Fitness-for-Service code (FFS code) should have proximity rules for evaluation of structural integrity of multiple cracked components. Although the rules should consider fracture behavior, such as brittle fracture, ductile fracture, and plastic collapse, those in the current codes are not divided by the fracture behavior. Application of the current alignment rules to plastic collapse of non-aligned multiple flaws should be validated because there are few studies for this issue. Thus, fracture tests of flat plates with non-aligned multiple flaws and finite element analysis (FEA) were performed for predicting collapse loads due to plastic collapse. A series of the fracture tests of flat plates and pipes with two flaws has been conducted, and a trend between the load reduction and the flaw locations was shown from the results. This trend shows that the defined net-section for non-aligned multiple flaw dominate the collapse load. For the validation the trend shown by the fracture tests, FEA was performed for predicting the measured collapse load. Equivalent plastic strain around the flaw tip dominates a collapse behavior, and an analytical collapse strain was determined for FEA. The collapse loads predicted by the collapse strain are correspond with the test results for any flaw locations. FEA conditions can interpolate and cover a wide range of flaw locations conducted by the tests. The load reduction rates due to flaw location changes of two flaws were estimated by parametric FEA. And the analysis results were mapped to investigate the trend of effect of flaw locations on the load reduction. The mapped results show that the load reduction rate depends on shorter flaw length of two flaws. This trend shown by the analysis results is corresponds with the trend shown by the fracture test results. These results are fundamental idea to make a flaw characterization rule in the FFS codes, such as ASME BPVC Section XI, for ductile fracture evaluation.


Prediction of Collapse Load Reduction Due to Non-Aligned Multiple Flaws

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

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