machine design

1. Machine Design
Presentation -1
D.M.Gamage
Institute ofTechnology
(NDT)
University of Moratuwa

2. Contents
1. Stress
2. Unit Stress
3. Strain
4. Direct Stain
5. Shear Stain
6. Stress-Strain Diagram for Ductile materials
7. Stress-Strain Diagram for Brittle materials

3. 1. Stress
•The force of resistance per unit area, offered by a
body against deformation is known as Stress.
•Stress =
𝑬𝒙𝒕𝒆𝒓𝒏𝒂𝒍 𝒇𝒐𝒓𝒄𝒆 𝒐𝒓 𝒍𝒐𝒂𝒅
𝑪𝒓𝒐𝒔𝒔 𝒔𝒆𝒄𝒕𝒊𝒐𝒏 𝒂𝒓𝒆𝒂
𝜎 =
𝐹
𝐴
where,
F= external force
A = cross section area
𝜎 = Stress

4. • stress per unit area is known as Unit Stress
Unit stress =
𝑠𝑡𝑟𝑒𝑠𝑠
𝑎𝑟𝑒𝑎
Unit stress =
𝜎
𝐴
2.Unit stress

5. 3.strain
•When a body is subjected to some external force,
there is some change of dimension of the body.
•The ratio of change of dimension of the body to
the original dimension is known as strain.
•Strain is dimensionless.

6. •Strain =
𝑬𝒍𝒐𝒏𝒈𝒂𝒕𝒊𝒐𝒏
𝑰𝒏𝒊𝒕𝒊𝒂𝒍 𝒍𝒆𝒏𝒈𝒕𝒉
•Strain =
𝒆
𝒍

7. 4.Direct Strain
•Direct Strain is define as a deformation per unit
length.
•This is known as normal Strain.
•Strain =
𝒆
𝒍

8. 5.Shear strain
•Shear strain =
𝑥
𝐿
=𝜃
•The shear strain or slide is
𝜃 𝑎𝑛 𝑐𝑎𝑛 𝑏𝑒 defined as the change
in right angle.
•It is measured in radius.
•Shear strain is dimensionless.

9. 6.Stress-Strain Diagram for Ductile materials

10. 7.Stress-Strain Diagram for Brittle materials

11. •Thankyou