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Influence of Plastic Deformation on the Residual Stress Distribution and Fatigue Behaviour of High Strength Steels Welds
Mráz, Ľ. ; Karlsson, L. ; Hamak, I. ; Mikula, Pavol ; Vrána, Miroslav
The effects of plastic deformation and cyclic loading on residual stress distribution have been studied at welds in high strength 800 MPa steel. Effects of residual stress levels on fatigue life are also presented. Tensile loading was used to induce precisely controlled plastic deformation at weld toes. Residual stress distributions were measured by neutron diffraction. The influence of fatigue loading on the residual stress level was much smaller than that of plastic deformation. A large drop of residual stresses in the vicinity of the welds was recognised after local straining at the level of 2%. Stresses decreased with up to 550 MPa in the region around the weld toe. The effect of local plastic deformation on fatigue properties was also found to be significant. Fatigue strength more than doubled compared to the non-strained as-welded condition.
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Neutron diffraction analysis of residual strain/stress distribution in the vicinity of high strength welds
Mráz, Ľ. ; Karlsson, L. ; Hamak, I. ; Vrána, Miroslav ; Mikula, Pavol
Residual stresses resulting from non homogeneous heat distribution during welding process belong to most significant factor influencing behavior of welded structures. These stresses are responsible for defect occurrence during welding and they are also responsible for crack initiation and propagation at the either static or dynamic load. The significant effect of weld metal chemical composition as well as the effect of fatigue load and local plastic deformation on residual stress distribution and fatigue life have been recognized for high strength steels welds. The changes in residual stress distribution have then positive effect on cold cracking behavior and also on fatigue properties of the welds [1-3]. Several experimental methods, both destructive and non-destructive, such as hole drilling method, X-ray diffraction, neutron diffraction and others, have been used to examine residual stress distribution in all three significant orientations in the vicinity of the welds. The present contribution summarizes the results of neutron diffraction measurements of residual stress distribution in the vicinity of single-pass high-strength-steel welds having different chemical composition as well as the influence of fatigue load and local plastic deformation. It has been observed that the chemical composition of the weld metal has a significant influence on the stress distribution around the weld. Similarly, by aplying both cyclic load or pre-stress load on the specimens, stress relaxation was observed even in the region of approximately 40 mm far from the weld toe.
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Residual Stresses Assessment in Coated Materials: Complementarity between Neutron and X-Ray Techniques
Rogante, M. ; Mikula, Pavol ; Vrána, Miroslav
The residual stress (RS) status induced in the substrate of coated materials by the coating process plays frequently a major role in lending the component’s characteristics. RS assessment can give, thus, a substantial contribution in justifying different cases of failure or else bad performance of coated components due to e.g. the coating delamination or to other occurrences which are not simply interpretable via the conventional mechanical tests or microstructure analyses. The adoption of both neutron diffraction (ND) and X-ray diffraction (XRD) techniques has revealed its usefulness in assessing the RS values in proximity of the coating interface area, respectively, without any layer removal or hole drilling at the extreme surface.
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