Fracture of Weld Including Mismatch Effect

摘要

On the one hand, the assessment of defect located in or around a weld joint is a very relevant topic for nuclearrnindustry since most of the defect detected during in service inspections are located in those areas. On the other hand, thernassessment of such defect can be very complex because of the presence around the crack tip of different material havingrnsometimes very different mechanical properties and metallurgical structures. Therefore, since years, an important R&Drnprogram has been conducted at EDF and some results are presented in this paper.rnFirst, a short description concerning the different parameters influencing the plasticity development in weldedrnstructures and so their fracture resistance is made. When considering welds having a sufficiently high fracture toughnessrnlevel, the crack starts to grow after a relatively large amount of plasticity occurs at the crack tip. In such situation, therndifference between the stress strain curves of weld metal, base metal and Heat Affected Zone is very important since thernplasticity develops in a very particular manner in all those materials. Therefore, the most important parameters, such as thernmismatch ratio (ratio between the yield strength of the different material), weld and structure geometry, type of loading, arernidentified to predict more precisely the fracture behavior of welded structures.rnThen, an alternative defect assessment procedure to include the mismatch effect based on the evaluation of thernyield load of the welded structures is proposed. This method so called Equivalent Material Method has been applied torndifferent configurations such as fracture specimens or pipes. The comparison between this method and the numericalrnanalyses is very good.rnFinally, the ability of finite element codes to described precisely the fracture behavior of welded structures isrnproposed. Different experiments on laboratory specimens such as single edge notched bend specimen and center crackedrnpanels in tension with a crack in the middle of a weld or at the interface have been conducted. Those experiments have beenrnsimulated using 3D elastic plastic finite element code. The results are compared in term of load, displacement, crack mouthrnopening displacement (CMOD) and Crack Tip Opening Displacement (CTOD). Moreover, stainless steel pipes with arnthrough wall crack in the middle of the weld have been tested in four point bending. The results of the corresponding finiternelement analyses have been compared with the experiment in term of bending moment, displacement, crack opening, strainrn(obtained using strain gages) and diameter reduction. All those results show the ability of finite element codes to predict thernbehavior of welded structures.