- Email: [email protected]
The fatigue durability GFRP under increased temperatures
Available online at www.sciencedirect.com Available online at www.sciencedirect.com
ScienceDirect ScienceDirect
Structural Integrity Procedia 00 (2019) 000–000 Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2019) 000–000
ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Procedia Structural Integrity 17 (2019) 651–657
ICSI 2019 The 3rd International Conference on Structural Integrity ICSI 2019 The 3rd International Conference on Structural Integrity
The fatigue durability GFRP under increased temperatures The fatigue durability GFRP under increased temperatures Lobanov Dmitrii S.aa, Staroverov Oleg A.bb Lobanov Dmitrii S. , Staroverov Oleg A.
Center of Experimental Mechanics, Perm National Research Polytechnic University, Perm, Russia, Center of [email protected]., Mechanics, Perm NationalbResearch Polytechnic University, Perm, Russia, [email protected] a [email protected]., b [email protected]
Abstract Abstract The actual tasks of the mechanics of composite materials are studies of the laws of deformation, fracture and mechanical behavior The actual tasks of thethemechanics materials are studies of the laws of deformation, mechanical behavior of composites under influenceof ofcomposite high and low (working) temperatures, climatic factors andfracture workingand dirty environments. No of the influence of high andanalysis low (working) temperatures, climatic factors and working dirty environments. No lesscomposites urgent taskunder is to study issues related to the of the conditions of failure, the accumulation of damage and the survivability less urgent taskduring is to study issues related to the analysis of the conditions of failure, the accumulation and thestudies survivability of composites cyclic loads. In connection with the above tasks, the paper presents the resultsofofdamage experimental of the of composites during cyclic on loads. connection the above tasks,fiberglass the paperplastics. presentsStudies the results experimental studies of the effect of high temperatures the In fatigue life ofwith aviation structural wereofconducted at the Center for effect of high temperatures on the fatigue life of aviation structural fiberglass plastics. Studies were conducted at the Center for Collective Use of the Center of Experimental Mechanics PNRPU. The objects of the study were samples of structural fiberglass Collective Usepurposes, of the Center Experimental Mechanics Theof objects of the study were of prepreg. structural fiberglass for aerospace whichofwere manufactured by serialPNRPU. technology autoclave molding from samples glass fiber for the aerospace were manufactured by serialwere technology of autoclave molding from glass fiber prepreg. In course purposes, of study, which static mechanical characteristics determined (refined), temperature dependencies of static tensile In the course of study, staticwere mechanical characteristics were determined (refined), temperature of static tensile strength and elastic modulus obtained, temperature dependences of fatigue life were obtained,dependencies and conditions for changing strength and elastic modulus were obtained, temperature dependences of fatigue life were obtained, and conditions for changing the fracture mechanisms of fiberglass samples were analyzed. the fracture mechanisms of fiberglass samples were analyzed. © 2019 The Authors. Published by Elsevier B.V. © 2019 Published by Elsevier B.V. B.V. © 2019The TheAuthors. Authors. Published by Peer-review under responsibility of Elsevier the ICSI organizers. Peer-review under responsibility of the ICSI 2019 2019 organizers. Peer-review under responsibility of the ICSI 2019 organizers. Keywords: composite materials, quasistatic and cyclic loads, temperature degradation, residual strength, damage accumulation Keywords: composite materials, quasistatic and cyclic loads, temperature degradation, residual strength, damage accumulation
1. Introduction 1. Introduction The use of advanced composites in critical structures is widespread in the aviation, aerospace and engineering The use As of advanced in critical structures is reliability widespreadand in the aviation, aerospace andofengineering industries. there is a composites constantly increasing demand for safety of structures made composite industries. As there is a constantly increasing demand for reliability and safety of structures made of composite materials, it becomes necessary to obtain experimental data on damage accumulation and failure of composite materials, in it conditions becomes necessary to obtain ones experimental dataD.S., on damage failure structures close to operational by Lobanov Slovikovaccumulation S.V. (2017), and Kucher N.K.ofet composite al (2013), structuresD.S. in conditions close to operational onestoby Lobanov D.S., Slovikov S.V. (2017), Kucher of N.K. et al (2013), Lobanov et al (2018), (2015). It is relevant carry out researches in experimental mechanics composites and Lobanovthe D.S. et alof (2018), (2015). is relevant totemperatures carry out researches in experimental of composites analyze effect high and low It (operational) on mechanical propertiesmechanics and fracture mechanismsand of analyze thematerials effect of and highsetting and low (operational) temperatures on and mechanical and fracture mechanisms composite temperature relations of elastic strengthproperties characteristics of composites used of in composite materials and setting temperature relations of elastic and strength characteristics of composites used in 2452-3216 © 2019 The Authors. Published by Elsevier B.V. 2452-3216 2019responsibility The Authors. of Published Elsevier B.V. Peer-review©under the ICSIby 2019 organizers. Peer-review under responsibility of the ICSI 2019 organizers.
