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Evaluation of low-cycle fatigue damage from striation measures. Comparison with the electrical potential method (Evaluation de l'endommagement en fatigue oligocyclique à partir des mesures d'enterstries. Comparison avec une méthode de suivi electrique)
influence of nugget diameter, successive spot welding end oxide film of the base metal (eg AI-4.SMg-Cu and SPCC) on tho fetiguo property of spot-welded joints is discussed, The tensile shear fatigue strength of spot-welded joints increased in proportion to the nugget diemater. Acid cleaning of the base metal was fairly useful as a countermeasure to prevent the degradation of the mecheniosl properties of the joints associated with successive spot welding. The treatment significantly lowers the electric contact resistance of the AI-4.5Mg-Cu alloy, resulting in an improvement of the nugget quality. Graphs, photomicrographs. 8 refs.
Frequency dependent vibrational reliobility of w e l d e d w i r e - - m i c r o j o i m in microeiostronlca--physlcal model. Rawicz, A. H. Reliability Eng and System Saf 36 1 pp 73-77 (1992) Frequency-dependent models of vibrational life-length of microwira joints applied in microslectronics have been developed. The developed fatigue models ere based on the theory and practice of dislocations and microproperties of metals, The experimental results obtained from long-lasting, high-frequency vibrational loads are presented, showing good egresmont with the model for numbers of cycles greater than 1 million. Copper wires and Cu plates are discussed. Graphs. 20 refs. Adhesive bonding in c o m b i n a t i o n w i t h spot w e l d i n g or clinching.
Budde, L. and Hahn, O. Welding in the World 30 1-2 ( J a n - F e b 1992) pp 26-32 The combined use of adhesive bonding and local joining methods such as spot welding and clinching with or without cut component is very fevourab~e as it uses the advantages of adhesive bonding and compensates at the same time for its drawbacks. Based on several examples, the technological aspects of production of such assemblies and the strength properties of steel and AI thin sheet parts assembled with this technique (fatigue and impact shear test) are described. Graphs. 3 refs.
Based on grain refinement studies by the previous investigators, a four-step thormomechanical processing was used to refine the conventionally cosrse-greined 7075-T651 AI alloy of two different thicknesses to small grain size. The influences of these processed fine-grained microstructures on the service properties and formability were then investigated. The properties investigated include ambient temperature axial tsnsion-tansJon fatigue, ambient temperature fatigue crack growth rate, optimal T6 temper conditions, straln-reta sensitivity (m value), work-hsrdening exponent (n value), planar anisotropy (At value) and normal anisotropy (r M value) at superplastic forming temperature. The various grain structures resulting from different thicknesses are examined and discussed. Evaluation of l o w - c y c l e fatigue damage f r o m striation measures. Comparison w i t h t h e eioctrlmd p o t e n t k d m e t h o d (Evaluation de I'end o m m q e m e n t en fatigue o H g o w c U q u . & p e r t i r des samaras d ' i ~ lea. Comperldson avec une ~ de suivi eioctrklue}. Chattier, J.,
Roux, R. and Gasc, C. Mem Etud Sci Ray Metall 89 3 ( M a r 1992) pp 153-163 (in French) A material, during s test of low-cycle fatigue, undergoes damage measured by s number D. The concept of effective stress by Rabotnov and Kachenov, extended by Lemaltre and Cheboche to fatigue materiels, is a model which can be applied both to the electrical measure and to the resistant section with a crack. For a given number of cycles, it is then possible to compare the damage values which have been measured by the two methods. This method has been tested on a stainless steel (Z2CN017-12) in different structural statos (hyperquenched, ageing, creepad). The tests are low-cycle fatigue in tensile-compressive test at 800 °C driven in imposed total strain (( = 0.006). The damage curves given by the two methods were compared and the different steps of damage were determined. The damage evaluated by electrical potential is not perceptible at the beginning of the crack. The measurement of damage is possible only when the propagation of the main crack is real. The creep, for a short time, induces initiation of the crack and, on the contrary, the ageing delays the propagation. This method a posteriori gives some useful information about the life of materials and enables one to know: (1) the number of cycles which are necessary to tho beginning of the propagation of the main crack; snd (2) the beheviour of the material during the propagation of the main crack. Photomicrographs, graphs. 19 refs.
