STRESS MECHANICS OF REINFORCED POLYESTER COMPOSITES

Abstract

This research investigates the stress mechanics of reinforced polyester composites when exposure to a sudden impact force, using experimental and analytical methods based on impact and Linear Elastic Fracture Mechanics (LEFM) test procedures. In this study, the stress distribution around crack tip and zone for 14 test samples with geometry 210 mm x 150 mm were investigated. KII stress intensity factors, critical stress, σC, shear stress, τnt the impact energy, E and impact strength, U were determined for each specimen. The mode I fracture toughness, KIC was found to be to be 4.97 MPa.m1/2 at a critical stress of 13.53 MPa while the mode II fracture toughness, KIIC was 1.31 MPa.m1/2 at a shear stress, τnt of 3.71 MPa. The effective thickness was found to be in the range of 80-100mm at fibre volume fraction, Vf of within 0.35-0.50. This was largely found to be as result of fibre bridging and crack arrest mechanisms. This mechanism prevented crack growth direction in specimens containing woven roving not to propagate along the original direction, but change the direction to an inclined path till failure with the exception of those containing soft and hard mat in which the crack grew in the original crack direction as the stress intensity increased. During the impact test, fibre stacking sequence played a vital role, thereby making specimens containing woven roving to resist impact damage and failure, and this resulted in fibre pull-out during fracture. The stress could be seen to concentrated at the crack tip and around the loading pins on a smaller level, compared to the level at the crack tip.

Keywords

• Analytical Methods,
• Critical Stress,
• Reinforced Polyester Composites,
• Shear Stress

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