Structural Health Monitoring (SHM) is required for early detection of damage in structural components to improve the
safety, reduce the cost, and increase the performance and efficiency of aircrafts. Currently available techniques have a
number of deficiencies prohibiting wide spread of SHM in aerospace applications. In this contribution we will present
the initial results of development at Luna Innovations of an all-fiber optic ultrasonic airframe SHM system that will be
able to address the deficiencies of solutions suggested/developed to date. In this contribution we will present the details
on design, development and testing of the prototype fiber optic SHM system.
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.
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.
We have incorporated arrays of conductive electromagnetic scattering elements such as straight copper wires and copper coils into fiber-reinforced polymer composites, resulting in materials with required structural and further electromagnetic functionality. The scattering elements provide controlled electromagnetic response for tasks such as filtering and may be used to tune the overall index of refraction of the composite. Integration of these metallic elements into traditional fiber-reinforced polymer composites has introduced other opportunities for multifunctionality in terms of self-healing, thermal transport and perhaps sensing applications. Such functionalities are the result of fiber/wire integration through textile braiding and weaving, combined with a new polymer matrix that has the ability to heal internal cracking through thermo-reversible covalent bonds. Multifunctional composites of this kind enhance the role of structural materials from mere load-bearing systems to lightweight structures of good thermo-mechanical attributes that also have electromagnetic and other functionalities.
We are studying the incorporation of electromagnetic effective media in the form of arrays of metal scattering elements, such as wires, into polymer-based or ceramic-based composites. In addition to desired structural properties, these electromagnetic effective media can provide controlled response to electromagnetic radiation such as RF communication signals, radar, and/or infrared radiation. With the addition of dynamic components, these materials may be leveraged for active tasks such as filtering. The advantages of such hybrid composites include simplicity and weight savings by the combination of electromagnetic functionality with necessary structural functionality. This integration of both electromagnetic and structural functionality throughout the volume of the composite is the distinguishing feature of our approach. As an example, we present a class of composites based on the integration of artificial plasmon media into polymer matrixes. Such composites can exhibit a broadband index of refraction substantially equal to unity at microwave frequencies and below.