Published: Jan 1998
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As composites are introduced into more complex structures with out-of-plane loadings, a better understanding is needed of the out-of-plane, matrix-dominated failure mechanisms. This work investigates the transverse tension fatigue characteristics of IM6/3501 composite materials. To test the 90° laminae, a three-point bend test was chosen, potentially minimizing handling and gripping issues associated with tension tests. Static testing of 50 specimens of nine different-sized configurations produced a mean transverse tensile strength of 61.3 MPa (8.0 ksi). The smallest configuration (10.2 mm wide, span-to-thickness ratio of 3) consistently exhibited transverse tensile failures. A volume scale effect was difficult to discern due to the large scatter of the data. Static testing of 10 different specimens taken from a second panel produced a mean transverse tensile strength of 82.7 MPa (12.0 ksi). Weibull parameterization of the data was possible, but due to variability in raw material and/or manufacturing, more replicates are needed for greater confidence. Three-point flex fatigue testing of the smallest configuration was performed on 59 specimens at various levels of the mean static transverse tensile strength using predominantly an R ratio of 0.1 and a frequency of 20 Hz. A great deal of scatter was seen in the data. The majority of specimens failed near the center loading roller. To determine whether the scatter in the fatigue data is due to variability in raw material and/or the manufacturing process, additional testing should be performed on panels manufactured from different sources.
composite materials, graphite/epoxy, transverse tensile strength, flexural fatigue, Weibull statistics
Assistant professor, University of Wyoming, Laramie, WY