Characterization and modeling of shear stress during manufacturing and thermal properties of structural composite materials

Abstract

An experimental methodology is presented to determine tool-part frictional interaction of composite parts and the structural integrity of sandwich structures when subjected to temperatures and pressures similar to those of autoclave processing. This methodology includes the development of a testing rig that mimics the deformation mismatch between tools and parts, and quantifies shear stress—that is, tool-part friction or shear stress of sandwich structures. Discrete and continuous friction characterization was performed to validate this testing methodology, and a semiempirical mathematical model was obtained to predict the tool-part frictional interaction as a function of different manufacturing variables including temperature, pressure, and part length. Moreover, a characterization of the shear strength of sandwich structures is presented where results indicate a strength decrease when temperature and pressure increase following an inverse-exponential trend for both cases. Furthermore, an alternative methodology to measure thermal properties of composite materials by radiation known as light flash analysis (LFA) is used to characterize diffusivity, conductivity, and specific heat of composite materials tested at typical manufacturing temperatures. Accordingly, this research portrays the mathematical considerations required for the testing of anisotropic materials. Thermal properties of cured composite samples with three different fabric weaves and two resin formulations were obtained, and results indicate that conductivity, diffusivity, and density are strongly influenced by testing temperature, fiber configuration, and fiber volume fraction.