Size effects due to secondary voids during ductile crack propagation

• Discrete voids at crack tip with secondary voids by nonlocal GTN model for matrix material.
• Parameter study with respect to properties of matrix material.
• Strong effect of size of secondary voids.
• Toughening possible for small secondary voids.
• Discussion by near-tip solution of a growing crack.

In the present study the size-effect due to a secondary void population during ductile fracture is investigated. Discrete primary voids are resolved in the process zone at the crack tip. A non-local GTN model is employed to describe the evolution of the secondary voids in the intervoid ligaments. The non-local GTN model contains an intrinsic length scale related to the size of the secondary voids. Hence, the ratio of the size of the primary and that of the secondary voids can be varied. The results show that small secondary voids can toughen the material. Such a behavior is in contrast to the prediction of cell model simulations. A theoretical reasoning of this effect and conclusions are given.