Observations of Deformation and Failure Processes in Fiber-Loop Tests

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Abstract
When tensile forces are applied to textile structures consisting of twisted, interwoven, interlooped, or entangled fibers, local deformations will often consist of a combination of tensile, bending, lateral compression and surface shearing, and unbending modes. The static-loop test combines the first three of these deformation modes, the sliding or dynamic-loop test adds the last two modes and readily lends itself to fatigue testing. The current paper reports on observations of filament deformation and fracture incurred during both static and dynamic-loop tests in contrast to what occurs during straight tensile tests. The damage processes observed include: opening of tensile cracks at surface flaws, catastrophic tensile failure, fiber flattening, coupled shear bands due to axial compression, surface shingling due to extreme shearing, gross filament dis tortion due to ploughing, crack branching accompanied by longitudinal splitting, surface wear, abrasion, and cutting. As expected, fibers with different tensile properties exhibit different combinations of deformation and fracture modes; like wise, different modes are manifested in the same fiber when testing is conducted at room condition and in liquid nitrogen.