual stress determination—lecture No.4 Stress determination method by X-ray(1), Phys. Test. Chem. Anal. (Part A: Physical Testing) 43 (7) (2007) 349–354. [57] C.H. Ma, J.H. Huang, H. Chen, Residual stress measurement in textured thin film by grazing-incidence X-ray diffraction, Thin Solid Films 418 (2) (2002) 73–78. [58] D.Q. Zhang, J.W. He, X-ray Diffraction Analysis and Effect of Residual Stress in Materials, Xi’an Jiaotong University Press, Xi’an, 1999. [59] M. Gelfi, E. Bontempi, R. Roberti, et al., X-ray diffraction Debye Ring Analysis for STress measurement (DRAST): a new method to evaluate residual stresses, Acta Mater. 52 (3) (2004) 583–589. [60] C.H. Ma, J.H. Huang, H. Chen, Residual stress measurement in textured thin film by grazing-incidence X-ray diffraction, Thin Solid Films 418 (2) (2002) 73–78. [61] J. Lin, N. Ma, Y. Lei, et al., Measurement of residual stress in arc welded lap joints by cosα X-ray diffraction method, J. Mater. Process. Technol. 243 (2017) 387–394. [62] T. Sasaki, K. Koda, Y. Fujimoto, et al., X-ray residual stress analysis of stainless steel using cosα method, Adv. Mat. Res. 922 (2014) 167–172. [63] L. Zhang, K.Y. Luo, J.Z. Lu, et al., Effects of laser shock processing with different shocked paths on mechanical properties of laser welded ANSI 304 stainless steel joint, Mater. Sci. Eng.: A (Structural Materials: Properties, Microstructure and Processing) 528 (13–14) (2011) 4652–4657. [64] H.C. Qiao, J.B. Zhao, Design and implementation of online laser peening detection system, Laser Optoelectron. Prog. 50 (7) (2013) 47–51. [65] B.M. Davis, R.D. Mcclain, U.W. Suh, et al., Real Time Laser Shock Peening Quality Assurance by Natural Frequency Analysis: US, (2005). [66] X.Q. Zhang, J.Z. Zhou, Z.T. Yang, et al., A technology of laser shot processing strengthening to improve fatigue life of components, Turbine Technol. 47 (3) (2005) 238–240. [67] H.L. Yang, J.M. Liang, Research on the quality inspection for blades’ laser shock processing, J. Tianjin Chengjian Univ. 16 (1) (2010) 37–40. [68] J.M. Liang, H.L. Yang, S.K. Zou, The processing monitor for aero-engine blades’ laser shock processing, Aeronaut. Sci. Technol. (6) (2008) 82–84. [69] S.K. Zou, Z.W. Cao, H.L. Yang, Natural frequency test of turbine blades in laser shock processing, China Mech. Eng. (6) (2010) 648–651. [70] J.J. Wu, J.B. Zhao, H.C. Qiao, et al., Acoustic wave detection of laser shock peening, Opto-Electronic Adv. 1 (9) (2018) 180016. [71] C.L. Qiu, L. Cheng, W.F. He, A condition monitoring method for laser peening based on the correlation between the adjacent aata, J. Vib. Shock 36 (4) (2017) 139–143. Jiajun Wu received his B.S. degree in Process Equipment and Control Engineering from Beijing University of Chemical Technology, Beijing, China, in 2016. Currently he is pursuing Ph.D. degree at Shenyang Institute of Automation, Chinese Academy of Sciences. His main research interest is laser shock processing online monitoring technology. Jibin Zhao is a professor in Shenyang Institute of Automation, Chinese Academy of Science. His research interests include computer-aided design, rapid prototyping and surface engineering. Hongchao Qiao is a professor in Shenyang Institute of Automation, Chinese Academy of Science. His research interests include laser shock processing and laser welding.
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Original research article
Evaluating methods for quality of laser shock processing ⁎
Jiajun Wua,b,c, Jibin Zhaoa,b, Hongchao Qiaoa,b, , Yinuo Zhanga,b,c, Xianliang Hua,b,c, Yongfei Yua,b,d
T
a
Shenyang Institute of Automation, Chinese Academy of Sciences, Shenyang 110016, Liaoning, China Institutes for Robotics and Intelligent Manufacturing, Chinese Academy of Sciences, Shenyang 110016, Liaoning, China University of Chinese Academy of Sciences, Beijing 100049, China d Northeastern University, Shenyang 110819, Liaoning, China b c
A R T IC LE I N F O
ABS TRA CT
Keywords: Laser shock processing Surface modification Development status Evaluating methods
Laser shock processing is an advanced surface modification technology that can effectively enhance the mechanical properties of alloy and metallic materials, such as micro-hardness, fatigue resistance and corrosion resistance, by using laser-induced plasma shock waves, and it has a wide applications in the field of aerospace industry. In this work, the development of laser shock processing is introduced briefly, the research of evaluating methods for quality of laser shock processing is summarized emphatically, and the study necessary of online measuring methods for quality of laser shock processing is indicated.
