STRESS-RELAXATION BEHAVIOR OF UNIDIRECTIONAL POLYETHYLENE-CARBON FIBERS - PMMA HYBRID COMPOSITE LAMINATES

Unidirectional composite laminates based on carbon fibers (CF) and hig hperformance polyethylene fibers (PEF) and their hybrids were prepared with partially polymerized methyl methacrylate (MMA) at room temperat ure, followed by heating at 55 degrees C (well below the softening poi nt of PEF, 147 degrees C) for 2 h. The stress-relaxation behavior of t he composites were determined and analyzed. It was found that at all s train levels the rate of stress relaxation decreased by the loading of CF in CF-reinforced composite laminates (CFRC); however, the reverse behavior was found in the case of PEF-reinforced composite laminate (P EFRC). An interesting observation of the study was that the rate of st ress relaxation decreased linearly in two steps in the case of PEFRC, whereas in the case of CFRC, it decreased in a single step. In the cas e of hybrid composites, the stress relaxation decreases in two steps a s in PEFRC. (C) 1998 John Wiley & Sons, Inc.