| The stay cable is one of the key factors of the cable-stayed bridge.It is the main load-bearing component and can transfer the main beam and deck load to the bridge tower.Due to the characteristics of low damping,large flexibility,and light weight,cable-stayed structures are prone to significant vibrations under dynamic loads such as earthquakes,wind and rain,traffic,and pedestrians.And as the span of the cable-stayed bridge becomes longer and longer,the length and flexibility of the cable will also increase,and the vibration control problem is also increasingly prominent.In response to this problem,this article starts with the vibration reduction measures for auxiliary cables of stay cables,and intends to use Shape Memory Alloy（SMA）instead of traditional steel strands as auxiliary cables.The main innovations of this article are as follows:1.By adjusting the mechanical properties and functionality of commercial nickel titanium alloys through heat treatment,the wide temperature range and high damping properties required for bridge applications are obtained;2.Through heat treatment of amorphous nickel titanium alloy,a new type of nickel titanium alloy wire with ultra-high elasticity and fatigue performance is obtained;3.Prepare nickel titanium alloy cable and evaluate its functional fatigue performance.The main research results of this article are as follows:1.After undergoing solution treatment at 700℃and aging heat treatment at different temperatures,commercial nickel titanium alloy wires were subjected to corresponding mechanical experiments.It was found that most of their stress strain curves turned into narrow hysteresis near linear elastic curves,with good functional fatigue resistance and significantly improved plasticity.After testing with a dynamic mechanical analyzer,it was found that its dynamic energy consumption capacity was strong,with a maximum loss factor of nearly 0.13,and the high damping temperature range was significantly improved,making it suitable for the temperature application range of bridge cables.Finally,fatigue experiments were conducted to investigate the effects of heat treatment temperature on the residual strain,energy consumption,and equivalent damping of the sample.2.After low-temperature heat treatment for different periods of time,amorphous nickel titanium alloy wires were subjected to corresponding mechanical experiments,and it was found that their ultimate strength was up to 1900 MPa,with a stress plateau of 800 MPa,much higher than the strength of commercial nickel titanium wires.Its plastic deformation ability has also increased from the original limit strain of 2.8%to 18%.Later,the dynamic mechanical analyzer test found that its dynamic energy consumption capacity is weak.Finally,a fixed strain cyclic fatigue experiment was conducted to investigate the effect of heat treatment time on the residual strain,energy consumption,and equivalent damping of the experimental sample.3.Compile commercial nickel titanium alloy wire into 7×7 cable.Through mechanical tensile tests,it was found that the mechanical properties of commercial nickel titanium alloy cables were similar to those of ordinary nickel titanium wires.After that,through fatigue experiments,it was found that the fatigue performance of the cable is the best at low temperatures.As the temperature increases,the fatigue performance gradually decreases,and the energy consumption ability increases.Finally,the fatigue section of the cable was observed using scanning electron microscopy,and microcracks on the surface of the broken wire were found.4.Using X-ray diffraction and transmission electron microscopy,observe and compare the phase,micromorphology,and electron diffraction of commercial nickel titanium alloy wires and amorphous nickel titanium alloy wires under different heat treatment temperatures.It is observed that heat treated commercial nickel titanium wires with precipitated phases have higher dynamic damping capabilities,indicating that the R phase nanodomains obtained through heat treatment are beneficial to energy absorption and dissipation.However,in addition to the austenitic phase,Ni4Ti3 precipitates were newly precipitated in the amorphous nickel titanium wire after heat treatment.This precipitation is not only conducive to the nucleation and precipitation of R-phase,but also improves the ultimate strength and stress plateau of nickel titanium wire,which is conducive to improving fatigue performance. |
