Analysis of Thermal Expansion Coefficients of Composites Reinforced with Plane Randomly Oriented Discontinuous Carbon Fibers

Thermal expansion coefficients (TEC) of composites reinforced with orientation-distributed carbon fibers have been theoretically analyzed. A solution procedure is formulated according to Eshelby's equivalent inclusion method (EIM) which takes into account the orientation distribution and the interaction of fibers. A procedure based on the lamination theory (LT) is also developed and compared with the EIM TEC are calculated for carbon fiber and glass fiber composites with several types of fiber orientation distribution. The difference between the TEC predicted by the EIM and the LT can be attributed to an interaction between fibers in the different laminae which was not considered in LT. While the EIM is consistent for glass fiber composites, a theoretical contradiction occurs for the prediction of the TEC of composites with orientation-distributed carbon fibers, when the volume fraction of fibers approaches to 100%. In a range of low fiber volume fraction, the difference between the predictions by the EIM and by the LT is smaller for carbon fiber composites than for glass fiber composites. And the difference is small compared with errors expected in the measurements. Both of the EIM and the LT may be used for the prediction of TEC of composites filled with orientation-distributed carbon fibers in the range of low fiber volume fraction less than about 40%.