1. Introduction With the development of high-end equipment such as aerospace, nuclear power, high-iron, ships and weapon, etc. The requirements of comprehensive properties for it’s part is getting higher and higher, which require not only high geometric accuracy, but also high service performance [1,2]. In order to improve the fatigue performance and mechanical properties of alloys and metallic materials, surface hardening technologies have been widely used in industrial community without changing the performance of matrix materials [3,4]. However, the traditional surface hardening technologies such as peening [5], rolling [6] and low plasticity burnishing [7], etc, which are gradually unable to meet the requirements of production and processing for high performance materials, because the depth of the residual compressive stress layer introduced on the surface of alloys and metallic materials with the treatment of traditional surface hardening technologies can only reach 75–250 μm at most. Laser shock processing (LSP) [8,9] is an advanced surface modification technology, which can introduce residual compressive stress layer with the depth of over 1 mm, at the same time, the surface specifications of materials (such as surface roughness, surface microhardness, residual stress distribution and deformation amount of parts,etc.) can be controlled accurately due to the process parameters (such as laser energy, pulse width and path trajectory, etc.) can be set accurately. So LSP can solve these difficult problems of traditional surface hardening technologies [10]. With the rapid development of both laser equipment and laser shock processing theories, LSP becomes more and more mature gradually and plays irreplaceable roles in many industries fields. However, about the research of evaluating methods for quality of LSP, which lack of systematic theoretical summaries. In order to deepen people’s overall understanding of both LSP and the evaluating methods for quality of LSP, in this work, the development of LSP is introduced briefly, the research of evaluating methods for quality of LSP is summarized emphatically, and the study necessary of online measuring methods for quality of LSP is indicated.
⁎
Corresponding author at: Shenyang Institute of Automation, Chinese Academy of Sciences, Shenyang 110016, Liaoning, China. E-mail addresses: [email protected] (J. Wu), [email protected] (J. Zhao), [email protected] (H. Qiao).
https://doi.org/10.1016/j.ijleo.2019.162940 Received 20 March 2019; Received in revised form 4 June 2019; Accepted 11 June 2019 0030-4026/ © 2019 Published by Elsevier GmbH.
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2. The development of laser shock processing The conception of LSP can be traced back to the 1960s, but the real research of LSP was started in 1970s, and it received widespread attention and rapid development after the 1990s. After decades of rapid development, LSP is becoming more and more mature, and it has widely used in aerospace, defence and military, nuclear power, weapons, automobiles and many other fields. The phenomenon of laser-induced shock waves was first discovered by an American scientist White R M [11] in the early 1960s, which can produce plastic deformation in the surface of metallic material [12]. Fairand et al. first used high power pulsed laserinduced shock waves to change the microstructure and mechanical properties of 7075 aluminum alloy in 1972 at Battlle Memorial Institute with the support of the National Science Foundation of the United States, and the research results showed that the yield strength of 7075 aluminum alloy is increased by 30% with the LSP treatment, which show a great development prospects of LSP [13]. Subsequently, more and more systematic researches about LSP were studied around the world. Among them, the researches of Fabbro et al. [14–17] are the most prominent. Since 1987, with the support of French Automobile Industry Association, Fabbro et al. mainly conducted systematic studies on the mechanism and model of laser induced plasma shock wave [14,15] and the changes of material properties with LSP treatment [16,15–17], etc. With the rapid development of laser equipment especially the high-energy nanosecond pulse lasers, LSP is attracting comprehensive attentions of more and more researchers in the field of surface modification. However, according to the existing public reports, only the United States have achieved the large-scale engineering applications of LSP [18]. 3. Evaluating methods for quality of laser shock processing After the treatment of LSP, the hardness, fatigue life, fatigue strength, wear resistance, corrosion resistance, surface roughness and fracture resistance of metallic materials can be increased significantly due to the changes of microstructure and the presence of compressive residual stresses in metallic materials [19,20]. Therefore, the evaluating methods for quality of LSP can be analyzed and summarized from the four aspects of hardness, residual stress, surface roughness and microstructure (show in Fig. 1 for details), where residual stress is the most important parameter to evaluate the quality of LSP [21,22], which should be analyzed and summarized emphatically (see Section 4 for detail). 3.1. Hardness Hardness, as an important property of material to resist deformation, which determines many technological applications [23]. The hardness of materials can be improved by the treatment of LSP due to high density arrays of dislocations [24]. For polycrystalline metals, the relationship between the strength of metallic materials and the dislocation density can be described by the Taylor equation [25].
ΔH = Kh MαGb ρ
(1)
Where, △H, M, G, b, α, Kh and ρ are the strength of metallic materials, Taylor factor, shear modulus of metallic materials, Burgers vector magnitude, constant, the slope of the Hall–Petch plot [26] and dislocation density, respectively. Generally, the hardness of alloys and metallic materials are proportional to the strength of alloys and metallic materials [27]. So the changes of strength of alloys and metallic materials can reflect the changes of hardness of alloys and metallic materials. The hardness is found to increase with the increasing of dislocation density. And the increasing amount of hardness with the treatment of LSP are depended by the conditions of LSP [28]. Zhang et al. investigated the effect of the LSP treatment on micro-hardness of Ti-6Al-4V alloy [29] (shown in Fig. 2 for details), and research results showed that the micro-hardness of the as-received Ti-6Al-4V alloy can be improved through LSP, which is attributed to the high-density dislocation near the surface of the specimen after LSP. At the same time, the LSP treatments with one single laser shock and two successive laser shocks respectively provide a 22.2% and 41.7% increase in the fatigue strength as
Fig. 1. Evaluating methods for quality of LSP. 2
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Fig. 2. Micro-hardness profiles at the surfaces of two specimens of Ti-6Al-4V alloy shocked with different shocks [29].
