摘要:

Abstract—The development of singular fields for defects in steadily loaded creeping structures is examined as a function of geometry and crack size using finite‐element analyses and results from the literature. Approximations for estimating the time‐development of the amplitude of the fields are examined and it is shown that simple approximations are expected to apply for a wide range of geometries. It is shown both theoretically and numerically that plasticity on initial loading produces crack tip fields closer to the steady state condition than those produced elasti

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01266.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—In the present study the effects of cold expansion of a hole on the location of fatigue crack initiation and life of LY12CZ alloy sheets are experimentally investigated and a quantitative expression of fatigue crack initiation life presented. Test results and analysis show that there may exist an optimum amount of cold expansion, for which both the coefficient of the resistance to fatigue crack initiation and the threshold are increased, and that the direction of cold expansion has no appreciable effect on fatigue crack initiation life. Observations show that, after cold expansion the fatigue crack nearly always initiates on the final entry face from which the mandrel is introduced into the hole during the final cold expansion process. Therefore it may be thought that the entry face is less resistant to fatigue crack initiation. In addition, the assumption of equivalence of residual stresses and also the strain hardening conditions on both the entry and exit faces may be questionabl

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01267.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The fatigue and fracture mechanics properties of rapidly solidified ultra‐high strength 7XXX series Al‐alloys have been studied. With respect to conventional high‐strength Al‐alloys, these materials exhibited a better fatigue‐endurance on both plain and notched specimens at low stress amplitude in constant amplitude fatigue tests, whereas the opposite occurred at high stress amplitudes. Fatigue crack growth tests indicated lower crack growth rates at low ΔK‐levels, but at intermediate and high ΔK‐values these materials were particularly prone to additional components of “static” crack propagation, which led to steeply inclined da/dNvs ΔKcurves. Moreover, the increase in tensile strength was linked with some loss of ductility and fracture toughness. Overload regions were characterized by a large amount of intergranular decohesion, possibly facilitated by the presence of incoherent particles at grain boundary regions and by the large strength differential between the matrix and precipitate free zone. The best results in terms of elongation to rupture and toughness were obtained by reducing the amount of Cr/Mn incoherent dispersoid‐forming elements, in order to lessen the tendency towards matrix‐dispersoid interface deco

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01268.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The significance of interaction effects has been studied in tests with a continuous repetition of blocks with low and high amplitude cycles under conditions characteristic for ultrasound fatigue. Significant retardation effects were observed. However, low‐intensity cycles, which according to a previous investigation might be harmless, did contribute to crack growth. Delayed retardation explains this observation. A fractographic analysis indicated the significance of surface roughness. Low‐amplitude cycles may induce a smoother fracture surface, and thus increase the crack growth rate at higher amplitudes. Accurate predictions are therefore problematic. For similar reasons, omitting numerous low‐amplitude cycles in random load experiments should be done with gre

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01269.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The possibilities and limitations of failure predictions, based on the determination of defect size and shape by NDE, on material characterization using standard testing methods and on calculations using a failure assessment program for personal computers have been investigated for a control valve casing by comparing analytical calculations with component test

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01270.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The effects of frequency andR‐ratio on the fatigue crack growth rate of the Al‐Li‐Cu‐Mg alloy 8090 have been assessed in air. Compact tension test pieces (B= 25 mm) were tested at constantPmaxusing a triangular waveform (CA) and the crack length was monitored by a four‐wire pulsed potential drop technique. Crack closure measurements were made during the test by a front face compliance technique.The crack growth rate was found to be dominated by the high level of crack closure and the fatigue fracture morphology. Two fracture types were identified; a highly deviated “shear” fracture mode which was in competition with a macroscopically flat “tensile” fracture mode. The tensile fracture mode was predominant at low test frequency, highR‐ratio and short crack lengths whereas the shear mode was predominant at high frequency, lowR‐ratio and long crack lengths. The transition from tensile to shear mode was primarily controlled by the effective stress intensity factor range, ΔKeff.The effect of loading variables on the transition was explained in terms of the diffusion distance of hydrogen relative to the effective cyclic plastic zone diameter. Test piece thickness had a secondary effect on the transition and this was explained in terms of gas

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01271.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—This paper describes the use of an optical crack monitoring system designed to examine the growth behaviour of short/long fatigue cracks in Waspaloy at room and elevated temperature. Its use at 19 and 500°C is demonstrated at stress ratios of 0.1 and ‐1. Fatigue crack formation was associated with slip band cracking at bothR= 0.1 andR= ‐1. At 19°C short crack growth atR= ‐1 andR= 0.1 could not be normalized by adopting a positive stress approach. The compressive part of the fatigue cycle atR= ‐1 contributed to short crack growth at 19°C and long crack gro

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01272.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.tb01265.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY