Local Approach to Notch Depth Dependence of CTOD Results

Abstract

SummaryThe effect of the notch depth on the critical CTOD value at cleavage fracture initiation was analysed by the local approach. Three-point bend CTOD specimens with different notch depth extracted from a high strength steel were tested at the lower shelf temperature. The critical CTOD values showed large dependence on the notch depth. Three-dimensional elastic-plastic finite element analyses were performed to investigate the crack tip stress fields for all specimen geometries. The numerical results showed that shallow and deep notch specimens exhibit very different near tip stress fields at the same CTOD level, which leads to the specimen geometry dependence of the fracture behaviour. The analysis of the notch depth dependence of CTOD results was conducted on the basis of two formulations of the local approach. In the first formulation, cleavage fracture was assumed to be controlled by the maximum principal stress. In the second formulation, the stress tensor ahead of the crack tip was fully described in terms of all principal stresses and cleavage fracture was assumed to be controlled by an equivalent stress for mode I loading. It was shown that both formulations of the local approach lead to geometry independent parameters, especially when the stress triaxiality effect is taken into account. Prediction of the notch depth dependence of CTOD results based on the local approach presented good agreement with the experimental data, particulary when stable crack growth prior to cleavage was not significant .

Estimation of the Fracture Probability Parameters for Specimens Made by JIS SM490A Steel

“…The probability of specimen fracture, specimen P , can be calculated as a function of δ , assuming values for { } It is worth mentioning that, the statistical distribution of critical CTOD can be written as Equation 7, including CTOD parameters m δ and b δ , which was also used in the studies of Ruggieri et al 4 .…”

“…The toughness scatter studies in mechanical failure were introduced by the weakest link probabilistic theory to obtain the material fracture toughness. Based on this methodology, Ruggieri et al 4 , Tagawa et al 5 , and Kawata et al 6 investigated the fracture toughness distribution obtained from the CTOD test. In Lin et al 7 , predictions for the fracture toughness are shown, taking into account the microstructure and temperature, using a quantitative weakest-link model.…”

Strength Mismatch Effects on Charpy Absorbed Energy and CTOD Fracture Toughness

“…stress. An effective stress 8,9) considering a random spatial distribution of microcracks was employed as σ eff in Eq. (2).…”

Weibull Model for Hydrogen-induced Fracture of High Strength Steel

“…It has been widely demonstrated the Weibull stress at brittle fracture initiation could be material constant. [7][8][9][10] Therefore, this Weibull stress criterion enables transferability analysis; effect of specimen geometry and size as well as loading mode on brittle fracture load can be predicted. With focusing on this local approach, a development of a new estimation method of hydrogen-induced unstable fracture in brittle manner has been advanced taking the deterioration of materials due to hydrogen into consideration.…”