Stress Concentration

What is it?

A stress concentration, or stress riser, is a point of high stress on a component. This concentration is usually the result of a structural feature, such as fillets, bolt holes, keyways, and similar. The stress in these areas is inherently higher than in the uniform section of the component by as much as a factor of two or more.

 

Why does stress concentration cause failure in critical components?

Components are less likely to fail when stresses are distributed evenly throughout the part. When stress is concentrated in a narrow region, fatigue life of the whole component decreases. Fatigue cracks will always propagate from the point with the highest stress, rapidly leading to failure.

How can you mitigate stress concentration?

Apply a zone of engineered residual compression to eliminate the stress concentration. At Lambda, we calculate the mean stress distribution required at each point throughout a finite element model of the high-stress region to overcome the reduced fatigue life caused by the stress concentration.

Knowing the mean and alternating stress distributions in service, appropriate CNC processing code, and pressure, files can be created to introduce the amount of residual compression necessary to mitigate the stress concentration.*

Introduction of designed compression by Low Plasticity Burnishing (LPB®) to overcome component weaknesses discovered in service is a common application of the technology.

Learn more about Low Plasticity Burnishing from Lambda Technologies Group and how it can eliminate stress concentration in your critical metal components.

 

*It should be noted that only localized stress concentrations can be addressedin this manner. A layer of deep surface compression added to the surface of a uniformly loaded section could increase the interior tension, possibly moving failure initiation subsurface.

Close-up of crack locations on F-16 wing cut out

FEA of F-16 wing cut out

Fatigue life increase of F-16 wing cut out after LPB treatment