Mater Sci Eng A A151 1 (15 Apr 1992) pp 19-27 Polycrystelline Cu was cyclically strained with constant plastic strain amplitude from a very wide interval (3 × 10-s to 1 × 10-2). Fatigue herdening/softening curves and the plot of the loop shape parameter vs the number of cycles are evaluated. The fatigue softening observed in Iow-ampJitude cycling is studied in detail. Measurements of the loop shape parameter which indicated the cyclic slip localization were accompanied by surface relief observations and electron microscope observations of the dislocation structure. Several mechanisms of fatigue softening are considered. The basic cyclic atress-atrain curve is evaluated, and the difference between this curve and curves using apparent saturation values of the stress amplitude is discussed. Photomicrographs, graphs. 29 refs. Low-cycle fatigue crack advance and life prediction. Oh, Y. J. and Nam,
A new concept is proposed for a fatigue process zone within which the actual degradation of the material takes place. This zone is described as the region in which the stress distribution of the HRR field approaches the maximum flow stress of the material (eg 304L, 4140, 1Cr-1Mo-0.25V, 12Cr-1Mo-0.25V), with the strain localization caused by a eliding-off process. In high-strain low-cycle fatigue conditions, this new concept is shown to be more roslistic for the prediction of fatigue life than that of previous work which has been based on a rough approximation. The proposed feature of the zone is experimentally supported by microhardness measurements. In particular, although this zone is formulated from continuum mechanics, it reflects microstructurel factors such as precipitates and stacking-fault energy. Using the developed fatigue process zone and strain intensification in the zone near the crack tip, a modified analytical model for prediction of the continuous low-cycle fatigue life is proposed. The exponent of the Coffin-Manson law obtained from the present prediction is suggested to be 1/(3n' + 1), which is different from the previously reported value of 1/(2n' + 1), and is shown to be in good agreement with experimental results for five alloy systems. Photomicrographs, graphs. 29 refs. Experimental data and calculated results a b o u t t h e fatigue endurance limit of metals under multiludal ~ Iced (VetlUdm- und Rechendeten zur D ~ n g f M t i g k e i t y o n M e t a l i l u h e n Wedlmlaffen Unter Mehrechclger Beenspruchung). Troost, A., Akin, O. and Klubberg,
F. Materialwissenschaft und Werkstofftechnik 23 1 (Jan 1992) pp 1-12 (in German) An extensive catalogue is presented of currently available experimental data on the fatigue endurance limit of metallic materials under muitiaxial Ioeding conditions, and these data are used to determine deviation ratios between experimental results of long-life fatigue tests and calculated values using five newer computation methods. A further statistical analysis of these deviations indicates that, in relation to the other failure criteria,the 'Qued ratieche Versegenshypothese' (QVH) is preferable for reliable application. The tabulated data includes 530 referenced loading cases (limited to various biaxiel states of combined normal and torsional alternating stress with sinusoidal synchronous or out-of-phase amplitudes and superimposed mean stresses) with experimental results (probability of survival PS = 50%) on metallic materials (unalloyed and alloy steels, non-ferrous metals and wrought AI alloys, cast irons and sintsred metals). 45 refs.
c o m p o u n d prepared by reactive
ng. MIZUKOSnl,I"t. ano ~nlDue, i~. J Jpn Inst Met 56 3 ( M a r 1992) pp 342-346 (in Japanese) In spite of the high specific strength and stiffness of the TiAI intermetellic compound, its poor ductility at room temperature makes this material difficult for practical use. it is therefore necessary to comprehend the fracture property of this alloy. The fracture toughness and fatigue crack growth rate of Ti-33.5 mass% AI-2.5 mace% Mn made by s reactive-sintering process have been examined according to the test methods of ASTM E-399 and E-647. The results obtained are summarized as follows. The fatigue crack growth rate increases with increasing stress ratio R. The relationship between the threshold stress intensity range AK~ and the stress ratio is expressed as follows: ~Km = 4.55(1-0.80 R), where 0.05 .~ R ~ 0.7. The fracture toughness of reactive-sinterad TiAI at room temperature is 14 MPs ~/m, which is greater than that of arc-melted TiAI because the grain size of reactive-sintered specimens is finer and more uniform than that of arc-melted specimens. Graphs, photomicrographs. 14 refs. L o w cycle fatigue behaviour o f a n e w t y p e of m i n i m
steel. Xia, Y.B.
