Hello and welcome Killingtim
An interesting problem to investigate.
1) Time is a very important variable with materials such as those you are dealing with, as the material response to load takes time to develop. Creep in some materials is one aspect of this.
2) The nature of the load plays a large part in the failure of materials, or even if they fail at all. Loads can be uniaxial, biaxial or triaxial or bending or whatever.
3) Temperature and moisture content are liekly to also be important variables with your material.
Much work has been done on a material that has many similarities, namely bread dough.
there is a whole chapter on this in the excellent Cambridge University book
Elasticity, Plasticity and the Structure of Matter
by Houwink and DeDecker
with many references.
Another book, (a New Scientist Popular Science book) has published data and discussion about the stress strain curves for blood vessels (after Shadwick)
Cats Paws and Catapaults