Abstract：Due to the extensive applications of metal structures with large thickness in character, the corresponding fracture toughness of structure is needed for the accurate assessment of structural failure. However, the dimension of cracked components along the direction of three-dimensional crack-tip line has significant impact on the fracture toughness of material, which is generally known as the “thickness effect”. The present research focuses on predicting the fracture toughness of material with arbitrary thickness by combining the finite element method (FEM) calculations with experimental data. First, the critical loads of a group of specimens of thin thickness at fracture are recorded by the three-point bending tests performed on single-edge notched beam SENB specimens. The critical energy release rate (ERR) of material is achieved by using the cohesive zone model (CZM) and virtual crack closure technique (VCCT). Second, the critical ERR is applied as a material constant in the FEM models. The maximum ERR criterion is applied to predict the critical load while crack initiates. The variations of several representative crack-tip fracture parameters (K, J-integral, T-stress and the out-of-plane constraint factor Tz) with respect to the thickness of specimen are calculated using the FEM, and the corresponding analysis is addressed subsequently. Finally, another three groups of X70 SEB specimens are tested to verify accuracy of the FEM results through comparison. The present work provides a reliable method to study the thickness effect on the fracture toughness of material, based on which, fracture toughness of metal material with arbitrary thickness can be predicted. Furthermore, the thickness and fracture toughness of material can be correlated through several three-point bending tests on thin SENB specimens, and the corresponding results can be depicted by a curve or mathematical expression. The present work will be beneficial to the reduction in experimental cost and structure integrity assessment.
2018, Vol. 39 
