Research Of Heat Transfer And Adhesion Properties Of Magnetorheological Elastomer

Magnetorheological elastomer(MRE)is a kind of magnetically controlled smart materials.Its mechanical properties are widely studied and are often used in shock absorption systems.In today's engineering applications,MRE is gradually being ex-plored for potential applications in electromagnetic RF absorbers,wall climbing robots,biomedical patches,and more.However,the current research on MRE performance in this application is still in a semi-blank state.These properties include magnetorheologi-cal elastomer thermal conductivity,surface mechanical properties,adhesion properties,etc.Therefore,the researchers prepare a small-size MRE film in the thickness direc-tion.In this thesis,the heat transfer capability as well as surface mechanical properties,surface adhesion propertiesof the MRE film are studied by experimental methods,as preliminary exploration of the intelligent application of MRE film.The main research contents of this thesis are as follows:This thesis first investigates the enhancement of thermal transport in Polydimethyl-siloxane(PDMS)thin films with aligned Carbonyl Iron particles(CIP)embedded,also known as magnetorheological elastomers(MREs).Flash method is used to measure the effective thermal conductivity of PDMS/CIP thin films in the direction parallel to the magnetic field.Under an external magnetic field,the CIPs form chain-like structures,which become effective thermal paths inside the composites.Hence,a significant in-crease in the thermal conductivity of aligned MREs has been achieved compared with the composites prepared without magnetic field.The effects of volume fraction of CIP,and pre-structured magnetic flux density have been studied also.The increasing of CIP volume fraction from 5%to 20%,brings about a twofold improvement of the thermal conductivity of the aligned MREs.For 2.5 ?m CIP doped MREs with a volume frac-tion of 10%,when pre-structured magnetic flux density changes from 0 mT to 100 mT,the thermal conductivity increases by 50%approximately.However,further increase of magnetic field intensity only leads to slight increase of thermal conductivity.SEM inspections demonstrate that the chain length keeps growing with the strength of pre-structured magnetic field while structure transition turns into lateral congregation as the strength of pre-structured magnetic field reaches 100 mT.An FEM model is proposed to investigate in detail the relationship of MREs thermal conductivity and inner chains.This work provides an effective way to improve thermal conductivity of MREs used for electromagnetic Radio-Absorbers and builds a connection of MREs thermal properties and its inner microstructures.Next,the surface mechanical properties of MRE are studied.Smooth surface MRE films are firstly achieved.Then,the roughness of the smooth surface is investigated.It is found that although the roughness increases with the increase of CIP mass fraction,the average arithmetic height of the surface is less than 1?m and the smoothness is good.It is found that the elastic modulus of MRE increases with the increase of CIP mass fraction,and it shows a significant upward trend when the mass fraction reaches 78%.The MRE surface energy is confirmed to be unaffected by the CIP mass fraction,possibly because the sample exhibits a thin layer of pure PDMS film.However,the experimental study of the surface adhesion of MRE showed a trend of decreasing first and then increasing with the increase of CIP mass fraction,and then the influence of stiffness change on the adhesion of smooth surface is introduced.