Design of Embedded Wireless Sensors for Real-Time and In-Situ Strain Sensing of Fiber Reinforced Composites

Abstract

The increasing demand of early detection of barely visible damage inside fiber reinforced polymer (FRP) composites has led to the development of advanced microsensors capable of measuring local strains and defects within FRP composites. One of the major challenges in this type of local structural health monitoring (SHM) is the development of embedded sensors which can be safely placed into FRP composites while maintaining their high strength and light weight. This paper presents the development and investigation of a set of wireless magnetostrictive sensors embedded within the FRP composites for in-situ and real-time monitoring of local strains inside the composites. Each sensor is a scalable thin film with a current thickness of 15 μm. Glass fiber reinforced polymer (GFRP) composite are investigated. The composite samples are made from 0° glass fiber fabric in an epoxy based resin. The sensors are embedded between the plies of FRP composites. Quasistatic tensile loading is applied to the sensor embedded FRP composites. An excitation planar coil placed close to the surface of the composites is used to send actuation signals to the sensors. During the loading on the composites, the local strains at the sensor increase, causing the magnetic flux change, which is measured by a pick-up planar coil located near the surface of the composite. The pick-up planar coil is connected to an external data acquisition system. This wireless excitation and sensing feature avoids any wire connections onto each sensor, which helps to maintain the light weight of the FRP composites, especially in large-sensor-array configurations. It has been found that the sensors have a nearly linear dependence between the sensor amplitude and the applied strain in the low strain region. At low strains, the strain sensitivity of the embedded sensors ranges from 4.12 μV/μe to 10.30 μV/μe. At higher strains, these sensors show a nonlinear response to the applied strains. The results indicate that these embedded magnetostrictive wireless sensors developed here are able to detect strains in situ and in real time within FRP composites while maintaining the light weight and high strength of these composites.