An experimental method to study the frictional processes during composites manufacturing

Composite parts manufactured by autoclave processes have manufacturing distortions due to unavoidable physical mechanisms that take place during the process. A good understanding of these mechanisms is required to manufacture parts with better dimensional fidelity and reduce the residual stresses locked in parts during manufacturing. One of these mechanisms is the friction between the tool and the part, and this mechanism can have a major influence on the final geometry of flat sections if the thermal expansion coefficients of the tool and the part are different. Tool interaction causes the stretching of the low shear modulus, curing composite and results in in-plane residual stresses with through-the-thickness gradients that cause distortion. In addition to the tool-part interaction, the prepregs laid up to form a corner section in more complex geometries may slip with respect to each other as a result of consolidation, causing stretching of fibres close to the inner surface of the parts manufactured in a female tool. In previous studies, considerable effort has been spent on modelling the tool-part interaction. These simulations are based on semi-empirical models, which should be calibrated according to geometrical deformations observed in manufactured parts. This paper presents an novel experimental method to directly measure the frictional shear stresses at prepreg/prepreg and prepreg/tool interfaces as a function of the development of cure throughout the Manufacturer's Recommended Cure Cycle (MRCC).