Structural Health Monitoring (SHM) implies the integration of non-destructive evaluation methods within a system to enable autonomous state awareness for structural-integrity. SHM systems have been optimized to cover wide areas as well as focus on specific “hot-spots” for both metallic and composite structures. They can be configured to monitor adverse “changes” such as fatigue cracks, corrosion, delamination, loose bolts or impact damage either in real-time or on-demand. Immediate benefits of SHM include drastically reducing inspection costs, minimizing preventative maintenance, increasing asset availability and extending remaining useful life of structures. Future benefits could include using SHM data to improve design-margin efficiency for lighter-weight structures, facilitating structural certification and/or quality assurance and dynamically controlling operating envelopes. MDC has emerged as an SHM industry leader, advancing the state-of-the-art in nearly every aspect of this discipline including novel architecture, infrastructure, sensors, hardware, packaging, modeling and algorithms, resulting in a robust portfolio of patented technologies.
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Structural Health Monitoring
Structural Health Monitoring (SHM) implies the integration of non-destructive evaluation methods within a system to enable autonomous state awareness for structural-integrity. SHM systems have been optimized to cover wide areas as well as focus on specific “hot-spots” for both metallic and composite structures. They can be configured to monitor adverse “changes” such as fatigue cracks, corrosion, delamination, loose bolts or impact damage either in real-time or on-demand. Immediate benefits of SHM include drastically reducing inspection costs, minimizing preventative maintenance, increasing asset availability and extending remaining useful life of structures. Future benefits could include using SHM data to improve design-margin efficiency for lighter-weight structures, facilitating structural certification and/or quality assurance and dynamically controlling operating envelopes. MDC has emerged as an SHM industry leader, advancing the state-of-the-art in nearly every aspect of this discipline including novel architecture, infrastructure, sensors, hardware, packaging, modeling and algorithms, resulting in a robust portfolio of patented technologies.
MD7 Digital SHM System
Current in-service monitoring techniques utilize a dense web of analog sensors connected by individual wires routed to centralized data acquisition and processing units. This traditional approach has a significant weight penalty, can be complex to install and is susceptible to EMI. To resolve these issues, MDC has developed a fully digital SHM solution. The MD7 system is composed of 3 core elements: the IntelliConnector™ miniature node for distributed data acquisition, the VectorLocator™ sensor assembly for guided-wave phased-arrays, and the HubTouch™ data accumulator for remote diagnostic processing. Each element of the MD7 system is networked on a 6-wire serial bus that carries the differential communication, synchronization and power signals, typically using flat-flexible-cable (FFC). Benefits of this distributed infrastructure approach include higher fidelity data through digitizing sensor signals at the point of measurement, reduced computational burden through local signal processing and feature reduction, and overall minimal mass through the elimination of cables, connectors and bulky off-the-shelf hardware.
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PZT-based SHM
The majority of MDC’s extensive SHM experience has made use of piezoelectric material. These elements can be used as sensors by measuring voltage differences across parallel electrodes when cyclically strained, or converselythey can be used as actuators by inducing expansion and contraction with an applied alternating electric field. Materials with piezoelectric properties are particularly attractive for SHM applications due to their high-frequency response and overall wide-bandwidth characteristics. Most research at MDC has indicated piezoceramic elements, specifically PZT (lead zirconatetitanate), to be the most suitable for practical SHM efforts since these wafers have balanced actuator and sensor constants, they are accessible, have well vetted properties and reasonable thermal stability. MDC’s assembly service strives to provide customers with robust PZT packages for repeatable testing using proven techniques to eliminate electrical interference, cross-talk, signal attenuation, and non-uniformities caused by typical fabrication and installation practices such as soldering wires or dilled-hole electrodes.
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CNT-based SHM
MDC has partnered with the Technology Laboratory for Advanced Materials and Structures (TELAMS) in the Department of Aeronautics and Astronautics at the Massachusetts Institute of Technology (MIT) to develop the next generation of advanced SHM technologies through the use of embedded carbon nanotubes (CNTs) to enable multi-physics, multi-functional capabilities within composite laminates. Several studies have shown that CNTs possess exceptional mechanical stiffness (as high as ~1 TPa) and strength, as well as excellent electrical conductivity (~1000x copper) and piezoresistivity (resistivity change with mechanical strain). Thus, they can be used to not only to reinforce composite structures to improve impact and delamination resistance, but also to enable novel SHM and NDE techniques. Vertically or horizontally aligned CNT forests can be transferred to composite pre-preg at room temperature through a “nanostitch” process. Radially aligned CNT can be grown in-situ on dry fiber tows or fabric to create “fuzzy-fiber” reinforced polymers (FFRP).