A Novel Method to Measure Laminate Shear Modulus Development of Interlayer Toughened Composite Laminates During the Curing Process

Abstract

There are established process models for thermoset composites to calculate residual stress development and process-induced deformations. For thermoset composites, laminate elastic constants during cure are required for the process simulation. Matrix material properties such as bulk modulus and shear modulus develop continually as cross-linking of polymer chains progresses. Elastic constants of laminates during cure are determined from material properties of fiber and matrix, using micromechanics models. Recently, interlayer toughened composites have attracted considerable interest because of their high delamination and impact resistance. A third phase, such as thermoplastic micro-particles, is incorporated in the interlayer, which increases the complexity of the laminate microstructure. Moreover, it is difficult to measure the material property evolution of the toughening particles experimentally. The complexity of the laminate microstructure and the lack of material data makes it difficult to calculate the elastic constants of laminates using standard micromechanics. Reliable methods to measure the elastic constants of these more complex laminates are required. In this paper, we present a new experimental method based on Timoshenko beam theory to determine the laminate shear modulus (G13) development during cure in a Dynamic Mechanical Analysis (DMA) equipment with a low-friction three-point bending clamp. G13 development of an interlayer toughened prepreg system, 3900- 2B/T800SC, was successfully determined by the proposed method. The influence of interlayer particles and the frequency on the laminate shear modulus development was studied. This method can be used for studying the processing behavior of more complicated laminates, validating new micromechanical models and improving the accuracy of processing simulation.