A Small-Scale Extensometer for Precise Strain Measurements of Thin Fibres with Millinewton Resolution

Thin fibres are very versatile components with outstanding mechanical characteristics. Therefore, there is great interest in the characterization of these properties. The strain measurement can only be realised contactless, as strain gauges or similar meth-ods cannot be applied. We propose a precise, yet simple, small-scale and cost-effective strain-measurement approach. Forces in the Newton range with millinewton resolution can be applied, which is hardly achievable by conventional methods, such as load cells. A brushless permanent magnet motor drive is used for force application, due to its reliable and repeatable torque vs. current ratio. An approach is presented to perform the motor characterization, necessary for precise measurements, using a conventional precision balance. It is shown that a repeatability of less than 1.2 percent of the actual reading can be achieved with a rather simple and cost-effective measurement setup. Possible fields of application are cost-effective substitution of conven-tional micro tensile testing machines and direct integration in devices.