Helena Polezhayeva

The effect of compressive fatigue loads on fatigue strength of non-load carrying specimens subjected to ultrasonic impact treatment

This paper provides description and results from an investigation aimed to determine whether loading histories specific to marine and offshore structures cause shakedown of compressive residual stress produced by high-frequency mechanical impact (HFMI) treatment and therefore affect fatigue resistance of welded joints improved by these methods. Fatigue tests were carried out to investigate the influence of compressive fatigue loads on fatigue strength of non-load carrying specimens with transverse attachments subjected to ultrasonic impact treatment (UIT). It was found that significant relaxation of compressive residual stresses is achieved under application of compressive cycles in fatigue testing. It was also observed that not only the magnitude of the applied compressive stress/mean stress affects relaxation of the compressive residual stress but also the number of applied compressive cycles. This relaxation may reduce the beneficial effect of HFMI treatment under application of load histories specific to marine structures.

Effect of Weld Toe Burr Grinding on Fatigue Strength of Transverse Welded Specimens Made From DH36 Steel

The effect of weld toe grinding on fatigue life of welded joint has been studied by a number of investigators who have established that improvement factor on fatigue life is greater for higher tensile steels as compared with mild steels [1]. To establish the effect of weld toe grinding on the fatigue strength of joints made from DH36 steel, transverse welded specimens were tested under constant amplitude loading. This work was carried out by DAEWOO Shipbuilding and Marine Engineering Co. within Lloyds Register/DSME Joint Project. It was shown that the improvement factor on fatigue strength due to weld toe burr grinding for DH36 steel is above 1.5 for high cycle fatigue range.© 2009 ASME

Ultrasonic Measurement of Residual Stresses in Welded Elements of Ship Structure

The objective of the study described in this paper is to identify the residual stress distribution and relaxation in standard welded specimens as well as in a large-scale welded panel imitating the critical, from the fatigue point of view, zones of ship structure. The residual stresses were measured after welding and in the process of fatigue loading of welded elements by the UltraMARS system that is based on using ultrasound. The measurements had shown that the maximum residual stresses near the welds (4-5 mm away from the weld) reach levels 290-320 MPa that are close to the yield strength of considered material both in welded specimens and in the large scale panel. Analysis of residual stress relaxation in the welded panel under the action of cyclic loading confirmed the fact that within the interval of applied stress ranges corresponding to the multi-cycle region of loading of the welded joints, the relaxation of residual stresses occurs mainly during the first cycle.