Study of Elastic-Plastic Fracture Parameters Through the Thickness of Fracture Toughness Specimens Using Silicone-Rubber Crack Impressions

摘要

Silicone rubber impressions of cracks in single edge notched, three and four point bend fracture toughness specimens were obtained for various degrees of applied displacement. The crack impressions were used to measure directly a number of elastic-plastic fracture parameters as functions of specimen geometry, ductile crack extension and position across the specimen thickness (i.e., constraint) (1) crack opening displacement (COD) measured at the original crack tip, (2) crack tip opening displacement (CTOD), measured at the growing crack tip, (3) crack opening angle, and (4) crack tip opening angle. Direct measurements of COD were compared with those indirectly determined by the conventional COD test and the potential of all the parameters as ductile fracture criteria assessed. The results show that both the COD at crack initiation, and the CTOD during growth, depend significantly on the degree of constraint, increasing by a factor of 2 from the central to near surface region of the specimens.