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Laser-defined graphene strain sensor directly fabricated on 3D-printed structure

A direct-write method to fabricate a strain sensor directly on a structure of interest is reported. In this method, a commercial graphene ink is printed as a square patch (6 mm square) on the structure. The patch is dried at 100 °C for 30 min to remove residual solvents but the printed graphene remains in an insulative state. By scanning a focused laser (830 nm, 100 mW), the graphene becomes electrically conductive and exhibits a piezoresistive effect and a low temperature coefficient of resistance of −0.0006 °C−1. Using this approach, the laser defines a strain sensor pattern on the printed graphene patch. To demonstrate the method, a strain sensor was directly fabricated on a 3D-printed test coupon made of ULTEM 9085 thermoplastic. The sensor exhibits a gauge factor of 3.58, which is significantly higher than that of commercial foil strain gauges made of constantan. This method is an attractive alternative when commercial strain sensors are difficult to employ due to the high porosity and surface roughness of the material structure under test.