材料力学中英文课件.pdf

Mechanics of Materials
1. What is the Mechanics of Materials?
It involves analytical methods for determining the
strength, stiffness (deformation characteristics ) and
safety of the load-carrying members.
工程中各种机械和结构都是由许多构件和零件组成的. 为保证
其能安全正常的工作, 必须要求全部构件和零件在承受外力时
具有一定的承载能力, 即:
(1) Strength--the ability to prevent failure.
(2) Rigidity--the ability to resist deformation.
(3)Stability--the ability to keep the original equilibrium
state.
任务: 研究构件在外力的作用下的受力, 变形和破坏规律. 在保证
构件安全又经济的条件下, 为构件选择合适的材料, 确定合理
的截面尺寸, 提供必要的计算方法和实验技术.
2. Essential Assumptions
(1) Continuity: The material made of the solid body is full
of the volume of the body.
(2) Complete homogeneity: Each and every particle of a
body is assumed to contribute equally to the resistance of
the force (sameness from point to point in the whole
vacuum of the body).
(3) Isotropy: Properties of materials are essential alike in
any direction.
(4) The deformations tolerated in engineering structures are
usually negligible parison with the overall
dimensions of structures. Therefore, for the purposes of
obtaining the forces in members, the initial un-deformed
dimensions of members are used putations.
Chapter 1. Tension pression
Introduction
1. Internal force
The resistance forces that set up within a body to balance the
effect of the externally applied forces are called the internal forces.
2. Method of section
用任一截面假想地把构件截成两部分以显示并确定内力的方法.
如图示, 用面将物体截为两部分, 研究任意一部分, 由平衡方程
可确定截面处的内力. 显然上下两面的力互为作用与反作用
力。
Stress and strain
1. Stress
The stress of a point is defined as:
∆P
x ∆Py ∆Pz
τ xx = lim
∆A→0 τ xy = lim τ xz = lim
∆A ∆A→0 ∆A ∆A→0 ∆A
Where, the first subscript of τ indicates that the plane
perpendicular to the x-axis is considered, and the second
designates the direction of the ponent.
The intensity of the force perpendicular to or normal to
the section is called the normal stress (tensile stresses,
compres