A study on crack growth in ductile materials

The stability of planar crack extension in ductile materials is revisited w ithin the framework of non-equilibrium thermodynamics. The cracked body is divided by a contour-domain integral curve into a global dissipative zone t o include plastic deformation and a local instability domain to include mat erial damage. It is shown that the crack propagation can be modelled as a c omposite structure with a self-governed evolution law. However, this system tends to reduce its free energy by means of the arrangement of mass and sh ape of damaged eo area. A stable state is reached if no exchange of energy between the damaged region and its surrounding, analogous to the instabilit y propagation in pressure tubes. The stability analysis reveals that the ch aracteristic size of damaged zone is an important parameter for all thermod ynamic forces. Finally, a scaling law is presented to obtain a unified para meter for ductile-to-brittle transition from the dimensional analysis. It i s also found that the crack-tip constraint plays an important role on the f ailure assessment if it controls the size of damaged area. (C) 1999 Elsevie r Science Ltd. All rights reserved.