Study On Bonding Quality And Bonding Surface Property Of Composites

As a new technology,the composite material bonding technology has the advantages of lighter structure weight,less stress concentration,etc.,and the surface treatment of the bonding surface directly determines the quality of the bonding.The use of peel plies to treat the surface of the composite material has the advantages of low cost and convenience.However,in practical use,it has been found that the quality of bonding obtained by using different peel plies to treat the composite material is not the same.At present,there are few studies on the effect of different peel plies on the quality of bonding atdomestic and abroad.It is not clear why the use of different peel plies affects the quality of bonding quality.And during the bonding process,the humidity of the environment will cause the material to absorb moisture,and the moisture on the bonding surface may affect the quality of the bonding.Therefore,the influence of the moisture absorption during the bonding process is also an important process parameter.The 970/T300 aviation prepreg is selected in this paper,the composite material laminate is prepared by autoclave molding process,and the surface of the composite material was treated with R60(Polyamide,dry),R60s(Polyamide,dry,coating),P60001(Polyester,dry),and EA9895(Polyester,wet)four different types of peel plies,preparation of test pieces by adhesive bonding for comparative analysis of mechanical properties.At the same time,the surface characterization and microstructure of the composite material is analysed after peel plies treatment were performed,the surface characterization results is compared with the mechanical test results,and the influence of different peel plies is analysed on the quality of the bonding.Meanwhile,the environment humidity by the temperature and humidity testing chamber is simulated,and the influencing trend and impact reason of moisture absorption on the quality of the bonding of the peel plies is investigated.The main findings are as follows:(1)Through the comparison of mechanical properties after bonding,it was found that compared to the surface without bonding treatment,the adhesive strength of the surface was greatly improved,and the mechanical properties were ranked from high to low as EA9895,P60001,R60,and R60 s.(2)Surface tests have found that the surface roughness after strippable treatment is significantly higher than that of the untreated surface.The surface energy also improved compared to the untreated,but the difference was not significant.The surfaces of polyesters and nylons after strippable treatment exhibit higher dispersivity and polarity,respectively.According to the wettability profile,it was found that the epoxy adhesive can be better enveloped by the track line formed by the polyester strippable surface.According to SEM,it was found that both of the two polyamide peel plies and the P60001 peel plies produced a flexible polymer residue when removed from the composite surface.(3)The results of elemental analysis tests revealed that the surfaces of polyesters and polyamides after strippable treatment had higher oxygen and nitrogen contents,respectively,and the presence of silicon was detected on the surfaces of R60 s peel plies and untreated ones.Different bonding surfaces with different stoichiometry will also affect the quality of bonding.(4)With the increase of hygroscopicity,the mechanical properties of composites have shown a significant decline.The mechanical strength of the two types of polyamide strippable cloth specimens increases with the hygroscopicity,and then rapidly decreases and level off.However,the wet peel plies strength of EA9895 during the pre-moisture absorption of the two types of polyester peel plies was lower than that of the P60001 polyester peel plies,and was later higher than the latter.The mechanical properties of the four samples became very similar after 40 days of moisture absorption.After the peel plies specimens were subjected to hygroscopic treatment at different times,the failure mode of the bonding joints was changed.After 40 days of hygroscopic treatment,all the failure modes became cohesive failure,and the failure mode in the early stage gradually changed to adhesion failure.In the untreated specimen,adhesion failure occurred at all times.(5)It can be seen from the SEM images taken after peeling off the bonding surface after wet heat treatment that more voids and defects are formed on the surface of the composite material,while some flexible polymer residues are also observed on the SEM.The surface nitrogen content of two kinds of polyamides after strippable treatment was improved by about 25% than before,indicating that more peel plies components remained on the surface and affected the chemical properties of the bonding surface.