Multiaxial fatigue life modelling using hybrid approach of critical plane and genetic algorithm

This paper presents a new hybrid approach for multiaxial fatigue life estimation, based on continuum damage mechanics theory and a genetic algorithm with critical plane model formulation. The hybrid model employs a genetic algorithm based setup for calibration with standard proportional and non‐proportional profiles to predict fatigue life for complex loading profiles. The model is evaluated using experimental fatigue life data for SS304 steel. Calibration using simplified profiles is in agreement with the requirement for cost‐effective experimental fatigue life testing. In‐phase and out‐of‐phase loads are used for calibration, and fatigue life is predicted for more complicated profiles. The results show good agreement between the estimated and experimental fatigue life, and calibration through simple loading histories to predict fatigue life for complex histories appears to be an effective solution using the proposed model. A brief comparison is presented with fatigue life estimation performance of the proposed model with models available in commercial codes. Proposed model found to be more consistent in fatigue life prediction against various loading conditions.     

The multiaxial weld root fatigue of butt welded joints subjected to uniaxial loading

In this study, the fatigue strength of inclined butt welds subjected to a proportional multiaxial stress state generated by uniaxial loading is studied in nominal and local stress concepts. The local methodologies studied included principal stress hypothesis, von Mises stress hypothesis and modified Wöhler curve method. Nominal methodologies included modified Gough–Pollard interaction equation, the design equation in Eurocode3 and the interaction equation in DNV standard. Results are evaluated along with data published in relevant literature. It is observed that both local and nominal stress assessment methods are able to estimate multiaxial fatigue strength. No obvious difference in fatigue strength is observed in the nominal stress concept, but the notch stress concept is able to capture a decrease in fatigue strength in shear‐dominated joints. It is concluded that modified Wöhler curve method is a suitable tool for the evaluation of fatigue strength in joints dominated by both normal and shear stresses.     

基于抗振动疲劳的薄板加筋设计分析

振动是航空薄板常见的载荷形式,通常采用加强筋来减小振动幅度,从而提高薄板寿命.研究薄板的抗振动疲劳加筋方法,探讨加强筋与板的连接方式以及加强筋的布置方向对薄板振动与疲劳的影响机制.首先,基于振动理论和板筋变形协调条件,建立加筋薄板的运动方程.然后,建立铆接、点焊和滚焊连接形式的加筋薄板有限元模型,探讨连接单元的动力学建模方法;在此基础上,研究连接形式和加筋安装方向对薄板结构动力学特性的影响;最后,结合动力响应分析探讨板筋连接方式和加筋安装方向对疲劳寿命的影响.研究结果表明,双向加筋薄板在低频振动时刚度高于单向加筋薄板,双向加筋有利于提高结构抗疲劳强度,铆接单向加筋薄板的振动疲劳寿命最短.     

涡轮盘篦齿裂纹扩展的有限元数值模拟

为了详细考察篦齿裂纹的扩展规律,对篦齿裂纹从齿尖一直扩展到即将完全穿透篦齿环的过程进行了数值模拟.含篦齿裂纹的涡轮盘有限元模型采用子模型法建立,使用M积分计算裂纹前沿的应力强度因子;在确定篦齿裂纹前沿每一节点处的局部扩展方向及距离后,通过样条曲线拟合出新裂纹前沿,并依靠自适应网格划分实现裂纹区有限元网格的更新.数值模拟结果表明,篦齿根部过渡圆角顶部可以视为裂纹缓慢扩展阶段与快速扩展阶段的分界点,在此之前篦齿裂纹以穿透型裂纹的形态以较低的速度进行扩展,在此之后篦齿裂纹开始向表面裂纹进行转化,并且平均扩展速度大大增加,分界点前的裂纹扩展寿命是之后的数倍.此外,由数值模拟结果还可以发现,增大篦齿根部过渡圆角半径以及减小相邻篦齿的间距,均有助于延缓篦齿裂纹的扩展.     

