Digital image correlation as a strain measurement technique for fibre tensile tests

A method is presented to test fibres in tension using direct strain measurement. This eliminates the need to test the fibres at multiple gauge lengths to correct for machine compliance, reducing the number of samples. Additionally, fibre slippage can contribute to the underestimation of the stiffness since this is not considered in the correction procedure. Steel fibres with a diameter of 30 μm, and a known stiffness of 193 GPa, were tested in tension using indirect methods and the direct strain method. Direct strain measurement resulted in a stiffness of 187 ± 12 GPa while the lowest and highest stiffness obtained by the indirect methods are 140 ± 2 GPa and 150 ± 4 GPa. The underestimation by the indirect measurement strain methods show the need for a new method. To demonstrate the applicability of the new test method to natural fibres, the properties of technical flax and bamboo fibres were determined.