A method for studying the frequency stability of materials during tests for multi-cycle fatigue of steel

V. V. Myl’nikov, E. Dmitriev
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引用次数: 1

Abstract

For trouble-free operation without loss of elastic and inelastic properties of particularly critical elements of electrical-to-mechanical vibration converters during a long period of cyclic operation, it is necessary, in addition to studying the fatigue characteristics of materials used for their manufacture, to study these alloys for frequency stability, since minor deviations in the frequency of natural oscillations lead to unacceptable errors in the operation of such high-precision products. To carry out such studies, we developed and constructed an original installation, in which sinusoidal loading is carried out according to the “soft” scheme of flat samples cantilever bending operating in self-oscillation mode. The frequency of cyclic loading in this installation is generated by current pulses, which are a response to the frequency of the test sample natural oscillations converted using electronics.  As a result, frequency equality is achieved in the test process. An algorithm for calculating stresses depending on the loading amplitude of steel samples of different geometric shapes was developed. It is shown that the stress on the sample calculated by the deformation amplitude in all cases is 8 – 10 % higher than the stress calculated by the force, regardless of the shape of the proposed samples. To verify the proposed research method, martensitic-aging steel was tested at loads close to the fatigue limit, since frequency stability in this range is of great interest. We obtained the frequency characteristics in the multi-cycle test area. It was determined that with an operating time of 50 million loading cycles, the frequency change was 0.75 Hz. The dynamics of frequency stability was revealed: the frequency changed most intensively during the first 10 million loading cycles, during this time the frequency changed by 0.54 Hz.
钢多周疲劳试验中材料频率稳定性的研究方法
为了在长时间的循环运行中无故障运行而不损失电转机械振动转换器的特别关键元件的弹性和非弹性性能,除了研究制造它们所用材料的疲劳特性外,还需要研究这些合金的频率稳定性,因为在这种高精度产品的运行中,自然振荡频率的微小偏差会导致不可接受的误差。为了开展此类研究,我们开发并构建了一个原始装置,其中根据平面样品悬臂弯曲在自振荡模式下运行的“软”方案进行正弦加载。在这个装置中,循环加载的频率是由电流脉冲产生的,它是对使用电子设备转换的测试样品自然振荡频率的响应。因此,在测试过程中实现了频率相等。提出了一种基于不同几何形状钢试件加载幅值的应力计算算法。结果表明,在所有情况下,由变形幅值计算的试样上的应力比由力计算的应力高8 - 10%,而与所提出的试样的形状无关。为了验证提出的研究方法,马氏体时效钢在接近疲劳极限的载荷下进行了测试,因为在这个范围内的频率稳定性非常重要。得到了多周期试验区的频率特性。在工作时间为5000万次加载循环时,频率变化为0.75 Hz。频率稳定性的动态变化揭示了:在前1000万次加载周期中,频率变化最剧烈,在此期间频率变化了0.54 Hz。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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