The Research On Multi-scale And Multi-physical Field Coupling Effect On Damage Of PVC Plate Material With Defects

High polymer materials,also known as high molecular materials,possess many features such as rich in resources,good formability,low cost and corrosion resistance,etc..They have been wildly applied in industries including machinery,electronics,energy,information and highly-sophisticated technology,etc.,or other military departments of national defense construction.One hotspots perspective in high polymer multi-field coupling research is embodied in to obtain multifunctional or functionally gradient materials by means of doping,modifying and recombining with high polymer as matrix materials.In the late 1990s,the research team headed by Yuan Longwei,a professor of Xiangtan university,made a series of uniaxial tensile test on nonconductive polymer samples(PolyVinyl Chloride:PVC)in order to study the force-thermal-magnetic field coupling effects in polymer materials elastic-plastic damage failure deforming process.They did tracking and measuring for the first time for that local peaks of magnetic effects caused by PVC materials damage in the process of crack propagation,and proposed the related theories in view of microscopic damage mechanism.The comprehensive advice given by project acceptance experts(the key project(19632030)supported by National Natural Science Foundation of China)not only indicated that the innovative achievements had gotten the international leading position in research of material damage mechanics of rheological body containing defects and had both the important theory significance and a broad application prospect,but also suggested that special attention and continued support should be paid to further experimental verification of the pyro-magnetic effect of polymer materials.This dissertation focus on the more improvement of testing instruments and related theoretical analysis for the force-thermal-magnetic field coupling research in process of PVC plates damage fracture and is the enlarging and deepening works of above-mentioned research.In this paper,PVC boards were made as experimental samples containing different forms of defects by precast and were tested under different uniaxial tensile speed to be damaged and broken.Multi-field coupling effects were studied both on the whole domain of high polymer materials and in the whole elongated process of samples under generalized external loads.That is to say the whole evolution process of temperature field and the thermal-magnetic field distribution rule in the whole material's dynamic damage-fracture zone under generalized external loads were researched,which means that the multi-field coupling effects of force,displacement,temperature and pyro-magnetic field were no longer confined to the position tracking of crack tip of magnetic induction intensity peak and its evolution process.On the basis of sublation in classical fracture mechanics and the microscopic analysis of materials,multi-scale or multi-field coupling constitutive model of high polymer with precast defects were investigated and numerically simulated.New phenomena and new theories about multi-scale constitutive model of polymer materials creep damage were explored and verified experimentally in order to provide theoretical framework and experimental evidence which guide the intelligent high polymer materials elaborate processing,the failure criterion of them under the complex service environment.The main researching and innovative results of this dissertation are as follows:(1)Materials crack propagation is a process of new fracture surface emerging and extending.It not only satisfies the equilibrium conditions in the body,those are in keeping with results of continuum thermodynamics,but also meets a set of new fracture surface 'equilibrium conditions including conservation of mass,momentum,moment of momentum,energy and entropy.In the view of classical fracture theory there is only a single condition such as energy equilibrium in the energy criterion.(2)Crack propagation is a non-equilibrium thermodynamics process.It must accord with the heat conduction and the entropy production according to the second law of thermodynamics or entropy production inequality.The irreversible crack propagation is inevitably accompanied by energy dissipation.These are subjected to further verification by experimental data.(3)A global force-thermal-magnetic field coupling integration test system in'one-key control' mode was developed.A magnetic measurement calibration and anti-jamming technology was creatively developed.A 'Three Dimensions Five Positions'(3D5P)arranged magnetic measurement sensor for weak slowly changing magnetic field detection was also improved.The proposed intensive magnetic sensor with three dimensional dynamic power supply technology could reduce the energy consumption of measuring magnetic components during working and avoid the working temperature among of them overlapping and overloading.It was a kind of theoretical innovation in physics experimental technology.A number of test methods and experimental characterization methods about polymer rheological deformation and fracture field coupling test means were explored.The original experimental results were obtained and achieved to be independent intellectual property rights.(4)The experimental results revealed that,even though in an open environment system,a cooling phenomenon existed during sample's elastic deforming.With the growth of stretching rate,the maximum cooling amplitude increased.Elastic cooling phenomenon showed that there was heat energy dissipating even in materials elastic deformation and the energy dissipation is especially obvious in their viscoplastic deformation.Numerical analyses indicated that the thermal energy dissipation area coupled congruously with the stress gradient distribution.The system input work of tensile load was dissipated through heat dissipation and electromagnetic energy dissipation besides viscous plastic deformation energy dissipation.(5)The induced relations between material volume strain and temperature change were revealed by means of heat transfer theory.When the material volume strain increment is positive,the volume deforming temperature falls down;when the material volume strain increment is negative,the volume temperature grows up and when the material volume strain increment is zero,the volume temperature maintains steady.(6)According to the energy balance equation,the PVC material's heat conduction equation including pyro-magnetic effect was deduced.The obtained coupling term ?1Ji,iT theoretically proved the existence of thermal induced magnetic effect.The thermomagnetic effect was not that the thermal response coupling with applied magnetic field,but was accompanied with that temperature gradient field which caused by material deformation and leads to the generation of magnetic field.These coupling magnetic effects occurred in the interval of high polymer material where temperature gradient change accumulated,and the direction change monotonously.The experimental results indicated that the pyro-magnetic effect was approximately an inplane effect.