Toughening mechanisms in rubber-modified glass fiber/unsaturated polyestercomposites

An important case of composite failure is the leakage of pipes and pressure vessels subjected to internal pressure. The primary damage mechanism leadi ng to leakage is transverse cracking parallel to the fibers. Effects of mat rix toughening on transverse cracking strains were therefore investigated f or GF/UP cross-ply laminates with matrices of different liquid rubber conte nt. The strain to the first transverse crack was increased from 0.2 to 0.6% with 10 wt% rubber. Debonding occurred at similar strains in GF/UP and GF/ UP-rubber. However, whereas debonding was almost simultaneous with transver se cracking in GF/UP, gradual growth of debonds to short cracks took place initially in GF/UP-rubber. This was followed by slow extension of short cra cks to a critical flaw size corresponding to unstable growth.