Failure criteria 2

[jpblasques]

Hi all

I am using a 3D formulation of the Tsai-Wu Strength index (TWSI) to assess the strength of a laminate. I would like to know if it is possible to decompose it into different contributions (like the tensile, compressive and delamination contributions)? That is, at a certain point of the laminate with a certain value of the TWSI I would like to know if the problem is tensile stress, compressive stress or delamination.

I have seen the Hashin failure criteria being used in parts corresponding to the tensile, compressive and delamination failures. However I have never used this failure criteria before and I don't know how accurate it is with respect to Tsai-Wu's. Anyone can give me a hint on this one?

Thanks in advance.
Zé

 

[SWComposites]

1) there is no validated way to determine the critical stress with the TW criteria, though you can make some guesses by comparing ratios of the various stress components; however

2) The Tsai-Wu, Hashin, and other ply failure theories give, at best, poor correlations to in-plane strength test data. And they do not at all correlate to delamination onsets (fracture mechanices based criteria are required in order to predict delamination).

For the results of an extensive evaluation of composite failure theories, see this paper:

M. J. Hinton, et. al., “A Comparison of the Predictive Capabilities of Current Failure Theories for Composite Laminates, Judged Against Experimental Evidence”, Composites Science and Technology, Vol. 62, 2002, pp 1725-1797.

along with many of the references listed therein.

 

[tstanley]

My understanding is that Tsai-Wu doesn't predict the failure mode. However, LaRC02 failure criteria is supposed to give some insight.

That is why I posted my question about the next round of the world wide failure excercise being discussed at a recent conference.

Tom Stanley