Stress and Strain
Stress
- Stress can be defined as a measure of the internal reaction to an externally applied force.
- Stress is measured in Pascals (Pa) and can be calculated by using:
\begin{align} \sigma = \frac{L}{A} \end{align}
- Where:
- $\sigma$ is the stress (Pa)
- $L$ is the external force/"Load" (N)
- $A$ is the effective area1 ($m^{2}$)
- There are 3 main types of stresses:
- Tensile stress:
- It is an Axial Stress (The force is along the axis of the member)
- It is a force that "EXTENDS" the member. (Pulling it apart)
- Compressive stress:
- It is also an Axial Stress
- It is a force that "CONTRACTS" the member. (Crushing it inwards)
- Shear stress
- This stress is NON-AXIAL.
- It is a force that is one member trying to "SLIDE OVER" another member
- Covered in detail later.
- Tensile stress:
Strain
- Strain is a measure of how much a material/member will deform under a certain force.
- It can be defined as the proportional change in length caused when a specimen is under an axial load and has no units. (It is a ratio)
- It can be found by:
\begin{align} \varepsilon = \frac{e}{l} \end{align}
Where:
- $\varepsilon$ is the strain
- $e$ is the extension (m) (This is found by $l_{final} - l_{original}$)
- $l$ is the original length (m)
page revision: 3, last edited: 04 Jul 2011 06:32