In table tennis recently complex racket designs are used consisting of a wooden or glass or carbon fiber reinforced racket frame with multi-layer rubber/foam covers with special top surface properties. Various rubber compounds and glues (adhesives) are applied in the build up of the multi-layer rubber foam cover to impart greater spin or speed (up to 160 km/h) onto the celluloid ball. In terms of material characteristics, important aspects of a successful table tennis racket design are related to the elasticity and damping of the entire sandwich system and the specific surface properties that generate the spin of the celluloid ball upon the impact contact with the rubber surface. All of the above polymeric materials involved in a racket design reveal a distinct viscoelastic behavior, which implies that their elastic, damping and surface properties depend on time (loading rate or frequency, aging) and loading level. Despite the high interest of applying scientific concepts to table tennis, there is currently no widely accepted methodology available to characterize and to determine the performance profile of table tennis rackets as a whole or of individual or combined polymeric material layers in terms of their viscoelastic properties and property functions. The objective of this study is the systematic characterization of performance properties of table tennis sandwich rubbers consisting of specific rubber cover sheets (pimpled-in and pimple-out) and sponge (cellular) rubbers under various loading conditions using polymer science based test methods. The experimental work involved various table tennis sandwich rubber types from different producers with different thicknesses. New and used material sheets were tested as full size specimens (racket size) and as sub-size specimens (circular discs with a diameter of 34 mm). Monotonic uniaxial compression tests were performed over a wide loading rate range to characterize the bulk behavior of the rubbers. Cyclic (dynamic) characterization tests were performed under compression over a frequency range of 1 to 200 Hz to determine the frequency dependence of the complex dynamic modulus, E*, the visco-elastic damping, tan?, the storage and the loss energy components and the frequency response functions (transmissibility). All of the above tests were performed at room temperature (23 °C) and at 50% relative humidity using a high rate servohydraulic test system. The results of this investigation are discussed in terms of loading rate and frequency dependent material property functions. Furthermore, a material science based methodology is proposed for the ranking and classification of the sandwich rubbers. The methodology proposed may be used for various purposes: (1) the Technical Committee of the ITTF may use it for the approval of new sandwich rubber products, (2) manufacturers may apply it for product development, quality assurance, technical support and marketing and (3) table tennis players and trainers may apply it for the selection of the optimum rubber for individual player profiles and for estimating the life-time of rubbers with optimum performance to enhance the effectivity of the training work while simultaneously reducing costs. Nevertheless, more detailed investigations are needed to characterize the surface properties (wear, reduction of adhesion), the fatigue behavior and the influence of temperature and other environmental conditions on all of the parameters mentioned above. What is also particularly needed, is a thorough comparison between polymer science based properties and property functions and subjective performance evaluations by top players. In establishing correlations between subjective (player based) and objective (polymer science based) material rankings, a powerful tool may be made available to support future product development efforts.
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