GFRP 복합재료의 섬유 배향과 함유율이 인장강도와 고속충격 흡수에너지에 미치는 영향

Abstract

GFRP (Glass fiber reinforced plastic composite materials) composites has superior strength/density and modulus/density ratios to metallic materials. In addition, GFRP composites has been widely used as aerospace and automobile application due to high impact absorbing property. Among automobile components, structural parts in interior / exterior application (Structural parts requiring impact resistance) is the one of promising applications for GFRP. The property of composites depends on the property of matrixes but fiber length, fiber aspect ratio, fiber content ratio, fiber orientation state of reinforcements directly affect the mechanical characteristics of composites such as tensile strength, impact resistance, elasticity coefficient, thermal and fracture characteristics. The purpose of this study was intended to examine the effects of fiber content and orientation on tensile test, high velocity impact test and IR test in GFRP composites by varying fiber content and orientation. From tensile strength, high speed shock absorption energy, and temperature distribution during tensile test by the orientation and content of fiber in GFRP, the following conclusions were acquired. Increment of tensile strength with 0° fiber orientation showed proportional increase with fiber content. Tensile strength with 90° fiber orientation showed similar strength value to strength of matrix at J=0.7 regardless of fiber content. Tensile strength ratio at 0° orientation was constant regardless of fiber content, but tensile strength ratio of 90° orientation was decreased with increased fiber content. For 10wt% of fiber content, J=0.3 of fiber orientation function had similar fiber strengthening effect with unidirectional fiber orientation at θ=30°. For 20wt% of fiber content, J=0.2 showed similar fiber strengthening effect with θ=20°. For unidirectional composite material, there is theoretical mixture equation to calculate the strength of composite from properties of matrix and fiber content. However, equation for tensile strength with fiber content and orientation is not available. In this study, empirical equation to estimate tensile strength out of fiber orientation and content was proposed. Method to analyze temperature distribution during crack propagation under tensile test of GFRP via IR thermography camera was suggested. Anisotropy in fiber orientation showed longer fracture time and lower maximum temperature. Through high velocity impact test, critical penetration speed by fiber orientation and content was determined. Speed (Pressure) near to critical penetration speed was affected significantly by orientation than content. Therefore, composites with unidirectional orientation, such as bumper for automobile, is effective for high velocity impact rather than critical penetration speed. This could be elucidated by the fact of less crack propagation in composite material except critical penetration speed. In addition, J=0.9 (More directionality) exhibited higher impact absorption energy under high speed than J=1.