SMALL PUNCH TEST FOR THICKNESS EFFECT ON FRACTURE TOUGHNESS OF FERRIC STEELS

Small punch (SP) tests had been carried out at the room temperature on round specimens with six kinds of thicknesses. The fracture surfaces and crack details were observed by SEM. The results showed that the SP energy and the fracture toughness increased with the thickness of the samples. From the test results and theoretical analysis,fracture initiation criterion based on fracture strain and fracture propagation criterion based on fracture energy density were proposed. With the continuum damage model,the FEA simulations got the results of the crack propagation process which agreed well with the experimental results. Fracture surface displayed typical ductile fracture,and the surface of the half-sphere part cut off by the punch was full of little bulgings around which there were micro cracks.