compared with the as-received specimens [29]. Hardness is an important indices to evaluate the ability of resist residual deformation and anti-destruction of alloys and metallic materials [30]. So the quality of LSP can be indirectly evaluated by testing the hardness of materials, this method has the advantages of simple convenient and practical. 3.2. Surface roughness Surface roughness is a critical parameter to characterize the surface state of materials and evaluate the manufacturing process, which has an important influence on the fatigue performance and mechanical properties of alloys and metallic materials [31,32]. The surface characteristics of materials can be described by the statistical data of surface roughness, which can achieve the purpose of characterizing the surface integrity of the material and evaluating the quality of LSP [33] Gill et al. studied the effect of LSP treatment on the IN718 SPF superalloy [34], and the surface profiles of IN718 SPF samples with and without LSP treatment were obtained by optical interferometer test. Their experiment results (shown in Fig. 3 for details) tell us that the roughness of materials will be increased with the treatment of LSP, which directly reflect the strong plastic deformation of the alloy surface. However, LSP has obvious advantages in maintaining the smooth surface morphology of alloys and metallic materials compared to these traditional surface hardening techniques [35]. MONTROSS et al. investigated the effects of shot peening and LSP on the A356 aluminum alloy and 7075 aluminum alloy [36], and results showed that the surface roughness of A356 aluminum alloy and 7075 aluminum alloy with the treatment of shot peening are 5.8 μm and 5.7 μm, respectively, while the surface roughness of A356 aluminum alloy and 7075 aluminum alloy with the treatment of LSP are 1.1 μm and 1.3 μm, respectively. The greater the surface roughness of materials, the deeper the shock crater. The residual compressive stress of materials and the fatigue life of materials will be decreased, which will lead to the problem of stress concentration caused by the deep shock crater [37]. As for aero-engine blades, steam turbine blades and other structures, low surface roughness can reduce the air resistance and enable the structural components can meet the requirements of gas dynamics better [38]. 3.3. Microstructure In general, the macroscopic properties of materials are closely related to the microstructure of materials. At the same time, the microstructure of the materials, which determine the service performance, application range, and service life of materials [39,40]. With the effects of laser induced plasma shock wave, the strain rate of material surface can be reached over 107s−1, the surface structure will be changed, the dislocation density will be increased and various sub-structures even nano-crystallization will be
Fig. 3. Surface profiles of IN718 SPF samples with and without LSP treatment [34]. 3
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Fig. 4. Schematic diagram of compressive residual stresses induced by LSP [46].
formed, which can significantly improve the mechanical properties of materials [41,42]. Tedan et al. investigated the effect of LSP on the dislocation transitions and grain refinement of Al-Mg-Si alloy [43], and proposed the grain refinement mechanism of LSP processed 6082-T651 Al alloy. In comparison with the untreated specimen, the dislocation density after LSP was found to be increased by a factor of 2.45, with various dislocation structures as an effect of severe plastic deformation due to plasma generation and the propagation of the dominant shock waves during LSP treatment. At the same time, the accumulation of dislocation structures contributes to the formation of the ultra-fine and even nano-sized grains. Zhang et al. found that the grain of magnesium alloys can be refined by the treatment of LSP, and the refining lever of magnesium alloys is increased with the LSP times [44]. 3.4. Residual stress LSP is an advanced surface modification technology based on the laser induced plasma shock waves. In the irradiation process between metallic material with laser radiation, when the laser power density is over 1 GW/cm2, it generates, through the expansion of a high-temperature, high-pressure surface plasma, a high-intensity laser-induced plasma shock wave which induces plastic strain in the near surface of metallic materials [45]. The schematic diagram of compressive residual stresses induced by LSP is shown in Fig. 4. When the shock wave is applied to the surface of metal material, the uniaxial stress will be generated along the propogation direction of shock wave, which will lead to plastically strained (Fig. 4a). After the action of shock wave, the volume of plastically strained is restricted and counteracted by the surrounding material, which will lead to biaxial compressive residual stresses on a plane parallel to the surface (Fig. 4b) [46]. The residual compressive stress in the surface layer of materials after the treatment of LSP, which has a significant effect on the fatigue resistance of materials and is a key factor in improving the fatigue life of materials [47]. Therefor, the residual stress of materials are usually used to evaluate the quality of LSP. The measurement of residual stress has two categories: offline measuring methods and online measuring methods. At present, the most common measuring methods of residual stress test are offline measuring methods, which have become very mature. But the offline measuring methods of residual stress are inefficient and unable to change the process in time. In order to achieve large-scale industrial application of LSP, it is necessary to develop the online measuring methods of residual stress to evaluate the quality of LSP [4]. 4. Measurements of residual stress Residual stress is widely used to evaluate the quality of LSP, measurement of the residual stress can be carried out by both offline methods and online methods. 4.1. Offline measurements There are several offline measuring methods of residual stress to evaluate the quality of LSP such as hole-drilling method, X-ray stress measurement, ultrasonic method, neutron diffraction and the velocity interferometer system for any reflector (VISAR), etc. Where the hole-drilling method and X-ray stress measurement are most commonly used. 4.1.1. Hole-drilling method The hole-drilling method, also known as little hole method or hole-drilling strain-gage method, was first proposed by Mathar in 1934 [48]. With decades of development, the American Society for Testing Materials (ASTM) issued the standard ASTM E 837 (Test Method for Determining Residual Stresses by the Hole-Drilling Strain Gage Method) in 1981, which was identified as the measuring method of residual stress [49]. 4
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Fig. 5. Measuring principle of hole-drilling method [52].
