摘要:

AbstractFatigue crack initiation and subsequent short crack growth behaviour of 2014‐5wt%SiC aluminium alloy composites has been examined in 4‐point bend loading using smooth bar specimens. The growth rates of long fatigue cracks have also been measured at different stress ratios using pre‐cracked specimens. The distributions of Sic particles and of coarse constituent particles in the matrix (which arise as a result of the molten‐metal processing and relatively slow cooling rate) have been investigated. Preferential crack initiation sites were found to be Sic‐matrix interfaces, Sic particles associated with constituent particles and the coarse constituent particles themselves. For microstructurally short cracks the dispersed SiC particles also act as temporary crack arresters. In the long crack growth tests, higher fatigue crack growth rates were obtained than for monolithic alloys. This effect is attributed to the contribution of void formation, due to the decohesion of Sic particles, to the fatigue crack growth process in the composite. Above crack depths of about 200 μm “short” crack growth rates were in good agreement with the long crack data, showing a Paris exponent,m= 4 in both cases. For the long crack and short crack growth tests little effect of specimen orientation and grain size was observed on fatigue crack growth rates, but, specimen orientation affected the toughness. No effect of stress ratio in the rangeR=0.2‐0.5 was seen for long crack data in

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb00011.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractCrack front shapes in relatively thick fracture toughness specimens of Sic particulate reinforced metal matrix composites have been analysed. They were found to have a common shape, that of a parabola. This shape is thought to arise as a result of a distribution of residual stress across the test‐piece. A simple analysis is used to derive an expression for an effective crack length which can be used to calculateKICvalues in specimens in which the crack fronts are excessively curved and do not meet relevant criteria for curvature in current standards for toughness testing of metallic material

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb00012.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe fatigue fracture features of low alloy steels in aqueous environments are investigated. It is revealed that microstructures, compositions and mechanical variables will affect the fracture mode. A series of fracture‐mode maps of structural steels are established and a corrosion‐fatigue‐mechanism map of 15 Mn dual‐phase steel is developed. The importance of fractography and fracture‐mode is e

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb00013.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe evolution of micromechanical stresses; flow stress, kinematic back stress and isotropic drag stress during room temperature, uniaxial, low cycle fatigue of overaged Al‐Mg‐Si alloy is studied. Continuous real‐time measurements of yield stresses are made in cyclic tension and compression, within the hysteresis loop, at different strain amplitudes, strain rates and number of cycles. An asymmetry is observed in flow stress and kinematic back stress in tension and compression half cycles during cyclic hardening and saturation. The phenomenological results have been analyzed in terms of kinematic and isotropic type microstructural mecha

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb00014.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractPrevious investigations have shown that for plain materials, the crack growth rate constants applied in an elastic‐plastic crack growth model may be obtained indirectly from the constants describing the low cycle fatigue capacity of the material. In the present study a simple EPFM crack growth model, based on bulk strain amplitude as the governing parameter, is assumed. The crack growth constants derived from the linear regression constants describing the LCF capacity of manually butwelded components are determined, and the validity of the resulting EPFM crack growth model is checked against measured LCF crack growth dat

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb00015.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractWe present a new approximation of the expected damage for Gaussian loads. The approximation is based on an exact relationship between the rainflow cycle count and the range‐pair exceedances count. This relationship links the intensity of rainflow amplitudes to expectations of marked crossings of the random load. The method is best suited for the fatigue life prediction for locally stationary Gaussian loads with slowly varying means and covariance functions. These results are illustrated with numerical example

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb00016.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe project has been concerned with the verification of theJ‐philosophy for initiation and growth of cracks on laboratory type specimens as well as on larger surface cracked plates. The analysis of the experiments involved extensive fully three‐dimensional finite element calculations. It was found that the initiation events for the six surface cracked plates occurred at approximately the sameJ‐value. A corresponding relation to the laboratory type specimen was less successful, mainly because of the short‐comings of current methods forJIC‐evaluations. A somewhat puzzling feature of the surface crack experiments was that unstable crack growth occurred immediately after crack growth initiation in four out of six tests, while some amount of stable crack growth was evident in the remaining two and in all of the laboratory type specimens. An evaluation of the surface experiments by a type of R6‐analysis was also performed. Using asKcrthe mean value from the surface crack experiments, it was found that the R6‐method yielded conservativ

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb00017.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper introduces a new method of investigation in the field of fretting. This method employs X‐ray diffraction for the characterization of surface layer damage through residual stresses and work‐hardening by tribologjcal action. The effect of hardness and material residual stresses upon the state of the surface have been studied. The results showed that fretting, being a surface phenomenon, created work‐hardening of soft material or work‐softening of hard material in the near‐surface layers. When the initial residual stresses were high, fretting could not modify them because they had already reached the saturation limit. A Pole figure shows that fretting modified the texture of the specime

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb00018.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractFatigue crack growth behaviour under intermittent overstressing was investigated in moist air, dry air, nitrogen and vacuum with low carbon steels under tension‐compression loading with a few tests under compression‐tension loading. A very small number of cycles of overstress applied intermittently during a very large number of cycles of understress below threshold caused significant acceleration, of about one hundred times, in crack growth rate as compared to the case of steady cyclic stress in the cases of moist air, dry air and nitrogen. In the region of low understress, the acceleration in moist air was appreciably less than that in dry air and nitrogen due to oxide‐induced crack closure. The acceleration in vacuum was smaller than that in other environments over all understress levels, possibly because of rewelding. There was no effect of an overstress sequence on the acceler

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb00019.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.tb00010.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY