Direct Write Fabrication of a Wear Sensor

This paper presents a novel design and fabrication of a wear sensor that can be additively manufactured using direct writing methods for in-situ monitoring of wear and abrasion of materials. The sensor design incorporates a circuit with closely spaced and narrow interconnect traces connected to a set of parallel resistors. The entire design is printed conformal to the surface of or embedded into a material to detect the depth of abrasion. Resistors are selected to provide linear variation in the combined resistance so that voltage resolution and detection accuracy are uniform as resistors are eliminated sequentially during abrasion. Two sensor prototypes with 200 $\mu \text{m}$ trace spacing were fabricated and tested. The first prototype utilizes commercial resistors and represents a baseline measurement. The second prototype incorporates printed Ruthenium resistors. Testing results showed that printed interconnect traces abrade cleanly during wear with no damage or chipping. Additionally, the printed resistor design resulted in a uniform voltage variation comparable to that of the commercial resistor design. The difference is attributed to the non-uniformity of the cross-sectional areas of the printed resistors, especially those with serpentine pattern. The printed resistor design enables embedding and integration of the sensor into abradable materials and coatings with minimal impact on performance.