Mechanisms governing the tensile,fatigue, and wear behavior of carbon nanotube reinforced aluminum alloy

This work is concerned with understanding the influence of reinforcement mechanisms of carbon nanotubes (CNTs) on mechanical, wear, and fatigue tests on an Aluminium-Silicon (AlSi) alloy. The reinforcement mechanism is presented through the observation of fracture morphology of the different tests. Results of mechanical properties, fatigue life performance, and wear loss is presented and discussed. It is shown that the CNTs reinforcement effect is active simultaneously in all previous properties and the reinforcement physical mechanism seems to be essentially due to a reinforcement effect of the interface that seems to be similar in all mentioned mechanical solicitations.     

高韧性高强度5A06铝合金焊接接头的力学性能

为提高5A06铝合金氩弧焊接接头的综合力学性能,本文开展了高韧性高强度焊丝研究,通过拉伸和疲劳性能测试以及断口分析研究了4mm厚5A06铝合金钨极氩弧焊对接接头的抗拉和疲劳强度以及断裂行为。结果表明,所研制的焊丝兼具高抗拉强度和疲劳强度,焊接接头抗拉强度最高达341MPa,断裂延伸率14.9%,较商用ER4043焊丝提高了32%和30.2%;2×106次循环次数对应95%存活率的疲劳强度特征值最高达44MPa,高出国际焊接学会(IIW)推荐值37%。     

沐阳闸交通桥承载能力分析研究

摘要：沭阳闸交通桥经过50多年运行,由于自然和人为因素的长期作用,交通桥各部位混凝土结构都逐渐出现老化,因此,有必要对其承载能力进行分析研究,为更好地评价水闸的安全状态提供数据标准,为单位运行管理提供科学依据。针对沭新闸交通桥实际状况,在现场安全检测、现场试验、工程复核的基础上,对其承载能力分析表明,交通桥混凝土碳化较严重,钢筋保护层不足,对钢筋耐久性有较大影响,在实际运行工况下,交通桥承载能力不足,存在严重安全隐患。     

水利工程泵送混凝土裂缝的防治措施浅析

摘要：水利工程混凝土结构需要长期承受各种荷载的作用,不可避免会产生裂缝、破损等情况。而泵送混凝土结构中裂缝的存在和发展,破坏了水工建筑结构的整体性,导致水工建筑物内部钢筋锈蚀,从而降低结构物的耐久性,并影响其正常使用,严重时甚至会危害人民群众的生命财产安全。对泵送混凝土裂缝的成因及防治措施进行了探讨,提出了应采取的防治措施,将混凝土裂缝带来的影响减小到最低。     

车载疲劳驾驶行为检测系统的研究与设计

针对汽车驾驶员的疲劳驾驶行为检测过程繁琐、算法复杂、检测装置部署易影响驾驶员等现状,为更加方便、快捷、有效的对疲劳驾驶做出监测和报警,提出基于ZigBee的车载疲劳驾驶检测方案.选取方向盘角度变化作为检测疲劳驾驶的突破点,使用TLE5012角度传感器,完成角度数据的采集,采用CC2530实现系统的无线通信.从采集到的方向盘角度数据中提取能反映疲劳状态的零速百分比和角度标准差两个特征,使用线性判别算法对驾驶人员的疲劳状态进行分类.仿真实验表明,该方法能够较准确的对疲劳状态进行判别.     

结构疲劳试验控制系统关键技术

介绍了多通道结构疲劳试验控制系统的原理和功能。总结了系统产品从早期面向小型结构件试验控制到面向大型结构件协调控制的发展历程。重点分析了最新产品采用的分布式控制技术、多种协调加载技术及其特点、试验配置技术、实时数据处理技术和试验载荷谱编制技术等关键技术。最后指出了多通道结构疲劳试验控制系统产品向软件智能化、界面图形化、模块通用化、产品系列化等方向发展的趋势。