Durability criteria for rubber parts of machines

Abstract

Natural and synthetic rubber (elastomeric materials) are used for fabrication of vibration dampers, shock absorbers, seismic isolation, bearing seals, compensation devices. These elements are applied both in machine manufacturing and in civil engineering. Elastomers absorb input energy much better than other construction materials and this fact gives them many engineering advantages. The disadvantages of elastomeric materials are ageing, accumulation of damage, i.e. changing the mechanical properties over time and lowering their operational capability. The durability of rubber elements under cyclic loading is determined according to various criteria: thermodynamic process of damage, energy damage criterion, entropic damage criterion, engineering damage criterion, dissipative damage criterion. Experiments show that the nature of the destruction process is unidirectional and irreversible. Deformation is accompanied by dissipative heating, which is also facilitated by low thermal conductivity of rubber. To calculate the durability of rubber parts, a large amount of experimental data is required, which is currently insufficient. In this paper, the dissipative damage criterion is considered, which allows determining the limiting number of loading cycles at a given operating temperature and damage parameter. The destruction occurs when the concentration of broken molecular bonds reaches a certain critical level, the numerical value of which is constant of the material. This value is called the damage parameter, which is a constant value for a given material, empirically determined. In addition, it is necessary to know the dynamic shear modulus of the material and the relative deformation of the element. Such approach allows to correctly appoint the grade of rubber for anti-vibration devices at the design stage.