2452-3216 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ICSI 2019 organizers. 10.1016/j.prostr.2019.08.087
652 2
Dmitrii S. Lobanov et al. / Procedia Structural Integrity 17 (2019) 651–657 Lobanov Dmitrii S., Staroverov Oleg A./ Structural Integrity Procedia 00 (2019) 000–000
critical structures. There are more and more researches aimed at studying behavior of composite materials under cyclic effects M.Haggui et al (2019), Movahedi-Rad et al (2019), Chen G. et al (2019), Fouchier, N. et al (2019), Růžek, R. et al (2018), Strizhius V. (2016). For composite materials based on a polymer matrix, the stages of changes in residual strength and stiffness properties during fatigue damage accumulation have been revealed Philippidis T.P., Passipoularidis V.A. (2007), Van Paepegem W. et al (2005), Maragoni L. et al (2016). Researchers outline direct and indirect methods for assessing residual properties of specimens of composite materials Philippidis T.P., Assimakopoulou T.T. (2008), Matvienko Y.G. et al (2016), Plekhov O. et al (2005), M.Haggui et al (2018), A. Maleki et al (2018), Dattoma, V., Giancane S. (2013), 21. Lobanov D.S. et al (2015). The direct methods are based on the results of quasi-static tests after preliminary cyclic exposure without fatigue failure. The indirect methods are focused on the use of non-destructive control systems, such as infrared thermoscanning and recording of acoustic emission signals in the process of cyclic loading. Increased temperatures can significantly affect deformation and fracture, fatigue life and the survivability of polymer composites. The work aims at an experimental study of the influence of increased temperatures on deformation and fracture of polymer composite materials (PCM) under cyclic conditions. To achieve the aim, a series of experiments were carried out using the research facilities of the Center for Experimental Mechanics (http://www.ckp-rf.ru/ckp/353547/). 2. Material, Experimental Facilities and Testing Techniques The study focused on the composite material specimens made by serial production technology based on VPS-48 fiberglass prepreg and VSE 1212 binder with a reinforcement scheme [0º/90º] 8 using the autoclave molding method. Mechanical properties of the composite were determined under preliminary quasistatic uniaxial tension tests taking into consideration ASTM D 3039 recommendations. The tests were carried out using Instron 5882 electromechanical system equipped with a temperature chamber with a working temperature range from -100 to +350ºС. The traverse speed was 2 mm/min. The groups of specimens were tested at temperatures of 22, 120 and 200ºС. To measure the longitudinal deformation of the specimens, Advanced Video Extensometer (AVE) Instron 2663-821 non-contact video extensometer was used. Its operation is based on determining the coordinates of the contrasting (white or black) coordinates of the measuring base marks printed on the working part of the specimen using the high resolution digital video camera. The use of the video extensometer is justified by the fact that it does not exert an additional mechanical effect on the specimen surface in the working area, and can also be used together with a heat chamber throughout the entire temperature range without restrictions. The field of view of the video extensometer is 200 mm, the video signal digitizing rate is one frame of information in 20 microseconds described by Lobanov D.S. et al (2018). The specimens were preliminary thermostatically-controlled under increased temperatures of 120 ºС and 200ºС. The temperature control mode included linear heating of the specimens to the selected temperature at a rate of 10°C/min and holding for 2 hours for the entire group of specimens and 0.5 hours after each subsequent fitting of the specimen. To select the cyclic loading parameters, the values of the elastic modulus, tensile strength, and relative elongation were determined. The methods of cyclic tests under increased temperatures complied with recommendations of the corresponding ASTM D3479 standards. The fatigue tests were carried out using Instron Electropuls E10000, the electromechanical system equipped with a temperature chamber with a working temperature range from -100 to +250ºС. At increased temperatures of 120 and 200ºС the thermostatically-controlled mode was similar. The specimens had thermomechanical fatigue life tests (the maximum number of fatigue fracture cycles (N max) at the parameters of cyclic loading: σmax = 0,5∙σB, where σB – strength limit, R = 0,1, ν = 20 Hz and a sinusoidal form of cycles. The study of changes in the residual strength and stiffness properties of the polymer composite specimens at a temperature of 120°C was carried out with a combination of the above techniques. The technique included quasistatic tensile tests with the determination of the nominal values of strength limit σB and Young's modulus E at increased temperatures. Later the value of fatigue life of the specimens N max was determined during cyclic tension wirth a frequency of ν = 15 Hz, coefficient of skewness R = 0,1 and the value of maximum stresses in cycle σ max = 0,5 σB. After that the specimens were subjected to cyclic pre-exposure with cycle life in the range (0,1 – 0,8) Nmax. The values of residual strength and stiffness characteristics of the studied PCM specimens were determined during quasistatic tensile tests at increased temperatures.
Dmitrii S. Lobanov et al. / Procedia Structural Integrity 17 (2019) 651–657 Lobanov Dmitrii S., Staroverov Oleg A./ Structural Integrity Procedia 00 (2019) 000–000
653 3
3. Results of Fatigue Tests at Increased Temperatures The results of the preliminary quasistatic tension tests of glass fiber plastic specimens at 22, 120 и 200ºС temperatures are given in Table 1. Таble 1. Results of preliminary static tensile tests at normal and increased temperatures Temperature , strength limit σB, MPa Young's modulus E, GPa °С 22
329±28
26,5±1,5
120
295±24
22,8±1,4
200
165±8
13,5±1,5
As a result of the cyclic tests, the values of fatigue life of the fiberglass specimens were obtained. The effect of the increased temperatures is reflected in the fatigue life degradation diagram (Fig. 1). To describe the behavior of the specimens during cyclic tests at increased temperatures, we introduce n’ value reflecting the change in the value of fatigue life as a result of damage accumulation, which is expressed as: 𝑛𝑛′ = 𝑛𝑛⁄𝑁𝑁
(1)
where n is a number of cycles up to failure at different testing temperatures; N is the nominal number of cycles up to failure at room temperature.
Fig. 1. Diagram of dependence fatigue life - high temperatures for fiberglass samples at the parameters of cyclic loading: σmax = 0,5∙σB, R = 0,1, ν = 20 Hz
The diagram of the fatigue life degradation is non-linear in nature. To predict the residual life of the PCM specimens at increased temperatures, a trend line was plotted on the diagram. The change in the stiffness properties of fiberglass specimens, as a result of the fatigue damage accumulation was evaluated using the indirect technique based on measuring the amplitude of displacements of the loading pattern specimen/traverse during the test. The change in the amplitude of the movements was recorded using WaveMatrix software. For example, Fig.2 shows characteristic diagrams of changes stiffness values of specimen during fatigue tests at various temperatures. The ordinate axis is R, and the abscissa axis n’ is the relative number of cycles to failure at various temperatures.
