Simulation of Cure Volume Shrinkage Stresses on Carbon/Vinyl Ester Composites in Microindentation Testing

Composites made with carbon fibers and vinyl ester have significant higher processing volume shrinkage compared to composites made with epoxies. During the curing, vinyl esters experience as much as three times the volume shrinkage as compared to epoxies (10 %Vol versus 3-4 %Vol). This difference in cure volume shrinkage may be the reason that the mechanical properties of carbon/vinyl esters are low compared to that of carbon/epoxy. Cure volume shrinkage of neat resins have been measured using a dilatometer. Interfacial shear strength (IFSS) measurements for different cure volume shrinkage were completed showing a reduction in strength as the cure volume shrinkage increased. LS-DYNA was used to model the volume cure shrinkage and resulting interface/interphase properties. Modeling results are dependent on the specific representative volume element (RVE) and boundary conditions used in the simulation. Cure volume shrinkage was modeled using a temperature drop on thermoelastic material (*MAT_ORTHOTROPIC_THERMAL). Following the temperature drop, the fiber was loaded with a rigid, spherical indenter to simulate the IFSS test (at constant temperature). Simulated resultant fiber-interphase, interphase-matrix, and fiber-matrix (in the case of no sizing) are reported as a function of cure volume shrinkage. Shearing stress distributions at the fiber-interphase and interphase-matrix are also presented.