Investigation of blunting line and evaluation of fracture toughness under mixed mode.pdf

Investigation of blunting line and evaluation of fracture toughness under mixed mode I/III loading in commercially pure titanium S. V. Kamat and M. Srinivas The blunting line and fracture toughness in commercially pure titanium under mode I and mixed mode I/III loading was studied. A modi? ed compact tension geometry was used for determining the blunting line as well as mixed mode I/III fracture toughness. The results showed that the constraint factor m in the blunting line equation under mode I loading was 1.84. Also, there was no effect of notch root radius on the slope of the blunting line. The blunting line slope under mixed mode I/III loading was found to be lower than that under mode I loading and agreed with empirical correlations. The fracture toughness under mode I loading was found to be higher for specimens with larger notch root radius. However, notch root independent fracture toughness could be obtained from blunt notch specimen tests using stretch zone width measurements. The fracture toughness was found to decrease with increasing mode III loading. MST/5322 The authors are in the Defence Metallurgical Research Laboratory,Kanchanbagh,Hyderabad 500058, India (sameeramukthi@ yahoo.co.in). Manuscript received 28 November 2001; accepted 6 February 2002. # 2003 IoM Communications Ltd. Published by Maney for the Institute of Materials, Minerals and Mining. Introduction Mixed mode I/III fracture has been the subject of several experimental investigations.1 ± 2 2 One of the main limitations of mixed mode fracture toughness evaluation is the lack of standard test procedures. In recent years, test procedures for the determination of mixed mode I/III fracture tough- ness have been suggested for both brittle23 as well as ductile materials.24 These suggested test procedures recommend specimen type and method for data analysis, and also de? ne fracture toughness parameters such as critical mode I component (Kic , Jic ), critical mode III component (Kii ic , Ji iic)