Polymeric materials are widely used in cable insulation, but the mechanical properties of insulation polymers are still not well studied and summarized, especially the fatigue behavior. This research aims to study the fatigue behavior of conduit polymer materials, viz nylon 6, polypropylene (PP) and calcium carbonate filled black colored polypropylene (PP (blk)) under different strain ranges and temperature conditions. Besides room temperature (25 °C) tests, low temperature (-40 °C) tests and high temperature (125 °C) for nylon 6, 65 °C for PP and PP (blk)) tests are also performed. All of the three materials are below their glass transition temperature in low temperature tests, so they are more brittle and fatigue life time is shorten obviously. High temperature gives polymers more viscosity, and fatigue life significantly extends. PP (blk) possesses the best fatigue behavior, followed be PP and nylon 6. Wei-Wong unified strain fatigue model was used to analysis fatigue data and predict fatigue life.
Thermal and mechanical analysis is conducted before fatigue tests. Thermal character, such as molecular degradation, glass transition and melting point, can be determined. Mechanical properties, such as ultimate tensile strength, elastic modulus and Poisson’s ratio were obtained from quasi static tensile tests. Scanning Electron Microscope (SEM) was employed to examine the failure structure.