Experimental Studies in Dynamic and Elastic-Plastic Fracture

Abstract

Dynamic fracture experiments have been conducted on a polymeric material Homalite-100 and heat treated 4340 steel and 7075-T6 aluminum using various specimen geometries. The experimental techniques of caustics, photoelasticity and strain gages have been used to evaluate the stress intensity factor describing the near tip stress field surrounding the dynamically moving crack. The data has been used to characterize dynamic fracture behavior of brittle and ductile materials as a stress intensity factor vs crack velocity relationship. The results obtained from the three techniques used have been critically compared and the validity of each technique is discussed under the experimental conditions studied. Results show that the techniques of caustics in transmission when compared with photoelasticity under dynamic conditions give lower values for the stress intensity factor. For opaque materials the results from the three techniques compare well. A direct method of evaluating J-integral in power law hardening materials using strain gages has been developed. The use of this new technique is demonstrated by obtaining an engineering estimate of the HRR singularity field size in annealed 4340 steel specimens.