A Portable Micro-Indentation Instrument Capable of In-Situ Testing the Mechanical Properties of In-Service Structures

Regular evaluation of the mechanical properties of in-service structures is crucial for their safety and longevity. A portable micro-indentation instrument was developed to test engineering structures. The core principle for designing indentation instrument—namely, the accurate measurement of indentation load and indentation depth—was discussed. A voice-coil motor, driven by a buck converter controlled via highresolution pulse width modulation, was employed to achieve high-resolution load measurements and ensure smooth, accurate load-depth curves at low indentation loads. The indentation depth was calculated by taking the sensor-measured displacement and subtracting both the contact zero point and the frame deformation estimated from machine stiffness. To improve the accuracy of measuring the contact zero point and frame deformation, a depth measurement module with 1.0 nm resolution was designed, ensuring accurate indentation depth measurements. Indentation tests on block and pipeline samples showed relative errors in the elastic modulus and hardness within ±10% and ±6%, respectively, demonstrating the reliability of the developed instrument. This instrument is valuable for assessing in-service structures' mechanical properties, critical for infrastructure safety and maintenance.