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Prediction of thermomechanical fatigue lives in metal matrix composites
of selected specimens were examined in a scanning electron microscope to determine the operative fracture micromachenismls). end t h e o m t l u l studies into t h e f ~ l g u e c r ~ k propagation • 7075 e l u m i n l u m - z l n c alloy under constant end variable amplitude loading. Kyriacou, S. A. Diss Abstr Int 52 10 (Apr 1992) 424 pp Both theoretical and experimental work performed in order to study the fatigue crack propagation beheviour of the 7075 "1"/351 Al-Zn alloy, under constant and variable amplitude loading, are described. For the theoretical aspects of the work, static, elastic and elaatic-plaatic finite element methods were utilized for the evaluation of residual stresses, caused by overloading, in the vicinity of the crack tip. The results have demonatreted that the plasticity caused by the loading part of the load cycle induces compressive residual stresses in the vicinity of the crack upon partial and/or full unloading. The experimental work has been carried out to ascertain the constant load amplitude fatigue crack growth beheviour, it has been established that the material does not exhibit a sigmoidal crack growth curve, but one of parabolic-like shape. An empirical crack growth law has bean derived to describe the constant load amplitude beheviour. It has been established that overloads cause substantial extension of the total life to failure owing to delays caused by overloading. The observed delay increases if block overloads are introduced, end crack arrest may occur. Finally, it is concluded that crack closure is responsible for the observed crack growth rate reductions. Wear behaviour of austempered ductile iron.Ahmadabadi, M.N., Nategh,
S. and Davami, P. Cast Metals ( n o w Cast Metal Sciences) 4 4 (1992) pp 188-194 Castings ere very widely used for critical friction and wear applications. As operating conditions are becoming more arduous, greater demands will be placed upon the casting industry to meet the requirements of the designer. This study wee undertaken to evaluate the wear resistance of 2.5% Ni, 0.4% Me austempered ductile iron, having a hardness of HB 270 end a high amount of retained auatenite, in the particular context of a railway braking application. Pin-wear test data are presented, comparing wear beheviour of this ADI grade with that of a pearlitic grey cast iron which is currently employed as a brake block material in Iranian passenger trains, end with a 3% phosphorus cast iron which was developed in the UK. Graphs, photomicrographs. 25 refs. D e v e l o p m e n t of t e x t u r e under the running surface of Shinkansen Line rails w i t h increasing accumulated service tonnage. Inoue, Y., Satoh, Y.
and Kashiwaya, K. J Soc Mater Sci Jpn 41 461 (Feb 1992) pp 212-218 (in Japanese) The beheviour of plastic deformation was analysed in terms of texture development under the running surface of Shinkanean Line rails, which differs depending on the accumulated service tonnage. The results are discussed in comparison with those of rolling contact fatigue tests. It was found that the texture development under the running surface of Shinkansen Line rail steels was similar to that in a teatpiace tested under the conditions of slip ratio 0% and maximum Hertz pressure approx 0.9 GPa. A texture appeared with an increase in accumulated service tonnage. However, the X-ray half-value breadth did not change. This proves that the examination of texture development is useful in detecting roiling contact fatigue damage, Graphs, photomicrographs. 8 refs. Fatigue damage in cross-ply t i t a n i u m metal m a t r i x composites containing center holes. Bakuckas, J. G., Johnson, W. S. and Bigelow, C. A. N92-18957/0/XAB (Jan 1992) 31 pp The development of fatigue damage was studied in (0/90)SCS-6Ti-15-3/ laminates containing centre holes. Stress levels required for crack initiation in the matrix were predicted using an effective strain parameter and compared with experimental results. Damage progression was monitored at various stages of fatigue loading. In general, a saturated state of damage consisting of matrix cracks and fibre matrix debonding was obtained which reduced the composite modulus. Matrix cracks were bridged by the 0° fibres. The fatigue limit (stress causing catastrophic fracture of the laminates) was also determined. The static and post-fatigue residual strengths were accurately predicted using a three-dimensional elaatic-plaatic finite element analysis. The matrix damage that occurred during fatigue loading significantly reduced the notched strength.
the applied end net stress intensity factor ranges in cyclic loading. The application of the functions to the analysis of monotonic end fatigue crack growth data is illustrated. Consideration of the 'bridging length scale' concept reveals the kinds of data required for accurately determining relevant material constants and for testing the validity of the modelling assumptions. Graphs. 34 refs. Prediction o f thermomachanicul fatigue lives In metal m a t r i x composites.
