摘要:
在国防与民用领域,一些装备和结构不可避免地会承受间断性的、高加载率的、重复性的强冲击作用,即所谓的重复冲击或冲击疲劳作用。要研究装备或结构的冲击疲劳行为,首先需要建立可靠的冲击疲劳试验技术或方法。本文基于传统的Hopkinson杆冲击加载技术,对其进行修改和功能提升。分析和研究了连续冲击时加载杆、试样、夹具等应力波传播问题,对作用于试样的冲击加载波的幅值、脉宽和应力波脉冲构型进行分析与调制,以及对在冲击疲劳试验中如何实现单脉冲加载进行理论分析。通过优化和改进撞击弹的撞击速度、长度以及弹体的几何形状实现了有效的加载波的幅值、脉宽和应力波脉冲构型控制。本研究主要提出了一种简单快速可适用于冲击疲劳试验的单脉冲加载方法,其原理为:通过设计加载杆的长度与材料参数,使试样和入射杆端面协同作用与分离,避免了加载杆上来回传播的应力波对试样的不规则随机二次或多次加载问题,实现了连续冲击时,每单次冲击对试样的单次加载功能。通过数值仿真和实际试验验证,证明了所提出的冲击疲劳单脉冲加载方法的有效性和可行性。最终建立了用于剪切冲击疲劳的加载装置,获得了TC4钛合金的剪切冲击疲劳应力-寿命曲线。
Abstract:
In the national defense and civilian fields, equipment and structures will inevitably be subjected to intermittent, high loading rates, and repetitive severe impact loads, which are the so-called repeated impacts or impact fatigue. To study the impact fatigue behavior of equipment or structures, it is necessary to first establish a reliable impact fatigue testing techniques or methodologies. This study modifies and enhances the conventional Hopkinson bar impact loading technique to meet this need. The stress wave propagation characteristics in the loading bar, specimen, and fixtures under successive impacts are analyzed in detail. The amplitude, pulse width, and waveform configuration of the impact loading pulses applied to the specimen are systematically analyzed and controlled. And a theoretical analysis on how to achieve single pulse loading in impact fatigue testing is provided. Effective control of the amplitude, pulse width, and the stress wave pulse configuration of the loading wave is realized by optimizing and modifying the impact velocity, length, and geometric shape of the projectile. This research primarily proposeds a simple and rapid single pulse loading method suitable for impact fatigue testing. The principle involves designing the length and material parameters of the loading bar such that the end surfaces of the specimen and the bar act in coordination and then separate, thereby preventing irregular and random secondary or multiple loadings caused by reflected stress waves. This design ensures that each individual impact in a continuous impact sequence results in a single loading on the specimen. The effectiveness and feasibility of the proposed impact fatigue testing technique have been verified through numerical simulations and experiments. Finally, a loading device for shear impact fatigue was established, and the shear impact fatigue stress-life curve of TC4 titanium alloy was obtained.