SIMPLE STRESS
STRESS is the intensity of force inside a solid. The basic unit of stress is the Pascal (Pa) which is Newton per square metre. In engineering it is more convenient to measured as the force (N) per square mm. This gives the common engineering unit of stress, MPa.
Tensile, Compressive and Shear stress
There are 3 types of stress in the world;
- Tensile = pulling apart
- Compressive = squashing together
- Shear = sliding apart
Any of these 3 types of stress are calculated the same way, with the same units - it the area that is different. Always think of what area must be broken when the component fails (the broken area).
What is a Stress?
STRESS is the intensity of force inside a solid.
It has the same units as Pressure (Pa, kPa, MPa, etc), so you could think of stress as pressure in a solid. The difference is, pressure acts equally in every direction, but stress has a certain direction.
Stress = Force/Area
The base unit for pressure and stress is the Pascal (Pa), but this is way too small for engineering use - except perhaps when measuring the pressure of air conditioning ducts or something. Certainly nothing compared to the stress required to break steel. In most engineering situations, the strength of a material is measured in MPa (MegaPascals)
Stress (MPa) = Force (N) / Area (mm2)
| DEFINE | Formula | Units | Diagram |
| Axial Stress (Tension or Compression) | Stress = Force / Area | MPa |  |
| Axial Strain (Tension or Compression) | Strain = extension / original Length | - |  |
| Shear Stress | Stress = Force / Area | MPa |  |
| Modulus of Elasticity (Young's Mod) | E = Stress / Strain | GPa | Slope of Stress:Strain diagram |
| Modulus of Rigidity (Shear Mod.) =~ 0.4E | G = S. Stress / S. Strain | GPa | Slope of S.Stress:S.Strain diagram |
| Shear Strain | Strain = movement / original Depth | - |  |
| Shear in Detail: Shear Strain is usually small enough to ignore the changes in L with angle. Angle is in radians. Area is the zone that would slide apart assuming it broke in shear. |  | ||
