摘要:

Abstract—Energy dissipation rate,D, and crack tip opening angle (CTOA) have been related for large amounts of ductile crack growth in a fully plastic two‐dimensional model of real elastic plastic material. SeveralJ‐type risingR‐curves have been constructed and related, some based on the cumulative energy dissipated and some as a characterising term that relates closely to the far‐fieldJcontour value. These two meanings co‐exist but the relationship is geometry dependent. For deep notch bend (DNB) cases the non‐dimensional groupLα/r* (whereLis normalised load, α is CTOA andr* defines the position of the instantaneous centre of rotation) governs the value of dJ. Certain DNB cases whereR‐curves vary with size are resolved by this group rather than by CTOA itself whereas for centre‐cracked tension there is a higher value o

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb01402.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—Equations are established for the final macro‐unstable behaviour of a fully plastic cracked component in terms of the energy dissipation rate. Control by this first differential of energy occurs when the second differential of the energy absorbed is negative, a condition easily met for crack growth in certain fully plastic cases. The driving force for the instability is a term,Ithat becomes greater than the lefm term,G, as plasticity occurs. The additional component is an exchange of elastic to plastic energy, a term that is system dependent and is thus the main driving force for a fully plastic ductile instability. A possible relevance to brittle fracture and to a system dependence of both initiation toughness and the whole crack growth resistance curve is discus

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb01403.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—Several experimental techniques used in fracture toughness tests are based on the “Plastic hinge” model that permits different fracture mechanics parameters to be determined. This model is only valid under the following conditions: small displacements, small stable crack growth, and small distances between knife edges and the apparent centre of rotation. A generalized model for a two‐dimensional situation is presented which permits a better representation of the phenomena that occur in a test involving crack growth and large displacements. The use of a two‐dimensional factor, that corrects the measured displacements by converting them into ones that would be measured under a one‐dimensional hypothesis, is proposed. In this way the same methodology used for CTOD determination, may ag

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb01404.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—Failure of ceramic materials occurs when the stress intensity factor of the most serious crack in a component reaches a critical value KI,C, the fracture toughness of the material. In case of ideal brittle materials the fracture toughness is independent of the crack extension and, consequently, identical with the stress intensity factor KI,Onecessary for the onset of stable crack growth. It is a well‐known fact that failure of several ceramics is influenced by an increasing crack‐growth resistance curve. The effect of increasing crack resistance has consequences on many properties of ceramic materials. In this report the authors discuss some aspects ofR‐curve behaviour as represented by stress intensity factors or e

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb01405.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—Slip line field and finite‐element analyses forJand crack tip opening displacement, δt, at plastic collapse are performed for an idealised weldment. The relationship between these two quantities is shown to depend on the nature of the loading (tension or bending), the ratio of yield stresses in weld and base materials, and on the width of the weld compared to the remaining ligament ahead of the crack. Cases where the weldment behaves as a single weld material are determined. However, it is also shown that there is a significant range of cases where the base material yield stress governs the relationship betweenJand δt, at collapse, even when the crack is located in weld metal.It is shown that the relationship betweenJand δt, at plastic collapse only occurs at loads very close to the collapse load unless the crack is located close to the weld/base boundary or the weld width is small compared to the remaining ligament ahead of the crack. More generally, the weldment behaves as a single weld material in terms of the relationship betweenJand δt, and conventional fracture assessments usingJor δt, are eq

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb01406.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—The transferability of fracture results between homogeneous and cladded specimens was studied in single edge‐notched bend specimens. The test material was of A533‐B steel with a clad layer deposited by a commercial strip welding process. The fracture resistance properties were developed independently for cladding and base material using homogeneous specimens of each material. The experimental data from tests on cladded specimens were analysed with the finite element method. The 3DJ‐values were compared with values evaluated using the measured crack extension in the cladded specimen and theJR‐data of the respective material provided from homogeneous specimens. A reasonably good agreement was obtained in this comparison for a limited amount of cra

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb01407.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—Mode I and mode II stress intensity factors for two half‐spaces connected by a circular patch were used to develop a mixed‐mode stress intensity factor (termed the stress indexKi) which can correlate the fatigue life of all spot weld geometries, base metals, and specimen dimensions. Empirical corrections were applied to Broek's equivalent stress intensity factor (Klq) to account for the weldment geometry (sheet thickness, nugget diameter, specimen width) and the effect of mean stress. The final expression, (Ki), is a measure of the notch‐root stress field in the location where crack initiation and early crack growth occur. The stress index (ki) should be a useful tool for spot‐weld fatig

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb01408.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—A mathematical model of crack propagation due to the formation of a fractal cluster of voids and microcracks is presented. The initiation of a microcrack from a pile‐up of dislocations in the vicinity of a crack tip is modelled. A method to determine the fractal dimension of a crack, based on the crack growth analysis, is developed. A crack length versus crack velocity relation, based on the physical mechanisms of crack growth and the fractal nature of a crack, is deduced. A formula for the time to fracture is obtai

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb01409.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—The distribution of hydrogen in the vicinity of a crack tip was studied using SIMS (Secondary Ion Mass Spectrometry) under different ratios of I/II mixed mode loads. Modified WOL specimens with kinked slits were employed in the course of the experimental work. Spectrographic measurements show that under I/II mixed mode loading, both in the HIC and in thermaxpdirections, there are two hydrogen accumulation peaks ahead of the crack tip, corresponding to the location of the maximum hydrostatic stress and maximum equivalent plastic strain, respectively. Based on results obtained over a range of loading conditions from mode I to a high KII/ KI, ratio, it is shown that the mode II component has a clear influence on both peaks. The conditions for hydrogen redistribution are discussed in terms of crack tip stress‐strain fie

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb01410.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—The conventional use of continuum ductile damage mechanics in finite element analyses identifies the “cell” in which damage occurs with the finite elements in which the distribution of stress and strain is modelled. Since the cell size is a fixed, metallurgically‐defined, property of the material being analysed, this methodology forces a minimum size for the finite element mesh. Mesh refinement is thereby disallowed. This paper presents one way of avoiding the problem by developing a mesh‐independent cell model which, with a fixed cell size, allows the finite element mesh to be refined to any degree within the cells. Procedures which average some state variables within the cells are introduced to prevent the localisation of damage after a certain critical stage is reached. The method has been tested in numerical simulations of (a) the deformation of a notched tensile bar, (b) a 35 mm compact tension specimen and (c) the first of the AEA spinning cylinder tests. There is a reasonable agreement between the results of the computer simulations and those of the ex

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb01411.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY