椭圆柔性铰链疲劳失效分析与寿命预测

针对柔顺机构中柔性铰链受到交变对称循环载荷的作用下,使柔性铰链最薄弱处容易产生应力集中,导致柔性铰链疲劳失效问题,以柔顺机构中椭圆型柔性铰链为研究对象,以材料力学中纯弯曲理论为基础,推导椭圆柔性铰链切口处最大集中应力计算公式;利用ANSYS仿真分析,对比验证了计算公式的准确性与可行性;在此基础上,通过引入线性回归方法,建立椭圆型柔性铰链寿命预测模型,既可以预测椭圆型柔性铰链的疲劳寿命,也可以解决疲劳失效问题。通过实例验证了该模型的正确性与有效性,可为其他类型柔性铰链的疲劳失效与寿命预测提供重要参考。     

含缺口结构压疲劳失效研究

结构的疲劳失效与内部的应力水平有着紧密的联系。这里阐述了压应力作用下结构内部裂纹的萌生和扩展机理，并介绍了循环压应力下的裂纹扩展计算方程，结合现代疲劳研究方法的新成果新方法对压应力条件下疲劳破坏研究的未来提出展望。     

40MPa高压空气瓶疲劳试验失效分析

结合高压空气瓶疲劳失效现象进行有限元应力分析和断口分析,研究高压空气瓶疲劳失效的主要原因。通过验证性循环疲劳试验,表明增加高压空气瓶内表面应力集中部位的表面无损检测和缺陷消除能够提高高压空气瓶的耐疲劳性能,对高压空气瓶的安全使用具有重要意义。     

疲劳裂纹的工程预测方法

应用腐蚀疲劳裂纹试验数据验证了文献「１」中疲劳裂纹扩展尺寸的通用计算公式;建立了用三组实测数据预测疲劳裂纹扩展尺寸的实用方法;并将通用计算公式推广用于预测工程构件上中疲劳裂纹状经,提出了构件疲劳裂纹形状扩展尺寸的通用计算公式。     

齿轮表层下疲劳失效的预测研究

以拖拉机变速箱主动弧齿锥齿轮为例,根据齿面沿深度方向剪切应力和剪切强度之比值分布进行表层下疲劳失效方式和疲劳源区域的预测分析和试验验证.通过齿轮剪切应力计算并与残余应力进行叠加分析,以及硬度与强度之间的转换关系,得到了齿轮沿齿面深度方向的应力与强度分布,以基于局部剪切屈服强度值方法判定准则,分析齿轮疲劳失效方式和相互转...     

薄膜疲劳失效预测方法与损伤机制的研究进展

薄膜材料的尺寸范围、结构以及其服役环境的特殊性,制约了薄膜失效行为、寿命预测及可靠性评估技术研究的开展。对薄膜疲劳寿命的预测方法进行综述,分析常用的单向循环加载法和悬臂梁弯曲法。详细介绍纳米级动态载荷法,包括连续刚度法和纳米冲击试验法,此法能够对实际服役环境更好地模拟,可以实现分相测试以及多种功能模块的原位定点检测,以及定量分析薄膜的疲劳性能。对薄膜疲劳损伤失效机制与寿命预测模型的研究进行探讨与展望,发现薄膜材料失效过程的研究与定量分析是今后研究的重点。     

动载滑动轴承疲劳失效过程研究

研究了动载滑动轴承疲劳失效过程,观察到轴瓦表面裂纹、第二相裂纹等类型。通过润滑计算得到轴心轨迹、油膜压力和合金层应力分布,对轴瓦失效过程进行了分析,结果表明,轴怕疲劳裂纹由轴瓦宏观应力分布和微观应力集中共同作用,当基体与第二相的Ｅ、μ相关工不多时,应力集中不明显,当基体与第二相的Ｅ、μ相差较多时,应力集中产生的影响不可忽略。     

Fretting fatigue analysis using a fracture mechanics based small crack growth prediction method

A complete life model for the nucleation and growth of a fretting fatigue crack has been developed. The nucleation of a fretting crack is predicted by superimposing the crack growth rate experienced under fretting conditions onto S–N fatigue data for the alloy. The growth model utilizes small crack growth rate data and a fretting fatigue stress intensity factor to account for the small crack sizes and higher stresses experienced under fretting fatigue conditions. The development of the propagation model within the established fatigue crack growth code AFGROW allows this approach to be readily used by members of the aerospace industry.     

Identification and prediction of cyclic fatigue behaviour in sandwich panels

The work describes the development of analytical model to identify and predict the cyclic fatigue behaviour of composite sandwich panels subjected to cyclic fatigue loading under 3-point bending conditions. Sandwich samples made from CFRP skin and Nomex core have been loaded with a mean displacement corresponding to 60% of the failure deformation, and subsequently subjected to cyclic loading under displacement control with different loading levels. The fatigue tests show that the stiffness degradation over the number of cycles is characterised by three different phases according to the loading level used. The evolution of the energy dissipated per unit volume versus the number of cycles has also been considered. The cyclic history of the stiffness degradation is developed here following an alternative approach to the one currently adopted. The approach involves the use of interpolation through empirical functions of the experimental data, with the coefficients of the interpolation based on the material properties of the sandwich structure and the type of loading. The alternative modelling approach presented in this work allows the prediction of the fatigue behaviour in sandwich structures without using a large number of test data currently needed in fatigue testing of sandwich panels.     

