An enhanced method to determine the Young’s modulus of technical single fibres by means of high resolution digital image correlation

Abstract

To obtain mechanical tensile properties of materials it is customary to equip the specimen directly with a device to measure strain and Young’s modulus correctly and only within the measuring length defined by the standards. Whereas a variety of tools such as extensometers, strain gauges and optical systems are available for specimens on coupon level, no market-ready tools to measure strains of single fibres during single fibre tensile tests are available. Although there is a standard for single fibre testing, the procedures described there are only capable of measuring strains of the whole testing setup rather than the strain of the fibre. Without a direct strain measurement on the specimen, the compliance of the test rig itself influences the determination of the Young’s modulus. This work aims to fill this gap by establishing an enhanced method to measure strains directly on the tested fibre and thus provide accurate values for Young’s modulus. It is demonstrated that by applying and then optically tracking fluorescing polymeric beads on single glass fibres, Young’s modulus is determined directly and with high repeatability, without a need to measure at different measuring lengths or compensating for the system compliance. Employing this method to glass fibres, a Young’s modulus of approximately 82.5 GPa was determined, which is in the range of values obtained by applying a conventional procedure. This enhanced measuring technology achieves high accuracy and repeatability while reducing scatter of the data. It was demonstrated that the fluorescing beads do not affect the fibre properties.

Single carbon and glass fibre properties characterised using large data sets obtained through automated single fibre tensile testing

“…The variation of stiffness with the applied strain in glass fibres has, to the best of the authors' knowledge, not been investigated yet in the literature. Only Huether et al [58] showed a decrease of the fibre stiffness with the applied load but did not discuss those results. They used a novel method to measure the fibre stiffness using resin beads and digital image correlation.…”

A Nondestructive Measurement Method of Optical Fiber Young’s Modulus Based on OFDR

“…This indicated that Young's modulus along the fiber could be obtained without damaging the fiber. Compared to methods in which the fiber needs to be to cut off, see [5][6][7], the OFDR method has incomparable advantages on measurement Young's modulus of the optical fiber. In addition, Young's modulus of the optical fiber employed can be achieved via the signal demodulation process illustrated in Figure 2 induced by the tensile strain in Figure 1b.…”

“…In 2012, Sokkar et al presented Young's modulus of a polymeric fiber by use of a transverse interferometric method based on the phase distribution of the micro-interferograms [6]. In 2018, Huether et al demonstrated an enhanced method to precisely determine Young's modulus of single glass fibers by means of optical images to track the beads [7]. However, the optical fibers employed in [5][6][7] have to be cut off for measuring their Young's modulus, which is a destructive behavior.…”

“…In 2018, Huether et al demonstrated an enhanced method to precisely determine Young's modulus of single glass fibers by means of optical images to track the beads [7]. However, the optical fibers employed in [5][6][7] have to be cut off for measuring their Young's modulus, which is a destructive behavior. Additionally, it is necessary to know the distributed Young's modulus along the axis of an optical fiber in most practical applications to estimate the pressure sensitivity and analyze the bending state as a special optical fiber sensor (e.g., polymer optical fiber sensors) [8,9], but the aforementioned method can only measure Young's modulus of one point on the optical fiber.…”

Fused filament fabrication: comparison of methods for determining the interfacial strength of single welded tracks

“…All specimens were gripped 15 mm on both ends and were tested at a speed of 3 mm/min with an initial load of 1 N. Extruded strands were tested with the same device but using a modified setup: a 50 N load cell was used and grippers controlled with pressurised air and optimised for fibre testing were used. This setup and the grippers were originally designed for testing single fibres of carbon or glass and are described in detail in [19]. In the work at hand, the device was used to determine tensile strength but no optical strain measurements were run.…”