Sehitoglu, H. and Karayeka, M. Metall Trsns A 23A 7 (July 1992) pp 2029-2038 To identify the role of silicon carbide particulate reinforcement on high-temperature thermomachanical fatigue beheviour OfAI 2xxx-T4, experiments have been conducted under thermomachenical out-of-phase and in-phase loading conditions. A general constitutive representation, bsaeq on Eshelby's inclusion theory, is used for the determination of volumetric average stresses and strains under cyclic loading of the metal matrix composite. This constitutive representation is used with a lifeprediction model, based on the matrix atrese-atrein bshaviour, which predicts contributions of fatigue, creep, and environmental damages to failure under both isothermal and thermomachnical fatigue loading, in isothermal fatigue experiments at 200 and 300 °C, pure fatigue damage and creep damage ere the dominant damage mechanisms in the short-life regime. In the long-life regime, however, the stress levels are too low to induce considerable creep damage, so oxidation damage becomes dominant. When fatigue damage is dominant, the model predicts • decrease in life, based on strain range, with increasing volume fraction of reinforcement. Based on stress range, improved fatigue lives are predicted with increasing volume fraction of reinforcement. The reinforced alloy exhibits longer lives when compressive hydrostatic stresses in the matrix at the high-tamperature end of the cycle reduce the creep damage. A fatigue design parameter f o r spot welds. Swellam, M. H, M. Diss Abstr Int 52 11 ( M a y 1992) 251 pp The development of fatigue cracks in galvanized low carbon and high-strength-lowalloy tensile-shear-spot weldments was inveatigeted using the AT&T Microhmater. The boundaries between the three stages of the fatigue life Were determined based on the resistivity measurements of the Microhmeter. Subsequently, the effects of sheet thickness, specimen width and nugget diameter on the total fatigue life and its stages were studied. Sheet thickness was found to have the largest effect on fatigue life while the nugget diameter had the least. The galvanized low C tansileshear specimens outperformed the corresponding high-strength-low-alloy specimens in the long-life regime. Finite element analyses together with the displacement match technique were used to determine the stress intensity factors for the tensileshear specimen. Several geometries were analysed and the effects of the sheet thickness, nugget diameter, specimen width and free length on the stress intensity factors Were determined. The stress intensity factors determined from the linear three-dimensional finite element analyses failed to correlate the fatigue data of tansile-sheer specimens with different dimensions. Consequently, an empirical /~ parameter based on the experimental fatigue data was derived. The K~ parameter collapsed the fatigue data of different spot-welded specimens into a narrow band for which a best fit was obtained. The best-fit equation helps estimate the fatigue life while the Ki parameter provides the designer with a useful tool for designing spot welds against fatigue and for studying the effects of varying any of the design variables on the fatigue performance of the spot welded joint without having to resort to extensive testing. Spot w e l d failure f r o m buckling-induced stressing of beams under cyclic bending and torsion. Kardomateas, G. A. Eng Fract Mech 42 3 (June 1992) pp 519-530 An important design constraint of spot-welded beams is the fatigue strength of the spot welds. The present study is concerned-with predicting th e cyclic life of spotwelded joints in beams under bending and torsion. First, the physical mechanism of buckling-induced stressing is analysed. The stress distribution is obtained from a two-dimensional buckling model. Afterwards, an expression for the J integral is found in terms of the geometric and loading parameters. This expression is used with a Paris" law type of fatigue crack growth to assess the fatigue life of the design. Subsequently, an analysis that explains the phenomenon for the case of torsion loading is provided. An example case is treated to obtain numerical results for the J integral and the number of fatigue cycles as a function of the applied loading or tt~e weld spacing. Graphs. 9 refs. A study o f the damage evaluation of w e l d heat affected zone. Lou, Z.-
