Stretch becomes shear when there is enough force. There is actually very little real evidence that axons re-grow within the CNS. Plasticity is a different phenomenon. In the peripheral nerve axons regenerate if they find a myelin sheet. If you want to study what happens to axons, you cannot first break them. If you cut the axons you end up studying the very complex remote consequences of denervation. One example would be crossed cerebellar diaschisis. My point is, that in TBI you always have a mix of tension, compression and tear. It is extremely difficult to determine what causes what. I think there is no good answer to your question.

There had been some papers written in the 1990s, on the results of shear forces in the brain causing diffuse atonal injury. These areas light-up as small discreet bright spots on MIR scans.