TWI Industrial Member Report Summary 90/1979
By H G Pisarski
The effect of specimen thickness on the critical values of COD and J integral at fracture was studied in a carbon manganese steel plate 100mm thick. Ductile brittle transition data from preferred geometry bend specimens showed that KIJ values obtained from JIc in 10mm thick specimens can overestimate KIc measured in 100mm thick specimens. Relaxation of stress triaxiality and changes in micromode of crack initiation with decreasing specimen thickness are considered to be factors causing the discrepancy between KIJ and KIc. The problems associated with using KIJ values, obtained from thin specimens, to predict defect sizes in thick structures are discussed.