Dynamic mechanical analysis (DMA) was applied to systematically investigate the low frequency damping properties of as-cast hypoeutectic Mg-Ni alloys. The results show that the as-cast hypoeutectic Mg-Ni alloys exhibi...Dynamic mechanical analysis (DMA) was applied to systematically investigate the low frequency damping properties of as-cast hypoeutectic Mg-Ni alloys. The results show that the as-cast hypoeutectic Mg-Ni alloys exhibit high damping capacities. The strain amplitude dependent damping curve has its own special characteristic, in which the damping is strongly related to the strain amplitude. The effect of the eutectic phase on damping and the mechanical properties of as-cast hypoeutectic Mg-Ni alloys were also discussed in detail.展开更多
In this paper, a new approach to free vibration analysis of a cracked cantilever beam is proposed. By considering the effect of opening and closing the crack during the beam vibration, it is modeled as a fatigue crack...In this paper, a new approach to free vibration analysis of a cracked cantilever beam is proposed. By considering the effect of opening and closing the crack during the beam vibration, it is modeled as a fatigue crack. Also, local stiffness changes at the crack location are considered to be a nonlinear amplitude-dependent function and it is assumed that during one half a cycle, the frequencies and mode shapes of the beam vary continuously with time. In addition, by using the experimental tests, it is shown that the local stiffness at the crack location varies continuously between the two extrerae values corresponding to the fully closed and the fully open cases of the crack. Then, by using the mechanical energy balance the dynamic response of the cracked beam is obtained at every time instant. The results show that for a specific crack depth, by approaching the crack location to the fixed end of the beam, more reduction in the fundamental frequency occurs. Furthermore, for a specific crack location, the fundamental frequency diminishes and the nonlinearity of the system increases by increasing the crack depth. In order to validate the results, the variations of the fundamental frequency ratio against the crack location axe compared with experimental results.展开更多
以热塑性聚氨酯弹性体(TPEE)的扣件胶垫为研究对象,首先利用万能试验机测得其荷载-位移非线性曲线。然后,借助非线性静力分析的有限元模型,计算车辆静载与弹条扣压共同作用下该类扣件胶垫的位移幅值及其对应的静刚度。最后,运用车辆-轨...以热塑性聚氨酯弹性体(TPEE)的扣件胶垫为研究对象,首先利用万能试验机测得其荷载-位移非线性曲线。然后,借助非线性静力分析的有限元模型,计算车辆静载与弹条扣压共同作用下该类扣件胶垫的位移幅值及其对应的静刚度。最后,运用车辆-轨道垂向耦合随机振动分析模型,探讨聚氨酯胶垫的常量刚度、频变刚度与幅频变刚度对车辆-轨道耦合系统随机振动频响特征的影响规律。研究结果表明:聚氨酯胶垫的静刚度具有显著的非线性特征,而且在20 k N扣压力与80 k N静轮载共同作用下聚氨酯胶垫的静刚度在19.1 k N/mm^37.9 k N/mm范围内变化,其均值与规范中假设的线性常量静刚度26.7 k N/mm相近;另外,与聚氨酯胶垫的幅频变刚度相比,它的常量刚度会严重低估轮轨系统65 Hz^150 Hz的频域响应。因此,如果车辆-轨道系统中有刚度非线性较强的高分子材料,就必须综合考虑这些材料刚度的幅变与频变特征,否则将难以准确预测轮轨系统及其周边环境振动的频域响应。展开更多
基金supported by the National Natural Science Foundation of China (12102424, 12202434, and 11972343)the Anhui Key R&D Program of China (202104a5020009)+1 种基金the Fundamental Research Funds for the Central Universities(WK2090000030)the Fellowship of China Postdoctoral Science Foundation (2022M713045)。
基金Projects(50571081 50671083) supported by the National Natural Science Foundation of China+1 种基金 Project(04G53042) supported by the Aeronautical Foundation of ChinaProject(2007E101) supported by the Natural Science Foundation of Shaanxi Province, China
文摘Dynamic mechanical analysis (DMA) was applied to systematically investigate the low frequency damping properties of as-cast hypoeutectic Mg-Ni alloys. The results show that the as-cast hypoeutectic Mg-Ni alloys exhibit high damping capacities. The strain amplitude dependent damping curve has its own special characteristic, in which the damping is strongly related to the strain amplitude. The effect of the eutectic phase on damping and the mechanical properties of as-cast hypoeutectic Mg-Ni alloys were also discussed in detail.
文摘In this paper, a new approach to free vibration analysis of a cracked cantilever beam is proposed. By considering the effect of opening and closing the crack during the beam vibration, it is modeled as a fatigue crack. Also, local stiffness changes at the crack location are considered to be a nonlinear amplitude-dependent function and it is assumed that during one half a cycle, the frequencies and mode shapes of the beam vary continuously with time. In addition, by using the experimental tests, it is shown that the local stiffness at the crack location varies continuously between the two extrerae values corresponding to the fully closed and the fully open cases of the crack. Then, by using the mechanical energy balance the dynamic response of the cracked beam is obtained at every time instant. The results show that for a specific crack depth, by approaching the crack location to the fixed end of the beam, more reduction in the fundamental frequency occurs. Furthermore, for a specific crack location, the fundamental frequency diminishes and the nonlinearity of the system increases by increasing the crack depth. In order to validate the results, the variations of the fundamental frequency ratio against the crack location axe compared with experimental results.
文摘以热塑性聚氨酯弹性体(TPEE)的扣件胶垫为研究对象,首先利用万能试验机测得其荷载-位移非线性曲线。然后,借助非线性静力分析的有限元模型,计算车辆静载与弹条扣压共同作用下该类扣件胶垫的位移幅值及其对应的静刚度。最后,运用车辆-轨道垂向耦合随机振动分析模型,探讨聚氨酯胶垫的常量刚度、频变刚度与幅频变刚度对车辆-轨道耦合系统随机振动频响特征的影响规律。研究结果表明:聚氨酯胶垫的静刚度具有显著的非线性特征,而且在20 k N扣压力与80 k N静轮载共同作用下聚氨酯胶垫的静刚度在19.1 k N/mm^37.9 k N/mm范围内变化,其均值与规范中假设的线性常量静刚度26.7 k N/mm相近;另外,与聚氨酯胶垫的幅频变刚度相比,它的常量刚度会严重低估轮轨系统65 Hz^150 Hz的频域响应。因此,如果车辆-轨道系统中有刚度非线性较强的高分子材料,就必须综合考虑这些材料刚度的幅变与频变特征,否则将难以准确预测轮轨系统及其周边环境振动的频域响应。