Modeling of crack bridging in a unidirectional metal matrix composite. Ghosn, L. J., Kantzos, P. and Telesman, J. Int J Fract 54 4 (15 Apr 1992) pp 345-357 The effective fatigue crack driving force end crack opening profiles were determined analytically for fatigue-teated unidirectional composite specimens exhibiting fibre bridging. The crack closure pressure due to bridging was modelled using two approaches: the fibre pressure model and the shear lag model. For both closure models, the Buackner weight function method and the finite element method were used to calculate crack opening displacements and the crack driving force. The predicted profile near the crack tip opening agreed well with the experimentally measured profiles for single edge notch SCS-6/Ti-15-3 metal matrix composite specimens. The numerically determined effective crack driving force, &Kerr, was calculated using both models to correlate the measured crack growth rate in the composite. The calculated AK~e from both models accounted for the crack bridging by showing • good agreement between the measured fatigue crack growth rates of the bridged composite and that of unreinforced, unbridged Ti matrix alloy specimens. Graphs. 18 refs. Simple a p p r o x i m a t i o n s f o r bridged cracks in fibrous composites. Cox,
B. N. and Lo, C. S. Acts Metall Mater 40 7 (July 1992) pp 1487-1496
Analytical functions approximating the ratio of the net and the applied stress intensity factors are presented for bridged cracks in fibrous composites. The approximations summarize extensive, accurate numerical calculations for mode I matrix cracks growing in specimens of several common shapes under uniform remote loading. The bridging tractions are assumed to be related to the crack opening displacment by laws appropriate to undirectional fibres coupled to the matrix by friction. The same approximating functions also represent the ratio of
Int J Fatigue May 1993
W., Wang, T,-J. and Zuo, J.-Z. Acta Mech Solida Sinica 5 2 (1992) pp 235-244
The damage evolution of the weld-simulated heat affected zone (HAZ) is atudied from the micro- and macroscopic points of view. The ductile and Iow-cycte fatigue (LCF) damage evolution laws of the HAZ have been examined in the framework of continuum damage mechanics. Two ahernetive laws of damage are proposed, which may meat the need for describing the damage evolution of ductile rupture and LCF fracture. 15MnMoVNRe is discussed. Photomicrographs, graphs. 11 refs. Fracture mechanics analysis on fatigue design curves f o r steel structures.
Sakano, M., Mikami, I. and Miki, C. Technology Reports of Kansai University 34 ( M a r 1992) 171-179 Fatigue crack progegation analysis is carried out on six types of welded joint under constant amplitude end variable amplitude stresses, applying the fracture mechanics concept to set the variable amplitude cut-off limit of fatigue design curves. The variable-amplitude cut-off limit can be obtained as the stress range at which Miner's summation calculated from the higher streSS side of the stress range hiatogrem reaches 1. The number of stress cycles where the cut-off limit is defined varies with the type of welded joint. Graphs. 18 refs. Fatigue tests f o r plata girder specimens w i t h f o u r types of vertical stiffener connections. Sakano, M., Mikami, I., Yonemoto, E., Kano, K.
and Yasuike, H. Technology Reports of Kansai University 34 ( M a r 1992) pp 149-160
Long-life fatigue teats are performed using plate girder specimens with four types of vertical stiffener connections to inveatigate the initiation and propagation behaviour of fatigue cracks end the fatigue strength of each stiffener-to-girder
251
S. and Davami, P. Cast Metals ( n o w Cast Metal Sciences) 4 4 (1992) pp 188-194 Castings ere very widely used for critical friction and wear applications. As operating conditions are becoming more arduous, greater demands will be placed upon the casting industry to meet the requirements of the designer. This study wee undertaken to evaluate the wear resistance of 2.5% Ni, 0.4% Me austempered ductile iron, having a hardness of HB 270 end a high amount of retained auatenite, in the particular context of a railway braking application. Pin-wear test data are presented, comparing wear beheviour of this ADI grade with that of a pearlitic grey cast iron which is currently employed as a brake block material in Iranian passenger trains, end with a 3% phosphorus cast iron which was developed in the UK. Graphs, photomicrographs. 25 refs. D e v e l o p m e n t of t e x t u r e under the running surface of Shinkansen Line rails w i t h increasing accumulated service tonnage. Inoue, Y., Satoh, Y.
