Engineering and working stress

Engineering stress

• For most stress/strain diagrams, stress appears to fall off near the end (during the necking down phase). This should NOT happen.
• Though, it is shown on most stress/strain diagrams as it does not show true stress, but engineering stress.
• Engineering stress is calculated using the ORIGINAL cross sectional area, even though the cross sectional area reduces during necking down. This explains why the stress drops.
• This is done for ease of calculation, otherwise the cross sectional area would have to be measured continuously.

Working stress

• Safe working stress is known as the maximum allowable stress that a material or object will be subjected to when in service.
• This stress is always lower than the Yield stress and the Ultimate Tensile Stress (UTS).
  • The ratio of Working Stress to the Yield Stress or UTS is known as the Factor of safety.
• Safe working stress is always less than the Elastic limit for a given material.