The increasing demand for in-service structural health monitoring has stimulated efforts to integrate self and environmental sensing capabilities into materials and structures. To sense damage within composite materials, we are developing a compact network microsensor array to be integrated into the material. These structurally-integrated embedded microsensors render the composite information-based, so that it can monitor and report on the local structural environment, on request or in real-time as necessary. Here we present efforts to characterize the structural effects of embedding these sensors. Quasi-static three-point bending (short beam shear) and fatigue three-point bending (short beam shear) tests are conducted in order to characterize the effects of introducing sensors, or suitable dummy sensors in the form of chip resistors, and commonly used circuit board material, namely G-10/FR4 Garolite on the various mechanical properties of the host structural composite material. Furthermore, various methods and geometries of embedding the microsensors are examined in order to determine the technique that optimizes the mechanical properties of the host composite material. The work described here is part of an ongoing effort to understand the structural effects of integrating microsensor networks into a host composite material.
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. We present work related to the development of embedded arrays of miniature electronic-based microsensors within a structural composite materials, such as GFRP. Although the scale and power consumption of such devices continues to decrease while increasing the functionality, the size of these devices remain large relative the typical scale of the reinforcing fibers and the interlayer spacing. Therefore, the question of the impact of those devices on the various mechanical properties is relevant and important. We present work on characterizing some of those effects in specific systems where sensors, or suitable dummy sensors, are arrayed with ~1 cm spacing between elements. The typical size of the microelectronic sensing element is ~1 mm, and here is orthorhombic. Of particular importance are the effects of inclusion of such devices on strength or fatigue properties of the base composite. Our work seeks to characterize these effects for 1 and 2 dimensional arrays lying in planes normal to the thickness direction in laminated composites. We also seek to isolate the effects due to the sensing elements and the required interconnections that represent the power-carrying and data communications capabilities of the embedded network.
This work is part of an effort to develop smart composite materials that monitor their own health using embedded micro-sensors and local network communication nodes. Here we address the issue of data management through the development of localized processing algorithms. We demonstrate that the two-dimensional Fast Fourier Transform (FFT) is a useful algorithm due to its hierarchical structure and ability to determine the relative magnitudes of different spatial wavelengths in a material. We investigate different algorithms for implementing the distributed FFT and compare them in terms of computational requirements within a low-power, low-bandwidth network of microprocessors.
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.