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| Hauptseite > Publikationsdatenbank > Design and FEA Simulation of Interference Fit and Autofrettage Process to Induce Residual Stresses in a High-Pressure Cell |
| Master Thesis | FZJ-2025-03068 |
2025
Forschungszentrum Jülich
Jülich
Abstract: High-pressure clamp cells for neutron diffraction experiments require specialized construction materials that do not attenuate neutrons, are not activated, are non-magnetic and can withstand high pressures. Previous research found two commercially available materials, Nickel-Chromium-Aluminium Alloy (NiCrAl) and Copper-Beryllium Alloy (CuBe2), for a compound cylinder clamped-cell designed for a maximum working pressure of 2.3 GPa. This pressure exceeds the yield strength of both materials and previously employed strengthening mechanisms to combat this issue were found unsuccessful. This work aims to enhance the mechanical strength of the NiCrAl inner cylinder to ensure safe usage of the clamped cell at high pressures of up to 2.3 GPa through autofrettage. The study also investigates the optimization of the interference fit between the inner NiCrAl cylinder and the outer CuBe2 cylinder, aiming to further reinforce the structural integrity of the cell. Through theoretical study and numerical analysis using ANSYS Mechanical [ANSYS], a swage autofrettage process is designed. A composite tungsten carbide mandrel with 0.04 mm interference to the inner surface of the cylinder is used to achieve a 20% peak overstrain, resulting in an increase of up to 872.7 MPa of compressive residual stresses in the hoop direction at the inner surface. The interference fit of the cylinders, using H7/r6 tolerance class, generates a contact pressure between 22.07 MPa to 186.3 MPa at the contact surface. After autofrettage and interference fit assembly, the compound cylinder cell withstands internal pressure of 2.3 GPa with a minimum safety factor of 1.18, indicating safe operation under these conditions. Based on the findings, it is suggested to perform autofrettage first on a straight cylinder, followed by machining its outer surface to a tapered profile for the subsequent tapered interference fit with the outer cylinder.
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