Resin transfer molding (RTM) of advanced fiber architecture materials promises to be a cost effective process for obtaining composite parts with exceptional strength. However there are a larger number of material processing parameters that must be observed, known, and/or controlled during the resin transfer molding process. These include the viscosity both during impregnation and cure. In-situ sensors which can observe these processing properties within the RTM tool during the fabrication process are essential. This paper will discuss recent work on the use of frequency dependent electromagnetic sensing (FDMS) techniques to monitor these properties in the RTM tool. Our objective is to use these sensing techniques to address problems of RTM scaleup for large complex parts and to develop a closed loop, intelligent, sensor controlled RTM fabrication process.
Frequency-dependent electromagnetic sensing (FDEMS) is a convenient and sensitive technique for monitoring in situ infiltrationand cure in the tool during the resin-transfer molding (RTM) process. The magnitude of the fluidity and viscosity as a function of the time and temperature, the time to infiltration at various ply depths, the effects of aging and elapsed time before infiltration of the RTM process, and monitoring of the cure cycle are four important areas where FDEMS is shown to significantly help in determining the RTM process procedure. l\ NONDESTRUCTIVE IN SITU FREQUENCY-DEPENDENT impedance sensing technique was reported previously (1-10) for measuring cure-processing properties of both thermoset and thermoplastic resins. The technique uses the frequency dependence of the resin's impedance to measure molecular ionic and dipolar diffusion rates. These molecular parameters can be used continuously throughout the process cycle to monitor the time and temperature dependence of events such as reaction onset, maximum flow, viscosity, gel, the buildup in modulus, evolution of volatiles, and reaction completion (1-10). The measurements can be made in a research environment to evaluate resin processing properties and in the manufacturing tool
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