A comparative study of fatigue crack driving force considering in-plane constraint effect

Nonlinear fracture mechanics parameters, OCTODp and OJ are implicitly used to characterize the crack driving force (CDF) in estimating Fatigue Crack Growth Rate (FCGR) in ductile material. However, in the presence of structure geometry effect, evaluation of effective CDF remains to be clarified. In this regard, a comparative study was conducted and the in-plane-constraint parameter was introduced to quantify geometry effect based on the constraint theory. Using modified boundary layer model (MBL) with multi-stage node releasing embedded, the effect of in-plane-constraint on OCTODp and OJ was investigated. Results indicate that OCTODp can demonstrate geometry effect on CDF, as it correlates well with plastic deformation. Compartively, the effective cyclic J-integral (OJop) was found to have a significant dependency only on the crack closure level, thus incapable of capturing the effect of geometry on CDF. A humpbacked curve was found between in-plane constraint level and OCTODp. Further investigation reveals that the gain of in-plane constraint on FCGR can be attributed to the interaction between in-plane constraint and crack closure, as well as the interplay between in-plane and out-ofplane constraint. This work not only reveals the mechanism of the in-plane constraint effect on CDF, but also provides a basis for establishing FCG model across different structure geometries.