Measurement of the resistance to stress cycling at 4.2 K of LHC dipole collars

At each operation cycle of the LHC machine, the field of the superconducting dipoles will be raised from the injection level to the collision level and then decreased again. This will induce a stress cycle inside the structure. The collars will have to withstand several thousands of stress cycles during their life. In this paper a description of the test apparatus built to assess the strength of different types of collars is given. The authors also present results of measurements and draw some preliminary conclusions regarding the influence of material properties, geometry and surface condition, on the endurance of the collars