Hysteretic and Elastic Properties of Rubberlike Materials Under Dynamic Shear Stresses

Abstract

The nature of hysteresis in products such as pneumatic tires, solid tires, and transmission belts is analyzed and the requirements of a laboratory test for evaluating the relative hysteretic characteristics of natural and synthetic rubber stocks are developed. The significance of various definitions of the ``hysteresis defect'' in rubberlike materials is discussed. A forced resonance vibrator in which rubber samples are deformed in shear at frequencies of 20 to 300 cycles/sec., shear strains of 0.05 to 0.35, and temperatures of −20 to +120°C is described. Experimental results obtained with natural rubber and GR‐S gum and tread stocks are presented. The hysteresis index ωη is found to be nearly independent of dynamic shear strain while the dynamic modulus G decreases moderately with increasing dynamic strain. Neither ωη nor G depends upon the height to diameter ratio of cylindrical samples. These results are at variance with those obtained by previous investigators who, employing compressive vibrations, have reported marked dependences of both modulus and friction upon dynamic strain and the ``shape factor'' of tread type stocks. In agreement with previously reported work, G is found to be independent of frequency and ωη only slightly dependent upon frequency, for treated type stocks. Results are presented for stocks based on Buna S type copolymers with varying monomer ratio and on N‐type Butaprenes, Neoprene, and butyl rubbers.