The objective of this work was to investigate methods for increasing the impact resistance of composite sheets made from glassfiber mat–reinforced polypropylene prepeg by varying its thermal history. A 60:40 (wt %) mixture of woven glass fiber–PP was crystallized at various temperatures and times to examine the effect of the thermal history (during cooling from the melt) on the degree of crystallinity and spherulitic morphology and to study the relationship between these factors and mechanical properties. The composite laminates were manufactured within a flat mold using a compression molding press and then crystallized from the melt in the range 106–156°C for 10, 30, 60, and 240 min in an air oven. The degree of crystallinity that developed in the matrix polymer was determined using differential scanning calorimetry (DSC), and the matrix morphology was examined by permanganic etching followed by scanning electron microscopy. The highest peak and failure energies during impact were achieved when maximum crystallinity was produced in the specimen crystallized at 134°C for 4 h. Electron microscopy of etched interior sections of impacted specimens has enabled a more detailed understanding of the impact behavior of these materials. The greatest improvement appears to result from an increase in the propensity of cracks to propagate along spherulitic boundaries by virtue of mechanisms facilitated by the results of the differential contraction of the crystalline and amorphous phases within the polypropylene. Differential contraction of the glass and polypropylene appears to be a less important factor, although voids created by such processes have to be taken into account. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1704–1715, 2001

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The most important concern in design of filament-wound composite pressure vessels reflects on the determination of the optimum shape and optimum laminate stacking sequence of composite vessels based on the matrix cracking pressure and burst pressure of composite laminates. In this study the Imperialist Competitive Algorithm (ICA) is used to find the optimum laminate stacking sequence of composite vessels that the design considerations are stability and strength constraints. the matrix cracking pressure of filament-wound composite pressure vessels made of different number of helical layers and different layers of Circumferential layers was calculated by using orthotropic material formulae and then, the burst pressure of composite vessels was calculated by using netting analysis. The optimum laminate stacking sequence of filament winding composite was found to maximize the matrix cracking pressure and the burst pressure by using Imperialist Competitive algorithm.

As a consequence of tropical climate featuring abundant rain and sunshine throughout the year, adhesive bonded joints undergo substantial exposure to moisture and elevated temperatures. It is known that the degradation of adhesive materials such as structural epoxy due to weathering could affect the overall bond performance of structural integrity of reinforced concrete such as carbon fibre reinforced polymer composites (CFRP) plate system. The objective of the study is to investigate the in-plane shear properties of structural epoxy material exposed to tropical environmental conditions using Arcan Test Method. The epoxy adhesive was casted in a closed metal mould to produce butterfly shaped specimens. The specimens were exposed to four conditions; laboratory, outdoor, plain water, and salt water. The specimens were tested for shear properties and failed in brittle form. Microstructure analysis was performed to study the fracture surface of the test specimens. The study showed that the tropical exposure conditions influenced the shear strength of the epoxy material, especially for those exposed to plain and salt water conditions, which were 32% lower than the control specimen for specimens exposed to plain water followed by salt water (26.6%), laboratory (25.4%) and finally outdoor (18.4%).