Study On The Mechanical Properties Of Single Lap Joints Made By Two-dimensional Triaxial Hybrid Braided Composites And Steel Sheet

Due to its high specific strength as well as stiffness,excellent fatigue and corrosion resistance,outstanding designability,fiber reinforced polymer(FRP)material has been widely used in modern industries including aerospace industry,automobile industry and shipbuilding industry.However,as a result of the challenges from its high cost and time-consuming processes,hybrid FRP-metal structures are inevitably used in engineering products.In addition,the woven FRP is usually more preferred instead of uniaxial FRP for those structures,because the woven FRP has more uniform in-plane mechanical properties.Recently,hybrid woven carbon/glass fibers has been employed as reinforcement phase to make low-cost composite.Therefore,the joints between hybrid woven composites and metals are inevitably needed for the hybrid FRP-metal structures.This work aims at investigating the mechanical properties of the joint composed of hybrid woven composite and steel,which has not been well understand so far.In order to study the mechanical properties of FRP-steel joint,both the experiments and the finite element method(FEM)analysis were applied in the work.First,the mechanical properties were investigated by various experimental tests.Then,the appropriate FEM model was established and validated based on the experimental results.Besides,based on the FEM model,the effects of various design parameters on the mechanical properties of the joints were systematically investigated to optimize the geometrical structure of the joints.Firstly,the mechanical tests including longitudinal and transverse tension and compression as well as shear tests were performed to obtained the basic material parameters of the hybrid weave FRP.Then,numerical simulations were conducted based on FEM model considering Hashin failure criterion.The FEM model was validated successfully since the simulation results matches well with the test data of the hybrid weave FRP.For the adhesive joint tests,the failure mode was demonstrated as interfacial failure and cohesive failure,and the average shear strength was 8.67 MPa.It was proved that the failure of the adhesive joint can be effectively simulated by the cohesive element based FEM model.For the riveting joint tests,the failure mode was demonstrated as the failure of the rivet under the combined effects of the tensile stress and shear stress.And composites failure in the region around the riveting hole was also observed duo to the local stress concentration.It was demonstrated that the failure of the riveting joint can be effectively simulated by the ductile damage based FEM model.Based on the validated numerical simulation models of adhesive joint and riveting joint,the FEM model including Hashin criterion,cohesive element and metal ductile failure criterion was developed to simulate the mechanical properties of the hybrid joints,which is verified to be applicable since the simulation results are agree well with the experimental data.For the hybrid joints,the failure of adhesive layer was firstly happened with the increase of displacement.Then the rivet was fractured after the total failure of the adhesive layer.The average shear strength was 9.25 MPa for the hybrid joints.Since the average shear strength of the hybrid joints are higher than that of the adhesive joints,the application of rivets can improve the mechanical properties of the strength of the adhesive joints.Additionally,the geometrical structures of the joints were optimized based on the developed FEM model by studying the influences of the design parameters on the mechanical properties of those joints.For the adhesive joints,the ultimate load decayed with the increase of the thickness of the adhesive layer or the overlapping length of the joints if the concerned parameters varies in a certain range.For the hybrid joints,the ultimate load decreased with the growth of the thickness of the adhesive layer,while it increased slightly with the increasing of the side-diameter ratio.For the hybrid joints,if all the rivets were arranged in one or two rows,the ultimate load firstly increased,and then decreased with the rising number of the rivets.For the hybrid joints with the same number of the rivets,if the joints were arranged in one row,the ultimate load was higher and the damage area of the FRP plate was smaller.Thus,by adding the aid patch and reducing the eccentricity,both the loading capability and the energy absorption can be improved simultaneously.