Experimental And Theoretical Investigation On Mechanical Properties Of Silane-modified Polyurethane Sealant

Silane-modified polyurethane sealant has been used in automotive,construction,electronic packaging,military and aerospace.It has the characteristics of well bonding,high tensile strength,strong recovery,excellent elasticity and wear resistance.In the actual application,different loading conditions and environmental factors have effects on the mechanical properties of this sealant.Therefore,it is of great significance to deeply understand the mechanical properties and influencing factors of silane-modified polyurethane sealant material.The main research contents and results of this thesis are as follows:(1)Silane-modified polyurethane sealant was subjected to uniaxial tensile experiments under different temperature,hygroscopic degree and strain rate conditions.The experimental results showed that the sealant material had temperature dependence and hygroscopic degree dependence under a constant strain rate.The material exhibits obvious rate dependence under high temperature and high hygroscopic degree.However,the rate dependence of this material is not obvious under normal temperature and humidity.(2)Multi-step cyclic loading experiments on the silane-modified polyurethane sealant at different temperatures were conducted.The experimental results showed that the material experienced stress relaxation under cyclic loading,and the viscous behavior was evidently observed in the first cycle.The cyclic stress relaxation of the materials was not obvious due to the higher cyclic strain loading history,while the cyclic stress relaxation of the material continued to occur for the lower strain loading history.The cyclic strength and the ability to resist cyclic loading of the material decreased with the increase of temperature and higher loading history.(3)To analyze the influence of temperature and strain rate on the mechanical properties of the silane-modified polyurethane sealant,combined with the non-linear viscoelastic behavior of the material,and the influence of factors such as temperature and strain rate on the mechanical behaviors based on the Johnson-Cook model.A new phenomenological constitutive model was proposed which considered the influences of temperature and strain rate.The nonlinear viscoelastic deformation behavior of silane-modified polyurethane sealant could be described by the proposed model.The prediction results were in good agreement with the experimental data,indicating that the proposed model can accurately describe the effects of temperature and strain rate on the mechanical properties of the material.(4)The experiments have shown that temperature and hygroscopic degree had effects on the mechanical properties of the material.In order to describe the influence of hygroscopic degree on the mechanical properties of silane-modified polyurethane sealant,based on the proposed constitutive model above,a nonlinear viscoelastic constitutive model affected by hygroscopic degree and strain rate was formed,and the parameters with the effect of hygroscopic degree were determined by the tests.Comparing the calculation results of the model with the experimental results showed that the model well described the influence of hygroscopic degree on the mechanical properties of the material.