CERN Accelerating science

Article
Report number	LHC-PROJECT-Report-1076 ; CERN-LHC-PROJECT-Report-1076
Title	Influence of Micro-Damage on Reliability of Cryogenic Bellows in the LHC Interconnections
Author(s)	Garion, C ; Skoczen, B
Affiliation	(CERN) ; (Cracow Tech. U.)
Publication	2008
Imprint	Dec 2007
Number of pages	9
In:	AIP Conf. Proc. 986 (2008) 100-107
In:	Conference on Cryogenic Engineering and Cryogenic Materials, Chattanooga, TN, USA, 16 - 20 Jul 2007, pp.100-107
DOI	10.1063/1.2900331
Subject category	Accelerators and Storage Rings
Accelerator/Facility, Experiment	CERN LHC
Abstract	To achieve maximum beam energy in the LHC the accumulated length of the interconnections between LHC main magnets has been limited to around 3% of the total magnetic length in the Arcs and Dispersion Suppressors. Such a low ratio leads to a very compact design of components located in the LHC interconnections. This implies development and evolution of high intensity plastic strain fields in the stainless steel expansion bellows subjected to thermo-mechanical loads at low temperatures. These components have been optimised to ensure high reliability standards required for the LHC. Nevertheless, initial damage can occur and lead to a premature fatigue failure. For structures in which plasticity is not confined to the crack tip region, standard failure mechanics, based classically on the stress intensity factor or the strain energy density release rate, can not be used. In the present paper, a constitutive model taking into account plastic strain induced g->a' phase transformation and orthotropic ductile damage is presented. This local approach is used to predict the impact of initial imperfections on the fatigue life of thin-walled LHC bellows expansion joints.

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