| The quality of car components is the basis of ensuring the normal driving of automobile,and the ball joint is an important part of automobile steering system,which determines the accuracy and safety of car steering.Ball joint works under high temperature and high pressure muchly,so the ball pin and the ball bearing will have violent friction action,which will lead to the wear failure of the ball joint structure.Polymer self-lubricating composite materials have excellent properties such as high strength,good self-lubrication and wear resistance The composite material is used as a friction pair material in the structure of automotive ball joints,which will improve the performance of automotive steering Reliability,reducing the use and maintenance costs of auto parts is of great significance.The ball joints structure generally uses metal steel and polyoxymethylene(POM)plastic to form a friction pair,but POM has limited high temperature resistance and wear resistance.In the absence of grease,the parts are prone to excessive wear and failure.Causing serious harm to the driving safety of the car.Polyimide(PI)is a kind of high temperature resistant anti-friction and wear-resistant material.As a friction pair material,it has been widely used in many engineering fields.It’s an ideal material to replace POM.In order to solve the friction and wear problems in the ball joints,this paper uses PI resin as the matrix material,PBO fiber and graphene oxide as the reinforcing phase,and uses the lanthanum salt modifier(LSM)to modify the surface of the PBO fiber.La-GO-La-PBO multi-scale reinforcement reinforced PI composite material was designed and prepared.The tribological behavior of La-GO-La-PBO/PI composites under dry friction was studied,and the effects of La-GO multi-scale surface modification on tribological properties of composites were analyzed.The details are as follows:(1)La-GO was used to modify the surface of PBO fiber,and the optimal modification process parameters were determined through TEM analysis,and La-GO-La-PBO multi-scale reinforcement and its PI-based composite material were prepared.GO-PBO fibers were used as the reference objects which formed by physical absorption of GO on the fiber surface and GO-PBO/PI composite materials were prepared The effect of La-GO modification on the mechanical properties of PI composites was studied by mechanical properties test and fracture SEM morphology analysis.The results show that La-GO composite modification can effectively improve the mechanical properties of La-GO-La-PBO/PI composites compared with single GO modification.When the LSM concentration is 0.3 wt%,GO mass fraction is 0.05,the mechanical properties of PI matrix composites are the best.(2)The PBO fiber before and after the surface modification treatment was characterized and analyzed by physical and chemical methods,and the structure model of La-GO composite modified PBO fiber was established.The structural model of La-GO modified fibers was established and the mechanism of the modification was analyzed.The results show that the lanthanum ions in the lanthanum salt modifier are successfully introduced into the fiber surface,and the lanthanum ions reacted with the GO to adsorb the GO to the fiber surface,increasing the roughness of PBO fiber surface and the number of active functional groups.GO and Lanthanum ions on the fiber surface can continue to perform chemical bonding and mechanical riveting with the PI resin when the PBO fiber is combined with the resin matrix,which enhances the interfacial adhesion of the fiber in the matrix and thus improves the mechanical properties of La-GO-La-PBO/PI composites.(3)In a dry friction environment,the effect of La-GO composite modification on the tribological properties of La-GO-La-PBO/PI composite materials was studied under different normal loads and reciprocating sliding frequencies.The research results show that the friction coefficient of composite materials decreases with the increase of normal load and reciprocating sliding frequency,and the specific wear rate is on the rise.Compared with pure PI and GO-PBO/PI composite materials,La-GO-La-PBO/PI composite materials have the lowest coefficient of friction and specific wear rate.La-GO modification helps to form a uniform and dense transfer film between the friction surfaces,which effectively improves the friction state between the friction pairs and improves the tribological properties of composite materials.In this paper,PBO fibers were modified by La-GO.The modification results were characterized,and the surface modification mechanism was charactered.The mechanical and tribological properties of La-GO modified PBO fiber reinforced polyimide composites were studied.A composite material with characteristics of excellent mechanical and tribological properties would provide experimental data and theoretical support for the development of new types of friction pair materials for vehicles... |
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