Cure Monitoring Techniques Using Embedded Sensors PDF Download

Assessing the exact state of cure of thermosetting polymer composite components using embedded sensors can allow the user to precisely control the cure cycle in order to achieve optimum cure. This is desirable in a field repair situation where a non-optimum cure cycle may have to be adopted. At present a wide variety of options are available. However, to be practical for bonded composite repair, especially field repair, it is important to assess these options against a range of criteria such as size, complexity, cure sensing ability, cost and the ability to measure other information after cure. The techniques reviewed fall into a number of categories defined by the property which is measured. These are electrical, acoustic, optical, thermal and other/indirect properties. of the techniques reviewed three techniques show most promise: viz. dielectrometry (electrical), spectroscopic (optical) and measurement of refractive index during cure (optical). The simplest of these techniques relies on the change in refractive index of the matrix resin during cure. A segment of cured resin is placed as a link between two lengths of a silica optic fibre. This fibre can then be placed in the uncured matrix. Light is transmitted through the fibre prior to cure but as the refractive index of the uncured resin approaches that of the cured resin the transmitted light intensity decreases until the fully cured state is achieved where no light is transmitted. The details of this refractive index technique are highlighted and show that a cure sensing system can be simple, low in cost and effective. Therefore this technique is recommended for further investigation.