and Kashiwaya, K. J Soc Mater Sci Jpn 41 461 (Feb 1992) pp 212-218 (in Japanese) The beheviour of plastic deformation was analysed in terms of texture development under the running surface of Shinkanean Line rails, which differs depending on the accumulated service tonnage. The results are discussed in comparison with those of rolling contact fatigue tests. It was found that the texture development under the running surface of Shinkansen Line rail steels was similar to that in a teatpiace tested under the conditions of slip ratio 0% and maximum Hertz pressure approx 0.9 GPa. A texture appeared with an increase in accumulated service tonnage. However, the X-ray half-value breadth did not change. This proves that the examination of texture development is useful in detecting roiling contact fatigue damage, Graphs, photomicrographs. 8 refs. Fatigue damage in cross-ply t i t a n i u m metal m a t r i x composites containing center holes. Bakuckas, J. G., Johnson, W. S. and Bigelow, C. A. N92-18957/0/XAB (Jan 1992) 31 pp The development of fatigue damage was studied in (0/90)SCS-6Ti-15-3/ laminates containing centre holes. Stress levels required for crack initiation in the matrix were predicted using an effective strain parameter and compared with experimental results. Damage progression was monitored at various stages of fatigue loading. In general, a saturated state of damage consisting of matrix cracks and fibre matrix debonding was obtained which reduced the composite modulus. Matrix cracks were bridged by the 0° fibres. The fatigue limit (stress causing catastrophic fracture of the laminates) was also determined. The static and post-fatigue residual strengths were accurately predicted using a three-dimensional elaatic-plaatic finite element analysis. The matrix damage that occurred during fatigue loading significantly reduced the notched strength.
the applied end net stress intensity factor ranges in cyclic loading. The application of the functions to the analysis of monotonic end fatigue crack growth data is illustrated. Consideration of the 'bridging length scale' concept reveals the kinds of data required for accurately determining relevant material constants and for testing the validity of the modelling assumptions. Graphs. 34 refs. Prediction o f thermomachanicul fatigue lives In metal m a t r i x composites.
Sehitoglu, H. and Karayeka, M. Metall Trsns A 23A 7 (July 1992) pp 2029-2038 To identify the role of silicon carbide particulate reinforcement on high-temperature thermomachanical fatigue beheviour OfAI 2xxx-T4, experiments have been conducted under thermomachenical out-of-phase and in-phase loading conditions. A general constitutive representation, bsaeq on Eshelby's inclusion theory, is used for the determination of volumetric average stresses and strains under cyclic loading of the metal matrix composite. This constitutive representation is used with a lifeprediction model, based on the matrix atrese-atrein bshaviour, which predicts contributions of fatigue, creep, and environmental damages to failure under both isothermal and thermomachnical fatigue loading, in isothermal fatigue experiments at 200 and 300 °C, pure fatigue damage and creep damage ere the dominant damage mechanisms in the short-life regime. In the long-life regime, however, the stress levels are too low to induce considerable creep damage, so oxidation damage becomes dominant. When fatigue damage is dominant, the model predicts • decrease in life, based on strain range, with increasing volume fraction of reinforcement. Based on stress range, improved fatigue lives are predicted with increasing volume fraction of reinforcement. The reinforced alloy exhibits longer lives when compressive hydrostatic stresses in the matrix at the high-tamperature end of the cycle reduce the creep damage. A fatigue design parameter f o r spot welds. Swellam, M. H, M. Diss Abstr Int 52 11 ( M a y 1992) 251 pp The development of fatigue cracks in galvanized low carbon and high-strength-lowalloy tensile-shear-spot weldments was inveatigeted using the AT&T Microhmater. The boundaries between the three stages of the fatigue life Were determined based on the resistivity measurements of the Microhmeter. Subsequently, the effects of sheet thickness, specimen width and nugget diameter on the total fatigue life and its stages were studied. Sheet thickness was found to have the largest effect on fatigue life while the nugget diameter had the least. The galvanized low C tansileshear specimens outperformed the corresponding high-strength-low-alloy specimens in the long-life regime. Finite element analyses together with the displacement match technique were used to determine the stress intensity factors for the tensileshear specimen. Several geometries were analysed and the effects of the sheet thickness, nugget diameter, specimen width and free length on the stress intensity factors Were determined. The stress intensity factors determined from the linear three-dimensional finite element analyses failed to correlate the fatigue data of tansile-sheer specimens with different dimensions. Consequently, an empirical /~ parameter based on the experimental fatigue data was derived. The K~ parameter