The standard of Japan Welding Engineering Society WES 2805 gives the procedure for safety evaluation of defects in welded structures on the basis of the
COD concept. The establishment of an appropriate relationship among applied load, defect size and
COD value, so-called.“
COD design curve”, is essential in the application of the
COD concept to the safety evaluation of structures. The
COD design curve adopted in WES 2805 takes the form
δ=3.5ea
Where
e: applied strain
a: equivalent through-thickness flaw size parameter
In practice, attention must be paid particularly to brittle fracture initiation from a part-through crack in a highly strain concentrated region. For practical use of the
COD design curve, experimental verification must be made about the relevancy of the LEFM-based equivalency of flaw size parameter
a for a general yielding condition, and also about the evaluation method of applied strain
e for a localized highly strained region.
In this study, bending tests using surface-cracked specimens were carried out, and it was shown that the determination procedure of parameter
a currently used in WES 2805 is reasonable even in the elastic-plastic regime. Furthermore, from the experiments using tensile specimens, in each of which two corner cracks existed in stress concentrated region, a way of defining the applied strain
e in the highly strained region with steep strain gradient in it and a new
COD design curve were proposed.
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