Mechanical properties and damage evolution of a structural sheet molding compound based on a novel two step curing resin system

Abstract

A novel two step curing resin system allows for the manufacturing of discontinuous, continuous and hybrid continuous-discontinuous sheet molding compound (SMC) with glass or carbon fibers. In this contribution, the discontinuous component of this innovative hybrid material, a structural glass or carbon fiber SMC, is characterized under quasi-static and dynamic loading conditions. Glass fiber SMC showed a positive loading rate sensitivity. For higher loading rates, maximum force and puncture energy increased significantly for charge (65%/67%) and flow region specimens (73%/64%). Carbon fiber SMC did not show a rate sensitivity. 1D flow of this material during compression molding leads to anisotropic mechanical properties due to fiber orientation. The microstructure of the material significantly influences damage evolution and failure, which was investigated by means of in-situ photography, SEM and μ-CT. The dominant failure mechanisms were interface failure and matrix cracking for the glass and the formation of inter-fiber fracture and inter-granular failure of pseudo-grain like microstructure for the carbon fiber SMC.