Finite element analysis model of the cumulative damage failure process in a continuous-fibre ceramic composite loaded in flexure

A finite element analysis (FEA) using macro-based input commands was used to model the cumulative damage failure process of a continuous-fibre ceramic composite loaded in flexure. The modelling was predicated by the subject material which exhibited asymmetric stress-strain response for uniform uniaxial monotonic tensile and compressive loading. The FEA model of the prismatic rectangular flexural beam was composed of separately meshed fibre and matrix elements loaded in four-point flexure. The cumulative damage process was modelled using a macro-based input code combined with an element 'kill' command that was used to change the stiffnesses of those fibre and matrix elements whose respective ultimate tensile strengths were exceeded by the resulting tensile stresses. Matrix elements were allowed to support compressive stresses up to the ultimate compressive strength of the matrix material. However, unsupported fibre elements (i.e. those coincident with 'killed' matrix elements) were not allowed to support compression. Even though the model did not explicitly include the behaviour of the interphase material, good agreement between the FEA results and experimental test results was found for the subject three-dimensionally braided Nicalon (TM) fibre-reinforced beta -SiC matrix composite.