摘要:

Abstract—The aim of this study is to investigate the effects of an intermittent rest period at 300°C, an overload in tension, and the combination of an overload and a subsequent rest period, on fatigue crack growth in AISI 4340 steel. The intermittent rest period was found to stop fatigue crack growth completely near the threshold level of ΔK.The alleviation effect of a rest period on crack growth was more distinct at lower levels of ΔK.With overload, the higher overload ratio caused a greater effect on crack growth rate. The reduced stress intensity factor caused by crack branching and an enhanced roughness of crack surfaces probably contribute to the retardation and arrest of fatigue crack growth. The most distinct retardation of fatigue crack growth was found after the combined treatment of an overload and a subsequent rest period. Compressive residual stresses following an overload and strain‐age hardening during the rest period at 300°C are suggested as assisting the arrest or retardation of fatigue crack prop

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01292.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The main objective of this research is to develop a model of fatigue crack initiation and early crack growth in resistance spot welds that is specimen independent. This objective is achieved by examining the stress state around a resistance spot weld. A general expression for the structural stress around the weld is formulated that is dependent only on the loading immediately surrounding the weld. As such, it is specimen independent.An additional objective is to explore the feasibility of applying this fatigue crack initiation model of life estimation using structural response data from finite element analysis (FEA). This numerical technique is often used for evaluating structural integrity of assemblies. Limited verification examples show that the structural stress range as calculated from FEA reaction load data is capable of describing fatigue crack initiation and early crack growth in cyclically loaded resistance spot weld

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01293.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The fatigue crack growth behavior of a recently developed, rapidly solidified, powder metallurgy, dispersion strengthened aluminum alloy, AA 8009, was studied at room temperature in laboratory air. Constant amplitude/constant ΔKand single spike overload conditions were examined. Alloy 8009 exhibited high fatigue crack growth rates and low closure levels in comparison to typical ingot processed aluminum alloys. It was proposed that minimal crack roughness and crack path deflection, along with limited slip reversibility, resulting from the ultra‐fine microstructure were responsible for the relatively poor (versus ingot processed aluminum alloys) da/dNversus ΔKperformance of AA

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01294.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Studies have been made of the micro‐and macroscopic features of a transverse shear fracture and a longitudinal shear fracture. The fatigue crack propagation mechanisms of mode‐II and mode‐III are described, which can be used to explain both fracture features and the crack shape. Finally a series of comparisons are made of mode‐I, ‐II and‐III fatigue crack propagati

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01295.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—An examination of PSB data pertaining to the effects of an air‐excluding environment and electric current on the fatigue life of polycrystalline Cu and 316 stainless steel in rotating bending reveals that the spacing and width of the PSBs are smaller throughout the fatigue test for those conditions which lead to increased fatigue life. Moreover, the life correlates directly with the square of the product of the surface area fraction of PSB patches and the density of the PSBs contained therein. These results suggest that in these cases slip‐homogenization is responsible for the increased fatigue life and not a consequence of it. A model is proposed for the observed relationship between slip band parameters and fatigue life, which is based on the strain concentration that exists at or near the PSB‐matrix interface. The mechanisms by which an air‐excluding environment or an electric current can increase slip homogenization are c

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01296.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Tests have been carried out on a 1 Cr‐Mo‐V steel at 565°C to describe creep crack initiation in two notched geometries. From metallographic observation the initiation times were observed to be approx. 8 and 13% of rupture lives for the sharp slit and blunter notch shapes, respectively. Based on only a few tests a relationship between the initiation timetiand the creep crack parameterJ* was found to be of the formti(J*)0.67= co

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01297.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—This paper provides a description of the features and mechanisms of facetted short crack growth in Ni‐base superalloys, and briefly reviews existing short crack growth models in terms of their application to Ni‐base alloys.The concept of “soft barriers” is introduced to produce a new two‐phase model for local microstructural effects on short crack growth in Waspaloy. This is derived from detailed observations of crack growth through individual grains. The model differs from all previous approaches in highlighting the importance of crack path perturbations within grains. Potential applications of the model in alloy development ar

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01298.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—A fatigue life estimation procedure based on a fracture mechanics approach is analytically developed for components made of a 4140 grade high strength steel. The maximum allowable flaw sizes for both static and cyclic loads are computed. For different stress levels and shapes of the defects, initially‐existing, allowable defect size versus number of operating cycles, as well as the thickness versus tolerable defect sizes curves, are presented. The maximum allowable operating cycles of components for non‐destructively detectable minimum defects are also estimated. From these estimations, a more realistic prediction of the safe service life of components is pos

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01299.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—In this note a relationship is established which shows that the product, εmintr, is dependent on the creep rupture strain, εrand the creep strain at the onset of the tertiary state, ε23. This relation has been found to give a good description of the experimental data of ICr‐0.5Mo

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01300.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01291.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY