Residual stress and its consequences

What does residual mean?
Residual stresses, also known as locked-in stresses, are referred to an specific amount of stress that exists in the absence of external loading or thermal gradients. So even if the members is not subjected t loading, it has s degree of internal stress.
What causes residual stresses?
many factors can cause residual stresses. Among all, manufacturing process is usually the first responsible. Processes such as casting, welding, machining, molding, heat treatment, plastic deformation during bending, rolling or forging are the most common manufacturing processes that creates residual stresses. Since most of our structural members are produced by heating or cold working, we need to consider the effect of this residual stresses in our calculations.
Consequences
Most of equations that are studied in material mechanics are presented without considering the effect of residual stresses. Residual stresses act exactly like common mechanical stresses. The only difference is that unlike mechanical stresses, residual stress is difficult to measure. All in all, residual stress decreases the overall capacity of steel members but to be more precise we need to have a closer look for each loading case.
Measuring methods for residual stress
x-ray diffraction
ultrasonic methods
magnetic methods
Electronic Speckle Pattern Interferometry
Hole drilling and strain gage technique
Core Hole drilling and strain gage technique

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