TITLE: In Situ Process Monitoring using Laser-Based Ultrasonics

Abstract:
(Introduction) In both the aerospace and automotive industries, polymer-based composite materials are increasingly being used to replace metallic structures. However, the economical use of these fiber reinforced materials is critically dependent on the development of robust and efficient manufacturing processes. To reduce the cost of fabricating complexly contoured polymer composite structures, manufacturers are actively developing low-cost alternatives to hand layup/autoclave curing and other labour and capital-intensive processes. Two methods that are being actively pursued for the manufacture of complexly contoured parts are resin-transfer molding (RTM) and compression molding of thermosets. However, manufacturing problems exist for both RTM and compression molding processes and the use of in situ monitoring techniques is thus essential for making these techniques more economical and establishing an optimum processing cycle. Ultrasonics offers the capability to monitor the viscosity, modulus and ultrasonic attenuation during the material processing, and these measurements can be used to either directly or indirectly control the key processing steps. However, a difficulty in using ultrasonics at elevated temperatures and pressures has been the poor reliability of conventional piezoelectric transducers. The noncontacting nature of laser-based ultrasonics make it an ideal candidate for in situ monitoring applications at elevated temperatures. This paper, presents results which demonstrate the capability of laser-based ultrasound to monitor the resin flow front along the inner surface of the mold during the RTM process and to monitor a sheet molding compound (SMC) during the cure cycle.

Source: Proceedings of the 'NDE applied to Process Control of Composite Fabrication' - Conference, 4-5 Oct 1994 St. Louis, Missouri. Publisher and Organizer: Nondestructive Testing Information Analysis Center (NTIAC) Texas Research Institute Austin, Inc. Austin, Texas [http://www.ntiac.com] [Buying the Proceedings]