and Wang, Z. G. Mater SciEng A A151 1 (15 Apr 1992) pp 29-35 Specimens of an Fe-Cr-Mn-N dual-phase stainless steel were solution-treated at 1050 and 1250 °C, yielding grain sizes of 10 and 32 iLm, resj~ectively. Low-cycle fatigue tests at constant strain amplitude ranging from 4 × 10-°to 1.2 × 10-2 were carried out at room temperature in air. The cyclic stress response, hysteresis loss/cycle and dislocation structure were investigated in the course of the cyclic deformation. No significant differences were noted in either the cyclic behaviour or the dislocation structure between the two hoet-trestment conditions. Cyclic hardening occurred in the very early stage of fatigue life. After passing through s maximum
250
A.~. ic s t r e e a - s t m i n response o f p o l y c w s t a i i i n e copper in a w i d e range eatic StTain a m p l l t u d e L Polak, J., Obrtlik, K., Hajek, M. and Vasek,
S.W. J Mater Sci 27 8 (15 Apr 1992) pp 2019-2025
Mechanical behavior o f SPF 7075 a l u m i n u m alloy. NSC78-O405-EO36-OOS/XAB (1992) 76 pp
F.tnter~re tOu~lhnees of,TiAI i n ~ e t a l l ~
of hardening, cyclic softening set in until fracture. The strain amplitude affects the initial hardening rate and hysteresis IOSS.Dislocation tangles ~ planar arrays of dislocations were observed after the first few cycles in the initial hardening stage, while the cyclic softening stage is cheracterlziKI by the formation of irregular bands or wail structures, in addition, grain boundaries were found to be effective barriers to slip dislocations during the initial hardening stage, while increased relaxation activities at grain and twin boundaries are evident during the cyclic softening stage. The observations suggest that the dislocation activities within the grains and at or near the grain boundaries are both responalbJe for the observed cyclic hardening and softening of the material under study. The failure mode for the specimens solution treated at 1050 °C was trsnegrsnuler while that at 1250 aCwas intergrenuler. The former has a fatigue life about twice that of the latter under identical total strain amplitude. Photomicrographs, graphs. 12 refs.
Investigation of yield strength and single cycle overload on crack closure. Kumar, R. Int Pressure Vessels and Piping 51 3 (1992) pp 329-348 Crack closure experiments were performed on 6063-T6 and 6061-T6 AI alloys, using a crack opening displacement gauge, for various overload ratios (1.67, 1.88 and 2.06). On the basis of these experiments some relationships ere developed. The daisy period after application of a single overload increases with increase in the magnitude of overload. The retardation is decreased with increase in prestraln for the same overload ratio. After the overload cycle, the increase in U values is less in the prestrained material than in the ss-reosived material. Crack growth rate also decreases after application of an overload cycle; it attains a constant amplitude crack growth rate and crack closure value after s certain number of cycles. For the same stress ratio, the delay period in the 6063-T6 alloy was found to be more than in the 6061-T6 alloy. The experimental results, when pJotted on log-log graph paper, show that J~)/NcAL VS overload ratio and crack length (when U = Umtn) vs overload ratio fit s straight line, from which the power laws are developed. Graphs. 14 refs. Eleatic-pieetic characterization of a cast m i n i m m a t e r i a l Joyce, J. A., Hackett, E. M. and Roe, C. NUREG/CR-5774/XAB (Jan 1992) 229 pp
steel pipe e l b o w
Tests conducted in Japan as part of the high-level vibration test programme for reactor piping systems revealed fatigue crack growth in a cast stainless steel pipe elbow. The tests conducted included monotonic and cyclic tensile tests, monotonic J-R curve tests, and cyclic elastic and elastic-plastic fatigue crack growth rate tests. The cyclic elastic-plaatic fracture behaviour of the stainless steel was of primary concern and was evaluated using s cyclic J-integral approach. The fracture surfaces
Int J Fatigue May 1993
Frequency dependent vibrational reliobility of w e l d e d w i r e - - m i c r o j o i m in microeiostronlca--physlcal model. Rawicz, A. H. Reliability Eng and System Saf 36 1 pp 73-77 (1992) Frequency-dependent models of vibrational life-length of microwira joints applied in microslectronics have been developed. The developed fatigue models ere based on the theory and practice of dislocations and microproperties of metals, The experimental results obtained from long-lasting, high-frequency vibrational loads are presented, showing good egresmont with the model for numbers of cycles greater than 1 million. Copper wires and Cu plates are discussed. Graphs. 20 refs. Adhesive bonding in c o m b i n a t i o n w i t h spot w e l d i n g or clinching.
