Analysis Of Visco-hyperelastic Behavior And Sealing Performance Of Polyurethanes

Polyurethane is widely used for hydraulic seals due to its excellent wear and pressure resistance and large deformation characteristics.Polyurethane is a viscohyperelastic material and its mechanical properties are both superelastic and viscoelastic.In this paper,uniaxial tensile tests,stress relaxation tests and step-by-step cyclic tensile tests are carried out on a polyurethane seal material to analyse its strain rate effect,viscoelastic relaxation characteristics and Mullins effect.The corresponding mechanical constitutive model is established through the experimental study,while the sealing performance of the polyurethane O-ring is numerically simulated to provide a guiding reference for the integrity of the sealing structure.The main research elements and conclusions are as follows.(1)Experimental study on the mechanical properties of polyurethaneThe uniaxial tensile test at different strain rates showed that the mechanical properties of polyurethane had a significant rate dependence,and the maximum stress at a tensile rate of 500 mm/min was 1.6 times higher than that at 5 mm/min when the constant tensile strain was 3.0;the polyurethane showed a significant Mullins effect and a significant instantaneous residual strain through the cyclic tensile test with stepby-step loading;the stress relaxation test The results of stress relaxation tests show that polyurethane has obvious stress relaxation phenomenon,and the relaxation modulus in the form of the Prony series was obtained;Equilibrium stress-strain curves and tensile stress-strain curves of polyurethane were obtained by both stress relaxation and uniaxial tension tests,providing an experimental basis for the development of a viscohyperelastic ontological model of polyurethane.(2)Polyurethane visco-hyperelasticity constitutive modelingTwo visco-hyperelastic constitutive models of polyurethane are constructed in this paper.One is to connect the hyperelastic model element in parallel with the viscoelastic model element containing damage and introduce a strain rate correlation function to describe the rate-dependent properties of polyurethane in tensile tests.This parallel model can better describe the tensile mechanical behaviour under small deformation conditions.The other one is based on the pseudo-elasticity theory and introduces a damage parameter to control the mechanical properties of the material and describe the stress softening behaviour of the material.The model has a larger error between the prediction results and the test results under small deformation conditions,but makes up for the inability of the first model to describe the unloading process.The two viscohyperelastic constitutive models constructed complement each other.(3)Analysis of polyurethane O-ring sealing performanceThe numerical analysis model of polyurethane O-ring was established using Abaqus finite element software to study the distribution of the maximum Mises stress and the maximum contact pressure on the sealing surface of the O-ring under different pre-compression and different oil pressures.The analysis shows that under the working condition,the Mises stress of the seal decreases with the increase of compression rate,and the decrease is more and more obvious with the increase of oil pressure,while the maximum contact pressure increases with the increase of oil pressure and compression rate;the deformation of the O-ring and the cylinder barrel and the contact surface of the groove is larger,the Mises stress distribution is not uniform and the difference is large,and the concentration phenomenon is obvious,which is the main cause of O-ring failure.This is the main cause of O-ring failure.