摘要:

AbstractFracture mechanics methods are used to assess the significance of cracking in any structure, but a tubular joint is very complex to analyse. However the improvements in numerical methods, such as stress analysis using finite elements, and extensive full‐scale laboratory testing (UKOSRP, ECSC, etc.) have allowed various workers to propose fracture mechanics models of tubular joints.This paper presents a critical review and comparison of these models. It concludes that simple plate models can provide upper and lower bound stress intensity factor solutions for cracked tubular joints. Stress intensity factors from three dimensional finite element analysis of a tubular joint are in reasonable agreement with semi‐empirical data. However, in the absence of a validated database the paper concludes that any analytical assessment of a crack in a joint should be viewed as tentat

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00678.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractOffshore structures are subjected to onerous environmental conditions. These conditions can cause cracking at tubular joints in these jacket structures and increasingly fracture mechanics is being applied to assess the cracks.There are a variety of fracture mechanics approaches to assessing cracks in tubular joints, all of which predict similar trends but give a wide variation of stress intensity factors. This variation is caused by the different models and inconsistent input parameters used.This paper presents a finite element study of a cracked tubular joint using several different structural models and consistent input parameters. The analysis includes both simple representations of a tubular joint, e.g. a plate model, and a full‐scale analysis on the joint. A comparison of the full‐scale analysis and the simple representations allow conclusions to be drawn on the applicability of simplifications to the problem and also allows errors to be quantif

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00679.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe achievement of full‐coverage during the application of shot‐peening to critical components represents a major concern in the aerospace and power generation industries. It has been accepted, for many years, that full‐coverage of such components is needed to attain the beneficial fatigue‐life effects of the treatment. It has also been proposed, by a number of industrialists, that partial‐coverage may apparently shorten the fatigue‐life of the component because of the presumed presence of tensile residual stresses in the uncovered areas. Three aspects of the investigation were accordingly examined. The first deals with theaccurate measurement of peening coverageusing a three‐dimensional surface profilometer arrangement. The second deals with the development of fatigue crack growth data for fully‐ and partially‐peened components using an instrumented rotating‐bend fatigue rig. The third deals with monitoring the residual stress field associated with different peening‐coverage using the dissection method. In order to highlight the effect of the treatment upon the fatigue behaviour of the tested components, both theoretical and experimental techniques were considered. In the theoretical work, three‐dimensional finite element analysis of circumferentially cracked notched and un‐notched cylindrical components was considered in the development of the corresponding stress‐intensity factor (KK1) under bending loads. The stress‐intensity factor vs crack length relationship was subsequently used in the experimental determination of fatigue crack growth rate data at the different stress levels examined. Accordingly, room temperature rotating‐bend fatigue tests were conducted on specimens made from medium carbon steel 080 M40 (En 8) and aluminium alloy (7075‐T6). Surprisingly, the results of both materials reveal that a life improvement of up to 50% can

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00680.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper deals with the effect of casting conditions and long‐term in‐service exposure on the Charpy‐V notch and creep properties of a 1Cr‐1Mo‐0.25V steel. The material is investigated under two conditions: (i) as‐cast in a thick part which produces a mixed ferrite‐bainite microstructure and (ii) as‐cast as a small ingot which produces a fully bainitic microstructure. The material from the thick part was taken from either the cold part (∽200°C) or the hot part (∽540°C) of a steam power casing which operated for about 150,000 h. A small shift in the ductile‐brittle transition temperature is shown after the long exposure time. This shift is related to segregation of phosphorus impurities along the grain boundaries as shown by Auger electron spectrometry. The bainitic microstructure exhibits a much better creep resistance compared to the thick part component material. Moreover, in the latter case, it is shown that long‐term in‐service exposure induces an increase in creep strain rate and a decrease in creep ductility at least for relatively short times to failure (≲1000 h). These variations in mechanical properties are briefly discussed in terms of microstructural changes. Scanning electron microscopy confirmed that grain boundary cavitation was responsible for decreasing the creep ductility at large

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00681.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractBoth the initiation and the propagation of creep cracks have been studied in a 1Cr‐1Mo‐0.25V steel at 550°C using CT type specimens. The material taken from a large turbine casing was investigated in two conditions: (i) unaged and (ii) after a long exposure in‐service time of about 150,000 h at 540°C. In both cases the material was found to be creep ductile, which is justified in terms of fracture mechanics applied to creeping solids. It is shown that fracture mechanics is unable to provide unique correlations with global load‐geometry parameters, eitherKorC* for all the stages of both crack initiation and crack growth. However there exists a unique correlation betweenC* and the time to initiation,ti. This correlation does not depend on the initial conditions of the material. During crack growth two stages are defined. Stage I is a transient regime in whichC* is almost constant, but the correspondence between the crack growth rate andC* is not unique since largely dependent on the initial loading applied to the specimens. It is shown that the apparent correlation between the crack propagation rate in stage II which corresponds to large crack growth rate is doubtful. A simplified method based on reference length and reference stress is used to calculateC* parameter and to simulate the load‐line displacement rate. The results obtained from this method are compared to those derived from finite element calculations published in the

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00682.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractIt is generally thought that, when a material is in its brittle to ductile transition, it is more difficult to design for crack arrest than to prevent crack initiation (cleavage). This report shows that this is not always true for weldments. Comparison is made between compact crack arrest (CCA),Ka, and crack tip opening displacement (CTOD),KJc, toughness for the same HY80 weld. The value ofKais shown to be much higher than the minimumKJcfor pop‐in fracture initiation. It is considered that the results support the conclusion of Japanese research workers (Arimochi and Isaka) that small pop‐ins (in the CTOD test) propagate and arrest without load drop. It follows that prediction of structural failure for weldments need not be based on minimum pop‐in toughness from CTOD

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00683.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper describes a model developed for predicting residual stresses and crack growth in residual stress fields, and the application of the model to crack growth from cold‐worked fastener holes in thick section aircraft components. Comparison with experimental results demonstrates that the model can provide useful predictions of critical crack length, and a capability for correctly predicting the maxima and minima in the crack growth rate for cracks from cold‐expanded holes. It also permits the observed asymmetry in cracking from cold‐worked fastener holes to be better under

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00684.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractFatigue life data customarily analyzed using the logarithmic transformation may be better analyzed using the Box‐Cox transformation. This transformation has the advantages of stabilizing the variance, simplifying the model and transforming to approximate normality. In addition, simple schemes for imputing run‐outs can be constructed and the endurance limit can be easily calculated.This paper considers in detail the use of the transformation on fatigue life data from a thick plate Al‐Zn‐Cu‐Mg alloy. It presents a simplified method for determining the transformation, and then uses the transformation to determine distinctions in quality between different lots and confidence intervals on the

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00685.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00677.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY