C. Hari Manoj Simha

Fracture Toughness of X70 Pipe Girth Welds Using Clamped SE(T) and SE(B) Single-Specimens

Shallow-notched single edge-notched tension (SE(T) or SENT) and deep- and shallow-notched single edge-notched bend (SE(B) or SENB) specimens with notches positioned in the weld and the heat-affected zone were tested. Crack-tip opening displacement (CTOD) versus resistance curves were obtained using both a single and double clip gauge consolidated in a SE(T) single-specimen. Up until the peak load the resistance curves from both gauging methods yield approximately the same results; thereafter the curves deviate. Interrupted testing showed that the crack had initiated below 50% of the peak load, and in some cases had propagated significantly prior to reaching the peak load.Copyright

Low-Constraint Toughness Testing of Two SE(T) Methods in a Single Specimen

Single-edge notched tension (SE(T) or SENT) specimens has been increasingly proposed as a low-constraint toughness test to measure toughness of line pipe materials, as the crack tip constraint approximates a circumferential surface flaw in a pipe under loading. The clamped SE(T) single-specimen procedures recently developed by Shen and Tyson [1, 2] and Tang et al. [3] have in common the use of a clamped single-specimen of similar geometry and rely on unloading compliance technique for crack size estimation. In the former case, a single clip gauge is attached to the integral knife edge and the crack-tip opening displacement (CTOD) is estimated by means of a J-integral-to-CTOD conversion, similar to the procedure of ASTM E1820. The latter uses a pair of clip gauges mounted to an attachable raised set of knife edges to estimate CTOD at the original crack tip position by a triangulation rule. Consolidating these two sets of clip gauges in a specimen makes direct comparisons of two SE(T) methods on identical test conditions: material, specimen geometry, equipment, test temperature and operator [4]. In this study, SE(T) testing employing these two SE(T) methods on a single specimen was conducted on BxB shallow-cracked (a/W∼0.35) specimens of two x70 pipeline girth welds. This paper discusses the details of two SE(T) methods and techniques on the same specimen.© 2014 ASME

Limit Load Solutions for Cracked Elbows Subjected to Internal Pressure and In-Plane Bending

In this article, limit load solutions for cracked elbows containing through-wall and part through-wall axial and circumferential cracks under internal pressure and in-plane bending loading are presented. For elbows with axial cracks, limit pressure solutions are presented, and modifications to existing limit moment solutions are proposed. The foregoing limit pressure and limit moment solutions are used in conjunction with a novel interaction curve to obtain limit load solutions for elbows with axial cracks under combined pressure and moment loading. If the applied moment and pressure are within (outside) the envelope of the interaction curve, no failure (failure) is indicated. Furthermore, limit pressure and limit moment solutions for circumferentially cracked elbows are developed using the same interaction curve. Limit loads computed with the solutions presented in this work are compared with experimental results and the agreement is found to be within acceptable limits after accounting for the uncertainties in the experimental results.

Damage-mechanics-based modelling of failure of squeeze-cast AM50 magnesium alloy

ABSTRACT Static and impact tests on bars and plates of squeeze-cast AM50 were used to calibrate a failure surface that depends on tri-axiality and Lode angle. Both notched and un-notched bars and plates were tested. Assuming isotropic plastic response, but asymmetry of work hardening in compression and tension, a damage-mechanics-based model is used to model static and impact loading. Predictions using the model are found to be in reasonable agreement with the experimental results; peak loads and ductility are well described by the model, particularly, for engineering applications. Qualitatively, the model predicts the crack growth in good agreement with observations for experiments wherein the tri-axiality is higher. Likewise, the predicted deformation and failure response are in good agreement with the experimental deformation and failure for higher tri-axiality experiments. We suggest that owing to the coarse grain size, at high levels of deformation, the response is not uniform which make continuum-based modelling a challenge. Nevertheless, the present effort is suitable for predictions of failure in engineering practice.

Estimating Lower Bound Limit Loads: No Iterations/Modulus Adjustment

We use the extended variational form of Mura and co-workers to estimate the lower bound limit loads for structures acted upon by a single load. Our scheme requires one elastic stress field either from a conventional finite element computation or analytical solution. No iterative stress field adjustments are required. We also adapt the scheme for structures with flaws by advancing a criterion that may be used to select sub-volumes of the structure that do not participate in the collapse. For structures with flaws, no ad hoc elastic modulus reduction at the stress concentration is required. Application of the proposed method is illustrated for some typical flawed and flaw-free structures and it is shown that the obtained multipliers are not overly conservative.Copyright