collapsed the fatigue data of different spot-welded specimens into a narrow band for which a best fit was obtained. The best-fit equation helps estimate the fatigue life while the Ki parameter provides the designer with a useful tool for designing spot welds against fatigue and for studying the effects of varying any of the design variables on the fatigue performance of the spot welded joint without having to resort to extensive testing. Spot w e l d failure f r o m buckling-induced stressing of beams under cyclic bending and torsion. Kardomateas, G. A. Eng Fract Mech 42 3 (June 1992) pp 519-530 An important design constraint of spot-welded beams is the fatigue strength of the spot welds. The present study is concerned-with predicting th e cyclic life of spotwelded joints in beams under bending and torsion. First, the physical mechanism of buckling-induced stressing is analysed. The stress distribution is obtained from a two-dimensional buckling model. Afterwards, an expression for the J integral is found in terms of the geometric and loading parameters. This expression is used with a Paris" law type of fatigue crack growth to assess the fatigue life of the design. Subsequently, an analysis that explains the phenomenon for the case of torsion loading is provided. An example case is treated to obtain numerical results for the J integral and the number of fatigue cycles as a function of the applied loading or tt~e weld spacing. Graphs. 9 refs. A study o f the damage evaluation of w e l d heat affected zone. Lou, Z.-
Modeling of crack bridging in a unidirectional metal matrix composite. Ghosn, L. J., Kantzos, P. and Telesman, J. Int J Fract 54 4 (15 Apr 1992) pp 345-357 The effective fatigue crack driving force end crack opening profiles were determined analytically for fatigue-teated unidirectional composite specimens exhibiting fibre bridging. The crack closure pressure due to bridging was modelled using two approaches: the fibre pressure model and the shear lag model. For both closure models, the Buackner weight function method and the finite element method were used to calculate crack opening displacements and the crack driving force. The predicted profile near the crack tip opening agreed well with the experimentally measured profiles for single edge notch SCS-6/Ti-15-3 metal matrix composite specimens. The numerically determined effective crack driving force, &Kerr, was calculated using both models to correlate the measured crack growth rate in the composite. The calculated AK~e from both models accounted for the crack bridging by showing • good agreement between the measured fatigue crack growth rates of the bridged composite and that of unreinforced, unbridged Ti matrix alloy specimens. Graphs. 18 refs. Simple a p p r o x i m a t i o n s f o r bridged cracks in fibrous composites. Cox,
B. N. and Lo, C. S. Acts Metall Mater 40 7 (July 1992) pp 1487-1496
Analytical functions approximating the ratio of the net and the applied stress intensity factors are presented for bridged cracks in fibrous composites. The approximations summarize extensive, accurate numerical calculations for mode I matrix cracks growing in specimens of several common shapes under uniform remote loading. The bridging tractions are assumed to be related to the crack opening displacment by laws appropriate to undirectional fibres coupled to the matrix by friction. The same approximating functions also represent the ratio of
Int J Fatigue May 1993
W., Wang, T,-J. and Zuo, J.-Z. Acta Mech Solida Sinica 5 2 (1992) pp 235-244
The damage evolution of the weld-simulated heat affected zone (HAZ) is atudied from the micro- and macroscopic points of view. The ductile and Iow-cycte fatigue (LCF) damage evolution laws of the HAZ have been examined in the framework of continuum damage mechanics. Two ahernetive laws of damage are proposed, which may meat the need for describing the damage evolution of ductile rupture and LCF fracture. 15MnMoVNRe is discussed. Photomicrographs, graphs. 11 refs. Fracture mechanics analysis on fatigue design curves f o r steel structures.
Sakano, M., Mikami, I. and Miki, C. Technology Reports of Kansai University 34 ( M a r 1992) 171-179 Fatigue crack progegation analysis is carried out on six types of welded joint under constant amplitude end variable amplitude stresses, applying the fracture mechanics concept to set the variable amplitude cut-off limit of fatigue design curves. The variable-amplitude cut-off limit can be obtained as the stress range at which Miner's summation calculated from the higher streSS side of the stress range hiatogrem reaches 1. The number of stress cycles where the cut-off limit is defined varies with the type of welded joint. Graphs. 18 refs. Fatigue tests f o r plata girder specimens w i t h f o u r types of vertical stiffener connections. Sakano, M., Mikami, I., Yonemoto, E., Kano, K.
and Yasuike, H. Technology Reports of Kansai University 34 ( M a r 1992) pp 149-160
Long-life fatigue teats are performed using plate girder specimens with four types of vertical stiffener connections to inveatigate the initiation and propagation behaviour of fatigue cracks end the fatigue strength of each stiffener-to-girder
251