Fiber microbuckling is the primary failure mechanism in unidirectional fiber-reinforced composites under compression. Due to processing or service conditions, damage (e.g., microcracks) exists at fibedmatrix interfaces. The effect of damage on the microbuckling of fibers is investigated in the present study. Based on the micromechanics analysis, the damage at interfaces is modeled as a linear spring against interface sliding, and the spring constant depends on the damage level. It is established that the critical strain for fiber microbuckling is relatively insensitive to the interface damage, but increases rapidly with the fiber volume fraction.
INTRODUCTIONFiber microbuckling has been identified as the mechanism for tensiodcompression asymmetry of long and aligned fiber-reinforced composites [ 11. Due to microbuckling of fibers, the compressive strength is only half of the tensile strength for fibrous composites (11. The effect of piastic microbuckling and fiber kinking in composites have been investigated (2-61. It has been observed repeatedly in experiments [7,8] that the compressive failure of fibers originates from a traction-free surface and subsequently propagates into the interior of the specimen, triggering a global failure of the test specimen. A simple model 191 has been developed to show that the initial microbuckling of fibers indeed starts from a traction-free surface. The model has been extended to incorporate the effect of elastic anisotropy of composites [lo]. It is established that the fiber buckling strain accounting for the anisotropy of composites is more than twice that for isotropic solids. However, these studies -.,are limited to ideal fiber-reinforced composites without any interface damage.