摘要:

AbstractThree‐dimensional finite element analyses of through‐thickness cracks in plate geometries are presented. It is shown that the local constraint variation towards the crack tip causes an increase in stress intensity which is neglected in analyses which assume a constant stress state throughout the geometry. This means that stress intensity factors for these types of crack geometries are a factor (1 — v2)‐0.5higher than generally reported in stress intensity handbooks.Analyses on crack tunnelling situations show that if plane stress dominates the global behaviour, an almost constant stress intensity across the thickness is reached for a relative tunnelling depth of a 2.5% of the plate thickness. For geometries which are not predominantly in plane stress this value will be somewhat larger. Crack front tunnelling does not influence the mean stress intensity across the thickness.Shear lips are shown to reduce the mean equivalent stress intensity (the mode I stress intensity which has the same energy release rate as the actual combined mode I, II and III loading) by a factor equal to the square root of the ratio between plate thickness and projected length of the crack front. This may explain the reduction in crack growth rate caused by shear lips during fatigue crack growth experiments. The reduction of the mode I stress intensity factor is considerably larger, which may cause a further reduction of fatigue crack growth rate for crack growth mechanisms that depend primarily on the mode I crack tip loading.Analyses on CNT and SENB specimens show that the conclusions reached on infinite plate models also hold for real structures. However for an SENB specimen with an uncracked ligament equal to the plate thickness, the overall constraint is larger than that of a pure plane stress situation, and the effect of stress intensity increases due to the constraint transition is less pro

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb00032.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThis report reviews some simple methods for determiningJcat the onset of cleavage fracture in a three‐point bend crack tip opening displacement test. It is concluded that acceptable estimates of J, can be made from specimen mouth opening displacement without precise measurement of crack lengt

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb00033.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractAn incubation period is often observed prior to the onset of creep crack growth. This paper presents a procedure for estimating its duration from a knowledge only of the stress rupture properties and creep ductility of a material. Comparisons are made with experimental data on type 316L stainless steel at 600°C and a 1% CrMoV low alloy steel at 550°C. It is shown that good agreement is achieved when allowance for a build up of damage in a process zone at the crack tip during the early stages of cracking is incorporated into the analysi

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb00034.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA procedure for CTOD calculation under slow stable crack growth conditions is presented in this work. This procedure gives more accurate CTOD values than those obtained using existing standards, and can be used in tests in which the slow stable crack growth is measured. An analysis of the errors made, when the traditional ([I], ASTM STP 668, pp. 307‐333) or the European Group of Fracture equations are used, is also made. A weighting factor on Δais proposed for tests without crack growth measureme

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb00035.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractStress corrosion cracking and corrosion fatigue of 12 Cr steel in sodium chloride solution has been investigated. Tests have been performed in air at room temperature and in aqueous solution with 22% NaCl at 80°C. The influence of corrosion pits on crack nucleation has been investigated. On fracture surfaces tested in environment (22% NaCl solution), crack initiation was observed in correspondence with corrosion pits; in this case fatigue life can be described using a fracture mechanics approach. The ΔKvalue for crack nucleation from a pit in rotating bending fatigue tests is very low in air (about 3 MPa√m). The results of slow strain rate tests on smooth specimens show that there is a threshold stress intensity,KISCC, of about 15 MPa√m and a plateau in stress corrosion crack growth rate of about 10

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb00036.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe room temperature fatigue strengths of A1‐7Si‐0.6Mg and A1‐SSi‐3Cu‐1Mg composites randomly reinforced with A12O3short fibres were determined using a stress ratio of 0.1, a frequency of 50 Hz. The fatigue strength of the composites under these testing conditions can be expressed by a single curve‐fitting equation. The effect of surface roughness on fatigue strength was also studied and the results show that these composites are not sensitive to surface roughness. The orthogonal growth of cracks is an important fatigue fracture mechanism in these composites. The residual strength decreased as the fatigue loa

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb00037.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe influence of the cyclic compressive excursion on the fatigue crack growth behavior of small surface cracks in Alloy 718 at 650°C is experimentally studied. Test conditions were chosen to simulate the cyclic plasticity found at notch locations in high temperature structural components. During cycling, the crack lengths were continuously monitored using the direct current potential drop method while the near field crack mouth opening displacement and global cyclic stressstrain behavior were measured using a laser interferometry technique and mechanical extensometry, respectively. Two aspects related to cyclic compressive excursion have been studied; crack closure and crack tip plasticity. Attempts have been made to use several modified ΔKexpressions as well as ΔJeffto account for the effects of closure and decrease crack tip plasticity. It was concluded that the compressive excursion is most prominent in this alloy in its effect on the global plasticity and the subsequent loss of constraint. Closure was not found to be significant in the consolidation of test da

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb00038.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe crack aspect ratio influence on the stress‐intensity factor of elliptical‐arc edge flaws in solid round bars under tension or bending loading is discussed. The relative crack depthξ=a/Dbetween the depthaof the crack's deepest point and the bar diameterDranges from 0.1 to 0.6, while the aspect ratioa/bof the flaw is made to vary from 0.0 (straight crack front) to 1.0 (circular‐arc crack front). For each value of ξ being considered, the maximum stress‐intensity factor is attained in correspondence to the deepest point on the crack front in the case ofa/b= 0.0, while it is attained near the external surface in the case ofa/b= 1.0. For intermediate aspect ratios, the stress‐intensity factor presents the maximum value at the crack's deepest point for ξ≤ξCRand near the free surface for ξ≥ξCR, with the critical relative crack depth ξCRgetting lower and lower as the para

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb00039.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe near‐threshold behaviour of a high‐strength low‐alloy steel used in helicopter rotors under variable amplitude loading is investigated in ambient air and in vacuum. Strong sequence effects occur, in particular a high decrease in crack growth rates after overloads of 40% on maximum load while keeping the amplitude constant. A detailed study of the retardation phenomenon due to the overloads provides an explanation for the different behaviour observed in air and in vacuum and has laid the basis for a method of predicting crack propagation under helicopter loading sp

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb00040.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.tb00031.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY