I've been working on a ballistics model for quite some time now, and I am getting close to finishing some parts of it, however, I am having trouble with bullet deformation. I simply have not found sufficient reference material to be able to complete the model. Is there a clear relationship between deformation and the strength of a target? Imagine two identical solid rods propelled into two different targets at equal velocity. The deformation rate in the first target is 1/m/Pa. The second target has a strength and/or density twice that of the first target. Will the deformation rate be twice that of the first target, or will it increase by square? Or is there some other relationship? Flesh has an average shear strength of 0.4 MPa, and structural steel 140 MPa. In flesh, a bullet has a deformation onset (how deep in does it begin to deform) of 7 cm, and a deformation rate of 1/m/MPa. At what point between these two materials, does the bullet go from penetrating and fragmenting inside the target, to shattering on impact? That's pretty much the issue at hand, how stress affects deformation. I know that bullet design and construction is an important part of its performance, but for simplicity, let's consider the solid rod scenario only.