A Study on a Dynamic Behaviour of Pop-in in Weldments and Its Application to the Assessment Method for Significance of Pop-in

Abstract

Initiation of pop-ins becomes a great obstacle in satisfying critical COD requirements for weldments because COD values at pop-ins are often lower than required ones. Though sonic countermeasures for such pop-ins may be possible, it is too difficult to completely avoid them by improvement of materials and welding procedures as the critical COD value is sensitive even to extremely local brittle zones.
Therefore, in the previous report, authors proposed the assessment method for significance of pop-in, which involved approval of pop-in in COD test when it was proved to be arrested in actual structures with reasonable background.
In this report, the proposed assessment method is further investigated in terms of the measuring meth-od and the theoretical approach. The results are as follows:
Dynamic behaviour of pop-in can be measured clearly and conveniently by the newly developed method to which magnetic induction effect is applied. By this method, it was shown that dynamic be-haviour of pop-ins occurred in COD test for an actual welded joint was similar to that for model welded joints, and so proposed assessment method is applicable to COD test on welded joints for practical use.
Finite element analyses made it clear that the 3-point bending COD test was severer than actual structures for propagation and arrest of a small brittle crack when the dynamic change of the K_ID value or the elastic energy release rate was considered. Hence it is pointed out that pop-ins found in the COD test for welded joints with low strength materials can also be arrested in actual structures.