New Approximate Fracture Mechanics Analysis Methodology for Composites with aCrack or Hole

摘要

A new approximate theory which links the inherent flaw concept and the theory ofcrack tip stress singularities at a bi-material interface has been developed. Three assumptions were made: (1) the existence of inherent flaw (i.e., damage zone) at the tip of the crack was postulated, (2) a fracture of the filamentary composites initiates at a crack lying in the matrix material at the interface of the matrix/filament. (3) a laminate fails whenever the principal load-carrying laminae fails. This will imply that for a laminate consisting of 0 plies, cracks in the matrix perpendicular to the 0 filaments are the triggering mechanism for the final failure. Based on this theory, a parameter KQ which is similar to the stress intensity factor defined for isotropic materials but with a different dimension was defined. Utilizing existing test data, it was found that KQ can be treated as material constant. Based on this finding a fracture strength prediction methodology was developed. The analytical results are correlated well with the test results. This new approximate theory can apply to both brittle and metal matrix composite laminates with crack or hole.