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 area
^{1}($m^{2}$)

- 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