Research On Mechanical Properties Of Particle Modified PVDF Matrix Composites

Polyvinylidene fluoride(PVDF)matrix composites have attracted the attentions of many experts and scholars in recent years.Modified composites are widely used in various fields of industry due to their excellent chemical stability,weather resistance,hydrophobicity and piezoelectric properties.In practical engineering applications,people focus on improving the piezoelectric and hydrophobic properties of PVDF composites,but pay less attentions to the mechanical properties and fracture damage of PVDF composites.In this dissertation,polymer composite films modified by SiO₂,carbon black(CB)and polypropylene(PP)are prepared.Uniaxial tensile experiments are carried out on modified PVDF polymer composite film under different notch forms,electric fields and temperatures.The effects of load,notch angle,temperature,voltage and other factors on the damage and fracture properties of the material are investigated.The main contents include the following aspects:(1)PVDF composite is prepared by solution casting and hot pressing.Uniaxial tensile test and cyclic load test are carried out by tensile testing machine.The effects of SiO₂content,notch type and notch size on the damage and fracture properties of PVDF composite films are studied.In addition,the elastic modulus,hardness and friction coefficient of PVDF composites are obtained by nano-indentation test and wear test.(2)The thermoelectric effects and fracture properties of PVDF composites modified by CB,PP and SiO₂are analyzed.CB/SiO₂/PVDF composites are further synthesized on the basis of mechanical studies on CB/PVDF and SiO₂/PVDF composites.PP/SiO₂/PVDF composite is prepared by spraying SiO₂/PVDF solution with PP non-woven fabric as support.The parameters such as capacitance and resistivity of CB/PVDF composites are measured by LCR tester.Uniaxial tensile test is conducted after uniform electric field is applied on the surface of the sample.The mechanical of the material under the combined action of electricity and force is analyzed.The shrinkage test and combustion test of PP/SiO₂/PVDF composites at different temperature are carried out.The thermodynamic properties of the modified composites are analyzed by TG-DTG.(3)The finite element simulation of PVDF polymer material is carried out.The model is verified by comparing with the results of uniaxial tensile test.On this basis,the influence of model parameters and boundary conditions on the mechanical properties of the model is studied.The results show that the setting position of cohesion unit has little influence on the maximum stress but significant influence on the failure strain.Then,the damage notch size and depth of the model are changed for numerical simulation.With the decrease of notch angle and the increase of notch depth,the bearing capacity decreases,and the stress decreases nonlinearly.The stress concentration is obvious in the damage process.(4)Based on the interaction force between SiO₂and PVDF particles,a interaction force model of composites is proposed.Considering the repulsion,attraction and uniform distribution of SiO₂particles,the relationship between the forces and the distance among particles is studied.The random distribution and statistical theory are introduced,the reinforcement mechanism of composites is analyzed.The influence of SiO₂distribution on the elastic modulus,tensile strength and ultimate strain of composites is studied.In this dissertation,the damage and fracture characteristics of PVDF matrix composites under different mechanical,electrical and thermal conditions are studied by experiments,theoretical analysis and numerical simulation.The damage and fracture mechanism of the modified PVDF matrix composites is clarified,which provides valuable theoretical guidance for engineering applications.