Thomas A. Plaisted

Modeling and testing of temperature behavior and resistive heating in a multifunctional composite

Heat-activated self-healing is a desirable property of multi-functional composite materials, particularly if the components of the material itself can be used as a heating element. The heating capabilities and resultant temperature changes of such a composite are investigated in this paper, using finite element modeling and then experimental testing. The composite to be tested consists of thin-wire copper fibers, chosen for particular electromagnetic properties, and an epoxy matrix, which will later be replaced by a self-healing polymer matrix. Direct electrical current is passed through the wires and causes heat dissipation throughout the composite, a process known as resistive heating. For this particular composite, a temperature of 80°C is desired, because at this temperature the polymer can heal within a reasonable amount of time. Using finite element simulations and testing of an actual sample, it was found that resistive heating can achieve the desired temperature using electrical power inputs as low as 0.1 W per square cm of composite panel. The temperature results from the experiments agree with the results from the finite element simulations.

Integrated Sensing Networks in Composite Materials

Increasingly, the demand to monitor structures in service is driving technology in new directions. Advances in many areas including novel sensor technologies afford new opportunities in structural health monitoring. We present efforts to develop structural composite materials which include networks of embedded sensors with decision-making capabilities that extend the functionality of the composite materials to be information-aware. The next generation of structural systems will include the capability to acquire, process, and if necessary respond to structural or other types of information. This work brings together many important developments over the last few years in several areas: developments in composites and the emergence of multifunctional composites, the emergence of a broad range of new sensors, smaller and lower power microelectronics with increased and multiple integrated functionality, and the emergence of algorithms that extract important structural health information from large data sets. This work seeks to leverage these individual advances by solving the challenges needed to integrate these into an information-aware composite structure. We present details of efforts to integrate and entrap connectorized microelectronic components within fiber/conductor braided bundles to minimize their impact as composite crack initiation centers. The bundles include conductors to transmit electric signals for power and communications. They are suitable for inclusion in woven composite fabrics or directly in the composite lay-up. The low-power electronic devices can operate on a multi-drop and point-to-point networks. Future directions include implementing in-network local processing, adding a greater range of sensors, and developing the composite processing techniques that allow sensor network integration.