The initiation and propagation of damage in composite laminates generate Acoustic Emission. The use of
real time AE monitoring has been quite extensive for in-service composite structures. In the present work,
experimental and numerical studies were performed to characterize the acoustic wave propagation in thin
glass/epoxy composite plates. Experimentally obtained and simulated emission signals were used to
identify and locate the source of the acoustic wave. Signal processing algorithms and a passive damage
diagnosis system based on AE techniques were proposed for continuously monitoring and assessing the
structural health of composite laminates. The local sensing and distributed processing features of the sensor
system result in a decreased demand for bandwidth and lower computational power needed at each node.
We summarize the methodology that we have used to address integrating sensing network into composite
materials for structural self diagnosis. First, we have examined the effect of stress concentration that arises
due to the embedment of sensors and external devices on the strength and endurance of laminated glass
fiber composites. To analyze the mechanical response of the composite material under study subjected to
in-plane or impact loads, we have fabricated a series of samples, with and without embedded (dummy)
sensors/micro-processors, using S2 glass fiber/epoxy, and have characterized their response by acoustic
emission. Guided by the corresponding results, we can select sensors and other necessary components in
such way as to minimize the impact of the embedded electronics on the material integrity and, at the same
time, to implement acoustic sensing monitoring functionalities within the material. A 4-tree hierarchical
network of PVDF sensors capable of acquiring signals typically related to resin micro cracking phenomena
has been developed and partially integrated into a cross ply laminate. The achieved results and ongoing
research will be discussed.
This experimental research is focused on examining the effects of stress concentration due to the embedded Structural
Health Monitoring (SHM) sensors on the structural integrity of glass fiber/epoxy laminates subjected to in-plane tensile
loads. Recent advances of health monitoring technologies have resulted in development of micro-dimensional sensors
that can be embedded into composite laminates. Notwithstanding their small sizes, such inclusions may affect the
response of the composite. Damage induced by the peak values of stress concentration around the embedded devices is,
in fact, one of the main concerns. To assess this and related issues, we have fabricated a series of samples with and
without embedded (dummy) sensors and micro-processors in S2 glass fiber/epoxy laminates, and systematically tested
the samples while continuously monitoring the response by the acoustic emission technique. In this manner we have
sought to address the process of damage initiation and evolution within the material. The results show that acoustic
events begin earlier on during the loading process, in specimens with embedded sensors and the source of the damage is
located near the sensors. These early events are associated with matrix failure at the sensor-resin interfaces through
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.