Study And Design Of The Variable Cross-Section Leaf Spring With SMA Fiber Composite Materials

The stiffness and damping of passive suspension can not be adjusted, and make the optimal damping effect only in specific road conditions, hard to adapt to different conditions. Sensors and actuating devices are installed in active suspension, so it can receive the signals of the vehicle running status, and adjust the stiffness and damping of the suspension by some control strategy, to adapt to complex road conditions. But active suspension has complex structure, high costs, energy consumption and so problems. Semi-active suspension's damping quality is close to the active suspension, but it has no special sensor and actuator, so compared with active suspension, it has simple structure, low energy consumption, low cost etc, thus semi-active suspension has become to be the hot spot in the research of car suspension in the word today.Traditional semi-active suspension meanly adjust vibration damping effect by adjusting damping. The semi-active suspension in this paper adjusts the effect of vibration damping by control it's stiffness and natural frequency, and has the certain innovation. As the key component of intelligent semi-active suspension, Shape Memory Alloy-SMA composites variable cross-section leaf spring is developed in the basis of the new intelligent material SMA and combined with advanced composite technology. By control it's stiffness, the effect of vibration damping the leaf can be adjusted. Since SMA composites variable cross-section leaf has no various valves, so it has more simple structure than ER/MR fluids semi-active suspensions. And it has the traditional leaf spring's characteristics of sturdy, thus it has a broad prospect.In this paper, the characteristics of the stiffness and natural frequency for variable cross-section composite material leaf spring with SMA fibers are investigated. The SMA one-dimensional constitutive relation is discussed based on Brinson thermodynamic model, and use the constitutive equation to calculate the restrained recovery characteristics. Then the variable curves of restrained stress, martensite content and modulus of elasticity with temperature are presented. Elastic properties and thermal elastic properties of fiber composites are studied, and the fundamental formulas of elastic properties and thermal elastic properties of laminated composites obtained from single-layer are introduced. SMA fiber and traditional fiber composites are mixed to be the new intelligent composite material. The hybrid formulas are derived, and the constitutive equations of composite structure are obtained consisting of composite elastic and thermo-elastic itself, SMA restrained force.The basic principle of Rayleigh-Ritz method is introduced, and then combining the fiber composite basic theory, SMA constitutive theory and restrained recovery characteristics, the mechanical model of variable cross-section leaf spring with composite materials embedded SMA fiber is developed. The equations of leaf spring stiffness and natural frequency is derived. By numerical calculation, the variation curves of stiffness and natural frequency with temperature are obtained, and the influences of ply angle and volume fraction of SMA fiber on the stiffness and natural frequency represented. The adjusting mechanism for the stiffness and natural frequency of the SMA fiber composite leaf spring with variable cross-section is revealed.