Long fiber thermoplastic composites under high-velocity impact: Study of fiber length

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Abstract
This study experimentally investigates the high-velocity impact response of long glass fiber-reinforced polypropylenes with different fiber lengths. The study considers three long fiber thermoplastic composites, i.e. 5, 10, and 20 mm prepared via a combination of extrusion and pultrusion processes and a crosshead die. An internal mixer was used to obtain an isotropic compound. The dispersion quality of each compound was confirmed using burn off test. A gas gun with a spherical projectile was employed to conduct high-velocity impact tests at three velocities of 144, 205, and 240 m/s. Internal mixer operation resulted in extensive fiber length reduction for all three long fiber thermoplastic lengths. Results from mechanical tests (Tensile and Izod impact) revealed an increasing value with increase in long fiber thermoplastic length, i.e. fiber length. High-velocity impact results showed higher impact performance for 20 mm long fiber thermoplastic compound compared to 5 and 10 mm long fiber thermoplastic containing specimens. Rate of increase in energy absorption from neat polypropylene to 5 and 10 mm long fiber thermoplastic compounds is much higher than from 10 to 20 mm long fiber thermoplastics. High-velocity impact tests indicated that there may be a threshold value for fiber length beyond which the fiber length plays a lesser role. Scanning electron microscopic analysis showed more fiber breakage at the impact point at a higher impact velocity than the lower end of high-velocity impact.

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