Failure mechanisms of short glass fiber reinforced poly(ethylene terephthalate) [SGFR-PET] were investigated on the surface as well as in the interior of uniaxially loaded tensile specimens. On the surface, tensile microcracks occurred mostly at the fiber ends. Tensile cracks grew following the microcracking. The grown cracks were bridged together with shear bands which had been formed at both tensile microcrack tips. The growth and bridging-together of the tensile cracks played an important role in the initiation of catastrophic fracture. In the interior, on the other hand, shear bands were formed in matrix around the fiber ends. With growth of the shear bands, shear cracks propagated along the fiber-matrix interface. The shear cracks induced pulling-out of the fiber from matrix, causing a voiding at the fiber ends. Growth of the voids exhibited strong effects on the fracture initiation. Based on the observation above stated, a model was proposed concerning to the microscopic failure processes in SGFR-PET.
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