Thermo-mechanical characterisation of low density carbon foams and composite materials for the ATLAS upgrade

• Main Author: Isaac, Bonad
• Published: University of Glasgow 2012
• Subjects: 530.412; QC Physics
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.549863

As a result of the need to increase the luminosity of the Large Hadron Collider (LHC) at CERN-Geneva by 2020, the ATLAS detector requires an upgraded inner tracker. Upgrading the ATLAS experiment is essential due to higher radiation levels and high particle occupancies. The design of this improved inner tracker detector involves development of silicon sensors and their support structures. These support structures need to have well understood thermal properties and be dimensionally stable in order to allow efficient cooling of the silicon and accurate track reconstruction. The work presented in this thesis is an investigation which aims to qualitatively characterise the thermal and mechanical properties of the materials involved in the design of the inner tracker of the ATLAS upgrade. These materials are silicon carbide foam (SiC foam), low density carbon foams such as PocoFoam and Allcomp foam, Thermal Pyrolytic Graphite (TPG), carbon/carbon and Carbon Fibre Reinforced Polymer (CFRP). The work involves the design of a steady state in-plane and a steady state transverse thermal conductivity measurement systems and the design of a mechanical system capable of accurately measuring material stress-strain characteristics. The in-plane measurement system is used in a vacuum vessel, with a vacuum of approximately 10¡5 mbar, and over a temperature range from -30±C to 20±C. The transverse and mechanical systems are used at room pressure and temperature. The mechanical system is designed so that it measures mechanical properties at low stress below 30MPa. The basic concepts used to design these measurement systems and all the details concerning their operations and implementations are described. The thermal measurements were performed at the Physics and Astronomy department of the University of Glasgow while the mechanical measurements were performed at the Advanced Materials Technology department, at the Rutherford Appleton Laboratory (RAL). Essential considerations about the measurement capabilities and experimental issues are presented together with experimental results. The values obtained for the materials with well understood properties agree well with the values available in the literature, confirming the reliability of the measurement systems. Additionally, a Finite Element Analysis (FEA) is performed to predict the thermal and mechanical properties of PocoFoam. The foam is created by generating spherical bubbles randomly in the computational tool MatLab according to the topology of PocoFoam. The model is transferred to the CAD program Solid works to be extruded and be transformed into PocoFoam. It is later on transferred to the FEA tool ANSYS to be analysed. Simulations of a specimen of density equal to 0.60g/cm3 are performed and the results are compared with the values measured for a specimen of density equal to 0.56g/cm3. The simulated results agree within 32% with the experimental values. The experimental results achieved in the studies undertaken in thesis have made a considerable contribution to the R&D of the stave design by helping to understand and optimise the current stave design and explore new design possibilities. The stave is a mechanical support with integrated cooling onto which the silicon sensors are directly glued.