Abstract
Structures containing large cracks and made in ductile materials may experience two types of failure mechanisms: ductile tearing or plastic collapse. Under displacement controlled loading ductile tearing is a stable crack growth mechanism. Plastic collapse leads to a much faster damage evolution.
Ductile tearing is the result of void growth and coalescence ahead of the crack front under the high strain concentration. This mechanism is slowed down by a high material hardening and under a high constraint. The global deformation of the structure is limited.
Plastic collapse is induced by plastic strain accumulation along slip lines. Slip lines depend on the geometry of the cracked structures and of the type of loading. Therefore plastic collapse produces large deformations of the structure.
Several studies (Nicak, 2009; Gilles, 2010; Le Delliou, 2017) on large ductile crack growth have been performed by Framatome, and EDF on deeply surface cracked plates made in Nickel base alloy 600. The tests were performed on Centre Cracked Tension specimens with a semi-elliptical surface crack. In this very tough material, the crack grew in its plane, but for large load levels, the plate was extremely deformed and a collapse mechanism appeared.
More recently, Tests on Fixed Grip SE(T) specimens in Nickel base alloy 600 were performed by CEA showing a different type of transition between ductile tearing to collapse in function of the crack length. The paper analyzes these experiments and simulates the ductile tearing using node release methodology. The prediction of the apparition of the collapse is obtained by determining collapse load with large displacement modeling.
From these results, a reconciliation of curves J-R of the CCT et SE(T) specimen will be done.
