Peak Tensile Residual Stress Research Articles

Assessment of Residual Stresses and Distortion in Stainless Steel Weld Joints

Welding introduces significant residual stresses in the welded structure/component due to non-uniform heat distribution during heating and cooling cycle. To control, reduce, or beneficially redistribute the residual stresses in weld joints, the stress distribution needs to be known. In the present study, weld joints of 10 mm thick 316LN stainless steel were made by multi-pass TIG and A-TIG welding processes and their residual stresses distribution and distortion values were measured and compared. While V-groove edge preparation was required for making multi-pass TIG weld joint, square-edge preparation was sufficient for making single pass A-TIG weld joint. Ultrasonic nondestructive technique based on the critically refracted longitudinal waves (LCR waves) has been used for the quantitative surface/sub-surface residual stress measurements in the weld joints. Distortion measurements were carried out before and after welding using height gauge. Peak tensile residual stress and the angular distortion values were lower in the A-TIG weld joint compared to that of the multipass TIG weld joint.

Residual stresses, microstructure and tensile properties in Ti–6Al–4V friction stir welds

This paper reports the results of a systematic investigation of residual stresses as a function of welding speed in a set of Ti–6Al–4V friction stir welds. The investigation focuses on residual stress but links these data with microstructural information derived from micrographs and hardness measurements as well as mechanical testing results. Residual stresses were determined using energy dispersive synchrotron X-ray diffraction, which allows phase specific stresses to be distinguished. The data presented in this paper demonstrate that welds with high tensile properties can be obtained, which also have relatively low peak tensile residual stress values of ∼30% of the tensile strength. The data also show a clear correlation between heat input and the width of the residual stress profile.

On the evolution of local material properties and residual stress in a three-pass SA508 steel weld

In multi-pass welds, the development of residual stress generally depends on the response of the weld metal, heat-affected zone (HAZ) and nearby parent material to complex thermo-mechanical cycles. Here, the evolution of local material properties and residual stress was investigated for each of these zones during the manufacture of a three-pass groove weld in SA508 steel. Residual stress distributions were measured by neutron diffraction for a sample in which only one weld bead had been deposited, and again for a completed three-pass weld. The evolution of material properties was also characterised by measuring local hardness and conducting tensile tests on small coupons that were extracted from the same welded specimens. Overall, the addition of subsequent weld passes resulted in lower peak tensile residual stresses in the weld as a whole, softening of the HAZ, modest cyclic hardening in nearby parent metal, and some softening in the low-carbon weld metal.

Comparison of residual stresses in Ti–6Al–4V and Ti–6Al–2Sn–4Zr–2Mo linear friction welds

In this paper, the levels of residual stress in the vicinity of linear friction welds in Ti–6Al–4V (Ti-64), a conventional α–β titanium alloy, and Ti–6Al–2Sn–4Zr–2Mo (Ti-6242), a near α titanium alloy with higher temperature capability, are mapped and contrasted. The alloys have significantly different high temperature properties and the aim of this work was to investigate how this might affect their propensity to accumulate weld residual stresses and their response to post-weld heat treatment. Measurements are reported using high energy synchrotron X-ray diffraction and the results are compared to those made destructively using the contour method. The strain free lattice plane d0 variation across the weld has been evaluated using the biaxial sin2Ψ technique with laboratory X-rays. It was found that failure to account for the d0 variation across the weld line would have led to large errors in the peak tensile stresses. Contour method measurements show fairly good correlation with the diffraction results, although the stresses are underestimated. Possible reasons for the discrepancy are discussed. The peak tensile residual stresses introduced by the welding process were found to be greater for Ti-6242 (∼750 MPa) than for Ti-64 (∼650 MPa). Consistent with the higher temperature capability of the alloy, higher temperature post-weld heat treatments have been found to be necessary to relieve the stresses in the near α titanium alloy compared to the α+β titanium alloy.

Process optimization of tape placement for thermoplastic composites

Abstract Despite the advantages of tape placement with its high production rate in manufacturing composite laminates, residual stress development and operation under non-optimum conditions remain as the drawbacks to be surpassed. The goal of this study is to develop a process optimization scheme for tape placement. Two objectives of optimization are separately considered; one is to minimize the peak tensile residual stress. The other is to increase the productivity by maximizing the processing speed. Two quality requirements act as constraints in the optimization procedure. First of all, the chosen process parameters should be conducive to good bonding between the tape and substrate; secondly thermal degradation should not be excessive. In order to determine temperature distribution, residual stresses, bond quality, and thermal degradation, previously developed process models were used. Nelder–Mead, a zeroth-order search algorithm, was employed to minimize the objective function. The numerical results showed that significant improvement could be achieved through optimization and a laminate with acceptable quality could be produced in situ.

Fatigue Properties of Steel with Super Rapid Induction Localized Quenching.

The aim of the present study is to make clear the factors controlling the fatigue strength of the locally hardened machine parts. Rotational bending fatigue tests were performed with special focus on the effect of a peak tensile residual stress generated at the quenching boundary on the fatigue properties of the super rapid induction hardened steel. Results are summarized as follows. (1) The final failure starts at the position of the specimen surface where the peak tensile residual stress has been generated near the quenching boundary. (2) The fatigue strength at 107 cycles of the locally hardened specimen is inferior to that of the non-hardened one because of such a peak tensile residual stress. (3) The effect of the peak tensile residual stress on the fatigue strength becomes smaller at higher stress amplitude because the relaxation of the residual stress occurs under stress cycling at such high stress levels. (4) Reduction of the fatigue strength due to localized hardening can be removed by introducing the cold working of the specimen surface after quenching.