恒幅载荷下桥式起重机疲劳断裂寿命的特性研究

发布时间：2018-01-10 13:41

本文关键词：恒幅载荷下桥式起重机疲劳断裂寿命的特性研究　出处：《太原科技大学》2016年硕士论文　论文类型：学位论文

【摘要】：桥式起重机在现代社会建设中扮演着非常重要的角色,是经济建设各部门应用非常广泛的一类特种设备。同时,桥式起重机失效引起的事故也越来越受到人们的关注。在所有的失效类型中,最主要的是桥式起重机主梁的疲劳断裂。应用断裂力学法研究疲劳断裂问题时,一般将裂纹扩展相关参数定为近似值,所求的裂纹扩展寿命就是确定的。但在实际情况中,由于材料属性、结构尺寸、初始裂纹尺寸、使用环境等参数的随机性,使得桥式起重机疲劳寿命计算成为一个复杂的统计问题,目前的评估方法精度有待进一步提高。针对以上的问题,本文采用了CT试验、Matlab数值模拟方法和Ansys参数化建模分析对恒幅载荷下桥式起重机疲劳断裂寿命特性进行了研究。首先,通过CT试验对疲劳参数进行研究,确定了Q235试件的a-N曲线,根据割线法和最小二乘法,确定常温下疲劳裂纹扩展速率参数C,m的随机分布特性。其次,以Matlab软件为平台,建立疲劳裂纹扩展三阶段的模型,把裂纹过程分为表面裂纹、中心裂纹和边缘裂纹。利用CT试验研究中得到的C,m的随机特性结果,采用Monte-Carlo随机抽样的方法对桥式起重机腹板—横隔板焊缝处裂纹扩展三阶段的寿命特性及其影响因素进行了概率统计分析。研究表明,表面裂纹初始深度的期望对最终寿命的评估有很大的影响,并且表面裂纹扩展所用的时间在疲劳裂纹扩展总寿命中所占的百分比很大,尤其在板厚较大时,经历了表面裂纹到穿透后就可认为达到结构破坏,而可忽略穿透型裂纹扩展时间。最后,以Ansys软件为平台,对桥式起重机整机进行分析,确定了桥式起重机最容易产生裂纹的位置。并提出基于Paris公式的Ansys有限元寿命评估方法,应用APDL语言建立腹板—下翼缘板处的参数化模型,模拟桥式起重机实际工况及裂纹扩展过程,并对恒幅载荷下桥式起重机疲劳裂纹扩展寿命进行了评估;另外,采用Ansys软件提供的相互作用积分法来计算应力强度因子,有效地拟合了桥式起重机恒幅载荷下的应力循环次数-裂纹尺寸关系,符合裂纹扩展的规律,提高了疲劳寿命计算的精确性。
[Abstract]:Bridge crane plays a very important role in the construction of modern society. It is a kind of special equipment which is widely used in various departments of economic construction. The accidents caused by bridge crane failure are paid more and more attention. Among all the failure types, the most important one is the fatigue fracture of the main girder of bridge crane. When the fracture mechanics method is used to study the fatigue fracture problem. The relevant parameters of crack propagation are generally defined as approximate values, and the crack growth life is determined. However, in practice, due to the properties of the material, the structure size, the initial crack size. Because of the randomness of the parameters such as environment, the calculation of fatigue life of bridge crane becomes a complicated statistical problem. The accuracy of the present evaluation method needs to be further improved. In this paper, the fatigue fracture life characteristics of bridge crane under constant amplitude load are studied by using CT test Matlab numerical simulation method and Ansys parametric modeling analysis. The a-N curve of Q235 specimen was determined by CT test, and the fatigue crack growth rate parameter C at room temperature was determined by Secant method and least Square method. Secondly, based on Matlab software, a three-stage model of fatigue crack propagation is established, and the crack process is divided into surface cracks. Central crack and edge crack. Random characteristic results of Cumm obtained from CT test are used. The probabilistic statistical analysis of the life characteristics and its influencing factors of the crack propagation at the weld seam of the web plate of the bridge crane is carried out by using Monte-Carlo random sampling method. The expectation of the initial depth of the surface crack has a great influence on the evaluation of the final life, and the time of the surface crack growth takes a large percentage of the total life of the fatigue crack growth, especially when the plate thickness is larger. After the surface crack to penetrate, the structure can be destroyed, but the crack propagation time can be neglected. Finally, using Ansys software as the platform, the analysis of the bridge crane machine is carried out. The location where cracks are most likely to occur in bridge cranes is determined, and the Ansys finite element life evaluation method based on Paris formula is proposed. The parametric model of web and lower flange plate is established by using APDL language to simulate the actual working conditions and crack growth process of bridge crane, and the fatigue crack propagation life of bridge crane under constant amplitude load is evaluated. In addition, the interaction integration method provided by Ansys software is used to calculate the stress intensity factor, and the relationship between the number of stress cycles and the crack size under constant amplitude load of bridge crane is fitted effectively. In accordance with the law of crack growth, the accuracy of fatigue life calculation is improved.
【学位授予单位】：太原科技大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TH215

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