Innovation based two-interval overlap test for failure prediction in measurement systems

An approach to predict failure in the measurement system is developed. Proposed approach uses confidence and tolerance intervals for the innovation of Kalman filter and it is based on the criterion of overlapping these intervals whereby it allows the detection of potential failures in the system. The proposed failure prediction method is well suited to realize detection of constant shifting and slowly varied failures, such as distortion in measuring instruments and gyroscope axes shifting in navigation systems. The method is simple and permits to solve the problem of failure prediction in the measurement system under the conditions of its practical operation.     

Reliability prediction system based on the failure rate model for electronic components

Although many methodologies for predicting the reliability of electronic components have been developed, their reliability might be subjective according to a particular set of circumstances, and therefore it is not easy to quantify their reliability. Among the reliability prediction methods are the statistical analysis based method, the similarity analysis method based on an external failure rate database, and the method based on the physics-of-failure model. In this study, we developed a system by which the reliability of electronic components can be predicted by creating a system for the statistical analysis method of predicting reliability most easily. The failure rate models that were applied are MILHDBK-217F N2, PRISM, and Telcordia (Bellcore), and these were compared with the general purpose system in order to validate the effectiveness of the developed system. Being able to predict the reliability of electronic components from the stage of design, the system that we have developed is expected to contribute to enhancing the reliability of electronic components.     

温挤压模具冷热疲劳早期失效模拟分析与探讨

生产某壳体零件的模具存在着严重的冷热疲劳早期失效现象,结合生产实际利用DEFORM有限元模拟软件对其温挤压过程进行了模拟.通过对比模拟分析可知得到凸模在工作时不同时刻时的温度值,不同模具预热温度和坯料温度下模具的最高温度分布以及急冷急热温度差范围.为了减缓模具的冷热疲劳,模具预热温度最好控制在200～300℃之间,坯料加热温度控制在800℃内.     

使用疲劳裂纹扩展数据的疲劳裂纹扩展的可靠性分析方法

利用现有的疲劳裂纹扩展数据或疲劳裂纹扩展试验的不完全数据 ,对疲劳裂纹随机扩展的可靠性进行了研究。基于疲劳裂纹扩展的确定性模型 ,导出了疲劳裂纹扩展的随机公式。利用现有的疲劳裂纹扩展数据或疲劳裂纹扩展试验的不完全数据 ,对疲劳裂纹扩展随机公式中的随机变量的分布进行了估计 ,得到了其分布的数字特征 ,用Monte Carlo方法得到了疲劳裂纹扩展寿命的失效概率的点估计。实例分析表明了本文方法的实用性和可行性     

活塞销疲劳寿命预测的研究

疲劳破坏是活塞销的主要失效形式。对活塞销进行了载荷分析、利用APDL语言建立了有限元分析模型。理论计算了活塞销的疲劳安全系数。基于有限元结果结合Goodman单轴、Sinse多轴修正的名义应力算法,计算预测了活塞销的疲劳寿命。进一步利用FE-SEFE软件进行了单轴、多轴两种方法的疲劳寿命预测,验证该活塞销满足疲劳设计要求,理论验证了FE-SEFE软件在预测高周疲劳寿命的可行性。     

失效率预计法在产品研发中的应用

介绍了失效率预计法的应用特点和方法步骤,并利用失效率预计法对直升飞机升降舵和方向舵控制系统进行了具体应用,结果表明在重大产品详细设计研发阶段利用该方法对产品的可靠性进行评价是非常有效的,而且该方法具有一定的通用性,既适用于评价电子产品,也适用于非电子产品.     

Detecting gear tooth fatigue cracks in advance of complete fracture

Some results from using vibration-based methods to detect gear tooth fatigue cracks are presented. An experimental test rig was used to fail a number of spur-gear specimens through bending fatigue. The gear tooth fatigue crack in each test was initiated through a small notch in the fillet area of a tooth on the gear. The primary purpose of these tests was to verify analytical predictions of fatigue crack propagation direction and rate as a function of gear rim thickness. The vibration signal from a total of three tests was monitored and recorded for gear fault detection research. The damage consisted of complete rim fracture on the two thin rim gears and single tooth fracture on the standard full rim test gear. Vibration-based fault detection methods were applied to the vibration signal both on-line and after the tests were completed. The objectives of this were to identify methods capable of detecting the fatigue crack, and determine how far in advance of total failure positive detection was given. Results showed that the fault detection methods failed to respond to the fatigue crack prior to complete rim fracture in the thin rim gear tests. In the standard full rim gear test all of the methods responded to the fatigue crack in advance of tooth fracture; however, only three of the methods responded to the fatigue crack in the early stages of crack propagation.     

Comparison of the fatigue life of F.F. shaft material according to various environmental temperatures

A rotary bending fatigue test was carried out with two kinds of materials, S43C and S50C, using the front engine and front driveshaft (F.F. shaft) of the vehicle. The specimens were heat-treated using the high frequency induction method (about 1 mm depth and HRC56∼60) and the test environment temperatures were -30 °C (-22 °F), +25 °C (+77 °F), and +80 °C (+176 °F) in order to determine the influence of the heat treatment and the temperatures. The fatigue life increased on the order of +80 °C, +25 °C, and -30 °C regardless of heat treatment. In comparison of the fatigue lives with the basis of the tested result at +25 °C, the fatigue lives of non-heated specimens decreased about 35%, but that of heat-treated specimens decreased by only about 5% at +80 °C, more than at +25 °C. And fatigue life of non-heated and heat-treated specimens were about 110% and 120% higher at -30 °C than that of +25 °C. The initiation of surface microcracks was observed at 0.2 fatigue life ratio in as-received S43C and S50C, but the average crack length in S50C was about 14% longer than that of S43C at the same fatigue life ratio.