Elastoplastic Buckling on the Bent Waveguide of CESR-Type SRF Cavity

Abstract

A superconducting radio-frequency (SRF) cavity module of CESR-type has been adopted for some advanced accelerators. During operation, the pressure in the liquid-helium vessel acts on the cavity wall, but an ultrahigh vacuum must prevail inside the cavity; the cavity structure must be thus pressure-tested at ambient temperature as a standard procedure for safety. During the pressure test elastoplastic buckling might occur on this SRF cavity and its bent waveguide section, being a shell-like structure. A nonlinear finite-element model for computation is established to assess the mechanism of buckling and post-buckling of the bent waveguide. Some test results with copper bent waveguides are presented. The critical pressure and buckling pattern are strongly affected by the material property and the thickness of the structure and the U-channel.

Effects of Material Properties on the Elastoplastic Buckling of an SRF Cavity Under External Pressure

“…The stress-strain curves tested with standard specimens in the previous work [10] are used here. Because these two test curves differ much from each other, various stress-strain curves are assigned to the models for calculation to assess the effects.…”

“…Curves A and B are to simulate the tested results with multi-linear curves, whereas the others are with bilinear curves. Young's modulus of curves A and B differs much from each other-105 and 44.2 GPa, respectively, as they were tested with separate niobium specimens and with separate equipment [10]. Curve C results from a bilinear approach of curve B; Young's modulus is thus also 44.2 GPa but with yielding stress of 52 MPa and second modulus , defined as the slope of the stress-strain curve in the plastic range, 1.8 GPa.…”

“…Preceding authors proved that elastoplastic buckling of the CESR-type SRF cavity would first damage its bent waveguide structure under an external pressure [10]. The related strength and buckling behavior of the KEK-type SRF cavity are investigated herein.…”

“…We used finite-element software (ANSYS) to calculate the limit pressure and buckling behavior, with an incremental arc-length control scheme to include the effects of nonlinearities of both the geometry and the material property. The material property in the calculation model is referred to the experimental stress-stress curves [10]. Both bilinear and multi- linear approaches for the stress-strain curve are adopted.…”

Analysis and Experiment of Deformation and Limit Load of Thin-Walled Shell Cavities

“…Fortunately, the finite element method has the ability to solve the problem. Lin et al [10] used the finite element method and experiment to discuss the elastoplastic buckling of the bent waveguide of the thin-walled shell cavity subjected to external pressure. In this study, we used the commercial software ANSYS  and the incremental displacement-controlled scheme to predict the limit load and the post buckling behavior of thin-walled shell cavity.…”