MATLAB平面桁架算例.docx

陈继乐 专业：工程力学 学号：1120150528SummaryIn this term, I have learned professional English class of Mr. Sun. There are five students in this class. Each of us would make a presentation in class. I have learned a lot. Here is the main content of my presentations.1. The Introduction of mechanics of materialsThe research object of mechanics of materials is structure member. Structure members include bar, rod, plate, shell and clump body. Bar and rod are the main objects of mechanic of material. The task of mechanics of materials is as following. Under the request that the strength, rigidity, stability is satisfied, offering the necessary theoretical foundation and calculation method for determining reasonable shapes and dimensions, choosing proper materials for the components at the most economic price. There are four assumptions of the solid deformable bodies including continuity, homogeneity, isotropy and small deformations. Basic types of the deformation of rods are axial tension, shear, torsion and bending. 2.Statically determinate problemsIf forces act on a body, the lines of action of these forces are in the same place, which called coplanar forces system. To a general coplanar force system, there are three independent equations which can determine 3 unknown quantities. That are , , , which mean the total force in x axis and y axis are equal to zero and the total moment of point O is equal to zero. When the number of equations is larger than or equal to the number of unknown quantities, it is a statically determinate problem. When the number of equations is less than to the number of unknown quantities, it is a statically indeterminate problem. And statically indeterminate problems can be solved by the conditions of compatibility.3.Plane trussesA truss is a structure that is made of straight, slender bars that are joined together to form a pattern of triangles. There are three assumptions of plane trusses. 1. the weights of the members are negligible.2 . all joints are pin. 3 . the applied forces act at joints. According to three assumptions, we can get conclusion that each member of a truss is a two-force body. And there are two methods of calculation of the forces in the members of a truss, 1. Method of joint. 2 .Method of section. 3. Compositive Motion of a ParticleIn practice, we often observe the motion with respect to a moving body. There may exist relationship between two different objects. There are two coordinate systems. A coordinate system fixed to the earth ground is called static coordinate system (SCS). A coordinate system fixed to a moving object relative to the earth ground is called moving coordinate system (MCS). There are three kinds of motion and their velocities. The motion of the moving point relative to the SCS is called absolute motion. The motion of the moving point relative to the MCS is called relative motion. The motion of the MCS relative to the SCS is called converted motion. The velocity and acceleration of the moving point in its absolute motion are called absolute velocity. The velocity of the convected point in its absolute motion is called convected velocity. The velocity of the moving point in its relative motion is called relative velocity. There exists relationship among the three velocities. At any instant of time, the absolute velocity of a moving point equals the geometric sum of its relative velocity and convected velocity. This is the theorem of composition of velocities of a particle. Those are the main contents of my presentations. I have learned a lot from the professional English class. When I do my first presentation, I was nervous and I didnt do well. But I made progress in the following class. After each presentation, Mr. Sun would tell me how I should do to do better. I find many shortcoming of mine. And I have learned the advantages of my classmates. I will study harder and I hope I can do better in the future. 总结 在本学期，我学习了孙老师的专业英语这门课程。这门课有5位同学。我们每位同学需要在课堂上做一个英语综述。我在本课上受益颇多，以下是我的几次英语综述的主要内容。1. 材料力学简述材料力学的研究对象是结构构件。结构构件可分为：杆件、板壳和块体，材料力学的主要研究对象是杆件。材料力学的任务是在满足强度、刚度、稳定性的要求下，以最经济的代价，为构件确定合理的形状和尺寸，选择适宜的材料，而提供必要的理论基础和计算方法。可变形固体有4种基本假设：连续性假设、均匀性假设、各向同性假设、小变形假设。杆件的基本变形形式有：拉压、剪切、扭转和弯曲。2. 静定问题如果外力施加在物体上，而且这些力的作用线处于同一平面，那么这种系统称为共面力系。对于一般的共面系统而言，有3个方程可以确定3个未知量，即， ，它们的意义是X轴、Y轴上的合力为零，O点的合力矩为零。当方程数目大于等于未知量的数目时，该类问题称为静定问题；当方程数目小于未知量的数目时，该类问题称为非静定问题。而非静定问题可由补充的相容方程解出。3. 平面桁架桁架是一个由直的、细长的杆件组成的三角型结构。对于平面桁架，有3种假设：1.构件的质量可以忽略；2.所有节点是固定的；3.外 力作用在节点上。计算桁架内力有两种方法，即节点法和截面法。4. 质点运动的合成在现实中，我们经常可以观察到相对于一个运动物体的运动。在这两个对象中可能存在某种联系。有以下两种参考系，把固定在地球上的参考系称为定参考系，简称定系；固定在其他相对于地球运动的参考系上的坐标系称为动参考系，简称动系。有以下3种运动和其相应的速度：1.动点相当于定参考系的运动，称为绝对运动；