Research On The Properties Of Heterostructure Adhesive Interface With Modified Short Carbon Fibers

The heterogeneous structure bonded by glass fiber reinforced plastic(GFRP)and aluminum alloy together not only maintains the performance advantages of traditional metal materials but also contains the characteristics of light weight and high strength of composite materials.However,the mechanical properties of the adhesive layer(epoxy resin)in heterostructures are far inferior to composite materials and metal materials,especially when the adhesive structure is subjected to shear loads.At that time the adhesive layer becomes the weakest part in the entire structure,which leads to cracks may be generated from the adhesive layer and propagate to the entire interface when the load increases and resulting in the failure of the heterostructure function.Therefore,strengthening the adhesive layer(epoxy resin)is an important way to improve the performance of the adhesive interface.But at this stage,there are a series of problems such as poor dispersion of short carbon fibers in the adhesive layer,poor mechanical properties of the modified short carbon fiber,low precision of the test specimen of the adhesive layer,and an unknown strengthening mechanism of the adhesive layer filled by the short carbon fibers.To deal with these problems,through the combination of theoretical analysis and process tests,this paper carried out the research on adhesive interface properties of heterostructure containing modified short carbon fibers(MSCF).Oxidized short carbon fibers were made by oxidation process to improve the dispersion in the adhesive layer.A grafting process was used to produce MSCF on the basis of oxidized short carbon fibers(OSCF)to improve the physical properties of carbon fibers.Separately,standard tensile test pieces and single-lap specimen were made to determine the effects of carbon fibers on the adhesive layer and adhesive interface,and the strengthening mechanism was determined by characterizing the fracture surface.Finally,the theoretical model was established on the basis of experimental data and mechanism analysis.The prediction of modulus and strength were obtain by theory analysis on the adhesive layer reinforced by carbon fibers.The results showed that OSCF had a good dispersion in the adhesive layer,which solved the problem of reduced tensile strength of the adhesive layer due to "agglomeration" caused by the short carbon fibers.Adding MSCF solved the problem of poor reinforcement effects of OSCF on the elastic modulus of the adhesive layer.In the experiment of standard tensile test piece,it was found that the tensile strength first increased and then decreased with the increase of OSCF and MSCF mass fraction,and the elastic modulus increased monotonously.When the failure occurred,the fiber had three forms of damage: debonding,breaking and pulling.In the experiment of the single-lap specimen,it was found that the tensile strength of the specimen increased first and then decreased with the increase of the MSCF mass fraction and the aspect ratio.When the length of the MSCF was basically the same as the thickness of the adhesive layer,the interface strengthening effect was the most obvious.The shear strength of GFRP / Al single lap specimen added by MSCF(1wt%,aspect radio: 40:3)was higher than the control group by 37.85%.When the failure occurred,adding the MSCF allowed GFRP to participate in the process of preventing crack propagation,thereby enhancing the interface performance.The predicted figures completed by establishing the model of tensile strength and elastic modulus of the adhesive layer added by short carbon fibers were in good agreement with the experimental results.