Abstract
According to some standards, fracture toughness tests loaded under bending are assumed to deform around a fixed plastic hinge point within the ligament ahead of the notch tip. The rotation factor,rp, defines the proportion of the ligament ahead of the crack tip to where this hinge point is located. In this paper, the concept of an SENB specimen bending about a fixed rotational point under loading was investigated. Experimental SENB tests were carried out on three different strain hardening steels, and the geometrical point of rotation was determined experimentally throughout the tests using a double clip gauge and the similar triangles principle. The experimental results were then used to develop and validate a series of different strain hardening property numerical models. By extracting the rotational factor from the different strain hardening property models, a relationship between strain hardening and a strain hardening corrected rotational factor, rp sh was established. This corrected rotational factor function was used to propose an improved equation for the calculation of CTOD and CTOD R-curves, which gave good estimations of CTOD when compared to values measured experimentally from sections through silicone replicas of the specimen crack-tip. The improved R-curve equation will be proposed for future amendments to the ISO 12135 standard.