Budde, L. and Hahn, O. Welding in the World 30 1-2 ( J a n - F e b 1992) pp 26-32 The combined use of adhesive bonding and local joining methods such as spot welding and clinching with or without cut component is very fevourab~e as it uses the advantages of adhesive bonding and compensates at the same time for its drawbacks. Based on several examples, the technological aspects of production of such assemblies and the strength properties of steel and AI thin sheet parts assembled with this technique (fatigue and impact shear test) are described. Graphs. 3 refs.
Based on grain refinement studies by the previous investigators, a four-step thormomechanical processing was used to refine the conventionally cosrse-greined 7075-T651 AI alloy of two different thicknesses to small grain size. The influences of these processed fine-grained microstructures on the service properties and formability were then investigated. The properties investigated include ambient temperature axial tsnsion-tansJon fatigue, ambient temperature fatigue crack growth rate, optimal T6 temper conditions, straln-reta sensitivity (m value), work-hsrdening exponent (n value), planar anisotropy (At value) and normal anisotropy (r M value) at superplastic forming temperature. The various grain structures resulting from different thicknesses are examined and discussed. Evaluation of l o w - c y c l e fatigue damage f r o m striation measures. Comparison w i t h t h e eioctrlmd p o t e n t k d m e t h o d (Evaluation de I'end o m m q e m e n t en fatigue o H g o w c U q u . & p e r t i r des samaras d ' i ~ lea. Comperldson avec une ~ de suivi eioctrklue}. Chattier, J.,
Roux, R. and Gasc, C. Mem Etud Sci Ray Metall 89 3 ( M a r 1992) pp 153-163 (in French) A material, during s test of low-cycle fatigue, undergoes damage measured by s number D. The concept of effective stress by Rabotnov and Kachenov, extended by Lemaltre and Cheboche to fatigue materiels, is a model which can be applied both to the electrical measure and to the resistant section with a crack. For a given number of cycles, it is then possible to compare the damage values which have been measured by the two methods. This method has been tested on a stainless steel (Z2CN017-12) in different structural statos (hyperquenched, ageing, creepad). The tests are low-cycle fatigue in tensile-compressive test at 800 °C driven in imposed total strain (( = 0.006). The damage curves given by the two methods were compared and the different steps of damage were determined. The damage evaluated by electrical potential is not perceptible at the beginning of the crack. The measurement of damage is possible only when the propagation of the main crack is real. The creep, for a short time, induces initiation of the crack and, on the contrary, the ageing delays the propagation. This method a posteriori gives some useful information about the life of materials and enables one to know: (1) the number of cycles which are necessary to tho beginning of the propagation of the main crack; snd (2) the beheviour of the material during the propagation of the main crack. Photomicrographs, graphs. 19 refs.
