Investigation of Size and Spatial Distribution of Defects in S2 Glass Fibers Using Continuous Fiber Bending Test Method

A novel continuous fiber bending test method was developed to measure the size and spatial distribution of defects in glass fiber. For this test method, a lubricated single S2-glass fiber is placed between two Kapton carrier films and subjected to pure bending deformation over a loading surface of prescribed radius of curvature that generates flexural strain in the fiber and creates fiber fracture at the largest surface defect locations. Tests are conducted over 870 mm of fiber length to generate statistical data. The same sample is then tested with a smaller radius of curvature surface to generate a higher flexural strain level to trigger additional fiber fractures at surface defects of smaller size. This sequence is repeated for loading surfaces with radii of curvatures ranging from ranges from 350 μm to 25 μm. For the 10-micron S2-glass fiber this corresponds to flexural strains range of 1.4 % to 11.6 %. By measuring the location of fiber breaks at each radius of curvature, the number of surface defects and the associated spacings between the defects are obtained for each level of flexural strain. The associated defect size is calculated using fracture mechanics. The test method generates a map of the defect size and spacing along the fiber length for the first time.