| As a dielectric elastomer material,silicone rubber composite material has been widely used due to its advantages such as large deformation,high dielectric constant,high energy density,low viscosity dissipation,short response time and excellent processing performance.The fatigue resistance of silicone rubber composites is a key factor affecting the service life of dielectric elastomer generators.Therefore,the study of fatigue life and hysteresis heat generation is very necessary for the design of silicone rubber materials and their products.Compared with traditional experimental research,the finite element numerical simulation method is very effective for solving the complex stress and strain problems of rubber products.It can provide theoretical guidance for the design of rubber materials and products in the early stage,and has the advantages of short cycle and low cost.This thesis aims to develop a numerical simulation algorithm based on the fatigue life and hysteresis heat generation of viscoelastic rubber materials under dynamic loads to guide the optimal design of silicone rubber composite materials and their products.The main research work of this dissertation is as follows:(1)Based on the theory of fatigue crack growth,a multi-axial fatigue life algorithm for rubber was developed using Python language.The fatigue life and cracking direction of natural rubber thin-walled ring-shaped specimens under multiaxial load were calculated.The fatigue life calculations under pure and tensile/torsional loads are distributed between the 0.7-1.0 times dispersion lines of the experimental data,and the calculated cracking direction is very close to the measured value,which verifies the reliability of the established rubber multiaxial fatigue life algorithm.(2)Using the developed rubber multi-axial fatigue life algorithm,the fatigue life of biaxial tensile specimens,dumbbell-shaped uniaxial tensile specimens,planar tensile specimens and cross-shaped specimens of silicone rubber were calculated,and the calculation results of fatigue life under tension and plane tension are experimentally verified.In order to take into account the electricity performance and fatigue life of the material,it was proposed to use the total energy density to evaluate the comprehensive performance of the material.The total energy density refers to the product of strain energy density and fatigue life.The cracking energy density(Wc),strain energy density(W)and the ratio of the two(Wc/W)under different biaxial degrees were calculated.The results show that W is the largest under equivalent biaxial stretching and Wc/W is the smallest,which indicates that silicone rubber may have the best overall performance under equivalent biaxial stretching.The above conclusions were verified by comparing the theoretical calculation values of the total energy density of silicone rubber materials under different loading modes.(3)Based on the theory of nonlinear viscoelasticity,a hysteresis heat generation algorithm for pure shear thin film specimens of silicone rubber is established.The effect of the number of layers on the hysteresis temperature rise of silicone rubber pure shear specimens under different strain peaks was studied.The results show that under a certain strain peak,the surface temperature increases linearly with the increase of the number of film stacks,and the larger the strain peak,the higher the surface temperature.In addition,the sensitivity of the crack growth characteristics of silicone rubber materials to temperature was studied.The results show that at high temperature,the crack growth rate(da/dN)of silicone rubber material has a power-law function relationship with the tearing energy(T),and under the same tearing energy,with the increase of temperature,da/dN increases sharply.The fatigue life of pure shear sheet of silicone rubber under different strains peak and temperatures was calculated.The results show that under a certain strain peak,the fatigue life decreases with the increase of temperature. |
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