A mini-Split Hopkinson Tensile bar (mSHTB) system is developed. The system employs small diameter polymeric bars, which can achieve a closer impedance match with the specimens, thus it provides a lower noise-to-signal ratio and a longer duration of tensile pulse, which results in a higher maximum strain. With the three element viscoelastic model, a characteristic method for reconstruction of the profiles of strain, particle velocity, and stress in an arbitrary cross section of a viscoelastic bar on the basis of the strain signal measured in one section is developed. Experiments using the mSHTB enable us to appropriately characterize the dynamic behavior of small-sized, low-impedance material under a particular range of high strain rate.

Due to the increase in the applications of foils, fibres, and yarns under dynamic loading, characterizing the behaviour of small-scaled material samples at high strain rates has become important. However, owing to the low mechanical impedance and the small size of such samples, the conventional split Hopkinson bar technique encounters serious problems, such as high noise-to-signal ratios, an undistinguishable transmitted signal, a short loading time, and difficulty in achieving large strain. A mini-split Hopkinson tensile bar (mini-SHTB) system has been developed to measure the constitutive relation of micro-scaled material specimens under high strain rates. The system employs polymeric bars of small diameter to achieve a closer impedance match with the specimens. This match ensures a lower noiseto-signal ratio in the transmitted signals and hence allows correct interpretation of the transmitted strain profiles. A series of experiments were carried out on different types and forms of material, such as aluminium foil, cellulose nitrate foil, badminton racket string, and so forth, to verify the applicability of the apparatus. Strain rates in the order of 10 2 were attained under this mini-SHTB system. The results confirm that the tensile stress-strain behaviour of small-sized specimens, with low mechanical impedance and under high strain rates, can be determined effectively and efficiently using this technique.

Wool's mechanical properties have been a subject of extensive research since the 1920s because wool fibers are normally subjected to both static and impact tensile loadings in their manufacturing processes and applications.Tensile behavior of wool fibers under quasi-static loads has been thoroughly studied both experimentally and analytically. The effects of moisture, temperature, non-uniformity, and the extent of crystallization and amorphous orientation in wool fibers have been previously investigated [1][2][3][4]. Various theoretical models have been proposed to explain the tensile behavior of wool fibers in terms of their microstructures [5][6][7][8][9].In spite of the advances of research on the mechanical properties of wool fibers under quasi-static loadings, few reports can be found in the open literature describing their impact response. Wool fibers are subjected to impact loadings in textile processing and in the service life of the finished wool products. A good understanding of the impact behavior of wool fibers is essential for their manufacturing and applications. Impact behavior has been experimentally studied and results have been published for textile fibers subjected to impact loadings at strain rates up to the order of 10 2 s -1 by using the apparatus of both Meredith and Holden, discussed in Lyons [10]. These fibers included polypropylene monofils, Orlon 42 acrylic fibers, cellulose acetate fibers, high-tenacity viscose fibers, polyethylene fibers [11], and nylon 66 fibers [10]. Few papers report on the impact response of wool fibers. Therefore, there is a need to develop a new laboratory set-up to obtain experimental data on how wool fibers respond to impact loading.In this study, a mini split Hopkinson tensile bar (mSHTB) was employed to obtain stress-strain curves of Lincoln wool fibers subjected to impact loadings at strain rates in the order of 10 2 s -1 . This method is different from the traditional method adopted by Meredith, discussed in Lyons [10]. * The split Hopkinson pressure bar (SHPB) is named after Bertram Hopkinson [12], who first used the stress wave propagation in a long metal bar to measure the pressures in impact events. In the 1940s, Davies [13] and Kolsky [14] modified and used two Hopkinson bars in series to measure the dynamic stress-strain response of materials, which were sandwiched in-between bars. To date, the SHPB has been widely used in the measurement of the stress-strain curves of various materials such as metals, polymers, concrete, metal foams, polymer foams, and nano-materials subjected to compressive loadings. Moreover, the traditional split Hopkinson bar has been modified and used to measure the impact response of materials subjected to uniaxial tension [15-18], torsion [19, 20], and combined torsion and compression [21,22].Abstract A new testing method using a mini split Hopkinson tensile bar was employed in the impact tests of Lincoln wool fibers. Stress-strain curves of Lincoln wool fibers subjected to impact loadings at strain rates in the order of 1...