| Pasting fiber reinforced composite materials(Fiber Reinforced Polymer,FRP)on the outer surface is an effective way to repair and strengthen damaged timber structures in ancient buildings.In recent years,CFRP has been successfully applied to the reinforcement and restroation of ancient buildings.However,the tensile strength and modulus of CFRP are much higher than that of timber,and the elongation at break is low.Uncoordinated deformation can easily lead to premature failure of the interface.Compared with CFRP,the properties of Flax Fiber Reinforced Polymer(FFRP)is similar to that of timber,and the interfacial stress transfer is more effective.Although the mechanical properties of FFRP are lower than CFRP,the reinforcement efficiency of timber beams is higher.Similar to other externally bonded FRP technologies,FFRP-timber interface performance directly determines the reinforcement effect of FFRP board.Based on the existing theory and mechanism of linear elastic CFRP-timber structure interface bonding,this paper adopts a single-sided shear peel test to systematically study the bonding performance of FFRP-timber structure interface,and analyzes the test results with finite element simulation.The verification provides an important reference for the design and analysis of non-linear elastic FFRP materials to strengthen timber structures,and promotes the large-scale application of green FFRP in engineering structures.The main contents of this article are as follows:(1)The FFRP composite sample was prepared by hand wet lay-up process,and the FFRP tensile stress-strain relationship was tested.Based on the material mechanics analysis,the stress-strain constitutive model of the FFRP material was established.(2)Study the wettability of the adhesive and the timber surface,the interfacial bonding mechanism of flax fiber-resin matrix and its effect on the interlayer shear strength of FFRP;Researches was made about FFRP performance,bond length and bond width,and their effect on the stress-strain distribution,failure mode,bond strength and stiffness of FFRP-timber structure interface.(3)Based on the single-sided shear test,FFRP-wood structure interface bond-slip model was established;the effective bond length model was found considering the properties of FFRP,wood and adhesive;theoretical analysis of the stress distribution of the FFRP-timber structure interface was made,and the finite element model was verified to the test results;the influence of FFRP properties on the bonding performance of the FFRP-timber structure and its mechanism was analyzed.The test results showed that the FFRP stress-strain curve has a two-stage properties;the mechanism of stress transfer in the FFRP-timber interface is to migrate from the loaded end to the free end,the interface has an effective transfer area;the increase of the bond width has little effect on the axial strain of the FFRP sheet,interfacial shear stress and the corresponding slip,but tensile utilization rate was lower when the sheets are wider;The modified Popovics model can fit the bond-slip relationship between non-linear material FFRP and timber. |
