| In the mechanical structure,cracks will reduce service life and affect safety performance.Traditional crack repair methods include drilling hole,stick steel plate,welding,etc.,and these methods can apply in certain occasions.However,they aren't suitable for thin-walled steel structure,such as garbage truck and wash car box.Carbon fiber reinforced polymer(CFRP)is of higher stiffness,higher strength,good design,anticorrosion,etc.CFRP reinforcing steel structure does not produce secondary stress and defects,and will apply widely in the crack repairing of steel structure.CFRP reinforcing steel structure will transfer the partial load of steel structure to CFRP through adhesive,so the steel structure,adhesive and CFRP bear the load as a whole part.Its failure modes are very complex,including steel plate's crack propagation,CFRP patch failure,adhesive stripping,etc.Adhesive stripping and steel plate's crack propagation are the main failure forms.If the adhesive strip,it will cause CFRP failure and the repair structure destruction.Steel plate's crack propagation will reduce the effective bearing section and shorten the service life of the structure.Therefore,under the national 863 project funding,the key technology and demonstration of construction machinery general parts remanufacturing(2013AA040203),the adhesive stripping mechanism and the fatigue property of CFRP repairing cracked steel plate are studied in this paper,by means of theoretical derivation,numerical analysis and experimental research method.The main research work and innovative achievements are as follows:(1)Based on the linear elastic mechanics theory,the theory stress formulas of CFRP reinforcing steel plate are derived.CFRP reinforcing steel plate is simplified to two-dimensional plane model.Adhesive shear stress,adhesive normal stress and CFRP longitudinal stress of CFRP reinforcing steel plate are deduced in detail,and the formula of maximum shear stress and maximum normal stress are also obtained.(2)Based on the cohesive zone model,the finite element model of CFRP reinforcing steel plate is established.It reveals the adhesive stripping mechanism and the stripping process by the finite element model.Compared with the "spring","collagen ","the Mindlin plate" simulation respectively,it is based on the continuum damage mechanics and linear elastic fracture mechanics.It can solve the problem of the convergence as the very thin adhesive and be unified description interface damage initiation and propagation.The adhesive stripping process can be divided into the elastic deformation,adhesive to soften and adhesive stripping.(3)Based on the linear elastic mechanics theory,the theory stress formulas of ladder CFRP reinforcing steel plate are derived.It is simplified to two-dimensional plane model.Adhesive shear stress,adhesive normal stress and CFRP longitudinal stress of ladder CFRP reinforcing steel plate are deduced in detail.It compares the bonding performance of ladder paste and aligned paste,and analyzes the influence of reinforcement parameters on the maximum shear stress and the maximum normal stress of adhesive.(4)According to the famous Paris formula,it is presented the fatigue analysis method based on the finite element model of CFRP reinforcing crack plate.Based on the cohesive zone model,the linear and nonlinear finite element models of CFRP reinforcing crack steel plate are established.The linear finite element model,treating steel plate as a linear material,is used to calculate the stress intensity factor of cracked steel plate.The nonlinear finite element model,treating steel plate as a nonlinear material,is applied to analysis adhesive damage mechanism.Based on the simulation results and experimental data,fatigue parameters of C and n value are obtained by the least squares.It forecasts the fatigue life of CFRP reinforcing crack plate.The CFRP reinforcement can improve the fatigue life of crack plate more than a dozen times to dozens times,(5)It's proposed fatigue limit calculation method of cracked steel plate repairing with hole and CFRP.The finite element model of notch steel plate reinforced with CFRP is established basing on the cohesive force theory.With the finite element model,theoretical stress concentration factor of steel plate strengthened by CFRP is calculated.By using experimental data and theoretical formula,it is calculated fatigue notch sensitivity and fatigue notch factor,and established S-N fatigue curve of notch steel plate strengthened by CFRP.The fatigue life has improved 292 times than the notch plate,which is much better than the CFRP reinforcing crack plate.(6)It5s proposed a multi-stage optimization method for CFRP reinforcing center hole steel plate.The method is two steps:first,the Latin Hypercube method is adopted for selecting test sample points,the moving least square is used to fit the agent model,and the adaptive response surface optimization method is adopted to optimize the thickness of basic laminate.Second,considering composite's manufacturing constraints,the stacking sequence is optimized by use of Optistruct software.The the stress of center hole steel plate is distributed more reasonable,and the maximum Mises stress is reduced by 56.6%. |
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