Mater Sci Eng A A151 1 (15 Apr 1992) pp 19-27 Polycrystelline Cu was cyclically strained with constant plastic strain amplitude from a very wide interval (3 × 10-s to 1 × 10-2). Fatigue herdening/softening curves and the plot of the loop shape parameter vs the number of cycles are evaluated. The fatigue softening observed in Iow-ampJitude cycling is studied in detail. Measurements of the loop shape parameter which indicated the cyclic slip localization were accompanied by surface relief observations and electron microscope observations of the dislocation structure. Several mechanisms of fatigue softening are considered. The basic cyclic atress-atrain curve is evaluated, and the difference between this curve and curves using apparent saturation values of the stress amplitude is discussed. Photomicrographs, graphs. 29 refs. Low-cycle fatigue crack advance and life prediction. Oh, Y. J. and Nam,
A new concept is proposed for a fatigue process zone within which the actual degradation of the material takes place. This zone is described as the region in which the stress distribution of the HRR field approaches the maximum flow stress of the material (eg 304L, 4140, 1Cr-1Mo-0.25V, 12Cr-1Mo-0.25V), with the strain localization caused by a eliding-off process. In high-strain low-cycle fatigue conditions, this new concept is shown to be more roslistic for the prediction of fatigue life than that of previous work which has been based on a rough approximation. The proposed feature of the zone is experimentally supported by microhardness measurements. In particular, although this zone is formulated from continuum mechanics, it reflects microstructurel factors such as precipitates and stacking-fault energy. Using the developed fatigue process zone and strain intensification in the zone near the crack tip, a modified analytical model for prediction of the continuous low-cycle fatigue life is proposed. The exponent of the Coffin-Manson law obtained from the present prediction is suggested to be 1/(3n' + 1), which is different from the previously reported value of 1/(2n' + 1), and is shown to be in good agreement with experimental results for five alloy systems. Photomicrographs, graphs. 29 refs. Experimental data and calculated results a b o u t t h e fatigue endurance limit of metals under multiludal ~ Iced (VetlUdm- und Rechendeten zur D ~ n g f M t i g k e i t y o n M e t a l i l u h e n Wedlmlaffen Unter Mehrechclger Beenspruchung). Troost, A., Akin, O. and Klubberg,
F. Materialwissenschaft und Werkstofftechnik 23 1 (Jan 1992) pp 1-12 (in German) An extensive catalogue is presented of currently available experimental data on the fatigue endurance limit of metallic materials under muitiaxial Ioeding conditions, and these data are used to determine deviation ratios between experimental results of long-life fatigue tests and calculated values using five newer computation methods. A further statistical analysis of these deviations indicates that, in relation to the other failure criteria,the 'Qued ratieche Versegenshypothese' (QVH) is preferable for reliable application. The tabulated data includes 530 referenced loading cases (limited to various biaxiel states of combined normal and torsional alternating stress with sinusoidal synchronous or out-of-phase amplitudes and superimposed mean stresses) with experimental results (probability of survival PS = 50%) on metallic materials (unalloyed and alloy steels, non-ferrous metals and wrought AI alloys, cast irons and sintsred metals). 45 refs.
c o m p o u n d prepared by reactive
ng. MIZUKOSnl,I"t. ano ~nlDue, i~. J Jpn Inst Met 56 3 ( M a r 1992) pp 342-346 (in Japanese) In spite of the high specific strength and stiffness of the TiAI intermetellic compound, its poor ductility at room temperature makes this material difficult for practical use. it is therefore necessary to comprehend the fracture property of this alloy. The fracture toughness and fatigue crack growth rate of Ti-33.5 mass% AI-2.5 mace% Mn made by s reactive-sintering process have been examined according to the test methods of ASTM E-399 and E-647. The results obtained are summarized as follows. The fatigue crack growth rate increases with increasing stress ratio R. The relationship between the threshold stress intensity range AK~ and the stress ratio is expressed as follows: ~Km = 4.55(1-0.80 R), where 0.05 .~ R ~ 0.7. The fracture toughness of reactive-sinterad TiAI at room temperature is 14 MPs ~/m, which is greater than that of arc-melted TiAI because the grain size of reactive-sintered specimens is finer and more uniform than that of arc-melted specimens. Graphs, photomicrographs. 14 refs. L o w cycle fatigue behaviour o f a n e w t y p e of m i n i m
steel. Xia, Y.B.