Dmitrii S. Lobanov et al. / Procedia Structural Integrity 17 (2019) 651–657 Lobanov Dmitrii S., Staroverov Oleg A./ Structural Integrity Procedia 00 (2019) 000–000
654 4
(2)
𝑅𝑅 = 𝑃𝑃 ⁄𝑢𝑢𝑎𝑎
where ua is the value of the amplitude of sample’s displacements during tests; P – is the load value under cyclic tension; nt – is a relative number of cycles up to fracture at different temperatures.
Fig. 2. Diagrams of changes in the relative values of the stiffness of the sample R during fatigue testing at various temperatures
A decrease in the relative value of the specimen stiffness R by 0.1 corresponds to a decrease in the specimen stiffness by 10%. Under the test temperatures of 120°C and 200°C, the dependences of R stiffness alterations had a similar view; the curves appeared on the straight section of the diagram after a smaller number of cycles compared to the curves obtained during the tests at room temperature. For the specimens tested at 200°C, fracture occurred with numerous delaminations throughout the working area of the specimen (Fig. 3); in the diagram of R specimen relative stiffness, this type of fracture corresponds to the interval (0.9 - 1) n’. a
b
c
Fig. 3. Fracture surfaces of specimens after fatigue life tests at 22 (a), 120 (b) and 200 ° C (c)
Under the testing temperatures between 22 and 120°С with respect to ASTM classification, the specimens fractured according to the LGM mechanism; under higher temperature of 200°С there comes the shift of fracture mechanisms into DGM and DMM (Fig.3). A significant destruction of the binder leads to a disruption of interlayer adhesion and development of multiple delaminations in the working area of the fiberglass specimens. 4. Constructing Diagrams of Fatigue Sensitivity of Fiberglass Composites at Increased Temperatures The relations of the residual properties alterations on preliminary cyclic loads and increased temperature (120°C) are presented in the form of the fatigue sensitivity diagram by Wil'deman V. E. et al (2018). The diagram of fatigue sensitivity in relative coordinates KBn’ – n’, where ′ (3) = 𝜎𝜎𝐵𝐵𝐵𝐵 ⁄𝜎𝜎𝐵𝐵 𝐾𝐾𝐵𝐵𝐵𝐵 is the factor of retention of the static strength in cyclic loading, with σ Bn and σB — the strengths after and before
Dmitrii S. Lobanov et al. / Procedia Structural Integrity 17 (2019) 651–657 Lobanov Dmitrii S., Staroverov Oleg A./ Structural Integrity Procedia 00 (2019) 000–000
655 5
cyclic loadings; 𝑛𝑛′ = 𝑛𝑛⁄𝑁𝑁 (4) is the relative number of cycles of preliminary loading, with n — the number of cycles of preliminary cyclic loading and N — the limiting number of cycles to failure at given parameters.
Fig. 4. Diagrams of fatigue sensitivity at normal and elevated temperatures (120°C)
The test results analysis at increased temperatures showed that, compared to the specimens tested at normal temperature, the decrease in the value of the residual tensile strength occurred in two stages, without a zone of the initial fatigue sensitivity (Fig.4). In the interval of fatigue sensitivity (0.1 – 0.8) n’, the change in the value of the coefficient of static strength retaining under cyclic loading (KBn’) did not exceed 5%, which corresponds to the stabilization stage. For the specimens under room temperature, the K Bn’ value in the interval of stabilization was 15% lower, compared to the specimens tested at increased temperatures. At the aggravation interval (0,8 – 1) n’, a sharp decrease in the residual strength followed by fatigue failure of the specimens occurred.
n’ = 0,1
n’ = 0,2
n’ = 0,4
n’ = 0,6
n’ = 0,8
n’ = 1
Fig. 5. Development of zones of local delamination on the surface of the working area of fiberglass specimens depending on the number of cycles passed
Fig.5 shows the surfaces of the working area of the specimens after preliminary cyclic loading with different cycle numbers. There are local delamination zones formed in the process of fatigue damage accumulation on the surface
656 6
Dmitrii S. Lobanov et al. / Procedia Structural Integrity 17 (2019) 651–657 Lobanov Dmitrii S., Staroverov Oleg A./ Structural Integrity Procedia 00 (2019) 000–000
of the specimens. This part of The work was performed as part of the fulfillment of the state task of the Ministry of Education and Science of Russia No. 9.7526.2017/9.10 Conclusion Methodological issues related to the combined effect of mechanical loads and increased temperatures have been worked out. A series of experimental studies have been conducted to study the influence of increased temperatures on fatigue life, relative stiffness and residual strength of structural fiberglass specimens. It has been outlined that when the temperature rises to 120°С, the fatigue life of fiberglass decreases at the given loading parameters by 20-30%, at the temperature of 200°С by 60-70%. The analysis of changes in the destruction mechanisms during fatigue life was made depending on the test temperature. The diagrams of fatigue sensitivity and stiffness changes for the fiberglass specimens were constructed and features of the residual strength alterations at increased temperatures were revealed. A study of the fracture surface patterns of the fiberglass flat specimens was made. It was noted that in the process of fatigue accumulation of damage, local heating and delamination intervals were formed on the surface of the specimens. Acknowledgements The research was performed at the Perm National Research Polytechnical University at support of the Russian Scientific Fund (project No. 18-79-00209). References Babushkin, A.V., Lobanov, D.S., Kozlova, A.V., Morev, I.D., 2013. Research of the effectiveness of mechanical testing methods with analysis of features of destructions and temperature