摘要
在当前的工程力学实验教学中,多数实验对象为单一的杆件或者简单的构件,缺乏对超静定多杆件系统的力学实验项目。车圈结构是日常普遍使用的自行车中的重要部件,力学上可以抽象为由封闭圆环和多根预应力拉杆组成的超静定结构。因此,本文对自行车车圈结构的力学实验进行了研究。
本文以为本科生开设车圈结构力学实验平台为应用目标,设计自行车车圈合理的实验方案,利用实验应力分析方法测试车圈结构的受力和形变,将得到的实验结果与理论计算和有限元计算的结果相比较,从中得出车圈结构的力学性能特征,同时分析了影响实验精度的各种因素,验证了其作为教学实验的可行性。具体而言,
本论文的主要研究内容和结论如下:
1)系统论述了国内外对车圈结构研究的现状,介绍了采用实验应力分析方法测试车圈结构的实验方案和实验原理;
2)建立了以封闭圆环和多根预应力拉杆所组成的车圈结构的力学模型,分别采用力法和有限元法,完成了对车圈结构的理论研究,并给出了车圈结构上测量点的应变和变形的理论预测值;
3)建立了车圈结构的力学实验平台,在车圈钢丝无预紧和均匀预紧的条件下,实际测量了车圈结构的静力变形和观察点的应变;
4)对比理论预测与实验测量结果发现,理论与实验结果具有较好的一致性,从而证实了该实验平台和实验方案的可行性,也说明了所采用的力学模型和分析方法的正确性;
5)文中还分析了实验误差的来源,提出了减小实验误差,提高精度的改进方案。以上研究,为开设一项新型的车圈结构的力学实验教学项目打下理论和实验基础。
Nowadays most of the experiment objects are some specimens and simple structures in mechanical experiment courses. There is a lack of experiments on hyperstatic system supported by many rods. The bicycle rim is one of the most important parts of daily-used bicycle. It can be described as a static undetermined structure supported by many rods in mechanical model. Therefore, this thesis does some research on the mechanical experiment of bicycle rim.
This thesis aims at opening one mechanics experiment course of bicycle rim for undergraduate students. Firstly, a reasonable experiment project of bicycle rim is designed. Secondly, analysis of a complexity structure-statically indeterminate model is presented for the rim and the stress and strain of actual bicycle rim is tested and measured using the experimental stress analysis method. Thirdly, the mechanical characteristics of the structures are educed by comparing the experimental results with the finite element results. The effects on accuracy of the experiment results are also discussed. Therefore, the feasibility of this experiment is validated. The main contents and conclusions of this thesis are listed as follows:
1) A general review on the current research situation of bicycle rim is presented. The scheme and the principle of experiment on bicycle rim with experimental stress analysis method are introduced.
2) The mechanical model of bicycle rim is established, which is a closed circle rod structure supported by many prestressed rods. The theoretical results which are calculated with mechanics of material method and finite element method of bicycle rim structure are given.
3) The mechanics experiment platform of bicycle rim is established. The strain and displacement of bicycle rim are measured when the spoke are prestressed and un prestressed.
4) The theoretical results and experimental results are compared with each other, and the results show that they agree well with each other, which invalidates the feasibility of the experiment platform and experiment scheme. It also shows that the mechanics model and research method is correct.
5) The source of the experiment errors is analyzed, and the scheme to reduce the errors and increase the accuracy is put forward.
All the work that this thesis has done can offer theoretical and experimental guides for realization a new item in mechanic experiment course.
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