Jäännössijännitteet

Jäännössijännitteet, known in English as residual stresses, are mechanical stresses that remain within a solid material after the original external loads are removed or after manufacturing processes. These stresses are self-equilibrating, meaning that within any given volume of the material, the sum of the stresses is zero. They can exist in metals, ceramics, polymers, and composites.

Residual stresses can arise from various sources. In metals, they are commonly introduced during manufacturing processes such as welding, casting, forging, machining, and heat treatment. For example, rapid cooling during quenching creates non-uniform expansion and contraction, leading to residual tensile stresses in some areas and compressive stresses in others. Surface treatments like shot peening or laser peening also deliberately introduce compressive residual stresses to improve fatigue life.

The presence of residual stresses can significantly influence a material's mechanical behavior. Compressive residual stresses are generally beneficial as they can enhance resistance to fatigue, fracture, and stress corrosion cracking. Conversely, tensile residual stresses can be detrimental, making the material more susceptible to these failure modes. Understanding and controlling residual stresses is crucial in engineering design and manufacturing to ensure the integrity and performance of components. Techniques like X-ray diffraction, neutron diffraction, and ultrasonic methods are used to measure residual stresses.