Nonlinear damping in cross plied laminates

Previous work by Gibson and Plunkett has shown that the damping factor in laminated composites of fiberglass with an epoxy matrix is independent of strain level up to about 2000 microstrain. Subsequent work at strains up to 10 000 shows that these large strains cause a permanent increase in damping factor with no measurable change in storage modulus. Low strain damping can be calculated from the dynamic modulus properties of the matrix and the static modulus of the glass fibers which shows that there is no interface dissipation. Prestraining above a certain critical level causes permanent cracks in the matrix material. The increased energy dissipation due to prestrain may be calculated reasonably well from the local crack density, an experimentally determined factor linking crack opening to energy dissipation, and a dissipation‐volume fraction integral. Such a calculation is consistent with a physical picture ascribing the additional energy dissipation to cracks opening and closing under tensile strain with a residual stress pattern due to permanent deformation during the initial overstrain. [This work was supported by NSF.]