SBIR-STTR Award

The feasibility of using minimum sized specimens from broken halves of Charpy specimens to fully characterize the transition range fracture toughness of reactor pressure vessel steels will be evaluated in Phase I. There are well known effects of specimen size on measured fracture toughness values. The use of specimens of minimum size requires accounting for these size effects. This will be done by using a combined constraint/statistical approach to interpreting cleavage fracture toughness measurements. Since substantial plasticity will occur during toughness testing, the J (elastic-plastic) integral parameter will be used to characterize the plastic stress/strain environment near the crack tip. Differences in constraint (stress triaxiality) as a function of specimen type and size will be treated by computing crack tip plastic stresses and strains and expressing these results in terms of a parameter termed Q. Long crack tip lengths sample more material than short lengths. Sampling size effects will be incorporated by using Weibull weak link statistics. The optimum fracture toughness specimen configuration which can be machined from one half of a broken Charpy specimen will be evaluated by a combined experimental and analytical study. Techniques for automatic machining of this configuration will also be evaluated. Anticipated Results /Potential Commercial Applications as described by the awardee:Phase I results should provide the basis for a definitive combined analytical and experimental verification of this technique to conduct cleavage range fracture toughness tests with minimal material. It should also provide a basis to develop a fully automated specimen preparation procedure involving minimum waste products.