摘要:

AbstractThe growth characteristics of small fatigue cracks were investigated under rotary bending in a low alloy steel prepared with two prior austenite grain sizes of 15 μm (fine grain) and 91 μm (coarse grain). The influence of grain boundaries on crack growth rate and the crack aspect ratio was examined, and the critical crack length above which linear elastic fracture mechanics (LEFM) is applicable was evaluated for a growing small crack. When the surface crack length is shorter than three grain diameters (3d), crack growth rates decrease near the grain boundaries. Aspect ratios are also affected by the microstructure and thus vary widely. Cracks longer than 3dare not influenced by the microstructure, but they grow faster than would be expected based on LEFM until their lengths reach 3d+ 150 μm. This behaviour may be attributed to the difference in crack closure between small cracks and large cracks. If the contribution of crack closure to the growth of small cracks can be established experimentally or analytically, the critical crack length above which LEFM is applicable would be 3d.However, because it is difficult to evaluate crack closure, 3d+ 150 μm is considered to be the critical crack length for engineering applicati

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1986.tb01207.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractA study of short crack growth for a medium carbon steel in low cycle torsional fatigue has been carried out in order to measure crack length and derive growth laws. Comparison with a previous analysis of uniaxial tests in low cycle fatigue for the same material provides a tentative basis for formulating an equivalent stress approach to describe uniquely the propagation of short cracks under multiaxial stress.

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1986.tb01208.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe fatigue crack growth rates of physically‐short cracks (0.5 ≤a≤ 1.0 mm), intermediate cracks (1

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1986.tb01209.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe cyclic plastic work of fatigue crack propagation,Qpw, and the effective surface energy,U, were measured for an annealed 1008 steel in humid air and dry nitrogen using calorimetryQpwwas not significantly affected by the humid air environment suggesting that the hydrogen generated by the oxidation of iron at the crack tip does not strongly affect the cyclic properties for this materialUwas identical and constant for the two environments for crack growth rates greater than ∼ 100 A/cycle. Below da/dN∼ 100 A/cycleUdecreased rapidly with decreasing δKin the humid air environment It was concluded from these two observations that the main effect of hydrogen on crack growth in this alloy was to lower the atomic surface energy, γ, thereby lowering the local fracture s

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1986.tb01210.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThis paper presents an investigation of the fatigue crack growth (FCG) behavior at fastener holes in a high strength steel, 30CrMnSiNi2A, before and after a cold‐expansion process. The fatigue life of coldworked specimens was significantly increased compared to non‐coldworked ones and increased the lower applied stress level.From a study of the residual stress distribution near the edge of the hole, it was found that the experimental residual compressive stresses in absolute values were much less than the calculated values derived by previous analytical methods. Thus, a simplified residual stress model for describing the FCG behavior at coldworked fastener holes is proposed, from which, the δKeffand fatigue lives of specimens after cold‐expansion can be predicted satisfactorily for engineering applic

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1986.tb01211.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThis paper describes the cyclic strain hardening behaviour and dislocation structures of material in biaxial low cycle fatigue at elevated temperatures. In this study, push‐pull, reversed torsion and combined push‐pull/reversed torsion tests were carried out using a type 304 stainless steel in air. While there was no significant difference between the cyclic stress amplitudes in the push‐pull and reversed torsion tests on a von Mises' base, combination tests exhibited a 40% increase in stress amplitude. Most of the dislocations in the first two types of test adopted ladder or maze structures, while in the later case cells were found. Changing the loading mode at a certain cycle, for example, from push‐pull to reversed torsion, revealed that stress amplitude depended mainly on the concurrent applied strain mode and furthermore, that the strain mode before the interchange had little or no effect on the stress amplitude after the interchange. Tests were also performed in order to examine how prestrained material hardened in the three different loading modes, with the following results: prestrained material in push‐pull or in reversed torsion exhibited an anisotropic stress response, while the material in the combined tests exhibited an isotropic response. These cyclic responses are discussed in connection with the dislocation

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1986.tb01212.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1986.tb01206.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY