유리섬유강화 폴리카보네이트의 응력이완과 점탄성거동

초록

The glass-fiber-reinforced-polycarbonate is utilized in various materials for better strength, stiffness, and fatigue life characteristics than pure polycarbonate. In this regard, it is essential to analyze not only the material strength but also the time-dependent behavior associated with viscoelastic deformation in the polymer matrix composite materials. In this paper, the stress relaxation of glass-fiber-reinforced-polycarbonate was studied according to the fiber weight fraction and strain rate to analyze the changes in material properties due to long-time load exposure. Stress relaxation tests with various strain rates were conducted on specimens having 10, 20, and 30 weight fractions of glass fiber. Based on the results, the Generalized Maxwell model was presented considering the effect of elasticity and viscosity. Moreover, based on the shear lag model, the relaxation modulus was predicted according to the fiber weight fraction, and the maximum error between the prediction and test results was found to be less than 2.02. In addition, the coefficients of strain rate sensitivity were calculated from the stress relaxation test according to the strain rate, and then the relaxation modulus prediction model was proposed based on the fiber weight fraction as well as the strain rate. Finally, the viscosity was derived from the proposed relaxation modulus prediction model. The primary viscosity, associated with the viscosity characteristics of initial stress relaxation region, slightly increased with the fiber weight fraction. The secondary viscosity, related with the viscosity characteristics of the overall region, decreased as the fiber weight fraction increased.

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