Failure Criteria

Jorgen,

thanks for your comments.

My replies are:

1) Yes, only monotonic loading to failure is of interest.

2) The strain state is far from homogeneous. A 4 constants MR material law was employed and of course the possibility you mention about less accurate local strains is taken very seriously. I do not have much to support my confidence in the model but the deflections of a number of points, which are fairly accurate. Also the work done by the testing machine up to failure is predicted quite well (less than the deflections though, around + 6%).

3)The model is calibrated for strains around 50%, but deflections have been verified even close to failure and the accuracy does not diminish.

4) The highest figure at the failure location is the strain energy density, only 75% of the maximum strain energy which is picked up by the model elsewhere. The principal stretch is even lower (56%), wjhile the true stress is somewhere in between (68%).

I have not found much on the web about the max chain stretch criteria, do you have any source to mention? I have found an article on UHMWPE where the authors have tried also criteria which I thougth where more suited to metals ( Mises stress, Tresca stress, hydrostatic stress, Coulomb stress), I might have a go.

5) The stress state is not exactly hydrostatic but it is true that at the failure location the strain state is more triaxial than elsewhere (in the sense strains are closer to each other). This might represent an inconvenience for maximum strain, for example, but I was hoping this would reflect on the strain energy value.

Thank you again for your input and looking forward for final comments and hints.

Have a nice weekend

Muzialis

It certainly sounds like an interesting dilemma.

I am curious, how high was the hydrostatic stress at the failure location compared to the Mises stress at the failure location, and compared to the Mises stress at failure in uniaxial loading? I am just trying to get a feel for how severe the triaxial stress is at the failure location.

The max chain stretch paper that you found might have been a paper that I wrote a few years ago. At that time I performed a study focusing on the failure of thermoplastics in monotonic loading, and I found that the max chains stretch was more accurate than other traditional stress and strain failure conditions.

- Jorgen

Jorgen,

thanks for your comments.

The hydrostatic stress at the failure location is of the same order of magnitude than Von Mises. In its turn Von Mises stress at the failure location is roughly 80% to the value in uniaxial tension.

Is there any source available for the maximum stretch criterium?

All the Best

Muzialis

Heres a [URL= https://polymerfem.com/forums/showthread.php?t=34 ]reference[/URL] to the chain stretch failure condition.

- Jorgen