Strain rate effects on thermoplastic composites with mechanical interlocking

Fiber reinforced thermoplastic composites are limited due to poor interfacial bonding between the nonpolar/nonreactive polymer matrix and fiber surface. Recently, a concept of controlled mechanical interlocking between fiber and matrix surface was proposed to improve the interfacial bonding in fiber reinforced thermoplastic composites. Study results show promising performance of the approach under static loading conditions. In this work, we study the effect of strain rate on the interfacial bonding behavior under dynamic loading conditions. A parametric study of the strain rate effect is performed for which different surface microarchitectures of a glass/polypropylene composite system are considered. A three network model is implemented for modeling mechanical behavior of polymer, which is calibrated using a set of stress-strain curves experimentally obtained at various strain rates. The strength calculations address both polymer fracture and detachment of the polymer matrix from the anchoring sites. The results show that under the strain rates ranging from 2 x 10(-4)/s to 2 x 10(-1)/s, even without any interfacial friction or adhesion, the interfacial shear strength could achieve close to 70% of the theoretical strength of perfect matrix-fiber bonding. It is observed that, while strain rate has appreciable effects on the fiber/matrix interfacial strength and can cause change of failure mode in some cases; its influence also depends on the geometry of the anchoring sites. Moreover, there is an optimal geometric configuration at which maximum failure strength is achieved. Graphic charts showing the dependency of interfacial strength on the strain rate and geometric configuration parameters are obtained.