Real Time Cure Monitoring and Control of Composite Fabrication Using Nondestructive Dynamic Mechanical Methods

Abstract

The techniques of mechanical impedance analysis (MIA) have been developed for the characterization of the dynamic mechanical properties of materials. The MIA concept is based on the vibrational analysis of the motion response of a material or structure to a controlled excitation. The frequency response function (FRF), can be obtained from the ratio of the fourier transforms of excitation and response signals. The FRF spectra contain the information needed to calculate the dynamic mechanical properties of a material, such as storage modulus (E’), loss modulus (E ”), and loss tangent (tan o). This MIA method is therefore useful for polymer viscoelasticity study. The spectra obtained during curing of thermosetting resins or composites can be used in real time to calculate the dynamic mechanical properties as a function of cure time and temperature. Optimal cure cycles of a new resin can be determined by using the MIA technique to characterize the phase transformation of the material. The MIA technique is found to be a sensitive and direct means for in-process monitoring of the overall cure states of composite structures of various geometries. The signals obtained can be integrated in a closed-loop feedback control system for composite fabrication.