Volume 21, Issue 6 (November 1993)
Maximum-Load Predictions in the Dugdale Model Using a Critical CTOA Criterion
An engineering method of elastic-plastic fracture analysis is suggested for plane-strain specimens under tension. The condition for an increment of crack extension is set by a critical increment of crakc tip opening displacement (CTOD). The CTOD increment divided by the incremental crack extension is a critical crack tip opening angle (CTOA), assumed to be constant for a material of a given thickness, characterizing the tearing resistance of material. Based on a finite-element analysis of crack tip deformation, a load term in the CTOD equation of the Dugdale strip yield model is modified to accommodate large and small scale yielding, for which cohesive stress in the strip is assumed greater than that for the plane-stress model Approximate generalization of the Dugdale model is suggested for finite-size specimens. A definition of CTOD is reviewed with a round and sharp crack tip. In a successive application of the CTOA criterion at a current extending crack tip, the integration of the incremental crack extensions and load increments after fracture mitration gives a relationship in which a maximum load is either a peak load or a limit load on an unbroken ligament. Material constants are evaluated so that the calculated loads agree with test loads at each crack extension. The proposed method is applied to various specimens of 304 stainless steel for which test data are available.