The Size Effect on J-R Curve for Construction Steels and its Prediction by Simplified Mechanical Model

Evaluation of mechanical properties from a small amount of test material is essential in a process of development of new alloys and monitoring of degradation and damage of in-service components. Miniaturization of test specimen together with a specimen reconstitution technique enable direct method of evaluation of mechanical properties if only a limited amount of material is available. Modern types of construction steels and alloys possess improved metallurgical and mechanical properties and also demonstrate a high level of fracture toughness. In these cases, correlation and correction of size effect on fracture toughness between different specimen sizes are needed. Within this contribution the size effect of J-R curve for two sizes of three-point-bend specimens is solved. The J-R curves of three-point-bend specimens with cross-section 10 × 10 mm and 3 × 4 mm of P91 and Eurofer97 steel were determined at room temperature. The existence of size effect is proven as larger specimens demonstrate higher J-R curves than smaller specimens for both steels. Simplified mechanical model based on fracture energies initially proposed by Schindler et al. is applied to describe experimentally determined J-R curves and to predict the observed size effect between used specimen sizes.