Simulation And Experiment Research On Damage Behavior Of The Adhesive Layer Of CFRP T-joint

CFRP T-joint is a kind of typical composite material orthogonal connection structure to transmit load between different orthogonal planes and it has been widely used in the structures of aerospace.However,CFRP T-joint is vulnerable to be damaged during the operating process due to the presence of a new internal combined interface when subjected to the tensile loads.What's worse,these damages often occur within the adhesive layer of the T-joint which are difficult to observe in time and will cause severe damage to the safety of structure.So the use of effective methods to detect the internal damage is needed.However,due to the lack of understanding of the damage behavior of the adhesive layer of CFRP T-joint,the development of CFRP T-joint damage monitoring is restricted.Therefore,it is very important to study the damage behavior of the adhesive layer of CFRP T-joint for the damage detection of CFRP T-joint.In this paper,the damage behavior of the adhesive layer of CFRP T-joint was studied by simulation and experimental methods.The main contents are as the followings:Firstly,the stress state of CFRP T-joint under external tensile load was studied by means of composite mechanics.Also,the damage judgment criterions of CFRP adhered and adhesive layer cohesive zone model were analyzed.Secondly,a finite element model of CFRP T-joint based on cohesive zone model was established to study the damage behavior.The results show that:(1)During the loading process,the adhesive layer between the skin and the L-plate is damaged firstly.(2)When the adhesive layer is not damaged,the stiffness of the adhesive layer is not degraded.With the increase of the tensile load,the peel strain and the shear strain of the adhesive layer increased linearly,and the strain of the vertical-plate as well as the displacement of CFRP T-joint increased linearly too.(3)When the adhesive layer is damaged,the stiffness of the adhesive layer is degraded.With the increase of the tensile load,the growth rate of the peel strain and the shear strain as well as the displacement is obviously accelerated,but the growth rate of the vertical-plate strain is decreased with the increase of the load.Until the adhesive layer cracks,the peel strain and the shear strain of the adhesive layer,the strain of the vertical-plate reaches the maximum.Finally,CFRP T-joints were prepared by autoclave process and secondary bonding.The damage behavior of the adhesive layer of CFRP T-joint subjected to the external tensile load was verified experimentally.The experimental results show that: The location of the crack,the displacement of the experiment and the strain variation of the vertical plate are consistent with the simulation.The strain variation law of the vertical-plate and the displacement variation law can provide the theoretical basis for the damage detection of CFRP T-joint.