Abstract
Formability of a continuous fiber-reinforced material is known to be influenced by its intraply shear behavior. This study investigates a 2 × 2 twill weave carbon fabric and the corresponding vinyl-based thermoset prepreg developed for press-cured structural parts. Intraply shear tests of bias-extension and picture-frame were conducted for a range of industrial-relevant processing conditions of temperature and shear rate. The dry fabric was characterized similar to the prepreg to isolate the influence of semi-cured resin on the woven prepreg fabric formability in shear. The shear deformation behavior of the prepreg, usually dependent on the fabric architecture, is found to be controlled by the state of the resin. The results clearly show the significance of the choice of process parameters on the prepreg shear behavior. It is demonstrated that preheating the prepreg to temperatures considerably lower than required to initiate cure can make the shear formability of the woven prepreg equivalent to the constituent (dry) reinforcement fabric. The actual shear angle measurement during the bias-extension tests demonstrates the level of inter-tow slippage for the prepreg fabric at relatively elevated temperatures. The comparison of normalized shear data from the two test methods helps to determine the improved procedure for prepreg fabric testing.
Highlights
Rapid-cure thermoset prepregs are being widely used in automotive structures to achieve lightweight solutions and contribute to reduce the overall manufacturing time [1,2,3]
The results indicate that the resin and the resin temperature have a significant influence on the force required to shear deform the prepreg fabric and affects the formability of the material, dependent upon the viscosity of resin
It has been determined with this study that the intraply shear behavior of the rapid-cure thermoset prepreg and that of its constituent dry fabric reinforcements converges at moderately elevated temperatures
Summary
Rapid-cure thermoset prepregs are being widely used in automotive structures to achieve lightweight solutions and contribute to reduce the overall manufacturing time [1,2,3]. The automotive sector still lacks high-volume manufacturing processes with short production cycle-times to compensate the high material costs. The existing manufacturing processes for continuous fiber-reinforced materials partially meet the challenges of automotive sector up to medium range of production volumes [4]. These processes involve significant level of automation at different manufacturing stages to achieve acceptable level of efficiency and repeatability. Preforming stage involves shaping a flat laminate of plies into a threedimensional form that is generally identified as a critical step to influence the overall production cycle time and quality of the composite parts. The automotive components, being smaller in size but often complex in geometry, makes it more challenging to reliably predict the deformation behavior of materials through preforming simulation, again largely dependent upon accurate properties of the material
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