K. Biswas

A numerical prediction of the temperature distribution in the thermionic cathode of a welding arc

Abstract The thermal phenomena at the surface of the thermionic cathode of a welding arc are influenced strongly by the mutual interactions of several physical processes. A steady-state axisymmetric finite-element model, incorporating the effects due to the main physical processes in the cathode of normal GTA operations, has been used to determine the spatial variations of the thermal fields. The model differs from previous model in that it considers cathode cooling due to the presence of flowing shielding gas. The calculated temperature distributions are compared with existing experimental data for a typical tip geometry, the numerical results agreeing well around the tip region, whilst the agreement is relatively poor in the regions away from the tip. Finally, the analyses are extended to certain common geometries to examine the consequences of changing the tip profile on the thermal behaviour.

The J integral analysis for implant specimens: A comparison for some notch geometries

Abstract Application of Rices path-independent J integral and its extended formulations is now well established to correlate the crack growth initiation for materials under extensive plastic deformation. An elastic-plastic finite element analysis suitably formulated to admit linear work hardening of materials for a circumferentially notched axisymmetric implant specimen, commonly used to determine the fracture resistant parameters of welded joints, has been carried out under contained yielding and monotonically increasing tensile loads. The direct procedure for estimating J around the smoothly blunted notch of two different shapes has been followed to examine the role of J as a notch tip characterizing parameter and to establish a possible relationship between J and other specimen parameters. The numerical results include notch tip parameters and near-tip deformation fields. Also, the effects of the difference in weld and base metal properties on J have been investigated here. Even though the results do not predict a unique J value, they may still be employed confidently for engineering purposes in view of the justification demonstrated by the nearly path-independent J solutions obtained from a rather crude finite element formulation based on linear displacement distributions. In the present paper, an attempt has been made to predict the specimen response with the available J relations and to explore the numerical solution sensitivity to the changes in notch parameters. The problem has been decomposed into two models; one representing the circumferential notch having its faces inclined to the axis of notch symmetry while the other refers to a parallel sided flat notch in the implant specimen. An axisymmetric FE analysis that employs linear displacement distributions of the elements, suitably modelled to admit linear work hardening of the materials for incremental flow theory, has been carried out under axisymmetric tensile loads. The numerical results include notch tip parameters and near-tip deformation fields for both cases. Also, the effects of the difference in weld and base metal properties on various J relations have been investigated for a typical notch geometry. We first consider the inclined notch test specimen where both elastic and elastic-plastic analyses have been performed, yielding some approximate expressions between J and other relevant specimen parameters. In the same way, relationships between the various J formulations, the applied loads and the various geometric parameters have been studied for the flat notched specimen. The advantage in the use of such unique expressions is that only one specimen variable is sufficient to determine the J integral and therefore the elaborate numerical procedures are avoided.

Notch tip deformation and J-integral analysis for implant weldability test specimen

Application of elastic-plastic fracture mechanics techniques to the problems of welded structure toughness evaluation is relatively new. In recent times, a subject of increasing interest is the correlation of Rices path independent J-integral and its extended formulations to crack growth initiation in materials under plastic deformation. The circumferentially notched implant weldability test specimen is now widely used to evaluate the fracture characteristics of weld-base metal composites due to its advantages of small size and associated low cost. In this paper, an incremental finite element analysis, suitably modelled to admit linear work hardening of materials, has been carried out for this specimen under monotonic load histories.As a sequel to an earlier work, the domain-independent property of suitable J solutions available in the literature have been critically examined from the viewpoint of applying J-criterion to this specimen. Some new results about J and the associated notch tip deformation patterns are obtained here. Also, the role of surface and line contributions under the integral signs in axisymmetric J has been discussed in the context of the present problem. Solutions presented demonstrate that the J-integral can be used as a useful notch-tip characterizing parameter for this test specimen.

On the Evaluation of Path Independent Integral for Circular ARC Crack

Considering appropriate energy balance laws, new conservation integrals consisting of path and area forms, have been derived by the authors for a two-dimensional stationary circular arc crack subjected to multiple loads. As a sequel to our previous work, we present here further numerical results in the finite element context and examine the invariant property of the integrals computed on several contours for various geometries. The first part of the investigation refers to the incremental elastic–plastic analyses under mechanical loads whereas in the second part; analyses have been carried out under thermal loads. Within the limits of computational accuracy, the present finite element results demonstrate that the path independence is well preserved over the integration contours for both types of loads.

Assessment of Structural Integrity under Dynamic Loading using Path-Independent Integral #

In the present work, the integral , originally developed for a 2D stationary circular arc crack in a homogeneous and isotropic material subjected to multiple loads, has been implemented into a finite element postprocessing program for examining the path-independence behavior under elastic deformation while employing rapidly varying mechanical load. Under different loading rates, the integral has been computed on several contours in order to describe the invariant property of the integral . Numerical results reveal that, within the limits of computational accuracy, the path-invariant property is well preserved over the integration contours for the present loading rates. The variation of the integral with respect to time has also been studied for both plane strain and plane stress conditions. The numerical investigations confirm that the performance of the integral is sufficiently impressive and therefore suggest applicability in fracture-related studies.