The hole-drilling method is one of the most commonly used methods for measuring residual stresses at the present stage, which is based on the fact that the residual stresses can be calculated from the measurement of surface strains which result when stresses are relieved by a hole. The measuring principle of hole-drilling method is shown in Fig. 5. The basic process of this method is to drill a small hole with a diameter of 1–4 mm in the center of the special strain gauge garland at first, then need to measure the released strain, the residual stress originally present at the hole position can be finally calculated based on these strain values [50]. The equations for calculating the residual stress are as follows [51]:
σ1 =
E E (ε1 + ε2) − ⋅ (ε1 − ε2 )2 + (2ε2 − ε1 − ε3 )2 4A 4B
(2)
σ2 =
E E (ε1 + ε3) − ⋅ (ε1 − ε3 )2 + (2ε2 − ε1 − ε3 )2 4A 4B
(3)
tan 2θ =
2ε2 − ε1 − ε3 ε3 − ε1
(4)
Where ε1, ε2 and ε3 are the residual strains measured by the sensitive gates R1, R2 and R3, respectively. σ1 and σ2 are the residual principal stress. θ is the angle between the direction of the residual principal stress σ1 and the sensitive gates R1. E is the longitudinal elastic modulus (Young’s modulus). A and B are the stress release factors, which can be derived by the elastic theory or determined by test methods using standard test samples. The hole-drilling method is a powerful technique for measuring the residual stress of materials after the treatment of LSP with the advantages of simple principle, easy to operate and economical, etc. However, the method is a destructive measure method, it is easy to cause the material damage during the process of drilling, which will affect the effects of measuring. At the same time, the method also has the limitation of low strain resolution. 4.1.2. X-ray stress measurement X-ray stress measurement is a nondestructive measure method based on the Bragg’s law [53] and the elastic theory [54], which utilizes the effect of variation of the crystal lattice interplanar distance on X-ray diffraction angle. The effect of variation of the crystal lattice interplanar distance on X-ray diffraction angle is shown in Fig. 6. The crystal grains of polycrystalline metals that have experience no residual stress are composed of atoms in their thermal positions froming highly ordered planes that consitute the
Fig. 6. Effect of variation of the crystal lattice interplanar distance on X-ray diffraction angle. 5
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Fig. 7. The principle of X-ray residual stress measurement.
crystal lattice. When a stress (external force) is applied, the force is distributed among the crystal grains, the result is that the crystal lattice’s interplanar distances are increased or decreased depending on the direction and angle of the stress with respect to the crystal planes [55]. In X-ray stress measurement, residual stress is determined by measuring this variation of the lattice interplaner distance and the elastic constants of the metal. The principle of X-ray residual stress measurement is shown in Fig. 7, wherein Fig. 7(a) and (b) are the sin2ѱ method and the cosα method, respectively. The lattice interplanar distance increases or X-ray tube decreases depending on the direction and angle of lattice planes with respect to the direction of the stress [56]. In the sin2ψ method, the variation of the lattice interplaner distance is detected by changing the angle of incident X-rays (ψ0). In the standard X-ray stress measurement, using 7 different directions (angles) of an incident X-ray beam is recommended. The angles of incident X-rays and the detector for detecting diffracted X-rays have to be changed by tilting them around the X-ray irradiation spot. The basic thinking of the sin2ψ method is: the macroscopic strain ε which corresponding to the residual stress σ is taken as the statistical result of the lattice strain εj in the corresponding region, and the residual stress can be calculated by measuring the lattice strain, which according to the principle of X-ray diffraction [57]. the residual stress can be calculated by the following equation [58]:
σφ =
1 1 s 2 2
⋅
{hkl} ∂εφΨ
∂ sin2 Ψ
(5)
{hkl} Where σφ is the stress in the specified direction of the Φ angle, εφΨ is the strain of the normal (hkl) plane spacing in the direction of
1
the Φ angle and the Ψ angle, and the 2 s2 is the X-ray elastic coefficient. In the sin2ψ method, the angles of incident X-rays and the detector for detecting diffracted X-rays have to be changed by tilting them around the X-ray irradiation spot. To achieve the acurracy in operation during the measurement, the surface region of the material that irradiated by X-rays should be in a plane stress state, which require the measure system needs high stablity and tight tolerences when setting up and during the measurement process. The cosα method is an another important method for residual stress measurement, the X-rays are 360°-omnidirectionally diffracted from the sample’s polycrystalline structure around the path of incident X-rays and are detected immediately by the 2 dimensional detector. The residual stress is determined from the change to the diffraction angle due to the effect of residual stress on the interplanar distances within the grain’s crystal structure. In this method, the measure system should have the ability to detector the complete Debye-Scherrer ring in a single exposure. According to the measure message of Debye-Scherrer ring (shown in Fig. 8), the surface residual stress can be calculated by following equation [59–62].
εα =
σx 2 2(1 + ν ) [n1 − ν (n 22 + n32)] + [n 22 − ν (n32 + n12)] + τxy n1 n2 E E
σx = −
E 1 1 ∂εα1 ⎤ ⋅ ⋅ ⋅⎡ 1 + ν sin 2η sin 2Ψ0 ⎣ ∂ cos α ⎦
(6)
(7)
Where εα is the strain, σx is the residual stress, n1, n2, n3 are the orientation cosine, respectively. E is Young’s modulus, ν is the poisson's ratio. Defining
n1 = cos η sin ψ0 cos ϕ0 − sin η cos ψ0 cos ϕ0 cos α − sin η sin ϕ0 sin α
(8)
n2 = cos η sin ψ0 sin ϕ0 − sin η cos ψ0 sin ϕ0 cos α + sin η cos ϕ0 sin α
(9)
6
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Fig. 8. The distortion of Debye-Scherrer ring collected by area detector [62].
n3 = cos η cos ψ0 + sin η sin ψ0 cos α
(10)
1 [(εα − επ + α ) + (ε−α − επ − α )] 2
(11)
a1 =
The principle of cosα method tell us that the residual stress is determined by the Debye-Scherrer ring, due to there are more measuring point in the ring, so the cosα method is more reliable than the sin2ѱ method [62]. The effects of LSP treatment on the residual stress, three-point bending fatigue performance of Ti–6Al–4V alloy were studied by Zhang et al. [29]. The residual stresses at the surface and subsurface of the laser-peened specimens were determined by applying Xray stress measurement technique. Their experiment results (shown in the Fig. 9 for details) showed that the surface residual compressive stress and the fatigue life of samples are increased significantly by the treatment of LSP. 4.2. Online measurements LSP is one of the most important surface modification techniques and LSP is regarded as a competitively alternative technology, which has obtained practical industrial applications in more and more fields [63]. In order to realize the large scale application of LSP, it is very necessary to develop the non-destructive online measuring method of LSP [64]. 4.2.1. Natural frequency method The natural frequency method for quality control measuring of LSP of samples by analysis the change value of a certain stage (or multi-stage) natural frequency shifts during LSP was first proposed by the US General Electric Company in the form of patent [65]. During the treatment of LSP, the residual compressive stress will be introduced into the alloys or metallic materials, while the natural frequency of alloys or metallic materials will be changed [66]. The natural frequency experiment of turbine blades in LSP was studied
Fig. 9. Effect of laser shock peening on Ti-6Al-4V alloy [29]. 7
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Fig. 10. Effect of laser power density on plasma acoustic wave signal amplitude at different distances in air [4].
by Yang et al. [67–69], they analyzed the variation of the natural frequency and the relationship between the residual stress at LSP point and the variation of the natural frequency, their experiment results showed that both the natural frequency (first-order & second-order) and the surface compressive residual stress of the turbine blades are found to increase similarly with the increasing of laser pulse energy, the residual stress is positively correlated with the variation value of first-order natural frequency. 4.2.2. Plasma acoustic wave signal amplitude method In the process of LSP, the plasma shock wave will propagate inside the materials, which cause high strain dynamic response of the material and produce plastic deformation. So the plasma shock wave is the directed power to realize the materials’ strengthening and determine the quality of LSP [4,70]. At the same time, the plasma shock wave will propagates in the air as the form of plasma acoustic wave. The plasma acoustic wave contain much important information about LSP, which can reflect the parameter variation characteristic in the process of LSP comprehensively [4,70,71]. So the real-time online measurements for the quality of LSP can be realized by the analysis and extraction of plasma acoustic wave [4,64]. Li et al. at Air Force Engineering University (China) studied the effect of laser power density on plasma acoustic wave signal amplitude at different distances in air by the plasma acoustic wave characteristic test and analysis experiment [4]. The experiment results is showed in Fig. 10. The plasma acoustic wave signal amplitude at different distances in air are increased with the laser power density, and their growth trend are very similar, and the difference in signal amplitude of the plasma acoustic wave at the same distance, which reflected the energy at the plasma explosion moment [4]. In the process of LSP treatment on alloys or metallic materials, with the increase of the energy of shock wave, the plastic deformation of alloys or metallic materials will become more obvious, then the residual compressive stress of alloys or metallic materials will be increased, which means that the effect of LSP become better, and will significantly improve the fatigue life of alloys or metallic materials. 5. Conclusion (1) After the treatment of LSP, the hardness, surface roughness, microstruture and residual stress of alloys and metallic materials are changed to a certain extent, which play important roles in the quality of LSP. (2) The evaluating methods for quality of LSP can be analyzed and summarized from the four aspects: hardness, residual stress, surface roughness and microstructure, where residual stress is the most important parameter to evaluate the quality of LSP. (3) With the repaid development of LSP, the existing offline evaluating methods have gradually failed to satisfy the production requirements of LSP, so it is necessary to study online evaluating methods for quality of LSP. Declaration of Competing Interest The authors declare no competing financial interests. Acknowledgements This work were co-supported by the NSFC-Liaoning Province United Foundation (U1608259), National Natural Science Foundation of China (51501219), National Key Development Program of China (2016YFB1192704) and National Key Technology Research and Development Program of the Ministry of Science and Technology of China (2015BAF08B01-01). References [1] H.C. Qiao, Y. Gao, J.B. Zhao, et al., Research process of laser peening technology, Chin. J. Nonferrous Met. 25 (7) (2015) 1744–1755. [2] Y. Gao, S. Tse, D. Zhang, et al., Experimental validation of the dynamic models of a high performance workpiece table under preloaded Hertzian contact, J.
