What is surface residual stress?

Residual stresses are those stresses that remain in an object (in particular, in a welded component) even in the absence of external loading or thermal gradients. In some cases, residual stresses result in significant plastic deformation, leading to warping and distortion of an object.

Why is residual stress compressive?

In general, compressive residual stress at the surface of a component is beneficial: it tends to increase fatigue strength and fatigue life, slow crack propagation, and increase resistance to environmentally assisted cracking, such as stress corrosion cracking and hydrogen-induced cracking.

What are the types of residual stresses?

Residual stresses can be used to benefit or hinder the performance of a component during operation by placing the material in either a compressive or tensile stress state. There are three types of residual stresses within a material: Type-I, Type-II, and Type-III.

How does residual compressive stress work?

In toughened glass, compressive stresses are induced on the surface of the glass, balanced by tensile stresses in the body of the glass. Due to the residual compressive stress on the surface, toughened glass is more resistant to cracks, but shatter into small shards when the outer surface is broken.

What is a way to introduce compressive residual stresses?

Introduction of Compressive Residual Stress by Means of Cavitation Peening into a Titanium Alloy Rod Used for Spinal Implants. Materials Sciences and Applications > Vol.4 No.7B, July 2013. Introduction of Compressive Residual Stress by Means of Cavitation Peening into a Titanium Alloy Rod Used for Spinal Implants.

How does compressive residual stress increases fatigue life?

Low-temperature grinding produces compressive residual stresses and improves fatigue life. This beneficial result is due to the mechanical grinding force applied to the surface which has a similar effect to surface peening.

What is residual compression?

Compressive residual stresses increase both the fatigue strength and resistance to stress corrosion cracking. They are intentionally formed by various processes such as shot peening, laser peening, low plasticity burnishing and autofrettage. These processes are cold working or strain hardening the material.

Is compressive residual stress good?

Compressive residual stress can have a very positive impact on fatigue performance because it acts to resist the applied tensile stress as it holds the crack faces shut, minimizing damage. To take advantage of this concept many compressive residual stress surface treatments have been developed.

How is residual stress measured?

Residual stress measurement by hole drilling method Hole drilling is the most commonly used stress relaxation technique for measuring residual stresses. Stressed material is removed by drilling a small blind hole in the area of interest and the material around the hole spontaneously finds a new stress equilibrium.

How is residual stress measured in welding?

One common method to measure residual stresses in crystalline materials is X-ray diffraction based method. In the discussed example a robotized X-ray diffractometer is used to measure residual stresses over a weld seam.