Abstract
The niobium is currently used for the construction of the superconducting radio frequency (RF) Crab Cavity for the particle accelerator LHC at CERN in Geneva. An alternative technique to traditional forming methods is the electrohydraulic forming (EHF), in which ultrahigh-speed deformation of blank sheets is performed by using shockwaves electrically induced in water. A big effort is made for the analysis of the forming processes by FEM simulations, which require the definition of an appropriate flow stress material model. With this aim, in the present work, a testing campaign was performed in tension on sheet specimens with a rectangular cross-section at different strain-rates, up to 103 s-1. The obtained results showed the material is strongly sensitive to strain-rate, as expected for a pure BCC metal. The data, were processed via a reverse engineering procedure, based on finite element simulations of the experimental tests. This methodology allowed the identification of a tabular flow stress model (MAT_224 implemented in LSDYNA) for the prediction of the material behaviour as a function of the plastic strain, strain-rate and temperature.
Highlights
The niobium is currently used for the construction of the superconducting radio frequency (RF) Crab Cavity developed in the framework of the High-Luminosity Large Hadron Collider (HL-LHC) at CERN in Geneva [1]
The final objective was the identification of a reliable strength material model to be used in numerical simulations of the forming process adopted to produce RF Crab-Cavity at CERN of Geneva in the framework of the HL-LHC upgrade
The experimental tests were performed at room temperature at 4 different strain-rates by covering 6 orders of magnitude
Summary
The niobium is currently used for the construction of the superconducting radio frequency (RF) Crab Cavity developed in the framework of the High-Luminosity Large Hadron Collider (HL-LHC) at CERN in Geneva [1]. The ability of the cavity to rotate the protons beam with the right frequency strongly depends on its shape, tight geometrical tolerances are required. These considerations explain the interest in the fabrication method. With respect to traditional methods, such a highly dynamic process can yield interesting results in terms of effectiveness, repeatability, final shape precision, higher formability, and reduced springback. During this process, the component is produced with speeds in the order of 100 m/s
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