The fuel efficiency and emission gas regulation of passenger cars are two important issues nowadays. The best way to increase fuel efficiency without sacrificing safety is to employ fiber reinforced composite materials in the body of cars since fiber reinforced composite materials have higher specific strength and stiffness than those of steels. Moreover, polymeric resin based fiber reinforced composites have high damping capacity and low coefficient of thermal expansion.
In this thesis, the impact behaviors of composite specimens were investigated using an instrumented Charpy impact tester with respect to fiber volume fraction, moisture content, resin type, surface treatment of fibers, dissimilar embedded materials (such as polyethylene fabric, polypropylene fabric, not-silane-treated glass fibers and Kevlar 29 fibers). Also, the impact energy absorption characteristics of composites were analyzed by considering fiber breakage, fiber pull-out and delamination. Then, the progressive impact fracture model was proposed to calculate the impact energy absorption characteristics of real size composite structures as well as composite test specimens.
For an example of real size composite structures, composite side impact beams were designed and manufactured using glass fiber reinforced composite materials since metals usually have lower capacity of impact absorption energy at low temperature. The optimum fiber stacking sequence and cross section for the composite impact beams were determined by static tests and finite element analyses using ABAQUS, a commercial software (H.K.S. Inc.).
To obtain the dynamic impact behavior of impact beams, a pneumatic impact tester with 30 miles per hour (13.3m/s) impact speed was developed. The impact tester was equipped with measuring sensors and was interfaced with a personal computer through analog digital converter. Using the developed tester, both the AISI 4340 steel impact beams and the composite ones were tested in the temperature range of -50 to 25℃ to measure impact absorption charcateristics and NDT (Nil ductility temperature) of materials.
