Increasing Safety and Quality in Automotive Design
Fiber optic sensors are immune to EMI, small, lightweight, and embeddable in materials. These inherent advantages of fiber optics makes them suitable to address some of the biggest challenges that the automotive market faces as it shifts to electric and carbon composite vehicles. Luna’s technology utilizes telecom grade, low costs fiber to provide thousands of strain and temperature sensing points. Whether using this to help develop safer and more efficient batteries or to understand structural health of composite body panels, Luna’s fiber optic measurement technique can help increase quality and safety in automotive design.
www.AutomotiveTestingTechnologyInternational.com NOVEMBER 2014ONLINE READER INQUIRY NUMBER096 Luna Innovationsf ber optic measurement technique can help increase quality and safety in automotive designStructural and thermal measurement The current shift in the automotive market toward electric vehicles is resulting in a move to offset battery pack weight by using carbon composite designs. This is resulting in a fundamental shift in measurement requirements of stress, strain and temperature. Standard sensor technologies such as resistive foil gauges for strain measurements and thermocouples for temperature, while readily available, are inherently limited in their ability to provide full-eld information. Luna Innovations is applying its technological advantage in ber optic measurement systems to distributed sensing applications. Luna has developed a ber optic-based, fully distributed measurement technique that provides a much more detailed view of the strain and temperature gradients within a system. This technology enables low-cost, fully distributed sensing capabilities with millimeter spatial resolution and high dynamic range. The sensors themselves are small, lightweight, immune to EMI, radiation-resistant, and can be embedded in or adhered to a materialfs surface. These capabilities lead to new insights into materials that can result in better designs. Carbon composites are being widely tested for use in both vehicle body panels as well as frames. Due to their non-homogeneity, performance properties are TOP: Strain distribution in a carbon composite panel with a single embedded 5m ber sensor. The panel is clamped at the root and loaded vertically downward at the tip. Strain gradients due to intentional defects are clearly visible ABOVE: Temperature distribution on a vessel wrapped with a single 5m ber sensor, with heating elements applied to two regions on the vessel extensive and complex physical and mechanical testing with single point sensors. By denition, these do not provide an accurate full-eld strain prole during testing. As an alternative, with a single optical ber sensor, an entire body panel can be instrumented and tested in both static and fatigue loading. The sensor can be run in a grid pattern across the panel, resulting in the ability to measure strain gradients at a very high spatial resolution. This enables weak points of potential failure to be located and monitored. With a better understanding of the overall panel strength, its design can be optimized for cost savings without sacricing structural integrity. In addition, once a design has been nalized, the ber sensor can be embedded into the panel or frame itself during the manufacturing process. This adds a previously inaccessible dimension to structural validation checks, either periodically or after a crash. A baseline strain prole of the body panel can be taken before the panel is shipped with the embedded sensor. During regular vehicle check-ups, the sensor can be scanned for changes in structural integrity over time. More importantly, after a crash, the strain prole can be measured for the effect of impact damage to the vehicle. This would now be a more objective method for verifying structural integrity, potentially resulting in improved safety. Obtaining a high accuracy temperature prole of each individual cell within an electric vehiclefs battery pack would greatly improve the efciency of the battery in terms of power output, as well as active control and regulation through the battery management system. Instead of being limited by the need to select individually specic temperature measurement locations and grappling with thermocouple electrical leads that threaten to short-out the battery pack, electrically immune ber sensors can be installed between cells to traverse the entirety of the battery pack. Temperature measurements can therefore be reported from all cells, and could also include multiple measurements per cell. This greatly helps in optimizing the design of the battery pack, and ultimately reduces the risk to the customer.