A shallow crack assessment scheme for generalised material behaviour in tension

Lau, C.L.; Lee, M.M.K.; Luxmoore, A. R.

doi:10.1016/0013-7944(94)00321-8

Cited by 6 publications

(17 citation statements)

References 4 publications

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“…using the bilinear curve gave a closer agreement over the range studied. The situation becomes even more complex when material behaviour has a perfectly plastic region immediately after the yield point, as further research by the authors [4] has shown that this type of material behaviour can produce plateaux in the J versus strain relationship.…”

Section: A Brief Review Of the Sensitivity Of The J-integral To Matermentioning

confidence: 98%

“…In previous work [2,3,4] undertaken at Swansea, J-estimation schemes for shallow cracked geometries (crack depth to specimen depth ratio a/W ~< 0.1) have been developed for remote strain loadings of up to 10 times the yield strain. These estimation schemes, developed from extensive two-dimensional (2D) plane strain finite element (FE) analyses for tension or pure bending loadings, allow engineers involved in defect assessment to obtain rapid J-estimations for real steels, without resorting to elaborate computations.…”

Section: Introductionmentioning

confidence: 99%

“…2D FE analyses showed that J-values for shallow edge cracks in both tension and bending are very sensitive to small changes in the material law [3,4,5]. The sensitivity of J to variation in material behaviour has been described in some detail in [5] and will be reviewed in Section 2.…”

Section: Introductionmentioning

confidence: 99%

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The sensitivity of J-integrals to material law variations for semi-elliptical surface cracks

1996

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In finite element analysis of cracked bodies, it is quite common to represent the material law (stress-strain curve) in a simplified form e.g. bilinear approximation. Many steels, however, have a more complex material law, which includes a perfectly plastic region before work hardening. Two dimensional finite element analyses have shown that fracture parameters, such as the J-integral, are very sensitive to variation in material law for shallow cracks, and the writers have now commenced three dimensional analyses for surface semi-elliptical cracks in plates. Some computations have been made for specimens tested experimentally by Dodds and Read [1], and the results show that what appears to be a reasonable approximation of the material law is inadequate in modelling the deformation behaviour, and that more accurate modelling of the material law, especially the plastic part immediately after yield, which may include perfectly plastic behaviour, is required for reliable results.

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Section: A Brief Review Of the Sensitivity Of The J-integral To Matermentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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The sensitivity of J-integrals to material law variations for semi-elliptical surface cracks

1996

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“…These analyses showed that the net section yielding (NSY) observed in single edge notch tension (SENT) specimens 1 , 3 did not occur in SENB specimens. Nevertheless, the J versus strain curves produced were still very sensitive to changes in material laws and crack sizes.…”

Section: Review Of Swansea J Estimation Schemesmentioning

confidence: 99%

“…Semi‐elliptical surface cracks are commonly developed by fatigue crack growth. The authors have previously developed J estimation equations for the assessment of these cracks based on the finite element analysis of two‐dimensional (2D) edge cracked models 1 –4 . These equations cover both tension and pure bending loading, and generalized material behaviour and, generally, provide conservative estimates of the actual three‐dimensional (3D) values because of the added restraint provided by the uncracked section in 3D.…”

Section: Introductionmentioning

confidence: 99%

J estimation for shallow semi‐elliptical surface cracks in wide plates under pure bending

Boothman

Lee

Luxmoore

et al. 1999

Fatigue Fract Eng Mat Struct

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Three‐dimensional finite element models have been used to predict the J versus applied strain behaviour of shallow semi‐elliptical surface cracks in wide steel plates. These models were loaded in pure bending up to fully plastic conditions that produced maximum strains remote from the crack of 10 times the yield strain. This study examined cracks with a crack depth to plate thickness ratio (a/t) in the range 0.05–0.15, and crack depth to crack half‐length ratio (a/c) from 0.2 to 0.57, in elastic‐hardening materials as well as those with a yield plateau before strain‐hardening. The results were found to differ significantly from those obtained from plane strain analyses, and a J estimation scheme was developed from the three‐dimensional results. Comparisons between the results obtained in this work and the J predictions provided by existing defect assessment methods show that the proposed equations are a significant improvement when large strains are likely.

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Jestimation for shallow notch SE(B) specimens: 3 and 4 point bending vs. ?pure? bending

et al. 1996

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Conventional fracture mechanics tests to measure the initiation toughness of a material under elastic-plastic conditions in terns of J (or equivalently CTOD, 5) commonly utilize deep-notch bend specimens, SE(B)s, subjected to three-point loading (see for example ASTM E-813 and E-1290 [1,2]). Sumpter [9] and Wu et al. [10] developed early J estimation schemes for shallow notch SE(B)s using limit load and slip-line solutions. The extensive plane-strain, finite element analyses recently described by Kirk and Dodds [5], Kirk and Wang [6] provide simple formulae to estimate applied J-values for a wide range of crack depth to specimen width ratios, a/W, and material strain hardening properties. These studies focused on small a/W ratios routinely employed in weldment testing. The estimation scheme divides J into elastic and plastic components, with a plastic "eta" factor to relate the measured plastic work done on the remaining ligament to Jp. For shallow crack specimens, use of the plastic component of the crack mouth opening displacment (CMOD), rather than load-line displacement, provides eta factors strongly insensitive to strain hardening properties of the material.Occasionally, testing procedures employ four-point loading which places the crack plane within a constant moment region and allows unobstructed access to both the tension and compression faces of the specimen, for example, to permit additional instrumentation. However, as of this writing no standard test methods for elastic-plastic fracture permit the use of four-point bending. Test procedures use similar geometric proportions for three and four-point loading of SE(B)s, with differences only in the loading arrangement; the region over which pure bending exists typically ranges from 2-3 x W. A longer span (S) may also be used to accommodate the four-point loading while maintaining conventional B x B or B x 2B cross-sections. Finite element analyses of these configurations reveal only minor differences with three-point loading in the J-CMOD relationship, and thus very similar plastic eta factors (for use with measured CMOD values).Int ~ourn of Fracture 77 (1996) RI2Recent studies by Luxmoore and co-workers [3,7] have demonstrated a marked effect of material strain hardening features, specifically the presence of L~ider's strain (see Fig. 1), on the increase of J with remote strain in shallow notch SE(B) specimens loaded in "pure" bending, i.e., a linearly varying displacement field imposed over the remote end of the specimen. The motivation to examine this configuration derives from the need to approximate conditions of global bending in a large structural component containing a small crack. The striking differences in the evolution of J for this configuration compared to those for three and four-point bending prompted this discussion.The "pure" bending configuration used by Luxmoore et al. [3.4] allows unconstrained plastic flow to develop over the full length of the specimen in much the same manner as occurs for a small crack in a large, tension ...

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A shallow crack assessment scheme for generalised material behaviour in tension

Cited by 6 publications

References 4 publications

The sensitivity of J-integrals to material law variations for semi-elliptical surface cracks

The sensitivity of J-integrals to material law variations for semi-elliptical surface cracks

J estimation for shallow semi‐elliptical surface cracks in wide plates under pure bending

Jestimation for shallow notch SE(B) specimens: 3 and 4 point bending vs. ?pure? bending

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