The determination of the stress state and its range in crack tip zone has not yet been solvedtheoretically and is almost impossible by customary experimental methods.

Based on the experimental results of local temperature field and pyromagnetic effect at the process zone of the crack-tip formed in the evolution period of defects, in this paper, the expressions of thermo-mechanical coupling and thermo-electromagnetic coupling effects in the basic equation group of rheological material containing defects are first proposed.

Results show that for the Graphite/Epoxy compsiste AS4/3502,the micromechanism of crack tip damage is microcrack initiation,growth and coalescence,which toughens the material through increasing its resistance to crack propagation.

Fracture criterion for mixed mode crack of composites based on the crack tip plastic zone

The unified solutions for the shape and size of mode I crack tip plastic zone are obtained based on the twin shear unified strength theory.

Then,by applying unified twin shear strength theory,the expansion angle and crack tip plastic zone of deep tunnel surrounding rock in rich water zone was studied,and the general solutions was obtained.

The experimental results of pyromagnetic effect revealed in the rupture process of rheological material with defects make known that:owing to the existence of internal temperature gradient leads to the occurrence of pyromagnetic effect in the fracture process zone at crack tip.