Study On The Bonding Surface Treatment Process And Its Mechanism Of Thermosetting Resin Based CFRP

In this paper,two kinds of thermosetting CFRP surface called TMJ and TMB,as the research object,are studied through a variety of surface treatment on the surface of CFRP,to explore the impact of surface physical and chemical properties on the surface of CFRP.Through the analysis of two kinds of CFRP and four kinds of adhesive bonded joints,their fracture morphology,strong pull and load displacement curve,surface physical and chemical changes caused by the influence of adhesive joint performance,and the mechanism of its influence are researched.By comparing and analyzing two different surface states of CFRP,different adhesives,we try to give the most suitable surface treatment technology for CFRP with different surface states,various kinds of adhesives.Through the analysis of the tensile strength and fracture morphology before and after the grinding and primer treatment,it is found that the difference between TMJ and TMB is only that there is a layer of densely-connected release agent on the surface of TMJ,but it will seriously affect all kinds of surface treatment.As a result,one minute of sanding of artificial sandpaper cannot completely remove the residual surface release agent.Compared to the TMB surface,the TMJ surface of the residual mold release agent has better connection with the epoxy adhesive and has worse connection with the polyurethane adhesive.Plasma treatment for epoxy adhesive has a very good performance,but for the PU adhesive bonding strength is less effective.Plasma treatment will also cause physical and chemical changes in the surface of the CFRP.It will form a large number of micron-scale ravines in the surface and improve the contact area,which is very effective for lower viscosity EP adhesive,but not for higher viscosity PU adhesive.Due to the introduction of oxygen-containing functional groups,such as hydroxyl,epoxy,while improving the surface free energy polar,plasma treatment is obvious for EP rubber surface with poor reactivity,but almost no effect for PU adhesive which has no significant reactivity with the oxygen-containing groups.Laser processing is a very effective treatment for roughness-sensitive epoxy adhesives and is also a very effective treatment for surfaces that are not easily removed due to unwanted retention during shipping or manufacturing.However,laser treatment is not effective for PU adhesive.But due to the presence of the weak boundary layer,laser treatment will reduce the bonding strength.In this paper,the mechanism of surface treatment to improve the bonding strength is showed.The connection between adhesive layer and the interface force is equal to the connection strength per unit area multiplied by the connection area.All the treatment must change these two points to change the strength of the adhesive joint.Plasma treatment will increase the content of active functional groups which can increase the formation of chemical bonds per unit area and increase the unit strength.At the same time,it can also increase the surface area and increase the connection area,to improve the strength of the joint.Laser treatment,grinding process will generating grooves,not only increased the surface area,but also produced a mechanical interlock structure,improve the strength per unit area joints.