- Email: [email protected]
Frequency and hold-time effects on low cycle fatigue life of notched specimens at elevated temperature
Fatigue strength of aluminium alloys. XXl. Takeuchi, K. Kei Kinzoku Yosetsu (J. Light Met. Weld. Constr). 1987 27, (1), 23-31 (in Japanese) Various aspects of fatigue of AI alloys due to low-cycle stress are reviewed, such as the definition of low,cycle fatigue expression of low cycle fatigue curves (Coffin-Manson rule, Bausquin rule, Langer method), comparison of low-cycle fatigue curves (2000 series. 5000 series, 7000 series. 6061, pure AI). results of fatigue tests (2014-T6. 5052-H32. Co061-T6. 7175-T73). and fatigue curves for individual alloys (5052-H32. 7075-T7531. 7475-3"7351 5083-0, 2024-T4, 2024-T351 ) under different conditions. Several models were proposed to treat the effect of the direction of stress on the fatigue strength. However, none of them appears to agree with experimental data satisfactorily. 18 refs.
the abnormal fatigue life drop is presented, Normally, interstitial atoms are in a position which minimizes the energy around a dislocation, the Sneak ordering sites, The ShoCk effect as a typical example of anelasticity, and the possiblity on atoms moving from attractive sites to repulsive ones when repeated stresses are applied are considered. A theory to explain the reduction of the fatigue life using Shock ordered atoms moving out by fatigue stress at the frequency of Snoek effect is discussed. Bending fatigue tests were conducted to obtain the relationship between fatigue life and Iced frequency at two different tempera. tures (298 and 333 K) for an Fe nitrided steel 30CrMoV. A sharp fatigue life drop was observed at a load frequency corresponding to the resonant frequency of the Shock effect for nitrogen atoms. The frequency was approx 3 hz at 298 K and shifted to a higher frequency, approx 6 Hz, at 333 K. Results reveal that the possible explanation to those .abnormal phenomena may be anelasticity. 23 refs.
Sensitivity of fatigue crack growth prediction (using Wheeler retardation) to data representation. Finney, J.M. ASTM J. Test. Eva/. Mar. 1989 17, (2), 75-81
Fatigue strength of aluminium alloy. XVII. Takeuchi, K. Kei Kinzoku Yosetsu (J. Light Met. Weld. Constr). Sept. 1988 28, (9), 1 7 - 4 2 4
Using the Wheeler model for predicting fatigue crack growth (in 7075-T651 and 2214-T651 alloys) as a case study, the likely errors in prediction form selecting literature calibration values are examined. From four methods of representi the same da]dN-&K data, errors in crack life prediction up to a factor of about three were obtained, Because calibration values are stress scale dependent, the influence of interpolations and extrapolations on predicted crack growth life is also examined. Large extrapolations may lead to errors in predicted life. also approaching a factor of three. 14 refs.
The propagation rate of fatigue fracture under variable repeating load is discussed, where Paris law is not applicable and the acceleration or retardation of fracture propagation occurs. The fracture propagation rate can be related to the effective stress intensity range AKeff, that is estimated from the stress intensity factor KoD or fracture opening in constant amplitude tests. The graphic data of 5083, 7N01 and 7075 alloy are quoted. 13 refs.
Effect of primary alpha phase on fatigue crack growth of Ti-6AI-4V alloy. Nozue, A. and Ukubo, T. J. Jpn. Inst. Met. Nov. 1988 52, (11), 1 0 5 7 - 1 0 6 2 (in Japanese) The purpose is to clarify fatigue crack growth behaviour in Ti-6AI-4V alloy consisting of primary alpha and matrix. The phase ratio of the primary alpha to the matrix was varied from approx 65-20% with the solution treatment. The temperature range for this treatment was between 11481228 K. Fatigue tests were carried out in the AK region from the fatigue threshold to the critical fatigue fracture under constant load amplitude with CT specimens of 6 mm thickness. The crack propagated preferentially in the primary alpha phase compared with the matrix. On the fracture surfaces of the primary alpha phases, comparatively flat facets were observed in the low AK region and the striations were clearly observed in the high &K region, In addition, martensite boundary cracks existed in the matrix, It was found that the primary alpha fraction mainly controlled the fatigue crack growth rate in the region of the stable crack growth. 13 refs.
