多轴向与单轴向振动环境下结构振动疲劳失效对比研究

发布时间：2018-02-15 09:50

本文关键词： 振动环境试验多轴向振动结构动力学响应振动疲劳疲劳寿命估计　出处：《南京航空航天大学》2016年博士论文　论文类型：学位论文

【摘要】：在航空、交通和机械等领域中,对产品和装备进行环境振动试验对提高其可靠性具有重要意义。当前的环境振动试验,一般采用在三个轴向依次进行单轴向振动试验的方式,来等效产品和装备在实际工况下所经历的多轴振动环境。该方法在应用过程中可能导致产品出现过试验或欠试验现象,其有效性及其与真实多轴振动环境的差异性受到业界广泛重视。基于此,本文对多轴向同时振动与单轴向振动疲劳试验开展了对比研究。研究了典型结构在单轴向振动环境与多轴向振动环境下的动力学响应。通过理论分析,有限元仿真和试验验证,探索了结构在不同振动工况下动力学响应的差异与联系,并对差异产生的原因进行了分析。研究结果表明在各轴向互不相关的三轴同时振动环境下,结构的动力学响应为各个方向单轴向振动时引起的动力学响应的叠加。若各轴向载荷间存在相关性,则其相关性对结构动力学响应存在明显的影响,并得到了不同轴向载荷间相关性对结构动力学响应的影响规律,为不同工况下结构振动疲劳失效行为的研究奠定了基础。提出了适合多轴向振动环境下结构疲劳失效的判定方法。通过激光测振仪和35670A动态信号分析仪对结构的一阶固有频率进行跟踪监测;利用动态应变测试系统对试件缺口部位的应变进行了实时监测。根据试验数据分析了多轴向振动环境下疲劳裂纹扩展与固有频率变化和应变变化的关系,确定了两种疲劳失效的试验判定准则,为开展多轴向振动疲劳试验奠定了基础。研究了不同载荷工况下结构的振动疲劳失效行为,以及各轴向载荷间相关性对结构疲劳失效行为的影响。对典型试件分别进行了多轴向同时振动、单轴向振动和单轴向依次振动疲劳试验,并且对试验结果进行了对比分析。研究结果表明相比于单轴向振动,试件在多轴向同时振动环境中的疲劳失效时间、裂纹源的位置以及裂纹扩展方式均存在差异,多轴向同时振动更容易使结构产生疲劳损伤,具有更短的失效时间。通过改变不同轴向载荷谱间相干系数和相位角,研究了不同轴向载荷间相关性对结构疲劳失效行为的影响,得到了载荷相关性对结构疲劳失效行为的影响规律。基于现有的多轴疲劳损伤估计理论,根据多轴向随机振动环境下结构动力学响应的特点,提出了频域内多轴向振动环境下结构疲劳寿命估计的方法。该方法采用von Mises等效应力功率谱密度将多轴应力问题转化为单轴应力问题,利用单轴应力疲劳寿命估计的频域分析方法对结构疲劳寿命进行估计。计算了典型构件在多轴向与单轴向随机激励下的疲劳寿命,并与实验结果进行了对比验证。对构件在多轴向同时激励与单轴向依次激励的疲劳损伤结果进行了对比分析,从理论上研究了多轴向振动环境下结构振动疲劳的多轴效应。
[Abstract]:In the fields of aviation, traffic and machinery, environmental vibration testing of products and equipment is of great significance to improve their reliability. The method may lead to the phenomenon of product being tested or undertested in the application of the method, which is equivalent to the multi-axis vibration environment experienced by the products and equipment under actual working conditions. Its effectiveness and its difference from the real multi-axis vibration environment have attracted wide attention in the industry. In this paper, the dynamic responses of typical structures under uniaxial vibration and uniaxial vibration are studied by means of theoretical analysis, finite element simulation and experimental verification. The difference and relation of the dynamic response of the structure under different vibration conditions are explored, and the causes of the difference are analyzed. The dynamic response of the structure is the superposition of the dynamic response caused by uniaxial vibration in various directions. If there is a correlation between the axial loads, the correlation has a significant effect on the dynamic response of the structure. The influence of the correlation between different axial loads on the dynamic response of the structure is obtained. It lays a foundation for the study of structural vibration fatigue failure behavior under different working conditions. A method for judging structural fatigue failure under multi-axial vibration environment is proposed. The structural fatigue failure is determined by laser vibration detector and 35670A dynamic signal analyzer. The first order natural frequency is tracked and monitored; The dynamic strain measurement system is used to monitor the strain at the notch of the specimen in real time. Based on the experimental data, the relationship between fatigue crack growth and natural frequency and strain variation in multi-axial vibration environment is analyzed. Two kinds of fatigue failure criteria were determined, which laid a foundation for multi-axial vibration fatigue test. The vibration fatigue failure behavior of structures under different load conditions was studied. And the influence of the correlation between the axial loads on the fatigue failure behavior of the structures. The multiaxial simultaneous vibration, the uniaxial vibration and the uniaxial vibration fatigue tests were carried out respectively for typical specimens. The results show that compared with uniaxial vibration, the fatigue failure time, the location of crack source and the mode of crack propagation are different in multi-axial vibration environment. Multiaxial simultaneous vibration can cause fatigue damage more easily and has shorter failure time. By changing the coherence coefficient and phase angle between different axial load spectra, the influence of the correlation between different axial loads on the fatigue failure behavior of the structure is studied. The influence of load correlation on fatigue failure behavior of structures is obtained. Based on the existing theory of multiaxial fatigue damage estimation and the characteristics of structural dynamic responses under multi-axial random vibration, the dynamic response of structures is analyzed. In this paper, a method for estimating the fatigue life of structures under multiaxial vibration in frequency domain is presented. The multiaxial stress problem is transformed into uniaxial stress problem by using von Mises equivalent stress power spectrum density. The fatigue life of structures is estimated by frequency domain analysis method of uniaxial stress fatigue life estimation, and the fatigue life of typical members under multiaxial and uniaxial random excitation is calculated. The results of fatigue damage caused by multi-axial excitation and uniaxial excitation are compared and analyzed. The multiaxial effect of structural vibration fatigue in multi-axial vibration environment is studied theoretically.
【学位授予单位】：南京航空航天大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O327

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