摘要:

Abstract—The residual stress fields at the tip of a fatigue crack have been evaluated using the Westergaard stress function. Using these values the loads at which the crack tip begins to open have been calculated to giveU, Elber's effective stress range factor, as a function of stress ratioR, the ratio of applied stress range to yield stress, Δσ/σy, and the cyclic strain hardening exponentn.The computed values ofUare shown to be in good agreement with measured values, and the predicted effect of prior high load cycles on the crack propagation rate at a lower cyclic load, on taking crack closure effects into account, is in excellent agreement with experimental res

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01107.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—On the basis of fatigue data derived from a large number of experiments, the load progression methods of Locati and Prot as well as a method operating on a thermometric basis have been comparatively evaluated in an experimental and analytical (statistical) study. The last‐named thermo‐method can provide useful estimates for a fatigue limit corresponding with ca. 0 to 5% probability of fracture with only 1 to 3 experiments.The Prot‐method, set up and evaluated in a certain way, provides a useful estimate of the fatigue limit and, additionally, an approximate indication of the width of the transition range of the corresponding Wöhler‐type tests after experiments on not less than about ten specimens.The load progression, contrary to the original Prot‐concept, must not necessarily be applied in a continuous mode, but can occur stepwise with increments Δσ smaller

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01108.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—Fracture surfaces of both service and laboratory fatigue fractures frequently show dark tongue‐shaped marks. In fatigue tests on 7075–T6 specimens such tongues were produced by high peak loads. Measurements indicated that a tongue is not formed during a single burst of crack extension but is the result of a number of successive pop‐ins requiring an increasing load. Therefore tongue formation is a quasi‐stable phenomenon. The tunnelling fracture in the centre of plate thickness is accompanied by unfailed ligaments at the plate surfaces which reduce the stress intensity at the crack tip. The effect of different material conditions and loading direction on tongue forming was studied. A new model was developed to describe the growth of a tongue. The model was in good agreement with the various test results. The analysis of the problem has some relevance to validity requirements forK1c. A formula pertaining to tongues proposed by Forsyth was slightly modified and found to be approximately correct for the presen

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01109.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—This work is concerned with the determination of the fatigue threshold ΔKthfor an aluminium alloy. No dependency of ΔKthwith grain size was observed. Crack closure concepts were applied in order to explain the effect of mean stress and environment. The opening loadPopwas determined by the compliance method. Results show no significant variation ofPopwith environment (air or vacuum) but partially explain the influence of mean stress on crack growth rates. Fractographic analysis (SEM) of fracture surfaces and evolution of compliance diagrams suggest that a change of mechanism in crack propagation occurs when stage I changes to stage II gro

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01110.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—Linear‐elastic fracture mechanics techniques were used to characterize the effect of temperature on the fatigue‐crack propagation behaviour of precipitation heat‐treated. Inconel X‐750 in an air environment over the temperature range 24 to 649°C. In general, crack growth rates were found to increase with increasing temperature, particularly at the highest test temperature (649°C). The effect of stress ratio on the fatigue‐crack growth behaviour of Inconel X‐750 was examined at 538°C, and results indicated that the elevated temperature fatigue response of this nickel‐base superalloy was relatively insensitive to stress ratio level at the growth rate levels studied. Metallographic and electron fractographic examination of Inconel X‐750 fatigue fracture surfaces revealed operative crack growth mechanisms to be a function of temperature and prevailing stress intensity factor. Under room temperature and intermediate temperature conditions (up to 538°C), all fatigue fracture surfaces exhibited a faceted crystallographic morphology at low crack growth rates followed by striations in the higher growth rate regime. At the highest test temperature (649°C), the fatigue crack was found to propagate by an i

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01111.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—High strain fatigue tests of Type 316 stainless steel have been carried out at room temperature and 600°C. Cold work reduces the life relative to the annealed condition when considered in terms of plastic strain per cycle but not when the total strain range is used. It also renders the material far more resistant to cyclically induced changes in strength than the annealed state in which the strength is more than doubled at 600°C. Strain ageing causes further instability and enhances the hardening and loss of ductility in the annealed material. Because of the large number of variables involved, comparison with other work is unable to identify the parameters most influential in determining endurance. It is argued that where a fatigue–creep interaction occurs, then cyclic hardening will promote a higher creep resistance in a sequential interaction and favour a fatigue dominated failure in a simultaneous intera

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01112.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—In this paper the strain distribution and the plastic zone size at a fatigue crack tip are discussed. From this analysis and considering the critical condition for plastic‐blunting, a simple analytical formula for calculating the threshold stress intensity range for fatigue crack propagation atR= 0 is proposed. It is found that calculated values are in good agreement with existing experimental resu

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01113.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY