iMechanica - bimaterial fracture mechanics - Comments

RE

Haimin Yao — Wed, 23 Jul 2008 13:08:22 -0400

Similar attempt has been made in Tahoe (http://tahoe.ca.sandia.gov/), a research-oriented finite element code developted by Dr. Klein, Patrick. You may find the 3D Xu-Needleman potential from the manual or the source code of Tahoe. Good luck.

thanx Aamir

shirangi — Tue, 14 Aug 2007 09:30:33 -0400

Hi Aamir,

thanks for your hints and very helpful arguments.

stay Happy

Hossein

Interfacial moisture diffusion

aamirmub — Fri, 10 Aug 2007 11:36:57 -0400

Dear Hossein

I have following comments to offer regarding your questions;

1. You are right that fracture toughness of the interface will change with changing moisture concentration. The fracture toughness at different concentrations can be determined experimentally and the moisture based fracture toughness data can be given in FE software (like msc.marc or abaqus).

2. The mechanism of capillary diffusion is considered responsible for the high diffusion rate at the interface, however, high diffusion rate at interface is still not accepted generally. There is evidence in its favour and against it. I think that it mainly depends on the preparation of underlying surface. The diffusion rates of as high as 10 times of bulk diffusion rate have been used in literature. It is very difficult to measure the interfacial diffusion rate.

3. The moisture concentration at the interface depends on many factors including the polymer and metal or non-metal substrates. Water can be present in oxide layer on metals in form of hydroxl groups or due to hydration.

For detailed study of the subject, I would recommend the research papers of Dr Ian Ashcroft (Loughborough University, UK) and Prof A.D.Crocombe (Surrey University, UK).

Regards

Aamir

Dear Joost J.

shirangi — Fri, 10 Aug 2007 04:03:39 -0400

Dear Joost J. Vlassak,

thanks alot for your kind reply. I find your papers very helpful. I hope we can remain in contact and exchange our experiences.

Stay Happy

Hossein Shirangi

Dear Hossein, We have

Joost Vlassak — Thu, 09 Aug 2007 09:19:09 -0400

Dear Hossein,

We have done some work on the diffusion of moisture into film stacks and how it affects adhesion. We have experimental results and a rather simple model that couples subcritical crack growth and diffusion. The model agrees quite well with the experimental results. We did experiments on dielectric (ceramic) film stacks, but I assume you would find similar effects for stacks that incorporate polymers.

You can find one iMechanica entry at http://www.imechanica.org/node/222. Another paper just got published (Youbo Lin, Ting Y. Tsui, and Joost J. Vlassak, "Water diffusion and fracture in organosilicate glass film stacks", Acta Materialia, 55, 2455-2464 (2007)).

Joost J. Vlassak

Hi Shailendra, actually

shirangi — Wed, 08 Aug 2007 11:21:39 -0400

Hi Shailendra,

actually you are right, but I am not considering the corrosion of copper lead frame at this moment. It makes the subject more complicated.

stay Happy

Hossein

updating cohesive zone

shirangi — Wed, 08 Aug 2007 11:19:22 -0400

Hi Yinlee,

thanks for your comment. What a bout a coupled moisture-thermomechanical peoblem. For example a moisture-saturated material which is under moisture desorption because of high temperature! moisture desorption increases the strength of interface and temperature rise reduced the interfacial fracture toughness. How can you update cohesive strength during moisture-thermomechanical analysis?

stay Happy

Hossein

Corrosion could be important

Shailendra — Wed, 08 Aug 2007 10:51:25 -0400

Depending on the constituents the metallic phase may corrode/ oxidize under the coupled effects of moisture and temperature. This may be necessary to incorporate as a part of degrading interface because

a. Corroded regions would essentially lose contact with the polymer.

b. Corrosion leads to volumetric increase that may induce residual stresses.

Overall a very interesting problem to address.

Thanks,

~Shailendra

I am not very familiarly

Ying Li — Wed, 08 Aug 2007 10:16:37 -0400

I am not very familiarly with your problem. However, I think your problems could be solved in this way:The fracture toughness of the cohesive element could be changed at the different sub-step in the finite element method (FEM), especially in the ANSYS if you want to calculate the thermal-structure coupled problem. You just need to set different material parameters in the soft wear.