A robotic approach based on microgripping for automated experimental tensile testing of natural microfibres

Abstract

This paper deals with first investigations of a novel approach for conducting tensile tests on single plant fibres using direct microrobotic gripping. These fibres, typically around 20 micrometers in diameter, are gaining significant interest as renewable bio-sourced products. Usual methods for tensile testing generally involve mechanical clamping jaws or adhesive sample holders. This new approach intends to bring greater precision and repeatability of the test through the use of microgrippers, force sensors positioned in close proximity to the fibre and positioning control. A microrobotic experimental platform has been developed. Two different grippers are designed to address the important issue of clamping, the test boundary conditions. Experimental investigations are conducted on 20 tensile tests, validating the viability of the approach. Young’s modulus and stress at failure are identified and are in good correspondence with results available in the recent literature of flax fibres. The gripping force exerted by the gripper is a primary factor influencing the repeatability of the test. Therefore, a method is investigated to estimate this force. First experimental results enable to establish that these forces are in tens milliNewton-range forces. This establishes the interest for future works in the design of instrumented grippers able to control gripping forces during tensile tests in closed loop. Overall, this paper states the interest of a microrobotic approach for tensile tests fibres that opens to several future works including the automation, allowing a large number of fibres to be tested, especially fibres of short length, in order to reduce statistical biases.