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Newsletter EnginSoft Year 6 n°4 - 29
ANSYS simulation of carbon fiber and
anisotropic materials
Introduction
The scope of this R&D is to develop a new
support, with an integrated cooling system, for
the replacement of the inner layer of the
Silicon Pixel Detector installed into the ATLAS
Experiment, working on the Large Hadron
Collider at CERN; for details, we ask our readers
to visit: www.atlas.ch/pixel-detector.html. This
replacement will become necessary because of
the radiation damage, with the detector being
very close, about 50 mm, to the high-energy
proton-proton interaction point.
The task of the support system is to hold the
detector modules in positions with high
accuracy, minimizing the deformation induced
by the cooling; this must be done with the
lowest possible mass because there are tight
requirements in terms of material budget. An
evaporative boiling system to remove the
power dissipated by the sensors is incorporated in the
support: thermal contact is made through a very
conductive light carbon foam to maintain the sensor
temperature sufficiently low, to limit the leakage currents
and hence the thermal run-away. The coolant should be a
fluorocarbons blend or CO2. The worst case is imposing a
cooling pipe design pressure of 10 MPa. The number of
Prototype of a stave with 2 carbon fiber pipes integrated into the carbon
foam and attached to the structural omega shaped laminate.
The ATLAS Pixel Detector during construction. Here we can see one of the cylindrical shells of
Pixel detectors formed by the longitudinal cooled supports called staves.
pipes could be 1 or 2 and the pipe material should be
carbon fiber or titanium. The structural strength of the
800 mm long support stave is given from a carbon fiber
“omega” shaped laminate.
Summary of the work
The design is based on thermal, mechanical and thermostructural
analyses of assemblies made of carbon fiber
composites. Calculation of the Tsai-Hill safety factors and
transversal strains in the
plies are required for
tightness assessment of
the pipe. Moreover, the
pipe lay-up optimization
against the internal
pressure has been made
together with estimations
of the thermal expansion
coefficient of the pipe
and omega laminates. We
used ANSYS and
ESAComp; input figures
Carbon fiber pipe production test using
braiding technology, before
impregnation with resin
for the ply properties, starting from fiber and matrix
values, are provided by a dedicated spreadsheet. To
validate the FEM simulations both Composite Laminate
Theory hand-made calculations on cross-check simple
models and experimental tests are used. Work is still in
progress to measure material characteristics and FEM
results: pull test on pipes performed with “braided”
technology, burst pipe pressure, thermal transmission