Effect of size on plasticity and fracture toughness

Abstract

The effect of thickness and width of CT specimens on the plastic zone size has been investigated. The investigation also examines the applicability of the various approaches to fracture toughness measurements such as ASTM E399 K Ic , J Ic , R-curve and a new procedure of K Ic determination proposed recently, to a steel which has medium strength and which undergoes pop-in type unstable crack extension during the toughness testing. The results show that in CT specimens with a constant aspect ratio prepared from a given material and loaded to a given stress intensity factor, the plastic zone size decreases, as the specimen width increases; on the other hand, the thickness has only a comparatively small effect on the plastic zone size. The new procedure of K Ic determination is verified with experiments on specimens with width to thickness ratio of about 50 and it gives a size independent K Ic value in specimens whose thickness is 4.5 times less than that required by ASTM E399. The new procedure gives a meaningful value of K Ic in a situation where all other methods such as ASTM E399 K Ic , J Ic and R-curve approach are observed to be inapplicable.