Trident separator window investigation

Matthew Brock (Oxford) 16th October 2012

Context

The picture to the right from Roger Forty’s presentation at Davos on the 3rd September shows a concept for Trident requiring a window separating the gases.

Two window concepts were proposed for investigation by finite element analysis

• Glass of varying thickness

• Polymer, possibly Mylar (polyester), possibly a film

x0

xd

Geometry

Loading

• Sheet is split into 20 horizontal strips 250mm high• Differential pressure applied from 1.74 mbar at the top to -1.74 mbar at the

bottom calculated assuming a density of 11.21 for C4F10 and 3.72 for CF4

• Fixed constraint around the external edges and at the beam pipe• Gravity also applied

6 mm thick glass stress

Glass failure stress of 30-90 MPa depending on grade so 6mm gives a reasonable margin.

6 mm thick glass Displacement

Variation with glass thicknessRich 2 window glass

Thickness (mm) Stress (N/mm2) Displacement (mm)4 21.25 32.245 15 * 16.456 9.245 9.57 6.825 5.968 5 * 3.999 4.083 2.8

10 3.274 2.04

Figures with a * are approximate. Error ocurred at peak stress node.

The model becomes less accurate with reduced thickness. Some random errors occur due to modelling problems. A single node error for 5mm and 8mm thickness means the peak stress is estimated.

Comparison of glass with polymersTrident window, various materials, 10mm thick

Material Stress (N/mm2) Displacement (mm) Min failure stress (N/mm2)Glass 3.274 2.042 30ABS 2.942 42.44 30PMMA (Perspex) 2.972 45.79 50Polycarbonate 2.944 53.97 60

• Displacement is much larger for polymers due to the lower Youngs modulus• FE model becomes unstable at thicknesses lower than 4mm but displacements

would be very large at this point.• Mylar film is available in 12-300 micron thicknesses but defection would be

beyond the linear range.• The materials chosen were those in the standard materials database. Polyester

is not in the database however the other polymers give an indication of the displacement.

Discussion points

• The modelling shows some quite high displacements and it may be worth making some physical models to verify this.

• What deflection of the window would be acceptable?• Should we be carrying out some optical modelling?• If we are going to consider a polymer which transparent material

would best survive the environment?