平板网架结构十字形板—焊接空心球连接疲劳性能的理论与试验研究

发布时间：2018-07-27 17:47

【摘要】：鉴于平板网架结构的众多优势,在我国不论其应用的规模还是数量上,均稳居世界前列。在平板网架结构上设置悬挂吊车,悬挂吊车所产生的反复交变荷载给网架结构带来疲劳问题。平板网架结构的疲劳主要包括杆件、焊接空心球及悬挂吊点连接的疲劳,而悬挂吊点连接的疲劳是平板网架结构疲劳破坏的关键部位。十字形板一焊接空心球连接作为悬挂吊点的主要方式之一,相关的疲劳理论研究及疲劳试验研究进展较为缓慢,且相关悬挂吊点的疲劳设计计算方法在我国现行的规范和规程中属于空白。上述种种因素给悬挂吊车在平板网架结构中的推广应用造成了很大的制约。在两项国家自然科学基金项目(50678109,51178286)的大力资助下,本文重点针对焊接空心球节点平板网架结构中十字形板—焊接空心球悬挂吊点的疲劳性能进行理论与试验研究。其相关的工作及结论总结如下： 1、采用ANSYS有限元软件,以不同规格匹配而成的25个十字形板—焊接空心球节点(材质均为Q235B)为研究对象进行单因素分析,重点讨论了节点相关尺寸的五个因素,即焊接空心球直径D、焊接空心球壁厚tx、十字形板宽度B、十字形板厚度tp和板球连接焊缝焊脚尺寸hf对节点应力的影响。基于分析结果,建立了十字形板—焊接空心球节点的热点应力集中系数的计算公式,其取值区间为3.176～5.365。研究结论揭示了应力集中和疲劳破坏源的关系,解释了十字形板—焊接空心球节点疲劳强度相对较低的原因,为建立以热点应力幅为参量的疲劳设计方法奠定了一定的理论基础。 2、设计了与本次疲劳试件相匹配的加荷装置,采用Amsler疲劳试验机(瑞士),顺利完成了25个十字形板—焊接空心球节点的常幅疲劳性能试验,得到了25个疲劳试验数据(6个异常)。收集了国内已有的9个常幅疲劳试验数据。将本文与国内共有的28个疲劳试验数据回归统计分析,得到了s-N曲线。 3、基于得到的常幅S-N曲线,以热点应力和热点应力幅为设计参量,建立了平板网架结构十字形板—焊接空心球节点两种表达形式的常幅疲劳设计方法；若以N=2×106为基准期,则[△σ]2×106=19.66Mpa,[△σh]2×106=62.44Mpa；上述常幅疲劳设计方法的建立为国家相关规范或规程提供了有益的补充,扩大了节点疲劳设计方法的的类别。 4、为了揭示十字形板—焊接空心球节点的变幅疲劳性能,采用代表性的加载模式对14个节点疲劳试件进行变幅试验,试验共取得14个有效的疲劳试验数据。通过对上述试验数据进行处理,采用线性累积损伤理论Miner法则和(?)Corten-Dolan非线性累积损伤理论分别对其变幅疲劳试件进行寿命估算,结果表明：采用Corten-Dolan理论对十字形板—焊接空心球节点进行疲劳寿命估算较为合理。 5、借助于电子显微镜和放大镜,进行了4个常幅和4个变幅典型疲劳试件疲劳断口的金相分析；揭示了十字形板—焊接空心球节点常幅和变幅疲劳破坏机理及断口特征,常幅疲劳断口的随机性远小于变幅疲劳断口；结合理论分析和金相分析,得出十字形板—焊接空心球节点中板肋端部是疲劳源的主要起始部位。 6、采用断裂力学对十字形板—焊接空心球节点进行疲劳寿命估算是可行的。理论估算值与试验结果的规律基本一致,但理论估算值与试验结果两者数值存在一定的误差,最大相差为30%；节点所含的先天性缺陷或类裂纹的大小对裂纹扩展寿命影响很大,但材料的断裂韧性对疲劳寿命影响较小。
[Abstract]:In view of the numerous advantages of the plate truss structure, in our country, the size and quantity of its application are all in the forefront of the world. The suspension crane is set up in the plate frame structure, and the repeated alternating load produced by the suspension crane brings fatigue to the grid structure. The fatigue of the plate truss structure mainly includes the rod, the welded hollow ball and the suspension. Fatigue of hanging point connection is the key part of fatigue failure of plate truss structure. As one of the main ways of hanging point, cross plate welded hollow ball connection is one of the main ways. The related fatigue theory research and fatigue test research progress is slow, and the fatigue design calculation method of related suspended suspension points is used. China's current codes and regulations are blank. All these factors have greatly restricted the popularization and application of suspension cranes in flat grid structures.
Under the support of the two National Natural Science Foundation (5067810951178286), this paper focuses on the theoretical and Experimental Research on the fatigue performance of the cross plate - welded hollow ball suspended point in the plate grid structure of welded hollow ball joints.
1, by using ANSYS finite element software, 25 cross shaped plate welded hollow ball joints (material Q235B), which are matched with different specifications, are used for single factor analysis. The five factors related to the node size are discussed, namely, the diameter of the welded hollow ball D, the welded hollow ball wall thickness TX, the cross plate width B, and the cross plate thickness TP. The influence of the size HF of the cricket joint weld bead on the stress of the joint. Based on the analysis results, a calculation formula for the hot spot stress concentration coefficient of the cross plate welded hollow ball joints is established. The value range is 3.176 ~ 5.365., and the relationship between the stress concentration and the fatigue failure source is revealed, and the cross plate welded hollow sphere is explained. The reasons for the relatively low fatigue strength of the points provide a theoretical basis for establishing the fatigue design method based on the hot spot stress amplitude.
