For classic friction dampers, the normal force on the contact interface is designed to be constant and cannot be easily adjusted post-manufacturing. The damping performance will attenuate when the working condition deviates from the target one. To overcome this issue, semi-active friction dampers are developed, where the normal force can be regulated by actuators to match the current working condition. However, the additional mass brought by the actuators limits their application prospects in the aerospace field. In this work, we propose a macro-fiber-composite-based adjustable friction damper (MFC-AFD) for typical thin-walled structures in aircrafts, which has the advantages of being lightweight, easy to install, and inherently fail-safe. The idea is to use the embedded MFC to drive the flexible structure of the damper to deform, thereby regulating the normal force. By adjusting the constant component of the normal force, the effective working range is expected to be enlarged, especially under non-target working condition. By controlling the second harmonic component, the optimal damping performance is expected to be further improved. We conduct the research using a combination of numerical simulations and experiments. To accurately and efficiently predict the damping performance of the MFC-AFD, a homogenization modeling method of MFC is proposed, and the corresponding experimental calibration technique is given. The harmonic balance-based nonlinear solver specifically for calculating the steady-response of electromechanically coupled structures is developed. Concerning the constant normal force control, a step-back to zero control law is established to eliminate the hysteresis behavior of MFC. In terms of the time-varying normal force control, a closed-loop control strategy in the frequency domain for the second harmonic component is proposed and realized. The vibration reduction effects of the MFC-AFD adopting the constant and time-varying normal force control laws are validated experimentally through a cantilever beam. Experiment results are in line with our expectations. When the vibration level is nearly 10 times of the target one, the reduction ratio recovers to 75% (i.e. close to the target working condition) by using the constant normal force control. There is an additional 32% vibration reduction compared to the optimal constant normal force when the time-varying normal force is properly controlled.

中文翻译：

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具有可调节法向力的基于 MFC 的摩擦阻尼器：概念、建模和实验

对于经典的摩擦阻尼器，接触界面上的法向力被设计为恒定的，并且在制造后不易调整。当工况偏离目标工况时，阻尼性能就会衰减。为了克服这个问题，开发了半主动摩擦阻尼器，其中法向力可以通过执行器调节以匹配当前的工作条件。然而，执行器带来的额外质量限制了其在航空航天领域的应用前景。在这项工作中，我们提出了一种用于飞机中典型薄壁结构的基于大纤维复合材料的可调摩擦阻尼器（MFC-AFD），其具有重量轻、易于安装和本质上故障安全的优点。其想法是利用嵌入式MFC来驱动阻尼器的柔性结构变形，从而调节法向力。通过调整法向力的恒定分量，有望扩大有效工作范围，特别是在非目标工作条件下。通过控制二次谐波分量，最佳阻尼性能有望进一步提高。我们结合数值模拟和实验进行研究。为了准确、高效地预测MFC-AFD的阻尼性能，提出了MFC均质化建模方法，并给出了相应的实验标定技术。开发了专门用于计算机电耦合结构稳态响应的基于谐波平衡的非线性求解器。针对恒法向力控制，建立了步回零控制律来消除MFC的滞后行为。针对时变法向力控制，提出并实现了针对二次谐波分量的频域闭环控制策略。通过悬臂梁实验验证了采用恒法向力控制律和时变法向力控制律的MFC-AFD的减振效果。实验结果符合我们的预期。当振动水平接近目标振动水平的10倍时，采用恒法向力控制，减速比恢复到75%（即接近目标工况）。当时变法向力得到适当控制时，与最佳恒定法向力相比，振动可额外减少 32%。