iMechanica - A short paper on T-stress of an interfacial crack in a bi-material strip - Comments

T-stress and crack stability

Jae-Hyun Kim — Fri, 26 Jan 2007 11:55:01 -0500

Dear Luoyu,

Thanks for your nice comments. I'm happy to hear that you have been interested in T-stress. Vlassak group in Harvard Univ. has conducted several fracture tests (DCB and 4 point bending) on a thin film layer sandwiched between two thick silicon substrates. The thin film is a low-k dielectric layer made of Organosilica Glass(it's very brittle). Oscillatory cracks (or wavy crack) have been observed in some specimens during 4 point bending tests. Our paper on T-stress was motivated by this observation. I have a discussion point:

- T-stress is a non-singular term in the eigen function expansion of a crack tip stress field. For an infinite homogeneous solid or bimaterial solid, it should be a good parameter for the crack stability. For a sandwiched thin layer(500nm thick), T-stress seems weak to govern the crack stability because it is the non-signular term. The crack in the sandwiched layer experiences a dramatic change in the stress state depending on its location in the layer(Fleck et al., 1991). I suspect the role of T-stress in this case. Would you comment this?

T-stress is still an active area in fracture mechanics

Luoyu Roy Xu — Thu, 25 Jan 2007 17:39:02 -0500

Dear Jae-Hyun,

Very nice paper. Your simplified results will be valuable to our fracture experiments such as DCB tests. Indeed, T-stress research is still an open area. Our paper on the T-stress changes across crack kinking will be published by ASME J of Applied Mechanics soon. Since an interfacial crack in a bi-material strip tends to kink into the weak part, the role of the T-stress is critical (as discussed by He and Hutchinson in 1989). We still have many topics on the T-stress to explore.

Roy

A short paper on T-stress of an interfacial crack in a bi-material strip

Jae-Hyun Kim — Wed, 24 Jan 2007 15:46:59 -0500

The attached file is on T-stress of an interfacial crack in a bi-material strip. The geometry of the problem is the same with that of Suo and Hutchinson (1990, IJF). Using a conservation integral technique, a formula for T-stress is derived with two numerical factors.

Any comments are welcomed.