New method for determining the bending modulus of solid and hollow fibers from deflection tests

Abstract

The bending moduli of solid and hollow glass fibers were determined by means of fiber deflection tests. The test method was modified by measuring both the vertical and horizontal displacements of the end of the deflected fiber, without increasing the number of tested fibers, in order to reduce the high scatter of conventional test results obtained by measuring only the vertical displacement. Upper and lower boundary curves of the fiber end displacements were determined to filter out inaccurate measurements, for example, when the neutral line of the fiber is not a plane but a spatial curve. The mean and coefficient of variation of the fiber bending modulus were estimated from the recorded coordinates of the fiber ends, applying two newly-developed statistical evaluation methods based on the individual coordinates or on their average. After comparing several evaluation methods, it was demonstrated that the individual coordinate-based method provided the least relative error of the average.