| In order to cope with the challenges of environmental pollution and energy crisis brought about by the rapid development of the automobile industry,lightweighting of automobiles has become a top priority.Carbon fiber reinforced composites(CFRP)have gradually become one of the most promising emerging materials in the automotive field due to their high elastic modulus,low thermal expansion,shear strength and other excellent properties.The disadvantages such as low modulus and easy occurrence of brittle failure limit its wide application.The use of high-strength steel plates instead of ordinary medium and low-carbon steel plates can also reduce the weight of the car body structure by reducing the thickness.Combining steel and CFRP into a steel/CFRP composite laminate not only has the advantages of two-phase,but also can take into account the cost,and has better energy absorption characteristics,specific strength,anti-collision performance and damage tolerance than a single material.limit.The bonding interface area structure of dissimilar materials can easily become the weakest part in the whole bonding structure,and the interface bonding strength is a key factor affecting the formability and strength of the laminate.The damage of the interface will greatly reduce the bonding strength,even lead to structural failure.The size of the interface region is only nano-scale,which makes it difficult to analyze and characterize.In order to solve the above problems,this paper uses hot stamping co-cured forming steel/CFRP composite laminates to carry out different surface treatments on the steel plates to obtain the best surface treatment methods for steel.Taking curing temperature,curing time,number of CFRP layers,etc.as the exploration factors,the experimental design is carried out by using the Central Composite Design(CCD),and the process parameters are carried out by the Response Surface Method(RSM)and IV the genetic algorithm.Joint optimization to prepare steel/CFRP composite U-shaped parts with good mechanical properties,bond strength and formability.The main research conclusions are as follows:(1)After different surface treatments of the steel,the results of the single lap joint experiment show that the fracture mode of the degreasing treated sample is steel/CFRP interface cracking,the section of the steel plate has almost no CFRP residue,and the bond strength is the lowest;the steel plate after acid etching treatment There is a small amount of fiber residue in the fracture,and the bond strength is improved;after grinding treatment,the bond strength is greatly improved due to the formation of a mechanical interlocking structure at the interface;after laser treatment,the fracture mode is steel/CFRP interface cracking,CFRP interlayer peeling and fiber fracture,the steel section has a large amount of fiber residual bond strength to achieve the maximum.The results of the one-side three-point bending test show that the adhesion between the degreasing and acid-etched samples is low due to the existence of gaps.After grinding and laser treatment,the interface between steel and CFRP has no gap,and the adhesion is good,which greatly improves the interface adhesion.(2)For the single-lap joint experiment using the center combination design,when the number of CFRP layers remains unchanged,as the curing time increases,aging(including CFRP delamination,fiber breakage,epoxy resin failure,etc.)The negative effect of CFRP interfacial bond strength is more obvious;when the curing time is constant,the ultimate load changes with the curing temperature,and is not affected by the number of CFRP layers;The load has little effect.The ultimate load of the steel/CFRP single lap joint is mainly affected by the curing temperature.The process parameters are obtained by rounding the curing temperature,curing time and the number of CFRP layers by analyzing the response surface curve and genetic algorithm combined optimization.,the ultimate load reaches about 5025 N.(3)For the one-side three-point bending experiment using the center combination design,since the number of layers is higher than that of the single lap joint,aging occurs at a shorter curing time;when the curing temperature,CFRP paving When the number of layers increases,the ultimate load increases significantly;when the curing temperature remains unchanged and the number of CFRP layers is a certain value,the ultimate load does not change with the curing time.The ultimate load of the steel/CFRP unilateral three-point bending test is mainly affected by the curing temperature and the number of CFRP layers,and there is an interaction between the two.Through the joint optimization of response surface curve and genetic algorithm,it is concluded that when the curing temperature,curing time and the number of layers are 153?,88 minutes and 14 layers,respectively,the ultimate load reaches about491 N.(4)For steel/CFRP composite U-shaped parts,the bottom area of the U-shaped parts is less thinned,and the carbon fibers in CFRP enter the micro-columnar structure formed by the laser surface treatment of the steel,which can increase the mechanical interlocking effect.CFRP bonds well.In the punch fillet area,the thickness reduction rate is the highest,the carbon fibers in CFRP do not completely enter the micro-columnar structure on the steel surface,and there are a few pores between the steel and CFRP,but there are no defects such as cracks.There is a resin-rich area in the sidewall area from thin to thick,and the closer to the punch fillet area,the greater the total thickness.The thinning rate is low in the fillet area of the die,and there are uneven pores.There is a thickness change in the flange area,there is no obvious crack,there is a small amount of pores,the forming quality is good,and there is no fiber scattered phenomenon. |
PDF Full Text Request