effects. Frattura ed Integrita Strutturale 24, 89–95. Chen, G., Zhang, W., Iizuka, T., 2019. The fatigue fracture characteristics of the bond zone of aluminum matrix composites (Al-12Si/ABOw) with Al-12Si alloys. Materials Science and Engineering A 755, 181–189. Colombo, C., Bhujangrao, T., Libonati, F., Vergani, L., 2019. Effect of delamination on the fatigue life of GFRP: A thermographic and numerical study. Composite Structures 218, 152–161. Dattoma, V., Giancane, S., 2013. Evaluation of energy of fatigue damage into GFRC through digital image correlation and thermography. Composites Part B: Engineering 47, 283–289. Fouchier, N., Nadot-Martin, C., Conrado, E., Bernasconi, A., Castagnet, S., 2019. Fatigue life assessment of a Short Fibre Reinforced Thermoplastic at high temperature using a Through Process Modelling in a viscoelastic framework. International Journal of Fatigue 124, 236–244. Habibi, M., Laperrière, L., Hassanabadi, H.M., 2019. Effect of moisture absorption and temperature on quasi-static and fatigue behavior of nonwoven flax epoxy composite. Composites Part B: Engineering 166, 31–40. Haggui M., El Mahi, A., Jendli, Z., Akrout, A., Haddar, M., 2018. Static and fatigue characterization of flax fiber reinforced thermoplastic composites by acoustic emission. Applied Acoustics. Kucher, N.K., Zarazovskii, M.N., Danil’chuk, E.L., 2013. Deformation and strength of laminated carbon-fiber-reinforced plastics under a static thermomechanical loading. Mechanics of Composite Materials 6, 669–680. Lobanov, D.S., Babushkin, A.V., Luzenin, A.Yu., 2018. Effect of increased temperatures on the deformation and strength characteristics of a GFRP based on a fabric of volumetric weave. Mechanics of Composite Materials 5, 655–664. Lobanov, D.S., Slovikov, S.V., 2017. Mechanical properties of a unidirectional basalt-fiber-reinforced plastic under a loading simulating operation conditions. Mechanics of Composite Materials 6, 767–772. Lobanov, D. S., Vildeman, V. E., Babin, A. D., and Grinev, M. A., 2015. Experimental research into the effect of external actions and polluting environments on the serviceability of fiber-reinforced polymer composite materials. Mechanics of Composite Materials 1, 69–79. Lobanov, D.S., Wildemann, V.E., Spaskova, E.M., Chikhachev, A.I., 2015. Experimental investigation of the defects influence on the composites sandwich panels strength with use digital image correlation and infrared thermography methods. PNRPU Mechanics Bulletin 4, 159–170. DOI: 10.15593/perm.mech/2015.4.10. Maleki, A., Saeedifar, M., Najafabadi, M. A., Zarouchas D., 2018. The fatigue failure study of repaired aluminum plates by composite patches using Acoustic Emission. Engineering Fracture Mechanics. Manteghi, S., Sarwar, A., Fawaz, Z., Zdero, R., Bougherara, H., 2019. Mechanical characterization of the static and fatigue compressive properties of a new glass/flax/epoxy composite material using digital image correlation, thermographic stress analysis, and conventional mechanical testing. Materials Science and Engineering C 99, 940–950. Maragoni, L., Carraro, P.A., Peron, M., Quaresimin, M., 2016. Fatigue behavior of glass/epoxy laminates in the presence of voids. International Journal of Fatigue 95, 18–28.
Dmitrii S. Lobanov et al. / Procedia Structural Integrity 17 (2019) 651–657 Lobanov Dmitrii S., Staroverov Oleg A./ Structural Integrity Procedia 00 (2019) 000–000
657 7
Matvienko, Y.G., Vasil’ev, I.E., Ivanov, V.I., Elizarov, S.V., 2016. Acoustic-emission evaluation of the process of destruction of a composite material under tensile, compression, and cyclic loads. Russian Journal of Nondestructive Testing 8, 443-456. Montesano, J., Fawaz, Z., Bougherara, H., 2013. Use of infrared thermography to investigate the fatigue behavior of a carbon fiber reinforced polymer composite. Composite Structures 97, 76–83. Movahedi-Rad, A.V., Keller, T., Vassilopoulos, 2019. Creep effects on tension-tension fatigue behavior of angle-ply GFRP composite laminates. International Journal of Fatigue 123, 144–156. Philippidis, T.P., Assimakopoulou, T.T., 2008. Using acoustic emission to assess shear strength degradation in FRP composites due to constant and variable amplitude fatigue loading. Composites Science and Technology 68, 840–847. Philippidis, T.P., Passipoularidis, V.A., 2007. Residual strength after fatigue in composites: Theory vs. experiment. International Journal of Fatigue. 29, 2104–2116. Plekhov, O., Palin-Luc, T., Saintier, N., Uvarov, S., Naimark, O., 2005. Fatigue crack initiation and growth in a 35crmo4 steel investigated by infrared thermography. Fatigue & fracture of engineering materials & structures 28 (1-2), 169 – 178. Růžek, R., Kadlec, M., Petrusová, L., 2018. Effect of fatigue loading rate on lifespan and temperature of tailored blank C/PPS thermoplastic composite. International Journal of Fatigue 113, 253–263. Strizhius, V., 2016. Estimation of the residual fatigue life of laminated composites under a multistage cyclic loading. Mechanics of Composite Materials 5, 611—622. Van Paepegem, W., Dechaene, R., Degrieck, J., 2005. Nonlinear correlation to the bending stiffness of a damaged composite beam. Composite Structures 67, 359–364. Wildemann, V.E., Spaskova, E.V., Shilova, A.I., 2016. Research of the Damage and Failure Processes of Composite Materials Based on Acoustic Emission Monitoring and Method of Digital Image Correlation. Solid State Phenomena 243, 163–170. Wil'deman, V. E., Staroverov, O. A., Lobanov, D. S., 2018. Diagram and parameters of fatigue sensitivity for evaluating the residual strength of layered GFRP composites after preliminary cyclic loadings. Mechanics of Composite Materials 3, 313–320.
