ABSTRACT

On the basis of the beneficial effect of compressive residual stresses on crack growth retardation, artificial compressive residual stress fields were induced to the through-thickness crack by local heating near the crack tip. To verify the delaying effect of the proposed technique, crack growth tests and some numerical analyses were carried out on three types of CT specimens in accordance with ASTM standard. Based on the results of tests and analyses, the retardation of fatigue crack growth was discussed quantitatively.

INTRODUCTION

In the fields of shipbuilding and ocean engineering, all the welded structures suffer cracking by various types of in-service loadings, such as impact, fatigue, and corrosion, etc. Recently, a large portion of cracking is ascribed to fatigue cracking which initiate at weld toes, and these fatigue cracks of welded structures can be divided in two types, surface and through-thickness cracks. As many researches have been carried out to extend the fatigue crack growth life of existing cracks, most of techniques for extending the fatigue life were restricted to repair and strengthening methods. Especially for the through-thickness cracks, a wide variety of repair methods (Haagensen, 1994) were developed, such as repair welding, hole drilling, clamping, grouting, TIG dressing and peening, etc. As widely known, most techniques for extending the fatigue life are time consuming and considerable costs are involved. Therefore, in this study, relatively inexpensive technique for fatigue life extension is proposed. On the basis of the beneficial effects of compressive residual stress on crack growth retardation, artificial compressive residual stresses were induced to the existing throughthickness crack by local heating near the crack tip in this paper. A local heating method is the most famous technique to extend the fatigue life in welded structures. Among this method, spot heating and Linde's method have been widely used.

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