Sensors and Simulation of Composite Manufacturing Processes

摘要

State-of-the-Art sensors are required to perform accurate simulations of composite manufacturing processes, so a comprehensive look at these processes should include a close look at them. The sensors used today in nondestructive evaluation as well as other areas of research are really quite different from what they were only a few years ago. The sensors that we have used are of two types: SMARTweave (an electrical method) and pressure sensors. The SMARTweave sensor grid system is described, and compared and contrasted to the more conventional methods of nondestructive testing in an earlier paper. (Strand, 1999). The pressure sensors reveal a marked drop off in signal as the free surface flow front approaches the sensor location, suggesting a venturi effect. The net result is the ability to measure both flow arrival times as well as subsequent vacuum and pressure levels at these sensor locations. Furthermore, it will be shown that the sensors remain linear from the vacuum regime into the pressure regime, making it possible to fully characterize critical flow phenomena in the vacuum assisted resin transfer molding (VARTM) process. Monocrystalline silicon pressure sensors were used. They operate on the resistive principle, even though, they are manufactured with semiconductor technology. The change of resistance in a monocrystalline semiconductor (a piezoelectric effect) is much higher than that in conventional strain gauges, whose resistance changes with structural geometric changes. An extremely small mechanical deformation can change the conductivity in a doped semiconductor appreciably. This mechanical deformation produces a compression or stretching of the crystal grid which in turn influences the conductivity. The result is that the sensitivity of monocrystalline sensors is higher than that of most other types (Konrad and Ashauer, 1999).