Study on the Anchorage and Durability Properties of Carbon/Glass Fiber Composite Rod
Author:Li Cheng Gao
Supervisor:xian gui jun
Fiber reinforced polymer composites(FRP)with light weight,high strength,excellent corrosion and fatigue resistance etc.,have became the significant structural materials in civil fields,and repalced partly the steel materials for reinforcing/strengthening/repairing the structures and the new-building structures.Carbon/glass fiber composite rods exploit the advantages of high mechanical properties of carbon fiber and low cost and high deformation of glass fiber,and gradually are used for prestressed cable and anchor structures.The anchorage performance and durability under harsh environment of carbon/glass fiber composite rods are the key problems for the design and application.Therefore,this thesis developed a wedge-type anchorage system for carbon/glass fiber composite rods.The mechanical analysis,finite element simulation and tests were adopted to reveal the stress transferring mechanism in the anchor.This thesis studied the degradation of mechanical properties under the coupling effect of elevated temperature,hydraulic pressure and distilled water(saline water)and the effect on the fatigue performance of carbon/glass fiber composite rods.The main research contents and findings of this study are as follows:(1)Research on the wedge anchorage mechanism of fiber reinforced polymer compositeThe mechanical analysis and tests were adopted to reveal the stress transferring mechanism in the anchor.The analysis and optimization the anchor parameters were conducted for the wedge anchorage system.The ultimate anchorage bearing capacity,anchorage efficiency and failure mode were obtained.The research results show the wedge-type anchorage system applied the chemical bonding of fiber reinforced polymer composite/adhesives and physical extrusion to exert the anchoring action.The stress distribution in the anchor was uniform and there was no slippage between the composite and anchor,the tensile property of composite was fully developed.(2)Research on the anchorage performance of carbon/glass fiber composite rodsAn effcient wedge-type anchorage system for carbon/glass fiber composite rods was developed.The finite element simulation and tests were adopted to reveal the anchorage mechanism.The research results show that the ultimate anchorage bearing capacity of carbon layer anchorage was low owing to the decrease of rod section;the mechanical anchorage had premature failure under the static and fatigue loads owing to initial rod damage from the extrusion;the ultimate anchorage bearing capacity of bonding type anchorage was low owing to the limit of bonding strength between carbon fiber rod and adhesives;the wedge-bond compound anchorage system had uniform stress distribution and there was no stress concentration in the anchor.The ultimate anchorage bearing capacity was high.(3)Research on the durability of carbon/glass fiber reinforced polymer rod immersed in distilled waterThe water absorption and long-term thermal/mechanical properties of composite rods were studied.The evolution law and mechanism of long-term thermal and mechanical properties of carbon fiber rod were studied and the long-term life prediction of interface bonding strength was also conducted.The research results show that the water absorption of carbon fiber rod conformed to Fick law.The immersed temperature and hydraulic pressure increased the diffusion rate of water molecule in the composite rod.The water concentration of composite rod increased with the radial position,immersed temperature,hydraulic pressure and immersed time.After immersion,the post-curing occurred in the resin of composite rod and the glass transition temperature increased obviously.Meanwhile,the water molecule entered into the composite rod and interacted with the resin,leading to the hydrolysis and plasticization of resin and the interface debonding of fiber/resin.The interface bonding strength decreased with the immersed temperature and time and tended to a stable value,and the stable strength retention was dependent on the interface type of fiber/resin.(4)Research on the durability of carbon/glass fiber reinforced polymer rod immersed in saline waterThe water absorption and long-term mechanical properties of composite rods were studied.The effect of immersed temperature,hydraulic pressure and saline solution concentration on the water absorption of composite rod was analyzed and the action mechanism of saline ions concentration on the water absorption was further revealed.The research results show that the radial and longitudinal water absorption of composite rod conformed to Fick law and the longitudinal direction had lower water absorption and larger diffusivity coefficient compared to radial direction.The immersed temperature increased obviously the water absorption rate of composite rod,the hydraulic pressure occupied the second and the effect of saline solution concentration was negligible.Immersion in saline solution led to the decrease of interface bonding strength of carbon fiber rod,and the effect of immersed temperature was most significant.(5)Research on the fatigue performance of carbon/glass fiber reinforced polymer rod immersed in elevated temperature and hydraulic pressureThe fatigue performance of composite rod was studied.The effect of wedge-bonding compound anchorage on the fatigue performance of composite rod was studied.The action mechanism of coupling environment on the fatigue performance was revealed and the evaluation method on the fatigue performance was put forward.The research results show that the fatigue performance of composite rod with the wedge-bonding compound anchorage improved 5.8~7.4 times compared to the mechanical anchorage system.The fatigue failure process was the debonding of shell/core interface,the redistribution of fatigue load and the fracture of shell layer.Immersion at elevated temperature and hydraulic pressure led to the fatigue life increased three times.The improvement mechanism was that the immersion improved the toughness of the resin and released the thermal stress of shell/core interface,decreasing the debonding probability of shell/core interface and the early cracking of resin.This thesis studied the wedge anchorage mechanism and put forward the novel anchorage system suitable for carbon/glass fiber reinforced polymer rod.The simulations and experiments were used to reveal the stress transferring mechanism in the anchor.Based on the Fick law and diffusion mathematics theory,the distribution of water molecule in the composite rod immersed in the coupling environment of temperature,hydraulic pressure and corrosive solution was quantitatively obtained.The degradation mechanism of thermal and mechanical properties of composite rod was revealed and the long-term life prediction model was put forward.The fatigue performance of composite rod under the coupling effect of temperature,hydraulic pressure and corrosive solution was studied.The effect of fatigue parameters and coupling environments on fatigue mechanism was revealed and formed the evaluation method on the fatigue performance of composite rod.