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

[摘要] 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. Upgradingthe ATLAS experiment is essential due to higher radiation levels and high particleoccupancies. The design of this improved inner tracker detector involves development ofsilicon sensors and their support structures. These support structures need to have well understoodthermal properties and be dimensionally stable in order to allow efficient coolingof the silicon and accurate track reconstruction. The work presented in this thesis is an investigationwhich aims to qualitatively characterise the thermal and mechanical propertiesof the materials involved in the design of the inner tracker of the ATLAS upgrade. Thesematerials are silicon carbide foam (SiC foam), low density carbon foams such as PocoFoamand Allcomp foam, Thermal Pyrolytic Graphite (TPG), carbon/carbon and Carbon Fibre ReinforcedPolymer (CFRP). The work involves the design of a steady state in-plane and asteady state transverse thermal conductivity measurement systems and the design of a mechanicalsystem capable of accurately measuring material stress-strain characteristics. Thein-plane measurement system is used in a vacuum vessel, with a vacuum of approximately10¡5 mbar, and over a temperature range from -30±C to 20±C. The transverse and mechanicalsystems are used at room pressure and temperature. The mechanical system is designed sothat it measures mechanical properties at low stress below 30MPa. The basic concepts usedto design these measurement systems and all the details concerning their operations and implementationsare described. The thermal measurements were performed at the Physics andAstronomy department of the University of Glasgow while the mechanical measurementswere performed at the Advanced Materials Technology department, at the Rutherford AppletonLaboratory (RAL). Essential considerations about the measurement capabilities andexperimental issues are presented together with experimental results. The values obtainedfor the materials with well understood properties agree well with the values available inthe literature, confirming the reliability of the measurement systems. Additionally, a FiniteElement Analysis (FEA) is performed to predict the thermal and mechanical properties ofPocoFoam. The foam is created by generating spherical bubbles randomly in the computationaltool MatLab according to the topology of PocoFoam. The model is transferred to theCAD program Solid works to be extruded and be transformed into PocoFoam. It is later ontransferred to the FEA tool ANSYS to be analysed. Simulations of a specimen of densityequal to 0.60g/cm3 are performed and the results are compared with the values measured fora specimen of density equal to 0.56g/cm3. The simulated results agree within 32% with theexperimental values. The experimental results achieved in the studies undertaken in thesishave made a considerable contribution to the R&D of the stave design by helping to understandand optimise the current stave design and explore new design possibilities. The staveis a mechanical support with integrated cooling onto which the silicon sensors are directlyglued.

[发布机构] University:University of Glasgow;Department:School of Physics and Astronomy

[关键词] QC Physics