8
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J. Wu, et al.
[3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53]
Mater. Process. Technol. 129 (1) (2002) 485–489. B.S. Xu, Nano Surface Engineering, Chemical Industry Press, Beijing, 2004. Y.H. Li, Theory and Technology of Laser Shock Processing, Science Press, Beijing, 2013. Kobayashi, Matsui, Murakami, Mechanism of creation of compressive residual stress by shot peening, Int. J. Fatigue 20 (5) (1998) 351–357. D.E. Mello, J.D.B. Goncalves, et al., Influence of surface texturing and hard chromium coating on the wear of steels used in cold rolling mill rolls, Wear 302 (1-2) (2013) 1295–1309. M.R.S. John, P. Suresh, D. Raguraman, et al., Surface characteristics of low plasticity burnishing for different materials using lathe, Arab. J. Sci. Eng. 39 (4) (2014) 3209–3216. J.J. Wu, J.B. Zhao, H.C. Qiao, et al., The application status and development of laser shock processing, Opto-Electron. Eng. 45 (2) (2018) 170690. P. Peyre, R. Fabbro, P. Merrien, et al., Laser shock processing of aluminium alloys. Application to high cycle fatigue behaviour, Mater. Sci. Eng. A 210 (1–2) (1996) 102–113. U. Trdan, M. Skarba, J. Grum, Laser shock peening effect on the dislocation transitions and grain refinement of Al–Mg–Si alloy, Mater. Charact. 97 (2014) 57–68. R.M. White, Elastic wave generation by electron bombardment or electromagnetic wave absorption, J. Appl. Phys. 34 (7) (1963) 2123–2124. Y.K. Zhang, J.Z. Lu, K.Y. Luo, General Introduction// Laser Shock Processing of FCC Metals, Springer Berlin, Heidelberg, 2013, pp. 1–14. B.P. Fairand, B.A. Wilcox, W.J. Gallagher, et al., Laser shock-induced microstructural and mechanical property changes in 7075 aluminum, J. Appl. Phys. 43 (9) (1972) 3893–3895. R. Fabbro, J. Fournier, P. Ballard, et al., Physical study of laser-produced plasma in confined geometry, J. Appl. Phys. 68 (2) (1990) 775–784. L. Tollier, R. Fabbro, E. Bartnicki, Study of the laser-driven spallation process by the velocity interferometer system for any reflector interferometry technique. I. Laser-shock characterization, J. Appl. Phys. 83 (3) (1998) 1224–1230. P. Peyre, R. Fabbro, L. Berthe, et al., Laser shock processing of materials, physical processes involved and examples of applications, J. Laser Appl. 8 (3) (2012) 135–141. Peyre, Berthe, Scherpereel, et al., Laser-shock processing of aluminium-coated 55C1 steel in water-confinement regime, characterization and application to highcycle fatigue behaviour, J. Mater. Sci. 33 (6) (1998) 1421–1429. G.X. Lu, T. Jin, Y.Z. Zhou, et al., Research progress of applications of laser shock processing on superalloys, Chin. J. Nonferrous Met. 28 (9) (2018) 1755–1764. Y.Q. Li, W.F. He, X.F. Nie, et al., Laser shock peening of GH4133 nickel-based superalloy, Rare Met. Mater. Eng. 44 (6) (2015) 1517–1521. Y. Lu, J.B. Zhao, H.C. Qiao, et al., Strengthening mechanism of TC17 titanium alloy warm laser shock peening, Surf. Technol. 47 (2) (2018) 1–7. T. Takata, M. Enoki, P. Chivavibul, et al., Acoustic emission monitoring of laser shock peening by detection of underwater acoustic wave, Mater. Trans. 57 (5) (2016) 674–680. B. Ahmad, M.E. Fitzpatrick, Analysis of residual stresses in laser-shock-peened and shot-peened marine steel welds, Metall. Mater. Trans. A 48 (2) (2017) 759–770. A.R. Oganov, A.O. Lyakhov, Towards the theory of hardness of materials, J. Superhard Mater. 32 (3) (2010) 143–147. P. Merrien, Laser shock processing of aluminium alloys. Application to high cycle fatigue behaviour, Mater. Sci. Eng. A 210 (1–2) (1996) 102–113. H. Luong, M.R. Hill, The effects of laser peening on high-cycle fatigue in 7085-T7651 aluminum alloy, Mater. Sci. Eng. A 477 (1) (2008) 208–216. C.S. Pande, K.P. Cooper, Nanomechanics of Hall–Petch relationship in nanocrystalline materials, Prog. Mater. Sci. 54 (6) (2009) 689–706. A.I. Slutsker, A.B. Sinani, V.I. Betekhtin, et al., Hardness of microporous SiC ceramics, Tech. Phys. 53 (12) (2008) 1591–1596. N.G. Guo, X.M. Luo, Y.Q. Hua, The effects of laser shock processing on microstructure and properties of metal, Mater. Sci. Eng. R Rep. 20 (6) (2006) 10–13. X.C. Zhang, Y.K. Zhang, J.Z. Lu, et al., Improvement of fatigue life of Ti–6Al–4V alloy by laser shock peening, Mater. Sci. Eng.: A (Structural Materials: Properties, Microstructure and Processing) 527 (15) (2010) 3411–3415. Iman Hejazi, Seyyed Ehsan Mirsalehi, Mechanical and metallurgical characterization of AA6061 friction stir welded joints using microhardness map, Trans. Nonferrous Met. Soc. China 26 (9) (2016) 2313–2319. Charles S. Montross, T. Wei, et al., Laser shock processing and its effects on microstructure and properties of metal alloys: a review, Int. J. Fatigue 24 (10) (2002) 1021–1036. R. Zhu, Y.K. Zhang, G.F. Su, et al., Finite element analysis of surface roughness generated by multiple laser shock peening, Rare Met. Mater. Eng. 47 (1) (2018) 33–38. C. Ye, S. Suslov, B.J. Kim, et al., Fatigue performance improvement in AISI 4140 steel by dynamic strain aging and dynamic precipitation during warm laser shock peening, Acta Mater. 59 (3) (2011) 1014–1025. A. Gill, A. Telang, S.R. Mannava, et al., Comparison of mechanisms of advanced mechanical surface treatments in nickel-based superalloy, Mater. Sci. Eng. A 576 (8) (2013) 346–355. G.X. Lu, Effect of Laser Shock on Surface Topography, Microstructure and Mechanical Behaviors of Superalloys, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, 2017. Charles S. Montross, T. Wei, et al., Laser shock processing and its effects on microstructure and properties of metal alloys: a review, Int. J. Fatigue 24 (10) (2002) 1021–1036. Y.D. Chen, J.Z. Pan, P.T. Liu, et al., Effects of surface roughness on bending fatigue properties of motor train unit wheel steel, Surf. Technol. 46 (2) (2017) 172–177. W.L. Yuan, Gas Dynamics, Science Press, Beijing, 2013. B. Zhou, T. Zhang, F. Lin, et al., Microstructures and mechanical properties of Ti6Al4V and 316L stainless steel impeller body made by electron beam selective melting, Rare Met. Mater. Eng. 47 (1) (2018) 175–180. D.E.R. Brockmann, T.E.M. Staab, F.G. Raether, The influence of sintering additives on the microstructure and material properties of silicon nitride ceramics investigated by advanced simulation tools, Phys. Status Solidi 214 (2017) 1600634. S. Amini, M. Dadkhah, R. Teimouri, Study on laser shock penning of Incoloy 800 super alloy, Opt. – Int. J. Light Electron. Opt. 140 (2017) 308–316. Y.E. Chang, Sergey Suslov, et al., Bimodal nanocrystallization of NiTi shape memory alloy by laser shock peening and post-deformation annealing, Acta Mater. 59 (19) (2011) 7219–7227. U. Trdan, M. Skarba, J. Grum, Laser shock peening effect on the dislocation transitions and grain refinement of Al–Mg–Si alloy, Mater. Charact. 97 (2014) 57–68. Y.K. Zhang, J. You, J.Z. Lu, et al., Effects of laser shock processing on stress corrosion cracking susceptibility of AZ31B magnesium alloy, Surf. Coat. Technol. 204 (24) (2010) 3947–3953. Peyre, Berthe, Scherpereel, et al., Laser-shock processing of aluminium-coated 55C1 steel in water-confinement regime, characterization and application to highcycle fatigue behaviour, J. Mater. Sci. 33 (6) (1998) 1421–1429. P. Peyre, R. Fabbro, Laser shock processing: a review of the physics and applications, Opt. Quantum Electron. 27 (12) (1995) 1213–1229. M.M. Quazi, M.A. Fazal, A.S.M.A. Haseeb, et al., Laser-based surface modifications of aluminum and its alloys, Crit. Rev. Solid State Mater. Sci. 41 (2) (2016) 106–131. J. Mathar, Determination of inherent stresses by measuring deformations of drilled holes, Tech. Rep. Arch. Image Library 56 (4) (1934) 249–254. Beghini, Bertini, Raffaelli, Numerical analysis of plasticity effects in the hole-drilling residual stress measurement, J. Test. Eval. 22 (6) (1994) 522–529. Y.Y. Santana, J.G.L. Barbera-Sosa, M.H. Staia, et al., Measurement of residual stress in thermal spray coatings by the incremental hole drilling method, Surf. Coat. Technol. 201 (5) (2006) 2092–2098. Y. Zhang, Y.P. Zhao, An effective method of determining the residual stress gradients in a micro-cantilever, Microsyst. Technol. 12 (4) (2006) 357–364. B.S. Yin, H.P. Zhao, X.H. Wang, Basic knowledge of residual stress determination—lecture No.7 residual stress determination by mechanical method, Phys. Test. Chem. Anal. (Part A: Physical Testing) 43 (12) (2007) 50–54. S. Hannusch, M. Stockmann, J. Ihlemann, Experimental method for residual stress analysis with fibre Bragg grating sensors, Mater. Today Proc. 3 (4) (2016) 979–982.
