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Material Stress (Stress Concentration)

(Definition according to www.NDE-ED.ORG  - "When an axial load is applied to a piece of material with a uniform cross-section, the normal stress will be uniformly distributed over the cross-section. However, if a hole is drilled in the material, the stress distribution will no longer be uniform. Since the material that has been removed from the hole is no longer available to carry any load, the load must be redistributed over the remaining material. It is not redistributed evenly over the entire remaining cross-sectional area but instead will be redistributed in an uneven pattern that is highest at the edges of the hole as shown in the image. This phenomenon is known as stress concentration."

In simple terms this means that any material which when cut, machined or altered may and often does reflect a change in load distribution. The redistribution of the load is defined as a concentration of stress. The very nature of manufacturing is to alter the composition of material in the most primary sense. As such, stress is a part of manufacturing that must be addressed. Much as a wooden plank will warp over time with the application of weight (or force) so changes metal, plastics, composites etc.

At Land Sea Air Manufacturing we understand stress concentration and we know how to prevent it. Most manufacturers plow through material to remove the maximum amount of material with the fewest movements of the tool. This creates stress and over time the material seeks to naturally relieve the stress. This is most often seen as warping. To counter the warping, material is "stress relieved" typically in an oven where the material is soaked in heat for an extended period of time while the material relaxes. During this process the material becomes soft and hence must be hardened. This process is repeated multiple times in certain projects increasing cost and lead time.

By understanding stress concentration at a more metallurgic level it is possible to avoid building stress into the material. If you don't build stress into the material, you do not have to relieve it nor do you have to re-harden the material. Land Sea Air Manufacturing understands material stress and through a combination of high speed machining, advanced tool paths and specific tool coatings we are able to eliminate several re-conditioning processes. The result... shorter lead times and lower prices.