Mechanics Of Materials Chapter 1 Preface Paper produces

Mechanics Of Materials

Chapter 1 Preface Paper produces large deformation Paper after folded

A bike frame is made of thin-walled steel pipes Why not reinforcing bars

The importance of basic mechanics idea Fan Qinsan The education of mechanics is a basic education

§ 1 -1 Tasks of Material Mechanics 1. Objects Concerned Deformable solids Structural Members Bars

2. Research Scope 1) Strength The ability to resist damages. Damages： Fracture Large plastic deformation

2) Stiffness The ability to resist deformations. Large elastic deformation

长轴的变形控制 Elastic deformation<Limitation

3) Stability The ability to resist buckling. 外压(a)和轴向压力(b)导致圆柱筒的失稳 失稳的大桥桥面

Tasks of Material Mechanics Under the condition satisfying the Strength, stiffness and stability, to solve the contravention between safety and economy, and to provide basic theory and numerical method for the design of rational configuration and dimension 构件在�足强度、�度和�定性的条件下，力求 合理地解决安全和��之�的矛盾，�构件�� 合理的形状和尺寸，��适宜的材料提供基本理 �和�算方法。

3. The Role and Specialties of the Course 1）the role of the course A basic course for the specialty of Civil Engineering Mechanical Engineering and Mechanics The first important course for the students to feel and to understand their specialties。

2）The Relation to Theory Mechanics Theory mechanics studies the external responses of rigidities. A B FA FB F F Material mechanics focuses on the internal responses and deformations. F FN F 3）Specialties：logically linked, plenty of concepts 4）How to study：best understanding of concepts, enhanced drilling 强化训练

§ 1 -2 Basic Assumptions of Material Mechanics 1. The assumption of uniformity and continuity 2. The assumption of isotropism 3. Small deformations 1）Material mechanics accepts and calculates deformations. 2）The deformations are much smaller than the dimensions of members. 3）The structural analysis is carried on the original configurations and dimensions.

３. Common deformable objects Plate Block Shell Cross-section Chain suspension Axial line Bar Objective for Mechanical materials Straight bar Equivalent section bar Curve bar Changeable section bar

4. Common deformations P P (a)Axial tension Tension compression P P (b)Axial compression

P P Shear deformation Me g j Me Torsion deformation

Me Me Bending deformation Tangshan Great earthquake in 1976 Combined load-----Tompuson(England) 23 th Olypics, Los, Angeles 洛杉矶 Beyond Two kinds of deformation

Question: What kinds of deformation for the bars in the Figure? (1)When C is not fixed completely, and it can transfer a little The deformations are occurred in ABC plane AB is tensile bar（tensile deformation） BC is compressed bar（compression deformation） (2) When C is fixed completely, and it Cannot transfer a little AB is tensile bar（tensile deformation） BC is compressed and bending bar（combined deformation）