Proceedings of SerbiaTrib '13

additional energy is dissipated due to frictionbetween rubber and metal parts.In previous authors research [2] it was observedthat friction between rubber and metal in such casehave a significant influence on the dampingcharacteristics of shock absorber. This paperanalyzes the development process of rubber orrubber-metal shock absorbers realized with freecontacts between the constitutive parts, startingfrom the design, construction, testing and operation,with special emphasis on the development ofrubber-metal springs for the buffing and draw gearof railway vehicles.2. DEVELOPMENT OF THE RUBBER-METAL SHOCK ABSORBERWith appearance of modern computer tools andvirtual product development, the developmentprocess of shock absorbers became more efficientdue to simulated experimental testing of virtualprototype. With virtual product development toolsit is possible to predict the absorbing capacity andservice life before the manufacturing of the productprototype which was not possible in classicaldevelopment process.The assembly of shock absorber with rubbermetalspring usually consists of a few rubber-metalelements separated with metal plates andprestressed with a central screw. A rubber-metalelement represents a metal carrier in the shape of acircular plate with natural or synthetic rubbervulcanized on both sides. Therefore, the advantagesof both component elements are involved: highabilities of displacement and amortization of rubberand large loads which are sustained by metal parts.These ensure the decrease of noise and amortizationof impact loads. Figure 1 shows the design ofbuffing gear spring assembly, while Figure 2 showsthe design of draw gear spring assembly.Figure 1. Rubber-metal spring assembly of buffing gearFigure 2. Rubber-metal spring assembly of draw gearAs already noted, these springs are used as antishockcomponents, so the main properties designermust take into account are absorbing capacity andstiffness of the spring. The most importantabsorbing characteristic of rubber is evaluated byits hysteresis. Hysteresis is the mechanical energyloss that always occurs in an elastic materialbetween the application and the removal of a load.If the displacement of a system with hysteresis isplotted on a graph against the applied force, theresulting curve is in the form of a loop. It dependsnot only on the elastomer type, but also on fillersand other compound ingredients as othermechanical properties.The authors defined a virtual productdevelopment procedure (Figure 3) for developmentof rubber-metal springs used in shock absorbers.The development procedure is based on applicationof modern viscoplastic rubber constitutive model(Bergström-Boyce), which besides higher accuracyof prediction, enables the assessment rubbercompound hysteresis and strain rate dependencewhich is not possible by application of hyperelasticmodels usual for rubber FE analysis. Theparameters of rubber constitutive model(Bergström-Boyce) are determined by uniaxialcompression at different strain rates and stressrelaxation test on the samples of the rubbercompound (35.7 x 17.8 mm) [3]. The samples arecompressed between hardened steel plateslubricated with machine oil in order to prevent thebarrelling of samples. Based on the performedexperiments, the database of model parameters forthe rubber compounds can be defined. Databasealso contains data about other significant propertiesof rubber compound, such as composition, commonmechanical properties, etc.The first step in procedure shown at Figure 3 isto determine the rubber compound for rubber-metalspring. From the formed database severalcompounds are selected based on criteria definedby widely known selection and service guide forelastomers [4] regarding the product specificrequirements (creep, low-temp stiffening, heataging,…) and the operating environment conditions(resistance to ozone, radiation, …). The selected13 th International Conference on Tribology – Serbiatrib’13 287