Measurement of Compressive Stress-Strain Response at Small-Strains

This study developed a measurement method capable of precisely evaluating the mechanical behavior of materials and microdevices in the small-strain region. The system integrates a motor-controlled z-stage, a microcontroller board, an operational amplifier circuit, and a force sensor, enabling synchronized force-displacement acquisition through custom control and serial communication. Calibration of the amplifier's variable resistor was performed to optimize the correlation between applied force and sensor output, yielding a relative error within ±2.0% when compared with a commercial universal testing machine. Vertical displacement accuracy was validated using a laser displacement meter at a target motion speed of 1 µm/s, showing a relative error of +0.1%. Accordingly, the platform provides a displacement resolution of 1 µm and a force resolution of 0.01 N. Compression tests were conducted on a polydimethylsiloxane (PDMS) sample fabricated at one-third of the standard ASTM D575-91 dimensions. Stress-strain responses measured by the proposed system and by the universal testing machine exhibited close agreement, and the compressive modulus estimated in the small-strain region showed a +5.3% deviation from previously reported values. These results confirm the reliability and repeatability of measurements in the small-strain region, supporting modulus estimation based on the initial linear slope under controlled compression. The developed platform is compact, straightforward to assemble, and cost-effective while maintaining high precision and operational stability. Its validated performance and reproducible calibration procedure make it suitable for laboratories requiring accurate characterization at low forces and small displacements. Potential application areas include polymer-based microelectromechanical systems (MEMS), soft robotics components, and microneedles, where precise, low-load compression testing and verifiable displacement control are essential for material evaluation and device design.