Research On The Effect Of Fillet On The Strength Of CFRP-Aluminum Alloy Single Lap Joints Under Different Relative Humidity

With the development of the automotive industry,lightweight technology has been paid more and more attention.And the mixing of multiple materials has become a trend with the development of the automotive industry.However,traditional bonding technology of material are not suitable for connection of non-materials such as CFRP(Carbon Fiber Reinforced Plastic,CFRP).Adhesive bonding technology can satisfy the connection between CFRP with other materials because of some advantages such as uniform stress distribution,high strength,little electrochemical corrosion and no damage to the adhesion materials.Therefore,adhesive bonding technology has gradually become the trend of material bonding technology.This paper studied on the effects of fillet on the strength of single lap joints by Al-CFRP single lap joints under different relative humidity through the ageing experiments and DIC(Digital Image Correlation,DIC)technology.The content is as follows:Firstly,the mechanical properties of aluminum alloy and CFRP were measured through quasi-static test and three-point bending test respectively.Then the paper studied on the moisture absorption behavior of epoxy adhesive specimens.Then,the paper studied on the effect of fillet on the strength of joints through quasi-static tensile.And considering the factor of moisture,it also studied on the studied on the effect of fillet for joints on strength under different relative humidity.Finally,DIC technology was used to study the effect of the fillet on the strain field of adhesive layer.Through analyzing the effect of fillet on the strain field of adhesive layer in nonageing and ageing condition,the reasons of effect of fillet on the strength were investigated.In addition,the effect of failure mode was analyzed through comparing all experimental group in different ageing period.Through the above researches,this paper can acquire the following conclusions:(1)Fillet increased the strength of single lap joints in non-ageing condition.And fillet also could increase the strength of joints under 40%RH and 100%RH environment ageing period.However,with the increasing of ageing time,the degree of strength changing of fillet and nonfillet joints got less and less.(2)It found that the strength of fillet and non-fillet joints decreased with the increasing of ageing time under same relative humidity.And the more relative humidity,the less strength of single lap joints.(3)The DIC technology was used to analyze the strain field.It found that fillet could change the position of strain concentration.And fillet weakened the effect of peeling force and shear force.This phenomenon indicated that fillet could increase the strength of single lap joint.In addition,through comparing the failure interface and failure mode,it found that the failure mode changed from mixed failure to cohesive failure with ageing time increasing.And fillet made the failure mode change from mixed failure of interface and cohesive failure to mixed failure of interface,cohesion and matrix failure.