According to dictionary, Momentum is: the quantity of motion of a moving body, measured as a product of its mass and velocity.

I suppose you are talking about "creep", "plastic strain increment" or "stress relaxation"? Where increments of deformation keep accumulating at a constant "rater" - similar to how a moving body keeps a constant "momentum".  Deformation rate is somehow similar to momentum.

If so - I do see some similarities, "momentum" could be seen as a suitable metaphor. But this will require a flexible and good willing audience to get away with.