Ultrasonic consolidation (UC) debulking of thermosetting prepreg for autoclave curing of composite laminates

Abstract

Debulking of prepreg (pre-impregnated resin system) layers during hand lay-up manufacturing of carbon fibre reinforced polymers (CFRP) is a key-step to reduce air content and maximise the mechanical properties of the final product. Debulking is usually performed using vacuum-bag cycles of 10–15 min applied after the lay-up of every three or five prepreg layers, leading to a considerable time-consuming process. In this work, the use of ultrasonic stimulation during vacuum is studied to improve the efficiency of the debulking process and reduce the number of operations in order to decrease the overall manufacturing time. Three CFRP laminates were laid-up using the proposed ultrasonic consolidation (UC) with three different exposition times (5, 10 and 15 min) and cured in autoclave. The UC debulking process consists in a vacuum cycle with ultrasonic waves sent to the uncured material through an ultrasonic transducer. In order to evaluate the efficiency of this process interlaminar shear strength (ILSS) and in-plane compressive properties were tested. Experimental results show for 15 min compressive properties comparable with the ones obtained from reference samples manufactured using the traditional debulking technique, and high improvements in terms of ILSS (>20%). Therefore, UC debulking process can be used during hand lay-up of prepreg in order to improve the interlaminar properties of the final part and reduce the debulking time by over 85%.