摘要:

Abstract—The fatigue strength of notched specimens of a rotor steel was examined under variable torsional loading which simulates turbine‐generator oscillations resulting from the high speed reclosing of transmission‐line circuit breakers. The local stress‐strain response at a notch root was analysed using Neuber's rule and the resulting complex strain sequences applied to smooth specimens. Using the rain flow analysis and the linear summation rule, fatigue lives of the smooth specimens were successfully predicted from constant amplitude fatigue life data in association with the cyclic stress‐strain curve obtained by the incremental step method. Experimental crack initiation lives for notched specimens subjected to variable torsional loading were in excellent agreement with the theoretical curves derived from results on smooth specimens. According to the view that fatigue damage is equated to crack length, the propagation life of a mode II crack along the notch root was predicted to be actually coincident with the life to crack initiation at the notch root denned in this study, i.e. the life at the stage of finding a continuous circumferent

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1983.tb00328.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—A method of combining long term creep data with relatively short term mechanical behaviour to provide an estimate of creep‐fatigue endurance is presented. It is proposed that the creep‐fatigue effect in high temperature cyclic deformation is governed by a difference in strain rate around the cycle and the associated variation in ductility with strain

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1983.tb00329.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—Near threshold, mixed mode (I and II), fatigue crack growth occurs mainly by two mechanisms, coplanar (or shear) mode and branch (or tensile) mode. For a constant ratio of ΔKI/ΔKIIthe shear mode growth shows a self‐arrest character and it would only start again when ΔKIand ΔKIIare increased. Both shear crack growth and the early stages of tensile crack growth, are of a crystallographic nature; the fatigue crack proceeds along slip planes or grain boundaries. The appearance of the fracture surfaces suggest that the mechanism of crack extension is by developing slip band microcracks which join up to form a macrocrack. This process is thought to be assisted by the nature of the plastic deformation within the reversed plastic zone where high back stresses are set up by dislocation pile‐ups against grain boundaries. The interaction of the crack tip stress field with that of the dislocation pile‐ups leads to the formation of slip band microcracks and subsequent crack extension. The change from shear mode to tensile mode growth probably occurs when the maximum tensile stress and the microcrack density in the maximum tensile plane direction attain crit

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1983.tb00330.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—Crack growth under cyclic loading has been studied by the finite element method. The calculation was made for plane stress conditions. The crack tip zone was modelled as a cohesive zone.The displacement of the free crack surface during unloading was found to be governed by the surrounding continuum and was independent of the details in the fracture zone. This means that crack closure upon unloading is directly related to the ultimate separation, of the cohesive zone, which in turn controls the residual plastic deformation left in the wake of the growing crack.If the distance over which closure takes place is rather small, closure may be very difficult to detect by the compliance techniqu

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1983.tb00331.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—A crack‐tip‐zone interaction model for creep‐fatigue crack growth is proposed. The basic details of the model are described. Experimental evidence in support of this model is presented. Existing data on creep‐fatigue crack growth interaction agree qualitatively with the model. Some quantitative evidence for the model is presented and more is being developed in cur

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1983.tb00332.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—Fatigue crack propagation behaviour in a cast Mg‐Al‐Zn alloy was examined. The fatigue crack growth rate of the alloy under constant amplitude loading and the threshold resulting from a number of tests are given. Delayed retardation after the application of a single tension overload is explored in detail and described by using the model proposed by Matsuoka and Tanaka. From these observations, it may be seen that the Matsuoka model can be applied to the cast magnesium alloy as well as steels and aluminium alloys. Changes in the extent of retadation and the overload affected zone size with respect to the ratio of peak‐to‐baseline stress intensity factor range are discussed. Two phenomena, delayed arrest and acceleration in the later stages of retardation are

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1983.tb00333.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—Fatigue data required for estimates of cracked component lifetimes are conventionally obtained by cyclic loading of specimens manufactured to a specific geometry. Crack growth in the specimen results in an increase in the stress intensity factor range and crack growth curves are calculated from the variation of crack length with time. An environmental fatigue study of the effect of high pressure hydrogen on the low cycle fatigue of a medium strength steel has shown that, due to effects of elapsed time in the environment and effects of specimen size, in certain circumstances this procedure may not yield geometry‐independent results which can be applied with confidence to cracked components. It is concluded that to obtain useful crack growth data in cases where fracture is influenced by diffusion or other strongly time dependent processes might require a modified approach to fracture mechanics testing procedu

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1983.tb00334.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—This paper describes results of an experimental program conducted to determine the influence of deep side‐grooves on fatigue crack retardation. The results indicate that side‐grooves significantly reduce the delay in fatigue crack growth caused by single peak overloads. It is suggested that the decreased retardation is due to simulation of plane strain conditions in the “thin” test sections by the stress field at the root of the si

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1983.tb00335.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1983.tb00327.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY