Abstract
By taking the rate effect of fracture toughness into account, fracture toughness behaviour under stable crack extension in DCB specimens was studied by numerical simulation for 4 kinds of testing with an abrupt change of defomation velocity during its testing (incremental, decremental, reverse (unloading and reloading) and relaxation tests). The simulated results were verified by some experimental works on PMMA, and the load P-displacement δ curves obtained experimentally in these tests were well explained by the simulation including the rate effect in fracture toughness. Both the simulation and the experimental work show that P gets larger (or smaller) in the incremental (or decremental) test, showing viscous characteristic in P-δ relation. The reverse test shows that crack continues to extend even in the unloading process, and it extends conspicuously in the relaxation test as the effect becomes dominant.
