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Tensile Material Properties of Carbon/epoxy Composite Laminates at High Strain Rates (탄소섬유강화 복합재료의 변형률 속도에 따른 인장물성의 평가)
Carbon fiber reinforced polymer (CFRP)composite materials have been widely applied to load-carrying structures due to their high specific strength and low material cost. They also have been applied to energy absorbing structures such as vehicles chassis, bumper beams of passenger cars and guardrails because they have excellent impact characteristics. Although many researchers have studied the impact characteristics of CFRP composites, their impact damages and impact energy absorption characteristics have not been thoroughly investigated with respect to strain rates.
The strain rates during the high speed tensile tests or automobile crash accidents are generally in the range of 0.001/s to 100/s and the elastic modulus and ultimate tensile strength in this range are different from each strain rate. In this study, tensile tests of CFRP composites were performed to measure varieties of the elastic modulus and ultimate tensile strength with respect to the strain rate in the range of 0.001/s to 100/s. The quasi-static tests were conducted using a static material testing machine Instron 8801 and the dynamic tests were conducted using a high speed material testing machine developed at KAIST. For accurate measurements of strain in composite materials, Digital image correlation (DIC)method was adopted using a high speed camera and the ARAMIS software. Tensile test specimens were designed based on the ASTM standards as the rectangular shape without tabs. The tensile tests at the strain rates 0.001/s to 100/s were conducted to investigate the effect of the strain rate
The static and dynamic tensile properties of the unidirectional CFRP composites have been obtained in order to predict the elastic modulus of the CFRP composite with various stacking sequences. As the results, the CFRP composite stacked with 4 is affected by fibre and its fracture strength, elastic modulus are consistent with respect to the strain rates. 4 and 4 are affected by matrix and its strength, elastic modulus are increasing with respect to the strain rates. Modified Yen and Caiazzo model has been proposed in order to describe the unidirectional CFRP composites as a function of the strain rates.
The static and dynamic tensile properties of the CFRP composites stacked with [0/90/90/0],[45/-45/45/45] and [0/45/-45/90] have been obtained. The prediction model of the elastic modulus of CFRP composites has been proposed by using the laminate theory.