Effects of gelcoat thickness on mechanical properties of woven glass/polyester laminated composite

Abstract

In this study, effects of gelcoat thickness on the mechanical properties and interfacial bonding of woven glass/polyester laminated composite are investigated by using threepoint flexural test and tensile test. The composites had been applied at variance thickness of gelcoat layers (0.25, 0.3, 0.35, 0.4, 0.45, and 0.5mm) using hand lay-up method. Samples were measured in two techniques for the flexural test, i.e., coated surface facing the loads (concave) and bare surface facing the loads (convex). Since the coated surface was concavely bent, greatest increase of flexural strength that acquired 5-fold of increase was shown by composite with 0.3 mm of gelcoat thickness for both measurements. The increasing of thickness to 0.35 mm and above deflated the rising percentage in flexural strength. This event was happened because of the gelcoat thickness ratio was greater than the matrix/reinforcement ratio. For tensile test, composite applied with gelcoat of 0.4 mm thickness exhibited the highest increase in strength. An increase of almost 38 % in tensile strength was recorded compared to the uncoated composite. Similarly, the increase in tensile strength reduced slightly when the gelcoat thickness was increased above 0.4 mm. The results demonstrate that the mechanical properties of the composite improve as the gelcoat thickness increases. However, the mechanical properties show no further improvement as the thickness is further increased above the optimum thickness.