Damage Processes in Reinforced Reaction Injection Molded Polyurethanes

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Abstract
The microdeformation and damage mechanisms in glass fiber reinforced reaction injec tion molded (RRIM) polyurethane composites have been studied. Two surface conditions represented the extremes in good and poor fiber-matrix adhesion. Deformation mecha nisms observed directly by an SEM technique with the specimen deformed in three-point bend were correlated with the number and amplitude distribution of acoustic emission (AE) events detected during tensile testing. Yielding of the unreinforced resin was accom panied by microcracking initiated at holes that produced AE with a peak at 43 db. A simi lar AE pattern observed in the untreated fiber composites was also identified with micro cracking at holes in the resin and at rod-shaped holes produced by debonded fibers. The amine-treated fiber composite exhibited considerably more AE activity in the yield and post-yield regions with additional peaks in the amplitude distribution at 59 db and 65 db. These were identified with microcracking at the well-bonded interface and fiber fracture respectively.