and Wang, Z. G. Mater SciEng A A151 1 (15 Apr 1992) pp 29-35 Specimens of an Fe-Cr-Mn-N dual-phase stainless steel were solution-treated at 1050 and 1250 °C, yielding grain sizes of 10 and 32 iLm, resj~ectively. Low-cycle fatigue tests at constant strain amplitude ranging from 4 × 10-°to 1.2 × 10-2 were carried out at room temperature in air. The cyclic stress response, hysteresis loss/cycle and dislocation structure were investigated in the course of the cyclic deformation. No significant differences were noted in either the cyclic behaviour or the dislocation structure between the two hoet-trestment conditions. Cyclic hardening occurred in the very early stage of fatigue life. After passing through s maximum
250
A.~. ic s t r e e a - s t m i n response o f p o l y c w s t a i i i n e copper in a w i d e range eatic StTain a m p l l t u d e L Polak, J., Obrtlik, K., Hajek, M. and Vasek,
S.W. J Mater Sci 27 8 (15 Apr 1992) pp 2019-2025
Mechanical behavior o f SPF 7075 a l u m i n u m alloy. NSC78-O405-EO36-OOS/XAB (1992) 76 pp
F.tnter~re tOu~lhnees of,TiAI i n ~ e t a l l ~
of hardening, cyclic softening set in until fracture. The strain amplitude affects the initial hardening rate and hysteresis IOSS.Dislocation tangles ~ planar arrays of dislocations were observed after the first few cycles in the initial hardening stage, while the cyclic softening stage is cheracterlziKI by the formation of irregular bands or wail structures, in addition, grain boundaries were found to be effective barriers to slip dislocations during the initial hardening stage, while increased relaxation activities at grain and twin boundaries are evident during the cyclic softening stage. The observations suggest that the dislocation activities within the grains and at or near the grain boundaries are both responalbJe for the observed cyclic hardening and softening of the material under study. The failure mode for the specimens solution treated at 1050 °C was trsnegrsnuler while that at 1250 aCwas intergrenuler. The former has a fatigue life about twice that of the latter under identical total strain amplitude. Photomicrographs, graphs. 12 refs.
Investigation of yield strength and single cycle overload on crack closure. Kumar, R. Int Pressure Vessels and Piping 51 3 (1992) pp 329-348 Crack closure experiments were performed on 6063-T6 and 6061-T6 AI alloys, using a crack opening displacement gauge, for various overload ratios (1.67, 1.88 and 2.06). On the basis of these experiments some relationships ere developed. The daisy period after application of a single overload increases with increase in the magnitude of overload. The retardation is decreased with increase in prestraln for the same overload ratio. After the overload cycle, the increase in U values is less in the prestrained material than in the ss-reosived material. Crack growth rate also decreases after application of an overload cycle; it attains a constant amplitude crack growth rate and crack closure value after s certain number of cycles. For the same stress ratio, the delay period in the 6063-T6 alloy was found to be more than in the 6061-T6 alloy. The experimental results, when pJotted on log-log graph paper, show that J~)/NcAL VS overload ratio and crack length (when U = Umtn) vs overload ratio fit s straight line, from which the power laws are developed. Graphs. 14 refs. Eleatic-pieetic characterization of a cast m i n i m m a t e r i a l Joyce, J. A., Hackett, E. M. and Roe, C. NUREG/CR-5774/XAB (Jan 1992) 229 pp
steel pipe e l b o w
Tests conducted in Japan as part of the high-level vibration test programme for reactor piping systems revealed fatigue crack growth in a cast stainless steel pipe elbow. The tests conducted included monotonic and cyclic tensile tests, monotonic J-R curve tests, and cyclic elastic and elastic-plastic fatigue crack growth rate tests. The cyclic elastic-plaatic fracture behaviour of the stainless steel was of primary concern and was evaluated using s cyclic J-integral approach. The fracture surfaces
Int J Fatigue May 1993