Constitutive modelling of anisothermal cyclic plasticity of 304 stainI i s t e e l . Ohno, N., Takahashi, Y. and Kuwabara, K. J. Eng. Mater. TechnoL (Trans. ASME) Jan 1989 111, (1), 1 0 6 - 1 1 4 Temperature-history dependence in anisothermal cyclic plasticity of 304 stainless steel is studied for the constitutive modelling within the temperature range from room temperature to 6OO'C. Cyclic plastic behaviour under in-phase and out-of-phase changes of temperature and a thermal.strain is analysed first by use of an elaborate constitutive model with its material constants determined from isothermal experiments; good agreement is obtained between the predictions and experiments, if it assumed that the internal change proper to higher temperature prevails under such thermomechanioal cycling. This finding leads one to extend the evolution equation of isotropical hardening so that it can be valid for more complex variations of temperature. The extended model simulates well the recent experiments of Niitsu and Ikegami under multi-step changes of temperature, 17 refs.
The affect of several finishing p r o c l e s on the fatigue resistance of hole surfaces. Lai, M.O. and Nee, A. Y.C. J. Eng. Mater. Technol. (Trans. ASME) Jan. 1989 111, (1), 7 1 - 7 3 This investigation examines the effects of different finishing processes on the fatigue life of premaohined holes in Assab 760 (1050 or En43) steel plates. The finishing processes studied were reaming, ballizing, and emery polishing. A general decrease in fatigue life with increase in surface roughness is observed for all the processes employed~ In comparing the different processes, for a constant surface roughness, polishing is generally found to give the longest fatigue life while bellizing, in spite of the greater compressive residual stresses induced on the surface of the finished hole. the shortest. The surprising phenomenon was found to be attributed to the amount of plastic deformation that occurred before fatigue loading. For Assab 760 steel, a prestrain in the radial direction of < approx 2.5% appeared to reduce the fatigue resistance of the material. 6 refs.
Frequency and hold-time effects on low cycle fatigue life of notched specimens at elevated temperature. Sakane, M., Ohnami, M., Awaya, T. and Shirafuji, N. J. Eng. Mater. Technol. (Trans. ASME) Jan. 1989 111, (1), 5 4 - 6 0 The frequency and hold-time effects on high temperature low cycle fatigue for round notched specimens (SS305) are described. Unnotched and notched specimens having different elastic stress concentration factors were fatigued under triangular and trapezoidal stress waves at frequencies ranging from 5-0.0001 Hz at 873 K. The three specific fracture characteristics were observed: cycle dependent, time dependent, and cycle-time dependent. The respective notch sensitivity oc~::urred in the respective fracture regime. The fatigue life of notched specimens was predicted from the elastic-plastic-creep cyclic FEM analysis using the linear damage rule and the strain range partitioning rule. Both the life prediction methods predicted the creep-fatigue life within almost a factor of two scatter band. 15 refs.
An abnormally shortened fatigue lifo of steels caused by anelasticity. Ishizaki, K. and Mineura, K. J. Mater. Sci. Jan. 1989 24, (1), 2::39-242 Some abnormal fatigue life shortenings dependent upon load frequency for several steels are discussed, A possible relation between anelasticity caused by interstitial atoms and
Int J Fatigue July 1989
(in Japanese)
Testing and Control Thermography study on fatigue fracture of metals. Huang, Y., Lin, X. and Xu, J. Acta Metal/. Sin. (Chine) J u n e 1988 24, (3), B 2 0 7 - B 2 1 3 (in Chinese) A high time resolution thermovision and an infrared detector with a diameter of 20 mm were used to detect the temperature distribution on the surface of samples which underwent rotation and bending fatigue at high speed. The relation between infrared radiation and local fatigue damage has been determined. A new non-destructive testing method for fatigue damage has been given. 3 refs.
The detection and measurement of overlapping fatigue cracks at welded joints by thin-skin electromagnetic fields. Haq, R., Michael, D.H. and Collins, R. Proc. R. Soc. London A Sept. 1988 419, (1856), 6 - 8 9 Fatigue cracks occur at different locations at the toes of welded steel joints, With continued Iced cycling it is often found that the cracks grow towards each other and the overlap in adjacent parallel planes. It is useful to be able to detect and measure overlapping cracks and the characteristic responses to be expected from these features are calculated for the alternating-current field-measurement method of non-destructive evaluation by thinskin theory. Typical signal profiles are calculated for probe traverses across the cracks and parallel to the edges, These are compared with experimental data obtained by using three pairs of overlapping notches with different proportions, cut in a mild steel block. The notches were interrogated by a thin skin field at a frequency of 6 kHz. The calculations show that overlapping cracks give rise to asymmetric cross-crack signal profiles, which do not occur for single cracks, and to characteristic changes in curvature in the probe response profiles. These features are well confirmed by the experiments. The results also show that traverses along the crack edges can be used to find the positions of the crack ends. 10 refs.
