Treatment of residual stress in failure assessment procedure

The effect of residual stress on component failure has been investigated using the distributions from current failure assessment procedures, and a residual stress profile simple to apply with less conservatism has been proposed for the weld geometries of T plate and tubular T joint. The stress intensity factors SIFs in the two weld geometries under various types of loads have been calculated using the Green s function method. The Green s functions were determined not only for the T plate but also for the tubular T joint with the built in ends. The use of a linear bending stress profile, derived from an analysis of measured residual stress distributions in T plate and tubular T joints, has been examined. The profile was validated with experimentally measured residual stress distributions in two materials, a high strength and medium strength ferritic steel and two geometries, a T plate joint and a tubular T joint for crack lengths up to half the plate or pipe thickness. Whereas the recommended residual stress distributions are geometry and material specific, it is shown that a simplified linear bending profile provides a possible guideline, applicable to a range of materials and geometries, where detailed information on weld procedures or residual stress profiles are unavailabl

Effect of residual stress on high temperature deformation in a weld stainless steel

This paper considers the measurement of residual stresses induced by mechanical loading in a weld Type 347 stainless steel. The work is based in part on an ongoing Round Robin collaborative effort by the Versailles Agreement on Materials and Standards, Technical Working Area 31, VAMAS TWA 31 working on Crack Growth of Components Containing Residual Stresses . The specific objective of the work at Imperial College London and HMI, Berlin is to examine how residual stresses and prior straining and subsequent relaxation at high temperature contribute to creep crack initiation and growth for steels relevant to power plant applications. Tensile residual stresses have been introduced in the weld by pre compression and neutron diffraction measurements have been carried out before and after stress relaxation at 650 oC. Significant relaxation of the residual stresses has been observed, in agreement with earlier work on a stainless steel. Preliminary results suggest that the strains local to the crack drop by over 60 after 1000 h relaxation at 650 oC for the weld steel. The results have been compared with finite element studies of elastic plastic pre compression and stress relaxation due to cree

A diffusion driven carburisation combined with a multiaxial continuum creep model to predict random multiple cracking in engineering alloys

A diffusion-based coupled oxidation, intergranular damage and multisite randomised crack growth model for environmentally assisted oxidation/carburisation and creep time dependent material is proposed. A combined grain boundary and grain mesh structure is employed for simulating surface hardening and intergranular cracking resulting from a surface gas/solid carbon diffusion and bulk creep interaction by assuming variations in their strength ratios. Using 316H properties at 550° C the predicted surface intergranular cracks, due to both carburisation and creep, and subsequent crack growth are analysed in terms of their rupture and failure strains are compared to as received 316H data to validate the model

Physical and numerical modelling of ram extrusion of paste materials: conical die entry case

A ram extrusion process with a conical die entry is analysed using a physically based analysis and a numerical modelling procedure involving the finite element method. The aim of the study is to test the applicability of the elastoviscoplastic constitutive model combined with an established boundary condition criterion for describing this forming operation. "Plasticine", a commercial modelling clay which exhibits an elasto-viscoplastic flow response, is used to study the nature of the material deformation. For the numerical modelling, an elasto-viscoplastic finite element program has been implemented. Satisfactory agreement, between experiment and simulation, is obtained for the force-time data and the material displacement fields which indicates that the bulk and interfacial constitutive relationships adopted, along with the associated numerical parameters, are an appropriate description of the flow behaviour of the system. The evolution of the deformation, within the material during the extrusion process, is interpreted. The study indicates that the procedures described may ultimately provide a numerical rheometric tool from which the effects of various process boundary conditions, on the evolution of paste material deformation, can be examined and quantified for the ram extrusion process with conical die entries. (C) 2000 Elsevier Science B.V. All rights reserved

Computational and experimental studies of high temperature crack initiation in the presence of residual stress

Residual stresses have been introduced into a notched compact tension specimen of a 347 weld material by mechanical compression. The required level of compressive load has previously been determined from finite element studies. The residual stress in the vicinity of the notch root has been measured using neutron diffraction and the results compared with those obtained from finite element analysis. The effect of stress redistribution due to creep has been examined and it is found that a significant reduction in stress is measured after 1000 h at 650 C. The implications of these results with regard to the development of damage in the specimen due to creep relaxation are examine