Abstract
In order to assess the suitability of hybrid composite structures for use in offshore environments, a micromechanical analysis of hybrid composites is undertaken. Of particular interest are the combined effects of defects and moisture on the material properties and failure initiation. A representative cell approach utilizing the finite element method is used to study stress distributions within dry and wet hybrid composites and the response of hybrid composites containing debonds to transverse loads. A failure subroutine is incorporated into the finite element analysis to predict failure initiation sites and the transverse failure strains. The tensile response of hybrid composites is studied utilizing a statistical model in which the fiber failure strains are represented with Weibull distributions. The contribution of load transfer to broken fibers is included in the analysis through the use of a classical shear lag formulation.
Results from the analysis indicate that the transverse failure strains are dependent on the debond size but relocation of the debond to a different interphase does not affect the failure strains. The load transfer to broken fibers contributes significantly to the composite modulus. The predicted longitudinal modulus and failure strains for a twelve ply hybrid panel are within 12% of those obtained from tensile tests. The longitudinal failure strains decreased with increasing composite length, carbon to glass volume ratios, and moisture absorption.