ScienceDirect ScienceDirect
Structural Integrity Procedia 00 (2019) 000–000 Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2019) 000–000
ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Procedia Structural Integrity 17 (2019) 651–657
ICSI 2019 The 3rd International Conference on Structural Integrity ICSI 2019 The 3rd International Conference on Structural Integrity
The fatigue durability GFRP under increased temperatures The fatigue durability GFRP under increased temperatures Lobanov Dmitrii S.aa, Staroverov Oleg A.bb Lobanov Dmitrii S. , Staroverov Oleg A.
Center of Experimental Mechanics, Perm National Research Polytechnic University, Perm, Russia, Center of [email protected]., Mechanics, Perm NationalbResearch Polytechnic University, Perm, Russia, [email protected] a [email protected]., b [email protected]
Abstract Abstract The actual tasks of the mechanics of composite materials are studies of the laws of deformation, fracture and mechanical behavior The actual tasks of thethemechanics materials are studies of the laws of deformation, mechanical behavior of composites under influenceof ofcomposite high and low (working) temperatures, climatic factors andfracture workingand dirty environments. No of the influence of high andanalysis low (working) temperatures, climatic factors and working dirty environments. No lesscomposites urgent taskunder is to study issues related to the of the conditions of failure, the accumulation of damage and the survivability less urgent taskduring is to study issues related to the analysis of the conditions of failure, the accumulation and thestudies survivability of composites cyclic loads. In connection with the above tasks, the paper presents the resultsofofdamage experimental of the of composites during cyclic on loads. connection the above tasks,fiberglass the paperplastics. presentsStudies the results experimental studies of the effect of high temperatures the In fatigue life ofwith aviation structural wereofconducted at the Center for effect of high temperatures on the fatigue life of aviation structural fiberglass plastics. Studies were conducted at the Center for Collective Use of the Center of Experimental Mechanics PNRPU. The objects of the study were samples of structural fiberglass Collective Usepurposes, of the Center Experimental Mechanics Theof objects of the study were of prepreg. structural fiberglass for aerospace whichofwere manufactured by serialPNRPU. technology autoclave molding from samples glass fiber for the aerospace were manufactured by serialwere technology of autoclave molding from glass fiber prepreg. In course purposes, of study, which static mechanical characteristics determined (refined), temperature dependencies of static tensile In the course of study, staticwere mechanical characteristics were determined (refined), temperature of static tensile strength and elastic modulus obtained, temperature dependences of fatigue life were obtained,dependencies and conditions for changing strength and elastic modulus were obtained, temperature dependences of fatigue life were obtained, and conditions for changing the fracture mechanisms of fiberglass samples were analyzed. the fracture mechanisms of fiberglass samples were analyzed. © 2019 The Authors. Published by Elsevier B.V. © 2019 Published by Elsevier B.V. B.V. © 2019The TheAuthors. Authors. Published by Peer-review under responsibility of Elsevier the ICSI organizers. Peer-review under responsibility of the ICSI 2019 2019 organizers. Peer-review under responsibility of the ICSI 2019 organizers. Keywords: composite materials, quasistatic and cyclic loads, temperature degradation, residual strength, damage accumulation Keywords: composite materials, quasistatic and cyclic loads, temperature degradation, residual strength, damage accumulation
1. Introduction 1. Introduction The use of advanced composites in critical structures is widespread in the aviation, aerospace and engineering The use As of advanced in critical structures is reliability widespreadand in the aviation, aerospace andofengineering industries. there is a composites constantly increasing demand for safety of structures made composite industries. As there is a constantly increasing demand for reliability and safety of structures made of composite materials, it becomes necessary to obtain experimental data on damage accumulation and failure of composite materials, in it conditions becomes necessary to obtain ones experimental dataD.S., on damage failure structures close to operational by Lobanov Slovikovaccumulation S.V. (2017), and Kucher N.K.ofet composite al (2013), structuresD.S. in conditions close to operational onestoby Lobanov D.S., Slovikov S.V. (2017), Kucher of N.K. et al (2013), Lobanov et al (2018), (2015). It is relevant carry out researches in experimental mechanics composites and Lobanovthe D.S. et alof (2018), (2015). is relevant totemperatures carry out researches in experimental of composites analyze effect high and low It (operational) on mechanical propertiesmechanics and fracture mechanismsand of analyze thematerials effect of and highsetting and low (operational) temperatures on and mechanical and fracture mechanisms composite temperature relations of elastic strengthproperties characteristics of composites used of in composite materials and setting temperature relations of elastic and strength characteristics of composites used in 2452-3216 © 2019 The Authors. Published by Elsevier B.V. 2452-3216 2019responsibility The Authors. of Published Elsevier B.V. Peer-review©under the ICSIby 2019 organizers. Peer-review under responsibility of the ICSI 2019 organizers.
2452-3216 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ICSI 2019 organizers. 10.1016/j.prostr.2019.08.087
652 2
Dmitrii S. Lobanov et al. / Procedia Structural Integrity 17 (2019) 651–657 Lobanov Dmitrii S., Staroverov Oleg A./ Structural Integrity Procedia 00 (2019) 000–000
critical structures. There are more and more researches aimed at studying behavior of composite materials under cyclic effects M.Haggui et al (2019), Movahedi-Rad et al (2019), Chen G. et al (2019), Fouchier, N. et al (2019), Růžek, R. et al (2018), Strizhius V. (2016). For composite materials based on a polymer matrix, the stages of changes in residual strength and stiffness properties during fatigue damage accumulation have been revealed Philippidis T.P., Passipoularidis V.A. (2007), Van Paepegem W. et al (2005), Maragoni L. et al (2016). Researchers outline direct and indirect methods for assessing residual properties of specimens of composite materials Philippidis T.P., Assimakopoulou T.T. (2008), Matvienko Y.G. et al (2016), Plekhov O. et al (2005), M.Haggui et al (2018), A. Maleki et al (2018), Dattoma, V., Giancane S. (2013), 21. Lobanov D.S. et al (2015). The direct methods are based on the results of quasi-static tests after preliminary cyclic exposure without fatigue failure. The indirect methods are focused on the use of non-destructive control systems, such as infrared thermoscanning and recording of acoustic emission signals in the process of cyclic loading. Increased temperatures can significantly affect deformation and fracture, fatigue life and the survivability of polymer composites. The work aims at an experimental study of the influence of increased temperatures on deformation and fracture of polymer composite materials (PCM) under cyclic conditions. To achieve the aim, a series of experiments were carried out using the research facilities of the Center for Experimental Mechanics (http://www.ckp-rf.ru/ckp/353547/). 2. Material, Experimental Facilities and Testing Techniques The study focused on the composite material specimens made by serial production technology based on VPS-48 fiberglass prepreg and VSE 1212 binder with a reinforcement scheme [0º/90º] 8 using the autoclave molding method. Mechanical properties of the composite were determined under preliminary quasistatic uniaxial tension tests taking into consideration ASTM D 3039 recommendations. The tests were carried out using Instron 5882 electromechanical system equipped with a temperature chamber with a working temperature range from -100 to +350ºС. The traverse speed was 2 mm/min. The groups of specimens were tested at temperatures of 22, 120 and 200ºС. To measure the longitudinal deformation of the specimens, Advanced Video Extensometer (AVE) Instron 2663-821 non-contact video extensometer was used. Its operation is based on determining the coordinates of the contrasting (white or black) coordinates of the measuring base marks printed on the working part of the specimen using the high resolution digital video camera. The use of the video extensometer is justified by the fact that it does not exert an additional mechanical effect on the specimen surface in the working area, and can also be used together with a heat chamber throughout the entire temperature range without restrictions. The field of view of the video extensometer is 200 mm, the video signal digitizing rate is one frame of information in 20 microseconds described by Lobanov D.S. et al (2018). The specimens were preliminary thermostatically-controlled under increased temperatures of 120 ºС and 200ºС. The temperature control mode included linear heating of the specimens to the selected temperature at a rate of 10°C/min and holding for 2 hours for the entire group of specimens and 0.5 hours after each subsequent fitting of the specimen. To select the cyclic loading parameters, the values of the elastic modulus, tensile strength, and relative elongation were determined. The methods of cyclic tests under increased temperatures complied with recommendations of the corresponding ASTM D3479 standards. The fatigue tests were carried out using Instron Electropuls E10000, the electromechanical system equipped with a temperature chamber with a working temperature range from -100 to +250ºС. At increased temperatures of 120 and 200ºС the thermostatically-controlled mode was similar. The specimens had thermomechanical fatigue life tests (the maximum number of fatigue fracture cycles (N max) at the parameters of cyclic loading: σmax = 0,5∙σB, where σB – strength limit, R = 0,1, ν = 20 Hz and a sinusoidal form of cycles. The study of changes in the residual strength and stiffness properties of the polymer composite specimens at a temperature of 120°C was carried out with a combination of the above techniques. The technique included quasistatic tensile tests with the determination of the nominal values of strength limit σB and Young's modulus E at increased temperatures. Later the value of fatigue life of the specimens N max was determined during cyclic tension wirth a frequency of ν = 15 Hz, coefficient of skewness R = 0,1 and the value of maximum stresses in cycle σ max = 0,5 σB. After that the specimens were subjected to cyclic pre-exposure with cycle life in the range (0,1 – 0,8) Nmax. The values of residual strength and stiffness characteristics of the studied PCM specimens were determined during quasistatic tensile tests at increased temperatures.
Dmitrii S. Lobanov et al. / Procedia Structural Integrity 17 (2019) 651–657 Lobanov Dmitrii S., Staroverov Oleg A./ Structural Integrity Procedia 00 (2019) 000–000
653 3
3. Results of Fatigue Tests at Increased Temperatures The results of the preliminary quasistatic tension tests of glass fiber plastic specimens at 22, 120 и 200ºС temperatures are given in Table 1. Таble 1. Results of preliminary static tensile tests at normal and increased temperatures Temperature , strength limit σB, MPa Young's modulus E, GPa °С 22
329±28
26,5±1,5
120
295±24
22,8±1,4
200
165±8
13,5±1,5
As a result of the cyclic tests, the values of fatigue life of the fiberglass specimens were obtained. The effect of the increased temperatures is reflected in the fatigue life degradation diagram (Fig. 1). To describe the behavior of the specimens during cyclic tests at increased temperatures, we introduce n’ value reflecting the change in the value of fatigue life as a result of damage accumulation, which is expressed as: 𝑛𝑛′ = 𝑛𝑛⁄𝑁𝑁
(1)
where n is a number of cycles up to failure at different testing temperatures; N is the nominal number of cycles up to failure at room temperature.
Fig. 1. Diagram of dependence fatigue life - high temperatures for fiberglass samples at the parameters of cyclic loading: σmax = 0,5∙σB, R = 0,1, ν = 20 Hz
The diagram of the fatigue life degradation is non-linear in nature. To predict the residual life of the PCM specimens at increased temperatures, a trend line was plotted on the diagram. The change in the stiffness properties of fiberglass specimens, as a result of the fatigue damage accumulation was evaluated using the indirect technique based on measuring the amplitude of displacements of the loading pattern specimen/traverse during the test. The change in the amplitude of the movements was recorded using WaveMatrix software. For example, Fig.2 shows characteristic diagrams of changes stiffness values of specimen during fatigue tests at various temperatures. The ordinate axis is R, and the abscissa axis n’ is the relative number of cycles to failure at various temperatures.
Dmitrii S. Lobanov et al. / Procedia Structural Integrity 17 (2019) 651–657 Lobanov Dmitrii S., Staroverov Oleg A./ Structural Integrity Procedia 00 (2019) 000–000
654 4
(2)
𝑅𝑅 = 𝑃𝑃 ⁄𝑢𝑢𝑎𝑎
where ua is the value of the amplitude of sample’s displacements during tests; P – is the load value under cyclic tension; nt – is a relative number of cycles up to fracture at different temperatures.
Fig. 2. Diagrams of changes in the relative values of the stiffness of the sample R during fatigue testing at various temperatures
A decrease in the relative value of the specimen stiffness R by 0.1 corresponds to a decrease in the specimen stiffness by 10%. Under the test temperatures of 120°C and 200°C, the dependences of R stiffness alterations had a similar view; the curves appeared on the straight section of the diagram after a smaller number of cycles compared to the curves obtained during the tests at room temperature. For the specimens tested at 200°C, fracture occurred with numerous delaminations throughout the working area of the specimen (Fig. 3); in the diagram of R specimen relative stiffness, this type of fracture corresponds to the interval (0.9 - 1) n’. a
b
c
Fig. 3. Fracture surfaces of specimens after fatigue life tests at 22 (a), 120 (b) and 200 ° C (c)
Under the testing temperatures between 22 and 120°С with respect to ASTM classification, the specimens fractured according to the LGM mechanism; under higher temperature of 200°С there comes the shift of fracture mechanisms into DGM and DMM (Fig.3). A significant destruction of the binder leads to a disruption of interlayer adhesion and development of multiple delaminations in the working area of the fiberglass specimens. 4. Constructing Diagrams of Fatigue Sensitivity of Fiberglass Composites at Increased Temperatures The relations of the residual properties alterations on preliminary cyclic loads and increased temperature (120°C) are presented in the form of the fatigue sensitivity diagram by Wil'deman V. E. et al (2018). The diagram of fatigue sensitivity in relative coordinates KBn’ – n’, where ′ (3) = 𝜎𝜎𝐵𝐵𝐵𝐵 ⁄𝜎𝜎𝐵𝐵 𝐾𝐾𝐵𝐵𝐵𝐵 is the factor of retention of the static strength in cyclic loading, with σ Bn and σB — the strengths after and before
Dmitrii S. Lobanov et al. / Procedia Structural Integrity 17 (2019) 651–657 Lobanov Dmitrii S., Staroverov Oleg A./ Structural Integrity Procedia 00 (2019) 000–000
655 5
cyclic loadings; 𝑛𝑛′ = 𝑛𝑛⁄𝑁𝑁 (4) is the relative number of cycles of preliminary loading, with n — the number of cycles of preliminary cyclic loading and N — the limiting number of cycles to failure at given parameters.
Fig. 4. Diagrams of fatigue sensitivity at normal and elevated temperatures (120°C)
The test results analysis at increased temperatures showed that, compared to the specimens tested at normal temperature, the decrease in the value of the residual tensile strength occurred in two stages, without a zone of the initial fatigue sensitivity (Fig.4). In the interval of fatigue sensitivity (0.1 – 0.8) n’, the change in the value of the coefficient of static strength retaining under cyclic loading (KBn’) did not exceed 5%, which corresponds to the stabilization stage. For the specimens under room temperature, the K Bn’ value in the interval of stabilization was 15% lower, compared to the specimens tested at increased temperatures. At the aggravation interval (0,8 – 1) n’, a sharp decrease in the residual strength followed by fatigue failure of the specimens occurred.
n’ = 0,1
n’ = 0,2
n’ = 0,4
n’ = 0,6
n’ = 0,8
n’ = 1
Fig. 5. Development of zones of local delamination on the surface of the working area of fiberglass specimens depending on the number of cycles passed
Fig.5 shows the surfaces of the working area of the specimens after preliminary cyclic loading with different cycle numbers. There are local delamination zones formed in the process of fatigue damage accumulation on the surface
656 6
Dmitrii S. Lobanov et al. / Procedia Structural Integrity 17 (2019) 651–657 Lobanov Dmitrii S., Staroverov Oleg A./ Structural Integrity Procedia 00 (2019) 000–000
of the specimens. This part of The work was performed as part of the fulfillment of the state task of the Ministry of Education and Science of Russia No. 9.7526.2017/9.10 Conclusion Methodological issues related to the combined effect of mechanical loads and increased temperatures have been worked out. A series of experimental studies have been conducted to study the influence of increased temperatures on fatigue life, relative stiffness and residual strength of structural fiberglass specimens. It has been outlined that when the temperature rises to 120°С, the fatigue life of fiberglass decreases at the given loading parameters by 20-30%, at the temperature of 200°С by 60-70%. The analysis of changes in the destruction mechanisms during fatigue life was made depending on the test temperature. The diagrams of fatigue sensitivity and stiffness changes for the fiberglass specimens were constructed and features of the residual strength alterations at increased temperatures were revealed. A study of the fracture surface patterns of the fiberglass flat specimens was made. It was noted that in the process of fatigue accumulation of damage, local heating and delamination intervals were formed on the surface of the specimens. Acknowledgements The research was performed at the Perm National Research Polytechnical University at support of the Russian Scientific Fund (project No. 18-79-00209). References Babushkin, A.V., Lobanov, D.S., Kozlova, A.V., Morev, I.D., 2013. Research of the effectiveness of mechanical testing methods with analysis of features of destructions and temperature