A thermal-mechanical fatigue crack-growth testing system. Perno~ J.J. and Mall. S. Exp. Tech. Feb. 1989 13, (2), 2 4 - 2 8 Components in high temperature machinery are often subjected to complex thermal and mechanical Ioadings. This usually leads to failure due to fatigue crack growth. In such instances, fatigue cracks experience simultaneous variation of temperature with cyclic stress or strain which is commonly referred to as thermal-mechanical fatigue (TM F). The investigation of the fatigue crack growth for TMF loading conditions is an important engineering problem. The objective is to present the development of a thermal-mechanical fatigue crack-growth testing set-up. Since this work involves materials which are of high cost and low availabiility leg titanium aluminide intermetallic alloys), test specimens must be small. The developed equipment features the capability of testing such small specimens, ie compact tension (CT) specimens. 7 refs
Crack measurement techniques for high-tomperature applications. Kirchner, T.E., Nagar, A., Domash, L. and Burstein, P. Exp. Tech. Dec. 1988 12, (12), 26-31 An application of fracture mechanics to durability and damage tolerance assessment of aerospace structures requires reliable measurment of crack length during crack-growth tests Advanced aerospace vehicles encounter variabte mechanical loads and thermal variations. Thus crack-growth measurement techniques at elevated temperatures are required, Current methods for determining crack length are based on measurements of physical quantities such as strain, compliance or potential drop. The changes in these quantities are calibrated with the changes in crack dimensions as the latter extends. New techniques are presented to measure the crack length directly while retaining the capability for automation. The key for the feasiblity for such a technique lies in the davelopment of a crack sensor. Two crack-sensor technologies based on laser and X-ray directions have the potential to meet the requirements for automated crack-length measurement at high temperature. Both technologies were investigated and cracks were imaged with laser and X-ray illumination, Further experiments on stainless steel 304 samples were conducted to establish if the laser camera would see a crack in a specimen that will self-illuminate at 1100°C and if an X-ray camera will see a crack in a specimen that could be at large angles to the X-ray flux. The experimental crack-length measurement showed that both the laser and the X-ray approaches were viable. The laser technique was selected based on.wider performance margins and system implementation considerations. 3 refs.
287
the abnormal fatigue life drop is presented, Normally, interstitial atoms are in a position which minimizes the energy around a dislocation, the Sneak ordering sites, The ShoCk effect as a typical example of anelasticity, and the possiblity on atoms moving from attractive sites to repulsive ones when repeated stresses are applied are considered. A theory to explain the reduction of the fatigue life using Shock ordered atoms moving out by fatigue stress at the frequency of Snoek effect is discussed. Bending fatigue tests were conducted to obtain the relationship between fatigue life and Iced frequency at two different tempera. tures (298 and 333 K) for an Fe nitrided steel 30CrMoV. A sharp fatigue life drop was observed at a load frequency corresponding to the resonant frequency of the Shock effect for nitrogen atoms. The frequency was approx 3 hz at 298 K and shifted to a higher frequency, approx 6 Hz, at 333 K. Results reveal that the possible explanation to those .abnormal phenomena may be anelasticity. 23 refs.
Sensitivity of fatigue crack growth prediction (using Wheeler retardation) to data representation. Finney, J.M. ASTM J. Test. Eva/. Mar. 1989 17, (2), 75-81
Fatigue strength of aluminium alloy. XVII. Takeuchi, K. Kei Kinzoku Yosetsu (J. Light Met. Weld. Constr). Sept. 1988 28, (9), 1 7 - 4 2 4
Using the Wheeler model for predicting fatigue crack growth (in 7075-T651 and 2214-T651 alloys) as a case study, the likely errors in prediction form selecting literature calibration values are examined. From four methods of representi the same da]dN-&K data, errors in crack life prediction up to a factor of about three were obtained, Because calibration values are stress scale dependent, the influence of interpolations and extrapolations on predicted crack growth life is also examined. Large extrapolations may lead to errors in predicted life. also approaching a factor of three. 14 refs.
