A Bending Method for Measurement of the Tensile Strength and Young's Modulus of Glass Fibers

Abstract

The tensile strength and Young's modulus of Johns‐Manville experimental drawn glass fibers were measured by a bending method which consists of twisting a loop in a fiber and pulling the ends until the loop breaks. The tensile strength observed by this method was two to three times higher than observed by the conventional straight fiber method, while Young's modulus was practically unchanged. These results may be accounted for by the presence of flaws, since the probability is small that the weakest flaw will occur in the loop, while the straight fiber will always break at the weakest flaw. The apparatus used, a modified Chainomatic balance, is described and the equation of the looped fiber is derived. The method is used to measure the maximum tensile stress and strain attained at the point of minimum radius of curvature of the loop as well as the breaking tensile stress and strain at the actual break point of the fiber. The stress at the break point was found to be as small as one‐half the maximum attained in the loop, showing that the strength of the fiber was not uniform.