摘要:

Abstract—Crack growth fatigue tests were carried out on 2024‐T3 specimens. Constant‐amplitude loading was periodically interrupted by 10 overload cycles. Intermediate heat treatments (T4) were applied to remove the residual stress in the crack tip zone and the crack closure wake behind the crack tip. Retardation effects induced by crack closure due to the previous load history were fully erased by the heat treatments. Overload effects were easily introduced again by new overload cycles afterwards. Crack growth rate results and fractographic observations indicate that primary crack tip plastic deformation (in virgin material) is more effective for crack extension than secondary plastic deformation in an existing plastic zone. This conclusion is significant for cycle‐by‐cycle crack growth prediction models for variable‐amplit

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01284.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Brush electroplating causes a marked reduction in the fatigue strength of the base steel. For the medium carbon steel reported in this paper, the fatigue limit is reduced 28.6% by nickel brush electroplating. A large number of short cracks are found in the nickel coating, and the coating usually suffers a high value of internal tensile stress. These are two reasons that cause the loss of fatigue strength. Shot peening has been used to minimize the loss of fatigue strength caused by brush electroplatin

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01285.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Fretting loads on the surfaces of structural components can cause accelerated growth of short cracks. The rate of growth will depend on the combined stress intensity factor resulting from both remote and local loading. Many stress intensity factor solutions are available for remote loading, but solutions for arbitrary fretting loads are not readily accessible. In this paper accurate crack‐line Green's functions are obtained from a boundary element analysis and then used to develop the Green's functions for loads on the edge of a half‐plane containing a slant crack at various angles to the edge. These latter Green's functions can be used to obtain stress intensity factors for arbitrary stresses (normal or shear) on the edge of the half‐plane without further stress analysis; simple integration procedures are all that is r

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01286.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—A Markovian method of crack propagation analysis is studied. Non‐physical negative and/or unbounded crack growth rates are avoided. The cumulative distribution function of the crack length is evaluated at a fixed time by using a technique based on Hermite moments which are calculated by means of classical Itô calculus. A numerical example illustrates the main features of the method. The agreement between theoretical results and experimental data is very satisfac

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01287.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Crack growth and closure behaviour of surface cracks in 7075‐T6 aluminium alloy are investigated under axial loading, noting the difference in fatigue growth behaviour at the maximum crack depth point and at the surface intersection point and also with through‐thickness crack growth behaviour. The plane strain closure response at the point of maximum depth of a surface crack is monitored using an extensometer spanning the surface crack at the midpoint of its length. The plane stress closure at the surface intersection point is observed by multiple strain gauges placed at appropriate intervals ahead of the crack tip and continuously monitored without interrupting the fatigue test. The crack opening ratio is found to be about 10% greater at the maximum depth point than at the surface intersection point. Under axial loading, the difference in plane strain crack closure behaviour between the surface crack and the through‐thickness crack is relatively small. Growth rates of surface cracks can be well described by the effective stress intensity factor range based on the closure measurements made in this study. The growth rates in terms of the effective stress intensity factor range seem to be slightly slower in surface cracks than in through‐thickne

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01288.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The Markov matrix, which is a statistical representation of a service load history, is generally derived using 32 or more strain levels, since this is considered an optimum level between computational effort and accuracy of fatigue life prediction. A recently developed model which predicts the distribution of closed loops and fatigue life from the Markov matrix, is limited in the number of levels which can be analysed because of computational restrictions. This investigation was undertaken to determine the change in the accuracy of fatigue life predictions as the number of strain levels used to represent the strain history is reduced. Since each discretized level is used to represent a range of strain values, a given discretized history will represent a family of histories. A technique is developed which gives the distribution of damage for the family of histories given the discretized history and the distribution of peaks and valleys within each strain interval. By comparing the predicted damage caused by the measured history to a conservative estimate of the distribution of damage for the family of histories, the range of possible error is calculated and used to determine the relationship between the number of strain levels used in the discrete history and the possible error in predicted fatigue damag

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01289.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Acceleration of crack growth by intermittent overloading was investigated at 650°C by using specimens of different thickness made of Type 304 stainless steel. When the hold time of overload was very short (∼20s), the crack growth rate was significantly accelerated (20–50 times) and the fracture surface morphology showed extremely ductile transgranular fracture by glide plane decohesion or microvoid coalescence, suggesting significant recovery of the material. In the thinner plate specimens, the crack growth rate under intermittent overloading was correlated well with the modifiedJ‐integral, i.e.J(C%) and agreed with the growth rate of static creep cracks in aJversus da/dtdiagram. In the thicker plate specimens, however, this is not the case and the growth rate was about 20% of that in the thinner plate specimens in theJdiagram. Transgranular fatigue type crack growth appeared in the low growth rat

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01290.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.tb01283.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY