Creep And Mullins Effect Of Silicone Rubber Under Biaxial Stress

Rubber is widely used in the automotive tire industry,rail transit and underground protection engineering and other important areas of people’s livelihood and national defense because of its unique properties such as hyperelasticity,viscoelasticity,excellent wear resistance and insulation.To date,the mechanical properties of rubber such as hyperelasticity and viscoelasticity have been studied by scholars in the field of material science and mechanics.Most of the research is mainly focused on the uniaxial stress state,and rarely involves the biaxial or triaxial stress state.However,the actual rubber components are usually under complex stress state,so it is of great scientific significance and practical value to study the mechanical properties of rubber under complex stress state.In this paper,the creep properties,non-linear viscoelasticity,time-stress superposition and Mullins effect of silicone rubber under biaxial tension are discussed through mechanical tests and theoretical analysis.The main research contents and conclusions obtained are as follows:(1)Design optimization of the shape and size of the biaxial specimen.Because there is no standard for biaxial tensile specimens at present,the biaxial tension cross-shaped rubber specimens with arm reinforcements were designed by using ABAQUS finite element analysis and simulation optimization.And the reinforcement sheet material type and the reinforcement arm geometry parameters were analyzed for the sample center.The deformation field in the central region of the specimen approximately conforms to uniform distribution and the stress in this region is equivalent to the nominal stress at the corresponding specimen arm.(2)Biaxial tensile creep properties of rubber and its time-stress superposition analysis.The strain-time curves of the cross-shaped silicone rubber specimens were obtained by biaxial tensile creep tests under different stress levels with specified different stress ratios in the two specimen arms.Based on Cauchy stress tensor and Left Cauchy-Green deformation tensor,a stress measure and a deformation measure are defined to characterize the degree of stress and deformation of the materials under biaxial conditions.The nonlinear viscoelasticity and the applicability of the time-stress superposition principle were discussed by analyzing the biaxial tensile creep behavior of the silicone rubber.It is shown that the short-term creep curves under different stress levels can be shifted along the logarithmic time axis to construct a master curve with broad time-domain at a given reference stress,and the shift factor depends on stress measure.This indicates that the creep behavior of rubber under biaxial stress state satisfies time-stress superposition principle,which provides an accelerated characterization for long-term mechanical properties of viscoelastic materials under complex stress.(3)Modeling of the Mullins effect of silicone rubber under biaxial stress.The uniaxial and equal biaxial cyclic tensile tests with stepwise increases in the draw ratio were carried out on the silicone rubber specimens.The tests reveal that the Mullins effect of the material is remarkable.Based on the pseudo-elastic theory and considering the damage evolution related to the maximum deformation experienced in cyclic loading,the Mullins effect is described by using the Ogden pseudo-elastic constitutive model.The results show that the Mullins effect of uniaxial cyclic tension and equibiaxial cyclic tension of the silicone rubber can be quantitatively described by the Ogden pseudo-elastic constitutive model.