Böhm Michał, Kluger Krzysztof, Pochwała Sławomir, Kupina Mariusz
Department of Mechanics and Machine Design, Faculty of Mechanical Engineering, Opole University of Technology, 45-271 Opole, Poland.
Department of Thermal Engineering and Industrial Equipment, Faculty of Mechanical Engineering, Opole University of Technology, 45-271 Opole, Poland.
Materials (Basel). 2020 Jul 4;13(13):2985. doi: 10.3390/ma13132985.
The paper presents the experimental fatigue test results for cyclic constant amplitude loading conditions for the case of the torsion of the PA4 (AW-6082-T6), PA6 (AW-2017A-T4) and PA7 (AW-2024-T3) aluminum alloy for a drilled diabolo type test specimen. The tests have been performed for the stress asymmetry ratios = -1, = -0.7, = -0.5 and = -0.3. The experimental results have been used in the process of a fatigue life estimation performed for a random generated narrowband stress signal with a zero and a non-zero global mean stress value. The calculations have been performed within the time domain with the use of the rainflow cycle counting method and the Palmgren-Miner damage hypothesis. The mean stress compensation has been performed with the S-N curve mean stress model proposed by Niesłony and Böhm. The model has been modified in terms of torsional loading conditions. In order to obtain an appropriate = 0 ratio S-N curve fatigue strength amplitude, the Smith-Watson-Topper model was used and compared with literature fatigue strength amplitudes. The presented solution extends the use of the correction model in terms of the torsional loading condition in order to obtain new S-N curves for other values on the basis of the = -1 results. The work includes the computational results for new fatigue curves with and without the mean stress effect correction. The results of the computations show that the mean stress effect plays a major role in the fatigue life assessment of the tested aluminum alloys and that the method can be used to assess the fatigue life under random conditions.
本文给出了PA4（AW - 6082 - T6）、PA6（AW - 2017A - T4）和PA7（AW - 2024 - T3）铝合金在钻孔空竹型试样扭转情况下，循环等幅加载条件下的疲劳试验结果。试验针对应力不对称比(R = -1)、(R = -0.7)、(R = -0.5)和(R = -0.3)进行。实验结果已用于对随机生成的具有零和非零全局平均应力值的窄带应力信号进行疲劳寿命估计的过程中。计算是在时域内使用雨流循环计数法和帕尔姆格伦 - 迈纳损伤假设进行的。平均应力补偿采用了Niesłony和Böhm提出的S - N曲线平均应力模型，并根据扭转加载条件对该模型进行了修改。为了获得合适的(R = 0)比S - N曲线疲劳强度幅值，使用了史密斯 - 沃森 - 托珀模型并与文献中的疲劳强度幅值进行了比较。所提出的解决方案扩展了修正模型在扭转加载条件方面的应用，以便在(R = -1)结果的基础上获得其他(R)值的新S - N曲线。这项工作包括了有和没有平均应力效应修正的新疲劳曲线的计算结果。计算结果表明，平均应力效应在测试铝合金的疲劳寿命评估中起主要作用，并且该方法可用于评估随机条件下的疲劳寿命。