2, a loading device matched with this fatigue test specimen was designed. Using the Amsler fatigue test machine (Switzerland), the constant amplitude fatigue test of 25 cross shaped plate welded hollow ball joints was successfully completed, and 25 fatigue test data (6 anomalies) were obtained. The existing 9 constant amplitude fatigue test data in China were collected. The s-N curves were obtained by regression analysis of 28 fatigue test data.
3, based on the obtained constant amplitude S-N curve, based on the hot spot stress and the hot spot stress amplitude as the design parameters, a constant amplitude fatigue design method for two expressions of the cross plate and welded hollow ball joints of the plate truss structure is established. If the N=2 x 106 is the reference period, [delta sigma]2 x 106=19.66Mpa, [delta sigma h]2 x 106=62.44Mpa], the above constant amplitude fatigue design side The establishment of law provides a useful supplement to relevant national codes or regulations, and expands the categories of nodal fatigue design methods.
4, in order to reveal the variable amplitude fatigue performance of the cross plate - welded hollow ball joints, 14 fatigue test specimens were tested with a representative loading mode, and 14 effective fatigue test data were obtained. By processing the above test data, the Miner rule of linear cumulative damage theory and (?) Corten-Dolan non The linear cumulative damage theory is used to estimate the fatigue life of the variable amplitude fatigue specimens. The results show that the fatigue life estimation of the cross plate welded hollow ball joints is more reasonable by using the Corten-Dolan theory.
5, with the aid of electron microscope and magnifying glass, the metallographic analysis of fatigue fracture of 4 typical fatigue specimens with constant amplitude and 4 amplitude variation is carried out. The failure mechanism and fracture characteristics of the common and variable amplitude fatigue fracture of the cross plate welded hollow ball joints are revealed. The randomness of the constant amplitude fatigue fracture is far smaller than the amplitude fatigue fracture. From the phase analysis, it is concluded that the end of the plate rib in the welded hollow spherical joints is the main starting point of fatigue source.
6, it is feasible to estimate the fatigue life of the cruciform plate welded hollow ball joints with fracture mechanics. The theoretical estimation values are basically the same as the experimental results, but there is a certain error between the theoretical estimated value and the test results, the maximum difference is 30%, and the congenital defects or the size of the crack like cracks in the joints have the crack expansion. The influence of fracture toughness on fatigue life is small.
【学位授予单位】：太原理工大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU356

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