Thermoforming-Stamping of Continuous Glass Fiber/Polypropylene Composites: Interlaminar and Tool–Laminate Shear Properties

Abstract

The results of interlaminar and tool–laminate shear tests performed on a twill 2 2 PP/glass fabric are described in this paper. The influence of the laminate temperature, pullout velocity and normal pressure on the interlaminar shear stress and friction coefficient are evaluated, as well as the effect of cooling the specimen from the melt to simulate real forming conditions. Opposite trends were observed for the variation of the shear stress and friction coefficient whether the tests were performed above the melt temperature of the matrix or above the crystallization temperature (135, 140, and 155 after cooling from the melt temperature. For the interlaminar shear tests, this was caused by the shift from an interlaminar to an intralaminar shear deformation mode occurring. For the tool–laminate shear tests, this was caused by the shift from matrix shear at the interface tool–laminate to direct Coulomb friction of the fibers with the tool with an increase of the normal pressure and/or an increase of the matrix viscosity with decreasing temperatures. Above the melt temperature of the matrix, the friction coefficient and shear stress were higher at the tool–laminate interface than in the interlaminar region while at temperatures close to the crystallization temperature they became lower at the tool–laminate interface. A summary of these observations is made and a discussion of their possible impact on the forming of parts is enlightened.