The propagation rate of fatigue fracture under variable repeating load is discussed, where Paris law is not applicable and the acceleration or retardation of fracture propagation occurs. The fracture propagation rate can be related to the effective stress intensity range AKeff, that is estimated from the stress intensity factor KoD or fracture opening in constant amplitude tests. The graphic data of 5083, 7N01 and 7075 alloy are quoted. 13 refs.
Effect of primary alpha phase on fatigue crack growth of Ti-6AI-4V alloy. Nozue, A. and Ukubo, T. J. Jpn. Inst. Met. Nov. 1988 52, (11), 1 0 5 7 - 1 0 6 2 (in Japanese) The purpose is to clarify fatigue crack growth behaviour in Ti-6AI-4V alloy consisting of primary alpha and matrix. The phase ratio of the primary alpha to the matrix was varied from approx 65-20% with the solution treatment. The temperature range for this treatment was between 11481228 K. Fatigue tests were carried out in the AK region from the fatigue threshold to the critical fatigue fracture under constant load amplitude with CT specimens of 6 mm thickness. The crack propagated preferentially in the primary alpha phase compared with the matrix. On the fracture surfaces of the primary alpha phases, comparatively flat facets were observed in the low AK region and the striations were clearly observed in the high &K region, In addition, martensite boundary cracks existed in the matrix, It was found that the primary alpha fraction mainly controlled the fatigue crack growth rate in the region of the stable crack growth. 13 refs.
Constitutive modelling of anisothermal cyclic plasticity of 304 stainI i s t e e l . Ohno, N., Takahashi, Y. and Kuwabara, K. J. Eng. Mater. TechnoL (Trans. ASME) Jan 1989 111, (1), 1 0 6 - 1 1 4 Temperature-history dependence in anisothermal cyclic plasticity of 304 stainless steel is studied for the constitutive modelling within the temperature range from room temperature to 6OO'C. Cyclic plastic behaviour under in-phase and out-of-phase changes of temperature and a thermal.strain is analysed first by use of an elaborate constitutive model with its material constants determined from isothermal experiments; good agreement is obtained between the predictions and experiments, if it assumed that the internal change proper to higher temperature prevails under such thermomechanioal cycling. This finding leads one to extend the evolution equation of isotropical hardening so that it can be valid for more complex variations of temperature. The extended model simulates well the recent experiments of Niitsu and Ikegami under multi-step changes of temperature, 17 refs.
The affect of several finishing p r o c l e s on the fatigue resistance of hole surfaces. Lai, M.O. and Nee, A. Y.C. J. Eng. Mater. Technol. (Trans. ASME) Jan. 1989 111, (1), 7 1 - 7 3 This investigation examines the effects of different finishing processes on the fatigue life of premaohined holes in Assab 760 (1050 or En43) steel plates. The finishing processes studied were reaming, ballizing, and emery polishing. A general decrease in fatigue life with increase in surface roughness is observed for all the processes employed~ In comparing the different processes, for a constant surface roughness, polishing is generally found to give the longest fatigue life while bellizing, in spite of the greater compressive residual stresses induced on the surface of the finished hole. the shortest. The surprising phenomenon was found to be attributed to the amount of plastic deformation that occurred before fatigue loading. For Assab 760 steel, a prestrain in the radial direction of < approx 2.5% appeared to reduce the fatigue resistance of the material. 6 refs.
Frequency and hold-time effects on low cycle fatigue life of notched specimens at elevated temperature. Sakane, M., Ohnami, M., Awaya, T. and Shirafuji, N. J. Eng. Mater. Technol. (Trans. ASME) Jan. 1989 111, (1), 5 4 - 6 0 The frequency and hold-time effects on high temperature low cycle fatigue for round notched specimens (SS305) are described. Unnotched and notched specimens having different elastic stress concentration factors were fatigued under triangular and trapezoidal stress waves at frequencies ranging from 5-0.0001 Hz at 873 K. The three specific fracture characteristics were observed: cycle dependent, time dependent, and cycle-time dependent. The respective notch sensitivity oc~::urred in the respective fracture regime. The fatigue life of notched specimens was predicted from the elastic-plastic-creep cyclic FEM analysis using the linear damage rule and the strain range partitioning rule. Both the life prediction methods predicted the creep-fatigue life within almost a factor of two scatter band. 15 refs.
An abnormally shortened fatigue lifo of steels caused by anelasticity. Ishizaki, K. and Mineura, K. J. Mater. Sci. Jan. 1989 24, (1), 2::39-242 Some abnormal fatigue life shortenings dependent upon load frequency for several steels are discussed, A possible relation between anelasticity caused by interstitial atoms and
Int J Fatigue July 1989
(in Japanese)
Testing and Control Thermography study on fatigue fracture of metals. Huang, Y., Lin, X. and Xu, J. Acta Metal/. Sin. (Chine) J u n e 1988 24, (3), B 2 0 7 - B 2 1 3 (in Chinese) A high time resolution thermovision and an infrared detector with a diameter of 20 mm were used to detect the temperature distribution on the surface of samples which underwent rotation and bending fatigue at high speed. The relation between infrared radiation and local fatigue damage has been determined. A new non-destructive testing method for fatigue damage has been given. 3 refs.
The detection and measurement of overlapping fatigue cracks at welded joints by thin-skin electromagnetic fields. Haq, R., Michael, D.H. and Collins, R. Proc. R. Soc. London A Sept. 1988 419, (1856), 6 - 8 9 Fatigue cracks occur at different locations at the toes of welded steel joints, With continued Iced cycling it is often found that the cracks grow towards each other and the overlap in adjacent parallel planes. It is useful to be able to detect and measure overlapping cracks and the characteristic responses to be expected from these features are calculated for the alternating-current field-measurement method of non-destructive evaluation by thinskin theory. Typical signal profiles are calculated for probe traverses across the cracks and parallel to the edges, These are compared with experimental data obtained by using three pairs of overlapping notches with different proportions, cut in a mild steel block. The notches were interrogated by a thin skin field at a frequency of 6 kHz. The calculations show that overlapping cracks give rise to asymmetric cross-crack signal profiles, which do not occur for single cracks, and to characteristic changes in curvature in the probe response profiles. These features are well confirmed by the experiments. The results also show that traverses along the crack edges can be used to find the positions of the crack ends. 10 refs.
A thermal-mechanical fatigue crack-growth testing system. Perno~ J.J. and Mall. S. Exp. Tech. Feb. 1989 13, (2), 2 4 - 2 8 Components in high temperature machinery are often subjected to complex thermal and mechanical Ioadings. This usually leads to failure due to fatigue crack growth. In such instances, fatigue cracks experience simultaneous variation of temperature with cyclic stress or strain which is commonly referred to as thermal-mechanical fatigue (TM F). The investigation of the fatigue crack growth for TMF loading conditions is an important engineering problem. The objective is to present the development of a thermal-mechanical fatigue crack-growth testing set-up. Since this work involves materials which are of high cost and low availabiility leg titanium aluminide intermetallic alloys), test specimens must be small. The developed equipment features the capability of testing such small specimens, ie compact tension (CT) specimens. 7 refs
Crack measurement techniques for high-tomperature applications. Kirchner, T.E., Nagar, A., Domash, L. and Burstein, P. Exp. Tech. Dec. 1988 12, (12), 26-31 An application of fracture mechanics to durability and damage tolerance assessment of aerospace structures requires reliable measurment of crack length during crack-growth tests Advanced aerospace vehicles encounter variabte mechanical loads and thermal variations. Thus crack-growth measurement techniques at elevated temperatures are required, Current methods for determining crack length are based on measurements of physical quantities such as strain, compliance or potential drop. The changes in these quantities are calibrated with the changes in crack dimensions as the latter extends. New techniques are presented to measure the crack length directly while retaining the capability for automation. The key for the feasiblity for such a technique lies in the davelopment of a crack sensor. Two crack-sensor technologies based on laser and X-ray directions have the potential to meet the requirements for automated crack-length measurement at high temperature. Both technologies were investigated and cracks were imaged with laser and X-ray illumination, Further experiments on stainless steel 304 samples were conducted to establish if the laser camera would see a crack in a specimen that will self-illuminate at 1100°C and if an X-ray camera will see a crack in a specimen that could be at large angles to the X-ray flux. The experimental crack-length measurement showed that both the laser and the X-ray approaches were viable. The laser technique was selected based on.wider performance margins and system implementation considerations. 3 refs.
287