摘要:

AbstractProcedures developed by Ainsworth and Smith and Webster to assess the remaining life of high temperature engineering components containing cracks are presented and applied to a practical example of a °CrMoV steel pressure vessel operating at 565°C. The general principles of the procedures are similar. Net section creep rupture is described in terms of the reference stress method and creep crack initiation and growth is predicted using the non‐linear (creep) fracture mechanics parameterC*. However, the details of each procedure are shown to differ. The main differences lie in the predicted times for net section creep rupture and creep crack initiation. Ainsworth's method predicts shorter creep rupture times than Smith and Webster's procedure. The initiation time using the Smith and Webster procedure is predicted to occur shortly after loading while Ainsworth's estimate is about 40% of the life of the vessel. Both procedures predict similar times for failure by creep crack initiation and crack gro

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00690.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper describes a versatile finite element technique which has been used to investigate the fatigue growth and stability of a wide range of structural defects of practical importance. The procedure automatically remeshes the three‐dimensional finite element model during the stages of crack growth. Problems analysed to date include the subsurface and breakout growth of internally initiated elliptical defects, the growth of semi‐elliptical surface cracks in leak‐before‐break situations, the development of quarter‐elliptical corner defects, the interaction and coalescence of two adjacent coplanar semi‐elliptical surface defects and the fatigue growth of a defect in

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00691.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractKnowledge of the creep behaviour of materials used in structures which operate for many years is of fundamental importance when assessing the integrity of such structures. The additional consideration of cracks which may occur in metals is also important. For discrete cracks, characterising parameters associated with the creep conditions at the crack tip may be evaluated to determine whether the crack will grow slowly, rapidly, or remain stationary. For arbitrary structures containing such defects, the finite element method is particularly effective for calculating the time‐dependent stress analysis. The particular fracture parameters can then be evaluated using algorithms based on existing technology for contour integration, and a new virtual crack extension technique. These features are described and compared in application to a laboratory compact tension specime

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00692.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe effect of an aqueous chloride environment upon the development and growth of short fatigue cracks from smooth specimen surfaces has been studied under fully reversed torsional fatigue loading conditions. Crack initiation and growth has been monitored using a plastic replication technique enabling a full history of cracking characteristics to be recorded. Corrosion fatigue conditions were achieved by complete immersion in a 0.6 M NaCl solution, of nominal pH value 6.0, with specimens corroding at the free corrosion potential. Variations to these conditions were obtained by the addition of concentrated hydrochloric acid enabling test solution pH values to be altered, typically pH values of 3.5 and 2.0 were obtained. Further information regarding the effects of the environment on the early stages of crack development were obtained by conducting two stage alternate immersion type testing conditions. Evaluation of these effects through previously established Elastic‐Plastic Fracture Mechanics models shows that the environment plays a major role during the early stages of microstructure‐dominated crack growth particularly as cracks approach major barriers to propagation and at decreasing levels of applied shear str

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00693.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe repair or replacement of defective structures can be avoided if it can be shown that the defects will grow a negligible amount in service. The most robust parameters for correlating the onset of crack growth between test and service conditions can be defined as contour integrals around the crack tip. For many years, integrals of this type have been available in the post processing part of the stress analysis program BERSAFE. The new release BERSAFE 90 will include the options of evaluating these parameters by replacing most or all of the contour integration by surface or volume integration. This method known as thegfunction method makes them equivalent to virtual crack extension methods for an elastic material. To obtain experience of the relative accuracies of the new and old options, calculations have been carried out on coarse meshes for elastic‐plastic materials with two dimensional, axisymmetric and three dimensional geometries under both mechanical and thermal loading for various tolerances and numbers of Gauss points. It is concluded that1The quantityJ*wcan often be calculated more accurately by using thegfunction than by taking a contour integral through nodes. However further experience is required before final guidelines can be issued.2Use of 27 rather than 8 Gauss points per element did not improve the accuracy in the case considered.3For uniform tensile loading of a central cracked block, both thegfunction method and the contour integration method give satisfactory accuracy even with only one element through the thickness. However displacement substitution produces values which are dependent on the number of Gauss points when there is only one such element.4A close tolerance is required for thermal problems in order to obtain path independent results when using either the contour integration or thegfunction

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00694.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractHigh‐speed photography has been used to study the behaviour of polymer specimens subjected to high velocity impacts that excite the specimen into strong, complex vibrations. These photographic data are correlated to the outputs of sensors located on the specimen, striker and supports. Optical and scanning electron‐microscope studies of the crack initiation zone and the size and texture of other features on the fracture surfaces are also correlated to other fracture data. To obtain better information about the threshold of crack initiation of these materials and other data difficult to obtain by impact testing, a new experimental method has been developed. To assist in predicting and analysing experimental data a desk‐top computer model has been devised with good visibility of the computing steps and how these relate to crack propagation in polymeric mate

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00695.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractCurrent standard fracture‐mechanics methods encourage sudden, explosive and total testpiece fracturing in which one catastrophic event produces one set of measurements. By demanding conformance to the overall elasticity requirement while relaxing thickness and crack‐length specifications and following a slow crack‐growth sequence, series of simultaneous measurements were made on single testpieces. From these measurements independent values of the Mode‐I critical stress‐intensity factor and strain‐energy release rate were determined. Polyethersulphone injection‐moulded discs were prepared as round‐compact testpieces. The crack grown from a chevron‐notch was propagated under control, slowly. A large number of measurements were made as the crack extended. The fractures were smooth, square to the body of each disc and had a stable crack path across the diameter. The independent fracture‐toughness values were small but their derived modulus agreed well with directly measured values of Young's modulus, thus confirming the elastic in

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00696.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe U.K. National Agency for Finite Element Methods and Standards (NAFEMS) is a government agency funded by the Department of Trade and Industry. The task of the Agency is to evaluate the standards used in developing FE programs in order to improve the general level of user competence in industry. The Agency has established Working Groups to consider various aspects of FE techniques. The responsibility of the Working Groups is to identify the analytical work required to investigate specific techniques and applications, and to ensure the execution of the work. One Working Group is concerned with finite element fracture mechanics and its activities are described in detail in this paper. Various categories of benchmark specifications were identified by the Working Group along with the need to provide educational input, guidance documents and a general interest in current developments and user requirements.

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00697.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.tb00689.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY