Elastic State of Stress in a Stalpeth Cable Jacket Subjected to Pure Bending

The selection and development of plastic jacketing compounds for multipair cables depend to a large extent on cable behavior during bending. Cable jackets are expected to be relatively flexible for ease of handling and installation while at the same time surviving large strains (up to 15 percent) without cracking, splitting, or severe wrinkling. Temperature extremes encountered in the field render these criteria even more stringent. Recently completed analyses have led to easily performed laboratory tests for the screening of candidate compounds with regard to some of 151 these requirements. Now, for example, the relative influence of various sheath-grade plastics on the bending stiffness of cables can be evaluated by conducting ordinary tensile tests. 1 In addition, the relative sensitivity of compounds to low temperature and high strain-rate cracking can be determined through impact tests on notched specimens. 1 Still, there remains the observation of slow crack growth at high temperatures during bending and the occurrence of wrinkles in cable jackets during duct installation at low temperatures. None of these phenomena nor how they are affected by cable parameters such as jacket moduli and thickness, flooding compound tackiness, and the depth of the corrugations in the underlying steel, is presently understood. This paper is devoted to a study of the state of stress in the jacket of a Stalpeth cable subjected to classical pure bending. The problem is treated within the framework of the linear theory of elasticity, which supposes small strains and rotations and an elastic material.