Study On Mechanical Properties Of Carbon-glass Fiber Hybrid FRP Tendons

Fiber Reinforced Polymer(FRP)has the advantages of light weight,high strength and good corrosion resistance,and has become a new type of materials used to replace steel bars in concrete structures.At present,researches on FRP tendons are mainly focused on their tensile properties.Two or more types of fibers are mixed as the reinforcing phase,and the brittle fracture problem of FRP tendons is solved by generating hierarchical fracture in the tensile state,which is similar to the plastic failure process of steel bars.In fact,FRP tendons may be in a coupled state of tension,compression,shear and bending stress at the same time in concrete members.Accurately grasping the basic mechanical properties of FRP tendons with tensile ductility is of great significance to their wide application in concrete structures.Therefore,different parameters of the bisphenol A epoxy vinyl carbon/glass fiber hybrid tendon(C/G-HFRP tendon)were systematically studied on tensile,compression,shear and interlaminar shear properties in this article.The main research contents are as follows:(1)According to the mixing theory,the different parameters of C/G-HFRP tendons were produced,including the volume fraction of carbon fiber(1/10～1/ 4),the distribution form of the carbon fiber(centralized or dispersed on the cross section)and the volume fraction of the total fiber(50%,60% and 70%),and the tensile test was carried out.The results showed that when the carbon fiber volume fraction was lower than its critical fiber volume fraction,the C/G-HFRP tendons exhibited obvious plastic failure characteristics under tension.The tensile stress-strain curve could be divided into linear elastic section,pseudo-yield section and stress hardening section.At the same time,the volume fraction and distribution of carbon fibers had a significant impact on the tensile ductility of C/G-HFRP bars.And,the tensile ductility of C/G-HFRP tendons became more obvious as the volume fraction of carbon fiber decreased.What’s more,when carbon fiber was distributed on the cross section,the tensile ductility of C/G-HFRP tendons was better than that of concentrated distribution,and when it yielded,the reduction of[ stress was smaller.By the way,the tensile properties of C/G-HFRP tendons were the best when the total fiber volume fraction was 60%.(2)The compressive strength of C/G-HFRP bars with different mixing ratios,mixing methods and fiber volume ratios were measured by the un-end-constrained compression test method,which was about 40% of its tensile strength.Most of the C/G-HFRP bars without end restraint started to break from the end under compression,and the transverse deformation occurred under the Poisson Effect,which led to split failure.In addition,the compressive strength of C/G-HFRP bars decreased as the content of carbon fiber increased,and the dispersed distribution of carbon fibers was better than the concentrated distribution.And the fiber volume ratio was negatively correlated with the compressive strength of C/G-HFRP bars.(3)The transverse shear test of C/G-HFRP bars with different mixing ratios,mixing methods and fiber volume ratios was carried out using compression shears,and the transverse shear strengths obtained were all above 200 MPa,which was about1/5 ～1/4 of its tensile strength.The failure process could be divided into three stages:fibers and resin worked together,the resin quit working,and the fibers were gradually bent to produce normal stress;the fibers bore all the load.(4)A new type of direct shearing device with clear force and simple operation was designed.At the same time,the interlaminar shear strength of C/G-HFRP bars was tested,combined with the short beam shear method and double-notch compression method for comparison.The results showed that the interlaminar shear strength of C/G-HFRP bars tended to increase first and then decrease,with the increase of carbon fiber content,and the strength of carbon fiber dispersed distribution was higher than that of concentrated distribution.In addition,there was a fiber volume ratio that can optimize the interlaminar shear performance of the C/G-HFRP bars.And among the three shearing methods,the direct shearing method could better reflect the influence of fiber mixing on the interlaminar shear strength of FRP bars.