THE USE OF LOAD SEPARATION CRITERION AND NORMALIZATION METHOD IN DUCTILE FRACTURE CHARACTERIZATION OF THERMOPLASTIC POLYMERS

Load separation is the theoretical basis for the single-specimen J-int egral experiment and the incremental calculation of J-integral crack g rowth resistance (J-R) curves. This criterion has been experimentally studied in nongrowing crack records in several materials, and more rec ently a new method to extend the applicability to growing crack experi ments has been proposed in testing steel. This article examines the ap plicability of the load separation criterion for evaluating ductile fr acture mechanics parameters in rubber-modified polystyrenes and therma lly treated polypropylene in the bending configuration. This criterion allows the load to be represented as the multiplication of two indepe ndent functions: a material deformation function and a crack geometry function. Its validity is evaluated with both stationary and growing c rack experiments. eta-factor calculation for smooth and side-grooved s pecimens was also tried using the simple method of Sharobeam and Lande s, in order to identify material dependency. This article also investi gates the applicability of the normalization method, based on the load separation criterion for evaluating J-R curves on PP and PS. A simple approach which combines a blunt notched and a precracked specimen exp eriment is proposed to determine the J-R curve of the materials studie d. The resulting J-R curves are compared with multiple specimen result s available in the literature for these materials. A good agreement be tween the J-R curves obtained from this simple method and from the mul tiple specimen technique was found. (C) 1996 John Wiley & Sons, Inc.