Study On Insulation And Thermal Mechanical Properties Of Epoxy Resin Modified By Hexagonal Boron Nitride

The lightweight of high-speed electric multiple units(EMUs)traction system can save a lot of electric energy and reduce the maintenance cost.Therefore,a lightweight method of using dry-type on-board traction transformer(OBTT)instead of oil immersed on-board traction transformer is proposed.Epoxy resin(EP)is used for dry-type OBTT pouring,but due to the high loss and poor heat dissipation conditions of dry-type OBTT,higher requirements are put forward for the thermal conductivity of epoxy resin.In this dissertation,hexagonal boron nitride(h-BN)was used as thermal conductive filler to modify epoxy resin.The effect of h-BN content on the properties of epoxy resin was studied based on molecular dynamics simulation and experimental test.Firstly,the molecular dynamics model of EP/h-BN composites with different h-BN content was established,and the thermal conductivity,glass transition temperature,thermal expansion coefficient and static mechanical properties of the composite model were calculated.The results show that when the content of h-BN is 40 phr,the EP/h-BN composite meets the requirements of dry-type OBTT thermal conductivity.At this time,the glass transition temperature of the composite material is increased compared with EP,and the rigidity of the material is also stronger.Then,the microstructure parameters of the model were calculated,and the variation law of thermal-mechanical properties was explained by microscopic mechanism.Secondly,the preparation scheme of the sample was determined based on the simulation results,and EP/h-BN composite samples with different h-BN content are prepared.The thermal conductivity of the sample was measured and compared with the calculated results of molecular dynamics.It is proved that the molecular dynamics model is effective and reliable.Then the volume resistivity,dielectric properties,breakdown characteristics,tensile and impact tests of the samples were carried out successively.The results showed that the electrical insulation performance of the epoxy resin composite did not deteriorate significantly after adding h-BN,but the toughness of the composite decreased,which increased the risk of cracking of the composite due to frequent vibration of EMUs trains during dry-type OBTT operation.Finally,in view of the decline of toughness of EP/h-BN composites,EP/h-BN composites were toughened by adding EHTPB to EP/h-BN composites with 40 phr h-BN content.The results show that the effect of improving the toughness of EP/h-BN composites is the best when the content of EHTPB is 10～15phr,and the thermal conductivity of EP/h-BN/EHTPB composites can meet the requirements of dry-type OBTT when the content of EHTPB is0～15phr.The addition of EHTPB will not lead to the deterioration of the electrical insulation performance of EP/h-BN composites.The comprehensive thermal-electro-mechanical test results show that when the content of h-BN is 40 phr and the content of EHTPB is 10 phr,the toughness of EP/h-BN/EHTPB composites can be significantly improved,and the thermal conductivity and electrical insulation properties of the composites meet the requirements of dry-type OBTT.