Highly Elastic Strain Gauges Based on Shape Memory Alloys for Monitoring of Fibre Reinforced Plastics

Abstract

Conventional strain gauges made of constantan or CuCr for instance have a low value for structural health monitoring issues in plastic composites. These strain sensor materials exhibit small elastic regions and show fatigue when dynamically loaded with strain levels over 0.3 percent. For this reason, these sensors would break or fail before the composite life-time and thus cannot be integrated into this kind of composite materials. Pseudoelastic thermal shape memory alloys are therefore used as strain sensors and integrated into composites in order to allow piezoresistive strain measurement and structural health monitoring in such materials. Thermal treatments are used to create sensor structures out of shape memory alloy wires. Pseudoelastic shape memory wires can be strained up to 8 percent repeatedly. Their gauge factor is higher than 5. Shape memory strain sensors are successfully embedded into glass fibre reinforced plastics and show a significant and reproducible resistance change when the composite is strained. The dynamic strength is magnificently higher compared to conventional strain gauges. Shape memory strain sensors are an efficient alternative to fiber-bragg-grating sensors and can potentially be used for strain measurements in different plastics and textile materials. Shape memory sensor structures can be embedded or applied and are good candidates for structural characterisation and monitoring applications.

Calibration of piezoresistive shape-memory alloy strain sensors

“…Temperature dependence and temperature compensation were not explicit part of this test series but are of enormous importance. The temperature behaviour of single pseudo-elastic SMA strain sensors is described in Ma¨der et al (2017). The blue curve in the diagram of Figure 11 shows this temperature dependence.…”

“…Due to the phase transformation and a difference in the specific electrical resistance of the crystal phases, a comparably strong resistance change takes place when the material is deformed. This results in a gauge factor above five (Ma¨der et al, 2017). The equipment to read the sensor signal is analogue to SSG.…”

Smart Pressure Film Sensor for Machine Tool Optimization and Characterization of the Dynamic Pressure Field on Machine Surfaces

“…3). SMA is capable to be used as a highly elastic and sensitive strain sensor [2,3]. Figure 3 shows an influence of the temperature on the electrical resistance-strain-characteristic, that needs to be considered.…”

Light Electric Vehicles for Muscle–Battery Electric Mobility in Circular Economy: A Comprehensive Study

“…In order to determine the operational reliability of the GFRP construction, strain gauges were applied to the GFRP components when operating the Cargo Cruiser vehicle to enable structural health monitoring (SHM) for reliability tests and possible reduction in safety factors in lightweight construction. Pseudoelastic shape memory alloys (SMAs) are successfully used for this purpose in order to achieve a long service life of mechanical sensors [17,18]. The readout of SMA sensors during vehicle operation was tested by an ESP32 microcontroller.…”