This paper introduces a hybrid composite material, where the structural carbon fiber tow is transformed into a piezoresistive damage localization sensor network, and the structural glass fiber operates as electrical insulation. The piezoresistive damage localization sensor network consists of an array of carbon fiber tows, each with increasing resistance, connected in parallel. Including a second orthogonal array enables accurate 2D damage localization of large-area composites. Impact tests were conducted, finding the sensor network able to reliably determine the location of damage in both orthogonal directions, pinpointing the exact location of damage. This illustrates a capability for in situ monitoring of large-area composites throughout the life cycle of the structure.
The automotive industry is rapidly transforming due to the growing demand for decarbonization. Electric Vehicles (EVs) are becoming increasingly common, and subsequent innovations regarding vehicle lightweighting can increase vehicle efficiency and further reduce carbon footprint. Lithium-Ion Batteries (LIBs) have become the most common power source used in EVs, but LIBs host some inherent challenges, namely thermal runaway. Thermal runaway can be caused by various mechanisms including thermal, mechanical, or electrical impacts which occur during extreme operating conditions. This kind of failure can result in battery fires and explosions that are extremely difficult to extinguish and pose a significant safety risk. A self-sensing LIB enclosure that monitors the temperatures of individual battery modules and provides an early warning signal may be a viable solution to the thermal runaway safety issue. This work studies a hybrid carbon and glass Fiber Reinforced Polymer (FRP) composite designed to replace the traditional metal LIB enclosure, lightweighting the EV design and allowing for condition monitoring sensors to be embedded during the manufacturing process. Battery enclosures have tight space constraints which prohibit surface mounted sensors, making sensor embedment essential. Embedded sensors also have the advantage of a protective composite layer that makes the sensor system more robust during manufacturing and operating conditions. However, this composite layer under which the sensors are sealed produces a time lag in detecting a temperature change within the battery enclosure. This time delay would reduce the efficacy of an early warning system. The purpose of this study is to lay the groundwork for a self-sensing condition monitoring LIB enclosure and characterize the composite enclosure’s temperature response at different layers. A theoretical design of said system is detailed, and a prototype enclosure sample instrumented with temperature sensors is fabricated. Experiments are performed to measure the temperature response of the self-sensing composite prototype when exposed to realistic thermal runaway conditions. This is accomplished through a novel experimental test set up that imposes a unidirectional heat transfer condition by exposing the composite sample to oven temperatures on the top surface and ambient temperatures on the bottom surface. A computational model is developed to predict the composite’s thermal response during different LIB failure temperatures. This finite element transient heat transfer simulation is tuned using initial experimental results and validated by subsequent thermal tests. This study produces a high accuracy thermal model which can be used to provide design optimization information, like the ideal placement of sensors, and predict the thermal response of a composite enclosure when exposed to different thermal loading conditions. The thermal simulation could also be utilized in future works to develop a temperature inference model which could predict LIB health from embedded sensor measurements. This work details the novel experiments and derived finite element model that characterize a potential LIB management system integrated within a self-sensing composite battery enclosure.
In recent years, structural health monitoring technology has received considerable attention for its potential to provide objective, accurate, and real-time assessment of structural conditions in comparison with the current periodic visual inspection practice. Battery-operated wireless sensors eliminate wires and make their installations easy. However, wireless data transmission consumes significant power and requires frequent replacement of batteries, which is particularly difficult for structures that are located in rural areas with poor accessibility. To address this obstacle, a low-power multi-hop wireless sensor network that monitors the vibration of large-size civil infrastructure is developed and validated in this work. The wireless communication devices employ special lowpower wireless devices that operate in the sub-GHz band, which allows for long-distance communication exceeding 1 km and easy deployment because no license is required. Data collection over wide areas is achieved through relay transmission (multi-hop communication), in which the wireless sensor data are received and retransmitted by surrounding sensors. A fail-safe function is built to achieve a sensor data collection rate of 99.999%. To save power, the communication timings are synchronized, and time-division communication is implemented, in which the wireless devices are made to sleep in time bands when communication is not needed. To validate this wireless sensor network, a field test was carried out to measure the acceleration response of a long-span suspension bridge, based on which the bridges natural frequencies and mode shapes were successfully identified. The field tests also demonstrated the ease of installation and operation of the wireless sensor system.
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