Mechanical Performance And Recovery Stress-Temperature Relationship Of FRP/SMA Composites

Due to the environmental influences(corrosion and weathering)and traffic loading(cyclic loading,dynamic loading,etc.),bridge structures are more likely to be damaged and fractured during service life,which has already been one of the most primary issues in bridge engineering.There are several traditional methods used to strengthen and repair bridge structures,such as increasing section,external reinforcing steel plate,external prestressing and so on;However,increasing section will increase self-weight as well,external reinforcing steel plate will also suffer corrosion and fatigue,and local cracks are easy to occur near the steering and anchoring devices of external prestressing.Therefore,it is necessary to explore new methods to strengthen and repair bridge structures.According to past research,compared with traditional strengthening methods,using composite materials for bridge rehabilitation and retrofits has its unique advantages in the field of infrastructural rehabilitation.Therefore,the paper focuses on research the feasibility of using composite materials combined with fiber reinforced polymer(FRP)sheets and shape memory alloy(SMA)wires to strengthen and improve service life of bridge structures,and the research of FRP/SMA composite specimens are conducted as follows:(1)In this paper,a large number of experimental tests about physical and mechanical properties of SMA and FRP were conducted,and the results were obtained.Firstly,the effects of prestraining level,times of cycling and loading rates on the uniaxial tensile properties of NiTi SMA wires were studied to determine the optimal prestraining level.Then the phase transition temperature of SMA wires were tested,and four characteristic phase transition temperature values of SMA wires were determined.Finally,the influence of the Current and powering-time on the temperature of SMA wires were tested.Uniaxial tensile mechanical tests of FRP and epoxy specimens were also carried out.(2)In this paper,two kinds of FRP/SMA composite specimens by made of CFRP unidirectional sheets embedded with pre-strain NiTi SMA wires were produced.The first type of composite specimens(type I)were prepared for the uniaxial tensile test,with considering variables of the number of SMA wires and SMA diameter;The second type of composite specimens(type II)were prepared for the restrained recovery test,with considering variables of pre-straining level.(3)In this paper,the restrained recovery test of SMA wires and FRP/SMA composite specimens(type II)were conducted to verify the feasibility of SMA phase transition induced by electrical heating method,with designing a set of electric devices including power supply,temperature recording device,temperature sensors and so on,and conducting restrained recovery test with the joint of universal testing machine.The test results suggest that recovery stresses of SMA wires showed an obvious rising trend with the rising of temperature,and the maximum recovery stresses of SMA wires and FRP/SMA composite specimens(type II)increased with the increasement of pre-straining levels,which verified the feasibility of the restrained recovery test of FRP/SMA composite specimens induced by electrical heating as well.