Fracture toughness test standards prescribe the shapes and types of specimens as well as test procedures. Prescribed standards can provide individual values of fracture toughness or resistance curve, where toughness parameters, such as stress intensity factor, K (stress intensity factor, SIF), J integral (path - independent contour integral) or crack tip opening, CTOD (crack tip opening displacement), recorded against crack opening / elongation. In other words, the standards prescribe obtaining Kic, K-R, Jic, J-R or CTOD. In the previous designations, the index record (Ic) refers to the possible first form of crack opening, while the letter designation "c" in the same index indicates that it is a critical value of the parameter.

https://www.researchgate.net/profile/Dzevad-Hadzihafizovic-2/publication/357380285_eXtended_Finite_Elementpdf/data/61cb56c2b8305f7c4b09a5f4/eXtended-Finite-Element.pdf?_sg%5B0%5D=6oWs3YLL2xiWANtChy5L1fDT2YerWq-5vHIGBh_sjKTKw9mriOek1xns0pZNwTrBIXBN-p2TMIJS0jFc7YMrRQ.oLxevPGMHTtIRK0-jjHUZE5WmHlU-tIh4U1XJZXnA8clZ5PlLstFSB-fnIJcZ1IBEc_6BRB2cN8_D1Wx2ilz7A&_sg%5B1%5D=RfBUq0COlJ_bK98cqUHwk1wWfsLy9KpDQQKnFFjC35jBaoAwBgq2Z-mTI-VtWkWhHP7gngn95EMtlC7l4fY-_ArcVbbgWRHeaiZ-S0PEVXDb.oLxevPGMHTtIRK0-jjHUZE5WmHlU-tIh4U1XJZXnA8clZ5PlLstFSB-fnIJcZ1IBEc_6BRB2cN8_D1Wx2ilz7A&_iepl=

https://www.researchgate.net/publication/357380285_eXtended_Finite_Elementpdf