ABSTRACT

A preliminary assessment was made of the influence of low temperature on the impact-generated fracture of a commercial glass-reinforced polymer composite produced by the pultrusion process. Impact tests were performed using an Izod testing machine on the composite specimens with a V-notch resulting in a fracture surface parallel to the fiber direction. Tests were conducted at 25°, -5°, -25°, and -50°C on both dry (as received) and wet (submerged for 12 hours) specimens. This paper reviews the existing data in the literature on low temperature fracture behavior of composites and compares the data obtained from these tests. Special emphasis was given to the influence of subzero temperatures on fracture behavior.

INTRODUCTION

Composite materials arebecoming very prominent and popular in the commercial sector. Manufacturers of fiber reinforced plastics (FRPs) are producing all kinds of bars, plates, and even structural shapes that are intended to compete with more traditional structural materials such as wood and steel. These new composites have several advantages over the traditional materials: composites are very light, have high strength-to-weight ratios, and are extremely stiff. As more of these FRPs are put into service, they will be required to perform in extremely adverse environmental conditions. Yearly temperature variations of 80°C or more, very dry to very humid climates, mechanical cycling, and physical abuse are contributing factors to the performance degradation over time. The question that arises then is how will these materials behave/perform under these extreme conditions? It is well understood that internal residual stresses exist in a fiber reinforced composite due to mismatch in the coefficients of thermal expansion between the fiber and the polymer matrix. These residual stresses exist at room temperature, and further cooling only increases these stresses, thus increasing the potential for microcrack development.

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