Autofrettage is a metalworking process that increases the fatigue life and pressure capacity of thick-walled cylindrical components by inducing beneficial residual compressive stresses in the inner wall. The process has been used since the early 20th century and remains critical for high-pressure component manufacturing.
The principle is straightforward: internal pressure is applied to a cylindrical component beyond its elastic limit, causing plastic deformation of the inner layers while the outer layers remain elastic. When the pressure is released, the elastic outer layers attempt to return to their original shape, but the plastically deformed inner layers prevent full recovery. This creates residual compressive stresses at the inner surface and tensile stresses at the outer surface.
The compressive residual stresses at the inner surface are highly beneficial for fatigue performance. When the component is subsequently subjected to operating pressure, the applied tensile stresses must first overcome the residual compressive stresses before the net stress becomes tensile. This effectively reduces the stress range experienced by the material, significantly extending fatigue life.
Typical autofrettage pressures range from 1.2 to 2.0 times the component's design pressure, depending on the geometry ratio (outer diameter to inner diameter) and the desired level of residual stress. The process is commonly applied to gun barrels, high-pressure pump heads, fuel injection components, and thick-walled pressure vessels.
RuikeWin's autofrettage systems provide precise control over the pressurization process, with programmable pressure profiles, real-time strain monitoring, and automatic detection of the yield point. Systems are available for pressures up to 15,000 bar, covering applications from common rail fuel systems to ultra-high-pressure industrial processes.
Case studies from our installations demonstrate significant fatigue life improvements. For thick-walled cylinder applications with diameter ratios of 2:1 to 3:1, autofrettage typically extends fatigue life by 3-5 times compared to non-autofrettaged components. For high-cycle fatigue applications (10^6+ cycles), the improvement can be even more dramatic.
The process is particularly valuable for components made from high-strength steels, where the cost of material failure far exceeds the cost of autofrettage processing. Industries including oil & gas, aerospace, and power generation routinely specify autofrettage for critical pressure-containing components.
