Sisäjännitteet

Sisäjännitteet, often translated as internal stresses or residual stresses, refer to stresses that exist within a solid material or structure in the absence of external forces or loads. These stresses arise from various manufacturing processes, thermal treatments, or mechanical deformations. They are essentially a self-equilibrating stress system within the material.

Common sources of internal stresses include welding, casting, forging, machining, and heat treatment processes like quenching and tempering. During welding, rapid heating and cooling cycles cause differential expansion and contraction, leading to locked-in stresses. Similarly, in casting, uneven cooling rates between the surface and the core of a casting create internal stress gradients. Mechanical processes like shot peening or cold working can induce compressive residual stresses on the surface, which can enhance fatigue life.

The presence and distribution of internal stresses can significantly impact a material's mechanical properties. Tensile residual stresses can reduce a component's strength and fatigue resistance, making it more susceptible to cracking. Conversely, compressive residual stresses can improve fatigue performance and resistance to stress corrosion cracking.

Measuring internal stresses can be done using various non-destructive and destructive techniques. Non-destructive methods include X-ray diffraction, ultrasonic testing, and hole drilling. Destructive methods involve sectioning the material and measuring the resulting dimensional changes. Understanding and controlling internal stresses is crucial in engineering design and manufacturing to ensure the integrity and performance of components.