Impact behavior of a short glass fiber reinforced thermoplastic polyurethane

The temperature dependence of critical strain energy release rate (G_c′) and standardized Charpy notched impact strength (CNIS) were measured for a thermoplastic polyurethane (TPUR) reinforced with 30 wt% of short glass fibers (SGF) over a temperature interval ranging from −150°C 23°C (RT) at two strain rates, 70 and 150 s⁻¹, respectively. Fractographic observation of fracture planes was used to qualitatively assess the fracture modes and mechanisms. Adhesion between the reinforcement and the matrix was excellent and the integrity of the fiber‐matrix interfacial contact was relatively insensitive to exposure to hydrolysis during the immersion in boiling water for 100 hours. At temperatures above −30°C, there was a large extent of plastic deformation in the vicinity of crack planes while at temperatures below −50°C, the extent of plastic deformation was substantially reduced. This resulted in a change in the major energy dissipation mechanism and led to a decrease of both CNIS and G_c′ values for SGF/TPUR composites. It was suggested that the plastic deformation of TPUR matrix in the immediate vicinity of glass fibers was the primary source of energy dissipation at temperatures above −30°C, while the friction and fiber pull‐out was the main dissipative process below −50°C. Over the whole temperature interval investigated, greater G_c′ values were obtained at higher strain rate of 150 s⁻¹, without any significant change in the fractographic patterns observed on the fracture planes. The CNIS/G_c′ ratio, used to assess suitability of CNIS for comparison of materials, changed with temperature substantially suggesting that the functional dependences of CNIS and G_c′ on temperature differ substantially. Hence, CNIS data do not provide a reliable base for material selection and for design purposes in this case.