Effect of Ultrasonic Peening and Accelerated Corrosion Exposure on the Residual Stress Distribution in Welded Marine Ste
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RODUCTION
RESIDUAL stress can cause premature failure even if the applied service stresses are reasonably low. Residual stresses combine with the applied stresses in-service. Residual stresses can be generated as a result of mechanical, thermal, and chemical manufacturing operations. Residual stresses must be considered in design assessments where safety of a structure is critical and/or the magnitude of residual stress is expected to be high. In addition, measurement of residual stress is required for modern surface treatment techniques which often need to be refined to obtain optimal compressive residual stresses for various materials. Statnikov et al.[1] invented the ultrasonic peening (UP) method in the 1970s. The method uses continuous ultrasonic vibrations transferred through a hardened material tip that is placed in contact with the surface being treated. The tools required for UP treatment are portable and relatively easy to use. The near-surface region of the material experiences high-rate plastic straining during the impact, and Kudryavtsev et al.[2] described that UP produces a 0.2- to 0.5-mm-deep and 2- to 7-mm-wide groove at the weld toe with a uniformly smooth surface finish. Statnikov[3] noted that UP is used by a number of industries, including those dealing with the manufacture and maintenance of welded structures and machinery components. UP alters the weld profile by introducing a smooth radius and therefore reduces the stress concenBILAL AHMAD, Research Student, is with the Department of Engineering and Innovation, The Open University, Walton Hall, Milton Keynes, MK7 6AA, U.K. MICHAEL E. FITZPATRICK, formerly with Department of Engineering and Innovation, The Open University, is now Lloyd’s Register Foundation Chair in Materials Fabrication and Engineering with the Faculty of Engineering and Computing, Coventry University, Priory Street, Coventry CV1 5FB, U.K. Contact e-mail: michael.fi[email protected]. Manuscript submitted July 19, 2014. Article published online December 19, 2014 1214—VOLUME 46A, MARCH 2015
tration, and introduces a compressive residual stress into the weld toe which Cheng et al.[4] found to extend to 1.5 mm below the surface. Martinez et al.[5] found that samples with attachments welded on both sides of a base plate showed an improvement in fatigue life of 2.25 times for a stress range of 80 MPa. Weich et al.[6] tried to correlate the depth of the UP groove to the surface residual stresses produced. Maddox et al.[7] carried out fatigue tests on UP-treated fillet-welded samples and also found increased life. A number of residual stress measurement techniques are now available. Each technique has its own inherent advantages and limitations. The selection of a technique for a particular measurement depends upon various factors such as sample material, geometry and dimensions of the component, desired measurement locations, stress components of interest, availability of technique, measurement accuracy, cost, and time involved. For the ultrasonically peened fillet-welded samples
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