Biblio

Dynamic strain sensing is necessary for high-temperature harsh-environment applications, including powerplants, oil wells, aerospace, and metal manufacturing. Monitoring dynamic strain is important for structural health monitoring and condition-based maintenance in order to guarantee safety, increase process efficiency, and reduce operation and maintenance costs. Sensing in high-temperature (HT), harsh-environments (HE) comes with challenges including mounting and packaging, sensor stability, and data acquisition and processing. Wireless sensor operation at HT is desirable because it reduces the complexity of the sensor connection, increases reliability, and reduces costs. Surface acoustic wave resonators (SAWRs) are compact, can operate wirelessly and battery-free, and have been shown to operate above 1000°C, making them a potential option for HT HE dynamic strain sensing. This paper presents wirelessly interrogated SAWR dynamic strain sensors operating around 288.8MHz at room temperature and tested up to 400°C. The SAWRs were calibrated with a high-temperature wired commercial strain gauge. The sensors were mounted onto a tapered-type Inconel constant stress beam and the assembly was tested inside a box furnace. The SAWR sensitivity to dynamic strain excitation at 25°C, 100°C, and 400°C was .439 μV/με, 0.363μV/με, and .136 μV/με, respectively. The experimental outcomes verified that inductive coupled wirelessly interrogated SAWRs can be successfully used for dynamic strain sensing up to 400°C.

Present work deals with prediction of damage location in a composite cantilever beam using signal from optical fiber sensor coupled with a neural network with back propagation based learning mechanism. The experimental study uses glass/epoxy composite cantilever beam. Notch perpendicular to the axis of the beam and spanning throughout the width of the beam is introduced at three different locations viz. at the middle of the span, towards the free end of the beam and towards the fixed end of the beam. A plastic optical fiber of 6 cm gage length is mounted on the top surface of the beam along the axis of the beam exactly at the mid span. He-Ne laser is used as light source for the optical fiber and light emitting from other end of the fiber is converted to electrical signal through a converter. A three layer feed forward neural network architecture is adopted having one each input layer, hidden layer and output layer. Three features are extracted from the signal viz. resonance frequency, normalized amplitude and normalized area under resonance frequency. These three features act as inputs to the neural network input layer. The outputs qualitatively identify the location of the notch.