effects. Frattura ed Integrita Strutturale 24, 89–95. Chen, G., Zhang, W., Iizuka, T., 2019. The fatigue fracture characteristics of the bond zone of aluminum matrix composites (Al-12Si/ABOw) with Al-12Si alloys. Materials Science and Engineering A 755, 181–189. Colombo, C., Bhujangrao, T., Libonati, F., Vergani, L., 2019. Effect of delamination on the fatigue life of GFRP: A thermographic and numerical study. Composite Structures 218, 152–161. Dattoma, V., Giancane, S., 2013. Evaluation of energy of fatigue damage into GFRC through digital image correlation and thermography. Composites Part B: Engineering 47, 283–289. Fouchier, N., Nadot-Martin, C., Conrado, E., Bernasconi, A., Castagnet, S., 2019. Fatigue life assessment of a Short Fibre Reinforced Thermoplastic at high temperature using a Through Process Modelling in a viscoelastic framework. International Journal of Fatigue 124, 236–244. Habibi, M., Laperrière, L., Hassanabadi, H.M., 2019. Effect of moisture absorption and temperature on quasi-static and fatigue behavior of nonwoven flax epoxy composite. Composites Part B: Engineering 166, 31–40. Haggui M., El Mahi, A., Jendli, Z., Akrout, A., Haddar, M., 2018. Static and fatigue characterization of flax fiber reinforced thermoplastic composites by acoustic emission. Applied Acoustics. Kucher, N.K., Zarazovskii, M.N., Danil’chuk, E.L., 2013. Deformation and strength of laminated carbon-fiber-reinforced plastics under a static thermomechanical loading. Mechanics of Composite Materials 6, 669–680. Lobanov, D.S., Babushkin, A.V., Luzenin, A.Yu., 2018. Effect of increased temperatures on the deformation and strength characteristics of a GFRP based on a fabric of volumetric weave. Mechanics of Composite Materials 5, 655–664. Lobanov, D.S., Slovikov, S.V., 2017. Mechanical properties of a unidirectional basalt-fiber-reinforced plastic under a loading simulating operation conditions. Mechanics of Composite Materials 6, 767–772. Lobanov, D. S., Vildeman, V. E., Babin, A. D., and Grinev, M. A., 2015. Experimental research into the effect of external actions and polluting environments on the serviceability of fiber-reinforced polymer composite materials. Mechanics of Composite Materials 1, 69–79. Lobanov, D.S., Wildemann, V.E., Spaskova, E.M., Chikhachev, A.I., 2015. Experimental investigation of the defects influence on the composites sandwich panels strength with use digital image correlation and infrared thermography methods. PNRPU Mechanics Bulletin 4, 159–170. DOI: 10.15593/perm.mech/2015.4.10. Maleki, A., Saeedifar, M., Najafabadi, M. A., Zarouchas D., 2018. The fatigue failure study of repaired aluminum plates by composite patches using Acoustic Emission. Engineering Fracture Mechanics. Manteghi, S., Sarwar, A., Fawaz, Z., Zdero, R., Bougherara, H., 2019. Mechanical characterization of the static and fatigue compressive properties of a new glass/flax/epoxy composite material using digital image correlation, thermographic stress analysis, and conventional mechanical testing. Materials Science and Engineering C 99, 940–950. Maragoni, L., Carraro, P.A., Peron, M., Quaresimin, M., 2016. Fatigue behavior of glass/epoxy laminates in the presence of voids. International Journal of Fatigue 95, 18–28.
Dmitrii S. Lobanov et al. / Procedia Structural Integrity 17 (2019) 651–657 Lobanov Dmitrii S., Staroverov Oleg A./ Structural Integrity Procedia 00 (2019) 000–000
657 7
Matvienko, Y.G., Vasil’ev, I.E., Ivanov, V.I., Elizarov, S.V., 2016. Acoustic-emission evaluation of the process of destruction of a composite material under tensile, compression, and cyclic loads. Russian Journal of Nondestructive Testing 8, 443-456. Montesano, J., Fawaz, Z., Bougherara, H., 2013. Use of infrared thermography to investigate the fatigue behavior of a carbon fiber reinforced polymer composite. Composite Structures 97, 76–83. Movahedi-Rad, A.V., Keller, T., Vassilopoulos, 2019. Creep effects on tension-tension fatigue behavior of angle-ply GFRP composite laminates. International Journal of Fatigue 123, 144–156. Philippidis, T.P., Assimakopoulou, T.T., 2008. Using acoustic emission to assess shear strength degradation in FRP composites due to constant and variable amplitude fatigue loading. Composites Science and Technology 68, 840–847. Philippidis, T.P., Passipoularidis, V.A., 2007. Residual strength after fatigue in composites: Theory vs. experiment. International Journal of Fatigue. 29, 2104–2116. Plekhov, O., Palin-Luc, T., Saintier, N., Uvarov, S., Naimark, O., 2005. Fatigue crack initiation and growth in a 35crmo4 steel investigated by infrared thermography. Fatigue & fracture of engineering materials & structures 28 (1-2), 169 – 178. Růžek, R., Kadlec, M., Petrusová, L., 2018. Effect of fatigue loading rate on lifespan and temperature of tailored blank C/PPS thermoplastic composite. International Journal of Fatigue 113, 253–263. Strizhius, V., 2016. Estimation of the residual fatigue life of laminated composites under a multistage cyclic loading. Mechanics of Composite Materials 5, 611—622. Van Paepegem, W., Dechaene, R., Degrieck, J., 2005. Nonlinear correlation to the bending stiffness of a damaged composite beam. Composite Structures 67, 359–364. Wildemann, V.E., Spaskova, E.V., Shilova, A.I., 2016. Research of the Damage and Failure Processes of Composite Materials Based on Acoustic Emission Monitoring and Method of Digital Image Correlation. Solid State Phenomena 243, 163–170. Wil'deman, V. E., Staroverov, O. A., Lobanov, D. S., 2018. Diagram and parameters of fatigue sensitivity for evaluating the residual strength of layered GFRP composites after preliminary cyclic loadings. Mechanics of Composite Materials 3, 313–320.