I appreciate your interest on this issue.
The first problem is that the Tsai-Wu failure criterion interacts too much. Specifically, interaction between fiber-mode and matrix-modes is not supported by experimental observation. Therefore, the predictions are erroneous.
Second, Tsai-Wu does not give you the failure mode. It predicts failure but it does not tell you how. This is a problem for the designer.
On the other hand, in the interacting criterion, the fiber-modes and interacting matrix-modes have been separated. The accuracy improves and, importantly form a design point of view, you get the mode of failure, either fiber- or matrix-mode, so now you know how to improve the design. Furthermore, industry does not use Tsai-Wu, but other FC such as max-strain, truncated max-strain, Hashin FC, and so on, all of which clearly give you the failure mode. I could have taken Tsai-Wu out and replace it for nothing, but I though that would be too drastic, and some designers in industry recommended to include the interacting criterion instead. Unfortunately commercial FEA packages lag behind on implementing modern material models, and they never take out anything off the code due to software legacy issues, so we are stuck with Tsai-Wu available in FEA codes, but on CADEC I want only the best.
Finally, let me tell you that we now have a beta-release of the online version of CADEC @ www.cadec-online.com No installation necessary. Viewed best using Firefox or Chrome. Please check it out and let me know what you think.
E. J. Barbero,
Professor, West Virginia University, USA
>>> 8/31/2011 9:35 PM >>>
Good Evening Dr. Barbero,
My name is __ and I am a senior in the Mechanical Engineering program at ___. I am currently doing some independent coursework with Dr. __ on composites FEA. I have been working with CADEC and ANSYS. I am enjoying the CADEC program, the UI is well laid out and it pairs well with the book. It has really helped with the learning process. The one issue I ran into though was the difference between versions. The version Dr. __ has been using is CADEC7, whereas I downloaded CADEC10 from the website. The real notable difference is the change in chapter 7 content. In version 7 Tsai-Wu is available as a choice for failure criterion, but in version 10 it has been replaced by Interacting Criterion. Understandably Tsai-Wu is an interacting failure criterion, but I was wondering why this change was made. It actually proved to be a minor setback when Dr. __ asked me to generate the Tsai-Wu failure! criterion for an example laminate as I couldn't find the selection in chapter 7. Whenever you have the chance to get back to me is fine, Dr. __ and I were only curious. I thank you for your time, and look forward to your response.