Fully plastic crack-tip fields for CCP and DECP specimens under tension innon-hardening materials

Detailed finite element analyses are performed for center cracked plate (CC P) and double edge cracked plate (DECP) in non-hardening materials under pl ane strain conditions. The objective is to systematically investigate the e ffects of deformation level, loading type, crack depth and specimen dimensi on on crack-tip fields and constraints of these two specimens. Special atte ntion is placed on (a) under what conditions the slip-line fields can be pr esent near the crack tip, and (b) determining what deformation mechanism ma kes the crack-tip fields significantly different in the two specimens at fu lly plastic state. The results reveal that (a) at load levels much smaller than the limit load (i.e., small-scale yielding) the crack-tip fields are close to the Prandtl field for both specimens, (b) the effects of crack depth a/W on the crack- tip field is not remarkable for CCP, but significant for DECP at the limit load, (c) as L/W greater than or equal to 2.4 for CCP and L/W greater than or equal to 2 for DECP, the crack-tip fields are independent of the specime n length L/W, (d) at the limit load, the crack face is under compression fo r all CCP, and (e) a compression (tensile) zone exists at the crack face of shallow (deep) cracked DECP. Moreover, it is found that there exist tensil e and compressive stresses along the vertical centerline of specimen for bo th CCP and DECP which result in a bending moment M-VL The difference betwee n M-VL and the moment generated by the applied far-field loads makes the cr ack opening stress non-uniform along the remaining ligament. Recall that th e slip-line fields for both the CCP and DECP have uniform opening stress al ong the ligament. At the limit load, therefore, the numerical crack-tip str ess fields can only approach to, but cannot attain to, the slip-line fields for both CCP and DECP specimens. In addition, through comparison of the different limit loads given for DECP specimens, the present results indicate that the limit load formula given by Kumar et al. (EPRI, 1981) is valid only for 0.4 less than or equal to a/ W less than or equal to 0.7, whereas the formula of Ewing and Hill (1967) c an be used for any crack depth. (C) 1999 Elsevier Science Ltd. All rights r eserved.