Showing papers by "Bhagwati Prasad Kashyap published in 2003"
TL;DR: In this paper, a simple instability condition for assessing the extent of plastic deformation in a workpiece prior to the formation of defects, is derived based on the Ziegler's continuum principles.
85 citations
25 May 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the superplastic forming grade sheets of AA8090 Al-Li alloy were observed to contain layers of different microstructure and microtexture across their cross-section along the normal to the rolling direction (RD).
Abstract: The superplastic forming grade sheets of AA8090 Al–Li alloy were observed to contain layers of different microstructure and microtexture across their cross-section along the normal to the rolling direction (RD). The surface layer (SL) material contained coarse equiaxed grains and the dominance of S {1 2 3}[6 3 4] texture whereas the center layer (CL) material contained fine elongated grains and the dominance of Bs {1 1 0}[1 1 2] texture. Tensile specimens, machined to represent the SL of 0.6 mm thickness from the surface towards center (SL), the CL of 0.6 mm thickness, obtained by removing the material of 0.6 mm thickness from each surface towards center (CL), and full thickness (FL) material of 1.8 mm thick, in a sheet of AA8090 Al–Li alloy, were deformed at optimum superplastic condition of strain rate=1×10 −3 s −1 and temperature=803 K to investigate the effect of loading direction. In SL material, the specimen parallel to RD exhibited maximum and the specimen perpendicular to RD exhibited minimum flow stresses. This trend was reversed in CL material. The anisotropy in flow stress could be explained on the basis of texture in the SL material, but the contribution of grain directionality became important in the CL material. The flow behavior of FL material was found to consist of the composite-like contributions of SL and CL materials.
20 citations
25 Jun 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effect of local strain developed on the microstructural variation along the gauge length of tensile specimens was studied and a model was proposed for cavity nucleation on the basis of inhomogeneity in microstructure and its implication in deformation mechanism.
Abstract: Superplastic deformation of Al–Li 8090 alloy was carried out to study the effect of local strain developed on the microstructural variation along the gauge length of tensile specimens. For this, separate specimens were deformed to failure at a constant temperature of 530 °C and at the strain rates within the superplastic regime. The strain distribution was found to be non-uniform with more deformation towards fracture tip and less towards the shoulder section of specimens. The grain size was found to decrease with increase in local strain whereas cavity size and cavity volume fraction were found to increase. The cavity growth in longitudinal direction is suggested to be controlled by power law but the same in transverse direction is controlled by diffusional process. A model is proposed for cavity nucleation on the basis of inhomogeneity in microstructure and its implication in deformation mechanism.
15 citations
02 Jan 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a methodology for estimating the stress field in the matrix surrounding a semi-constrained inclusion was proposed, where the stress free misfit volume associated with the inclusion was partitioned into semi-consstrained and constrained components.
Abstract: A methodology for estimating the stress field in the matrix surrounding a semi-constrained inclusion is proposed. The stress free misfit volume associated with the inclusion was partitioned into semi-constrained and constrained components. The objective was achieved by carrying out a series of sectioning, cutting and imposition of constrained misfit displacement on an imaginary notch of geometry identical to that of the inclusion–matrix contour. The stress field was computed using elastic finite element analysis for plane stress condition. The misfit displacement model thus developed was applied to compute the stress field around a hydride blister grown under controlled thermal boundary condition in Zr–2.5Nb pressure tube (PT) alloy and was validated by interpreting the hydride platelet orientation in the matrix surrounding the blister. Finally, an assessment of the structural integrity of the Zr–2.5Nb PT material containing hydride blister was made in view of this analysis.
13 citations
TL;DR: In this article, the effect of seam welding on the critical properties such as texture, microstructure, hydriding behaviour and residual stress for both the routes as well as the mechanical anisotropy developed due to seam welding are investigated.
8 citations
TL;DR: In this paper, a methodology for determination of the complete pole figure with quantitative texture parameters for Zr-2.5%Nb pressure tubes is reported, which requires a special test setup that can combine the pole figure data obtained from both the reflection and the transmission techniques.
Abstract: Preferred orientation or crystallographic texture of Zr-2.5%Nb pressure tubes for a pressurized heavy water reactor (PHWR) affects all the critical in-reactor properties. The preferred orientation has to be measured to standardize the process route for getting the desired in-reactor properties. The quantitative determination involves determination of the complete pole figure and calculation of Kearns parameters from the pole figure data. Independently, neither the X-ray reflection nor the X-ray transmission technique can provide the full pole figure data. The literature reports only partial pole figures. Quantification of texture based on partial pole figures may lead to errors in estimation. For a complete pole figure determination, it is required to merge the data from both the reflection and the transmission techniques. This requires a special test setup that can combine the pole figure data obtained from the two techniques. In this paper, a methodology for determination of the complete pole figure with quantitative texture parameters for Zr-2.5%Nb pressure tubes is reported.
2 citations
TL;DR: In this paper, the effect of texture on residual stress has been studied for seamless Ti-3wt%Al-2Vwt% tubes, in pilgered and annealed conditions, by superimposing the residual stress measurements on the pole figure obtained by texture measurement.
Abstract: Some inaccuracies are possible during the near-surface residual stress measurement of textured material by X-ray diffraction using the standard multiexposure technique. Diffraction intensities depend on factors like inclination of the sample, the rotation of the beam, and the position of detectors. Low intensity due to texture can result in increased percentage error observed stress values. Anisotropy of elastic constants in textured materials can further increase the errors in measured stress. In the present study, the effect of texture on residual stress has been studied for seamless Ti-3wt%Al-2Vwt% tubes, in pilgered and annealed conditions, by superimposing the residual stress measurements on the pole figure obtained by texture measurement. A general approach has been developed for accurate determination of the stress tensor in textured material. This consists of the selection of inclinations giving rise to high intensity peak, the selection of rotation angles symmetric to the pole figure to get similar intensity from both the detectors (where this is not possible one detector with low intensity is shut off), and the calculation of the bulk X-ray elastic constants using the single crystal elastic data and texture. Cold worked Ti-3wt%Al-2Vwt% tubes had the highest stress along the rolling direction and that is compressive in nature. The principal residual stresses in the pilgered tubes were along the rolling and transverse directions, and annealing leads to reduction and reorientation of the stresses.