Comparison Between Fracture Mechanics and Local Approach Models for the Analysis of Shallow Cracks

Abstract

This contribution shall introduce the application of the fracture mechanics and damage mechanics on flawed specimens by comparing the methods, especially with regard to the evaluation of shallow cracks. The investigations introduced here were conducted on specimens removed from a segment of a shape-welded vessel made of 10 MnMoNi 55. Using round notched tensile specimens the required parameters were determined for the local approach model by Rousselier. Following this the local approach model was used for calculating the macroscopic failure behaviour of CT-specimens and three-point bending specimens with long and shallow cracks. The crack depth to width ratio of the CT-specimens was approx. a/W = 0.56, that of the three-point bending specimens a/W = 0.55 and a/W =0.07. Using experimental results and numerical calculations on the basis of the damage model according to Rousselier it is possible to examine the influence of specimen geometry and a/W-ratio on the crack initiation value Ji and the crack resistance curve. Thus an evaluation of fracture mechanics methods is possible. The course of the multi-axiality of the stress state is a possibility of assessing the transferability of crack resistance curves. In calculating the multi-axiality during a running crack it is shown how the multiaxiality changes as a function of the crack propagation

Void growth and damage models for predicting ductile fracture in welds

“…Usually, σ 1 is calibrated from tensile tests on axisymmetric notched tension specimens. The values of σ 1 observed in the literature range from 0.6 σ y to 1.2 σ y 12 –18 . The constant D is generally taken between 1.5 and 2, and f 0 can be estimated from chemical composition of the material.…”

Experiments and numerical approaches to ductile tearing in an 2024-T351 aluminium alloy

“…The residual stresses resulting from this insu cient drop in stress falsify the computed crack growth. To avoid such a problem, an additional critical void volume fraction f c was introduced by some authors [8,16,17]. If the calculated void volume reaches this critical value f c , the stresses are lowered to zero.…”

An experimental and numerical investigation of fracture resistance behaviour of a dissimilar metal welded joint

“…After f c , the increase in void volume fraction gets accelerated and final fracture of the material point occurs at final void volume fraction f f . In the continuum damage mechanics models, these parameters are determined from combined numerical simulation and metallurgical observations of microscopic voids as described in references [21], [27], [31], [37] to [39], [42], and [43]. For the materials under consideration here, the details of the selection of the parameters will be discussed in the next section.…”