FE calculations for the bolted helium vessel - CERN
Transcript of FE calculations for the bolted helium vessel - CERN
FE calculations for the bolted helium vesselMay 6th 2015
F. Carra, L. Dassa, N. Kuder
FE calculations for the bolted helium vessel 206/05/15
Intro
Safety
Safety valve
● PS=1.8 bara (=0.8 barg)
● Vtot = 160 L
Intro
Load cases
Pre-tuning always present
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Intro
Scheme1 - Main model
with bolts,
highest preload
2 - Cavity sub-model
(linear)
7 - analytic submodel for
welded bolt covers on
plates
6- analytic sub-model for
welded bolt covers on
flanges
4 - analytic sub-model
for bolts (according to
VDI 2230 Part 2
5 - Simplified FEM model
for sealing plate weld
8 - Main model with
bolts, smallest
preload
3 - Cavity model Elasto-
plastic
Strength
assessment
9 - Cavity model thermo-
mechanical
Not yet
performed!!!Not yet
performed!!!
FE calculations for the bolted helium vessel 406/05/15
Helium vessel
Baseline
Model simplified win order to facilitate the FE analyses
Thickness of the cavity reduced according to material removal during BCP
FE calculations for the bolted helium vessel 506/05/15
Combining effect of bolt pretension, pressurization and pretuningBolt pretension 3800 N
Gravity 9806.6 mm/s2
0.2 mm
Pressure 0.18 MPa
Thermal expansion 0.2 mm
Fixed support
Scale
x100
Cavity submodel
Helium vessel
Loads and boundary
conditions
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Helium vessel
Stress
Maximum stress: 110 MPa
Max allowable stress: 187 MPa (Ti Grade 2)
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Helium vessel
Deformation
Maximum deformation: 0.62 mm
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Cavity
Stress (1)
Stress Intensity: “preload + pressure + pretuning”
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Cavity
Stress from the submodel (1)
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Stress Intensity: “preload + pressure + pretuning” -> sub-model
It is mandatory to split the
total stress in :
• primary stress
• secondary stress
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Stress due to pressure (primary stress)
𝑃𝑚 < 𝑓𝑃𝑙 < 1.5𝑓 -> no local stress 𝑃𝑙 + 𝑃𝑏 < 1.5𝑓∆(𝑃 + 𝑄) < 3𝑓
LINEARIZATION Cavity
Stress (2)
Stress due to pre-tuning (secondary stress) not present
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Cavity
Stress from the submodel (2)
Pressure ONLY
Stress due to pre-tuning (secondary stress) not present
ONLY primary stress
FE calculations for the bolted helium vessel 1206/05/15
Cavity
Stress Linearization
LINEARIZATION on primary stress (only pressure)
𝑃𝑚 < 𝑓𝑃𝑙 < 1.5𝑓𝑃𝑙 + 𝑃𝑏 < 1.5𝑓∆ 𝑃 + 𝑄 < 3𝑓
FE calculations for the bolted helium vessel
• Red: membrane stress
• Green: bending stress
• Blue: membrane + bending stress VERIFIED
06/05/15
Cavity
Elastic-plastic analysis (1)
THIS IS NOT A STRENGHT ASSESSMENT.
Analysis performed only to have an idea about the plastic
behaviour
Equivalent stress
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Cavity
Elastic-plastic analysis (2)
THIS IS NOT A STRENGHT ASSESSMENT.
Analysis performed only to have an idea about the plastic behaviour
Total principal structural strain 1: 0.00511 / -6.07e-06
Total principal structural strain 2: 0.000694 / -0.000378
Total principal structural strain 3: 3.6e-06 / -0.00519
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Cavity
Buckling
Load multiplier = 48 wrt to p = 0.18 MPa
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before
preload
direction of relative plate movement
Welds modelled as the edge-face contacts. Contacts established after the bolt preload to prevent the weld prestressing.
Weld seams for plates
Model
FE calculations for the bolted helium vessel 1706/05/15
Weld seams for platesANSYS reaction moments and forces attached to the 3D solid weld seam.
Results from FEM
FE calculations for the bolted helium vessel 1806/05/15
Fixedsurface
Surfacewhere theloads areapplied
Weld seams for plates
Strength assessment in Ansys
Maximum stress (linearized): 142 MPa (with raw and fine mesh)
Max allowable stress: 187 MPa (Ti grade 2)
FE calculations for the bolted helium vessel 1906/05/15
Bolts
Model
δ
Mb
-Mb
Sliding
δ
Pressure 0.18 MPa
Bolt line
Threaded hole
---- Fixed jointsWasher imprinted face
Frictionless contact
Bolt modeling in ANSYS
FE calculations for the bolted helium vessel 2006/05/15
Bolts
For the maximum values of the bending moment and shear force from ANSYS:
Results form Ansys
Max. axial force PA [N] 3955
Max. bending
moment
Mb [Nmm] 1648
Max. shear force T [N] 245
Applied preload: 3800 N
Warning: the shear load evaluated
with simplified model is > 362 N
A part of the pressure load is
carried out by the weld seams.
The geometry of the beam corresponding to the bolt has
been derived from the VDI 2230 Part 2
FE calculations for the bolted helium vessel 2106/05/15
Bolts
VDI strength assessment
Axial stress σa [MPa] 276
Bending stress σb [MPa] 129
Shear stress τ [MPa] 107
Equivalent stress σeq [MPa] 445
Safety factor k - 1.9
For the operating conditions
For the assembly conditions
Minimum preload: 2280 N
Maximum preload: 3800 N
(60% of scattering allowed)
Utilization factor: 45% (usually around 80%)
Assembly Permitted Preload: 4490 N
Warning:
Procedure for preload definition could be modified since it seems that
the preload required is even lower.
Minimum length of engagement
• Actual length: 9 mm
• Minimum length: 6.9 mm
Surface pressure
• Evaluated 97 MPa
• Maximum : ? (1340 for Ti Grade 5)
FE calculations for the bolted helium vessel 2206/05/15
FE calculations for the bolted helium vessel 23
Bolts
Open questions
Washers:
• Yes? Not?
• Which type?
• Locking effect?
Galling ->Which coating to prevent it?:
• Dioxide?
• Molykote?
06/05/15
Weld seams for
bolts cover
FE calculations for the bolted helium vessel 2406/05/15
Bolts
Contact between plates
The joints don’t open.
Contact between plates to be
improved (in some cases)
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Thermal effects
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Optimization
The scope
Promising results: we think we are able to reduce the weight by 30 kg without loosing in stiffness
FE calculations for the bolted helium vessel 2706/05/15
Future tests
Test are planned for:
• Friction between titanium threads and between bolt head and
plate
• Traction test on bolts at room T and at 2 K
• Shear behaviour of the bolts at room T and at 2 K
• Friction between Titanium plates at room T and at 2 K
• Test of a dummy vessel
• Coatings on bolts
Cavity calculation will be performed again in order to verify the not
clarified points:
• with higher preload on bolts
• with friction
Very conservative hypothesis:
• No friction between plates (-> all the shear load carry out by the
bolts)
• Pressure (1.8 bara) due to the vacuum failure considered as
permanent load on the cavity
• Very low preload on the bolts
FE calculations for the bolted helium vessel 2806/05/15
Tank RFD
Similar strength assessment will be performed for the tank of the RFD cavity
FE calculations for the bolted helium vessel 2906/05/15