The stiffness (aka. tangent modulus of the stress) can be represented as a symmetric 6-by-6 matrix, i.e. it has 21 independent components in the most general case. In the linear case, this matrix is constant, whereas in the non-linear case it depends on the current state of deformation. The following questions addresses both the linear and the non-linear case.
- Is there any material with a dense stiffness matrix? By this I mean that none of the entries are zero.
- If so, is there any material for which all the 21 components are independent of each other?
- If the answer to 2. is no, then which material has the most independent components?
I want to explicitly include meta-materials as possible candidates, i.e. structures with homogenizable mechanical response functions.