Finite Element Analysis of Interfacial Failure of Syntactic Foams subjected to Uniaxial Compression

Syntactic foams are hollow particulate filled composites which are extensively used as core materials in sandwich structures for different applications requiring high specific strength and low density. Hence, understanding the failure behavior of syntactic foams is essential to appropriately make use of them in design. Failure in energetic materials is dominated by processes which occur at a scale of several hundred microns of magnitude smaller than the scales of the structural components in which they are commonly used. This study addresses the finite element analysis of hollow glass microsphere based syntactic foams to characterize the stress distributions and stress concentration factors around the particulate inclusion in an epoxy based polymer matrix system. Finite element analysis was performed by applying uniaxial compressive loads on a single particle reinforced matrix model generated using ANSYS FEM package. This was further extended to particles with different wall thicknesses. Further, the stress distribution and stress concentration factor in the region of polymer adsorbing immediately to the outer shell of the glass microsphere is analyzed. The interface between the outer shell of the glass microsphere and the epoxy resin is simulated using contact analysis. In this model of two-phase syntactic foams, the parameters used for analysis are material properties of hollow glass spheres and epoxy resin, various wall thicknesses for the hollow glass microspheres and coefficient of friction values for the contact elements. Hence, the stress concentration factor is found to be high along the interface. For the two particles analysis, the presence of a glass microsphere with the same radius ratio resulted in high stress concentration centers at the interface of the second microsphere. Also, the SCF at the second interface increased with increase in radius ratio of the glass microspheres of the second particle. In gradient structures, there are substantial SCF increases at interfaces which are sometimes more than three-fold. In addition, SCF values significantly increase with increase in radius ratio values.