Effect of Fiber Draw Ratio and Fiber Weight Fraction on Creep, Fatigue and Dynamic Mechanical Behaviour of Self-Reinforced Polypropylene Composite

Abstract

The creep, fatigue and dynamic mechanical behaviour of the SRPPCs was studied by using TA Instruments DMA 2980 machine. Dynamic mechanical analysis was done in the temperature range 30 to 110^oC at 1Hz using the single cantilever flexural mode. The test was carried out at in the amplitude controlled single frequency mode at 5Hz, stress ratio(R=1), temperature 35^oC and 140 minutes experimental time. Fiber draw ratios of 2, 5, 8, and 11were used for the Dr Sample category, while fiber weight fractions of 3, 6, 9, and 12were selected.  The incorporation of drawn polypropylene fibers improved the stiffness and fatigue resistance of the self-reinforced composite especially at high draw ratio (11) and high fiber weight fraction (12). Good correlation was found between both fiber draw ratio and fiber weight fraction with mechanical properties of the composite. Short-term isothermal creep tests were carried out using single cantilever tensile mode on the two sample categories at different temperatures ranging from 30 to 90^oC under an applied stress of 5MPa. Remarkable improvement on creep resistance occurred when fiber draw ratio and fiber weight fraction were maintained at 11 and 15wt% respectively. Burger's models could satisfactorily be applied to analyse the short-term creep behaviour of the composites. Creep master curves were created using time-temperature superposition principle (TTSP). Using the master curves, creep deformation of order 10⁸ minutes could be predicted. The temperature dependence of the shift factors could best be described by the Arrhenius equation. All these positive gains made in mechanical properties are attributed to fiber drawing which enhances molecular orientation (crystalline regions) and minimizes segmental movement of the chain molecules