Deposition of Stress and Temperature Sensors on Steel Surfaces by Masked Wire-Arc Spray
摘要
Strain gauges were fabricated on steel surfaces via a 100 µm thick insulating alumina layer, followed by wire-arc deposition of Ni–Cr through a 3D printed polymer mask. The metallic serpentine traces, 100 µm thick and 0.75 mm wide, were designed to produce small (240 mm2) and large (900 mm2) sensors with unloaded resistances ranging from 17 to 30 Ω. Tensile and four-point bending tests demonstrated a linear correlation between the electrical resistance of the resistive track and applied strain. Samples subject to cycling presented hysteresis, wherein the resistance of the gauge did not return to its original value, which could be attributed to densification or crack formation in the coating. Upon sequential loading, however, gauge resistances reached a steady state. Moreover, strain gauges were deposited on the outer wall of a steel pressure vessel to investigate responsiveness following injection of a hydraulic fluid. The gauges were sensitive enough to detect individual step changes in internal cavity pressure. Finally, to differentiate between changes due to strain and temperature, a surface thermocouple was fabricated using the steel substrate and an insulated constantan wire through the sample as the thermocouple materials. A Ni–Cr coating was sprayed on the surface to electrically connect the wire to the surrounding substrate, forming a thermocouple junction. The empirical findings in this study demonstrate the feasibility of manufacturing strain gauges with masked deposition for structural health monitoring.