Direct-write sensors for damage assessment in composites

Structural composites are often subjected to various conditions such as impact load, abrasion, environmental exposures (temperature, humidity). In this work, a new process, direct write to deposit sensors directly onto conformal surfaces is developed to monitor the health and assess the residual strength of composite structures. The method is based on thermal spray and laser cutting technologies, and it enables fabrications of embedded strain, temperature, moisture sensors and also offers the potential for wireless interrogation of real-time measurements. Fine powder particles are injected into the small plasma where they are heated and accelerated onto the part. The process is controlled by a 6-axis articulated robot to ensure precision pattern registration. The direct write sensors are deposited directly onto the composite surface unlike commercially available foil-based strain gages which are glued-on or have a Kapton backing. Mechanics-based models and inverse analysis techniques are also developed to process collected data and re-construct meaningful damage states, which allow, for example, quantification of accumulated damage. The integration of accurate a priori information and the sensor measurements are critical in developing successful diagnostic and prognostic systems. Furthermore optimizing locations of sensor network, types of sensors are critical in satisfying performance/sensitivity requirements.