Effect of Plate Thickness on Fracture Toughness by Means of Elastic-Plastic Fracture Mechanics

The effect of plate thickness on fracture toughness in terms of J-integral concept, Jc, has been investigated using a heavy section A533B steel (165mm in thickness) which has highly uniform toughness in thickness direction except for surface layer. Notched bend specimens were prepared from this uniform region by varing thicknesses from 3mm to 100mm in order to minimize the metallurgical effects and tested at various low temperatures.The results are summarized as follows:(1) A new, simple technique of Jc estimation is proposed. According to this method, Jc values can be easily obtained using only the information from COD test which is represented by fracture load and critical clip gage displacement.(2) There exists an evident effect of plate thickness on fracture toughness in cleavage fracture. Using KC which is converted from Jc, the effect is formulated as follows:KIC=KC/ (1+2.3βC) 1/2, β2C= (KC/δY) 2/Bwhere KIC is plane strain fracture toughness and KC is fracture toughness at plate thickness of B. δY is yield stress.