열습 환경하에서 CFRP 모자형 단면부재의 충격특성 평가

Abstract

To obtain collision safety, design parameters should be considered, which could induce proper absorption of impact energy by car body. Therefore, structural members of automobiles should have sturdiness to enable passenger safety and proper deformation to absorb collision energy. To fulfill the opposite demand at the same time, many safety measures have been implemented. Thin-walled member for front section of in many car bodies has been adopted to absorb collision energy via plastic deformation. However, high oil price demands further improvement of fuel mileage, and light-weight vehicle has the utmost importance. In spite of attempts to utilize the existing structural member for car body, demand for improved fuel mileage cannot be met, and significant environment due to rapid development of industries and overwhelming number of vehicle should be reflected into vehicle design. To solve the various issues in vehicle design, carbon fiber reinforced plastics (CFRP) has been implemented in vehicle design, which has not only superior rigidity and strength but also better heat and corrosion resistance compared to the existing structural member. In addition, CFRP is widely adopted in secondary structural member including primary member in certain application. CFRPs have light weight and high strength. CFRP composite materials, which are reinforced with carbon fiber, features superior heat and corrosion resistance, and these benefits enables the gradual applications on aerospace industries and sports-entertainment business. Exceptional corrosion resistance enables the acceptance in maritime structural members such as ship and oil-drilling machineries. However, CFRP composite materials have the weakness in hygrothermal environment and shock resistance. Especially, moisture ingress into composite material under hygrothermal environment can change molecule arrangement and chemical properties. In addition, interface characteristics and component material properties can be degraded. Especially, interface in CFRP composite materials, which transfers load from matrix resin to reinforced fiber, is key factor to determine physical properties of composite. In this study, interface characteristics in CFRP composite materials were focused to be researched and tested. Previous researches on composite material have been conducted only on moisture absorption behavior and strength evaluation on CFRP stacking plate and structural member. Research on morphological evaluation is not explored significantly. Therefore, structural members with hat-shaped section, which are adopted in the actual automobile vehicle, were prepared for different stacking configurations. Moisture absorption characteristics and strength evaluation was empirically conducted after long-term exposure of differently stacked CFRP hat-shaped section member under hygrothermal environment. Optimal design data that can be applicable to actual transportation vehicle will be provided via identification of stacking configuration with optimal collision characteristics that could mitigate strength degradation from harsh hygrothermal environment. To understand moisture absorption behavior and strength degradation of CFRP hat-shaped sectional member by moisture impregnation, moisture absorption test and static/collision collapsing test was conducted. The following conclusions were acquired.

1. For the hygrothermals in CFRP composite materials, at approximately 0.5% of moisture absorption rate, the most absorption rate appears at the beginning time, but the moisture absorption rate decreases to some degree over 1.0% of the moisture rate. 2. It is found that the moisture absorption characteristics depend on the stacking sequences in the CFRP composites. Especially, a main role in the absorption rate could be considered as an agreement of absorption direction to 0 degree of fiber direction, which means a stacking sequence. 3. Through testing both moisturized-absorption sample and non-moisturized sample, in case of moisturized-absorption sample, the hygrothermal phenomena occurs in inter lamina due to the moisture ingress and the bonding strength becomes to be weaker. Ripped-edge of the most out sequence, 90 degree generated less by the moisture ingress and the stable collapsing mode appears more than that with collapsed shape and absorbed samples. 4. It is found that the strength in changes of stacking angles decreases more than that in changes of the number of interfaces through performing of both static and impact collapsing testing. At initial collasping time, the decreasing phenomena appears because of the ductile characteristics of moisture ingress in the brittle CFRP composite materals; however, stable collasping phenomena, i.e. the characterictics of bending made the mean loading and absorbed energy higher. 5. It was found that approximately 50% of impact loading of static loaded sample with moisture is decreased more than of impact loaded sample with moisture.