2. Stress and Strain Flashcards
What is the definition of stress?
Stress, σ = F / A
Units: N/m^2 or Pa
In reality, what must we consider with stress when designing things?
Think of an equation too.
- In reality, stress isn’t perfectly distributed and acts as predicted. So we apply a safety factor to the equation to determine the maxium stress of a design.
What will happen to the stress when a hole is present?
How can we work out the maximum stress?
- Stress won’t be evenly distributed now, so more stress will be present the closer to the hole you are.
- Therefore, we can use a concentration factor, Kt and mean stress to find the maximum stress in the system.
True or False:
Changes in geometry don’t cause stress distribution to change.
- False, sudden changes in geometry do cause changes in the way stress is distributed as shown below
What is Shear Stress? (Give the formula)
- Shear stress is the force applied parallel to an area (rather than perpendicular).
- Same units as stress.
True or False:
Stress is a vector force.
- True, this means that we can have normal stress and shear stress as components of our total (resultant) stress.
Define Strain, also give its formula.
- Strain is the change in length (or extention/constraction) divided by the original length.
- The equation and units are below:
Define Young’s Modulus, and equation.
- Young’s modulus describes a materials stiffness
- Young’s modulus is equal to stress over strain:
What is the relationship between stress and strain called?
Hooke’s Law
What happens (in reality) when we stretch a bar?
The bar will thin at the edges while also getting longer.
Define Poission’s ratio and its formula.
It describes how much a bar stretches in the x and z directions using the x direction. Equation shown below
What is the equation for shear strain?
How can we relate shear strain and stress together using shear modulus?