9
Optik - International Journal for Light and Electron Optics 200 (2020) 162940
J. Wu, et al.
[54] M.W. Lu, X.F. Luo, Foundation of Elasticity Theory, Tsinghua University Press, Beijing, 1990. [55] H. Suzuki, K. Akita, H. Misawa, X-ray stress measurement method for single crystal with unknown stress-free lattice parameter, J. Appl. Phys. 42 (5A) (2003) 2876–2880. [56] K.M. Lü, Basic knowledge of residual stress determination—lecture No.4 Stress determination method by X-ray(1), Phys. Test. Chem. Anal. (Part A: Physical Testing) 43 (7) (2007) 349–354. [57] C.H. Ma, J.H. Huang, H. Chen, Residual stress measurement in textured thin film by grazing-incidence X-ray diffraction, Thin Solid Films 418 (2) (2002) 73–78. [58] D.Q. Zhang, J.W. He, X-ray Diffraction Analysis and Effect of Residual Stress in Materials, Xi’an Jiaotong University Press, Xi’an, 1999. [59] M. Gelfi, E. Bontempi, R. Roberti, et al., X-ray diffraction Debye Ring Analysis for STress measurement (DRAST): a new method to evaluate residual stresses, Acta Mater. 52 (3) (2004) 583–589. [60] C.H. Ma, J.H. Huang, H. Chen, Residual stress measurement in textured thin film by grazing-incidence X-ray diffraction, Thin Solid Films 418 (2) (2002) 73–78. [61] J. Lin, N. Ma, Y. Lei, et al., Measurement of residual stress in arc welded lap joints by cosα X-ray diffraction method, J. Mater. Process. Technol. 243 (2017) 387–394. [62] T. Sasaki, K. Koda, Y. Fujimoto, et al., X-ray residual stress analysis of stainless steel using cosα method, Adv. Mat. Res. 922 (2014) 167–172. [63] L. Zhang, K.Y. Luo, J.Z. Lu, et al., Effects of laser shock processing with different shocked paths on mechanical properties of laser welded ANSI 304 stainless steel joint, Mater. Sci. Eng.: A (Structural Materials: Properties, Microstructure and Processing) 528 (13–14) (2011) 4652–4657. [64] H.C. Qiao, J.B. Zhao, Design and implementation of online laser peening detection system, Laser Optoelectron. Prog. 50 (7) (2013) 47–51. [65] B.M. Davis, R.D. Mcclain, U.W. Suh, et al., Real Time Laser Shock Peening Quality Assurance by Natural Frequency Analysis: US, (2005). [66] X.Q. Zhang, J.Z. Zhou, Z.T. Yang, et al., A technology of laser shot processing strengthening to improve fatigue life of components, Turbine Technol. 47 (3) (2005) 238–240. [67] H.L. Yang, J.M. Liang, Research on the quality inspection for blades’ laser shock processing, J. Tianjin Chengjian Univ. 16 (1) (2010) 37–40. [68] J.M. Liang, H.L. Yang, S.K. Zou, The processing monitor for aero-engine blades’ laser shock processing, Aeronaut. Sci. Technol. (6) (2008) 82–84. [69] S.K. Zou, Z.W. Cao, H.L. Yang, Natural frequency test of turbine blades in laser shock processing, China Mech. Eng. (6) (2010) 648–651. [70] J.J. Wu, J.B. Zhao, H.C. Qiao, et al., Acoustic wave detection of laser shock peening, Opto-Electronic Adv. 1 (9) (2018) 180016. [71] C.L. Qiu, L. Cheng, W.F. He, A condition monitoring method for laser peening based on the correlation between the adjacent aata, J. Vib. Shock 36 (4) (2017) 139–143. Jiajun Wu received his B.S. degree in Process Equipment and Control Engineering from Beijing University of Chemical Technology, Beijing, China, in 2016. Currently he is pursuing Ph.D. degree at Shenyang Institute of Automation, Chinese Academy of Sciences. His main research interest is laser shock processing online monitoring technology. Jibin Zhao is a professor in Shenyang Institute of Automation, Chinese Academy of Science. His research interests include computer-aided design, rapid prototyping and surface engineering. Hongchao Qiao is a professor in Shenyang Institute of Automation, Chinese Academy of Science. His research interests include laser shock processing and laser welding.
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