FE calculations for the bolted helium vessel May 6th 2015 F. Carra, L. Dassa, N. Kuder.
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Transcript of FE calculations for the bolted helium vessel May 6th 2015 F. Carra, L. Dassa, N. Kuder.
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
IntroSafety
Safety valve
● PS=1.8 bara (=0.8 barg)
● Vtot = 160 L
IntroLoad cases
Pre-tuning always present
06/05/15 FE calculations for the bolted helium vessel 3
IntroScheme1 - 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 vesselBaseline
Model simplified win order to facilitate the FE analysesThickness 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 vesselLoads and boundary
conditions
FE calculations for the bolted helium vessel 606/05/15
Helium vesselStress
Maximum stress: 110 MPaMax allowable stress: 187 MPa (Ti Grade 2)
FE calculations for the bolted helium vessel 706/05/15
Helium vesselDeformation
Maximum deformation: 0.62 mm
FE calculations for the bolted helium vessel 806/05/15
CavityStress (1)
Stress Intensity: “preload + pressure + pretuning”
FE calculations for the bolted helium vessel 906/05/15
CavityStress from the submodel (1)
FE calculations for the bolted helium vessel 10
Stress Intensity: “preload + pressure + pretuning” -> sub-model
It is mandatory to split the total stress in :
• primary stress
• secondary stress
06/05/15
Stress due to pressure (primary stress)
-> no local stress
LINEARIZATION CavityStress (2)
Stress due to pre-tuning (secondary stress) not present
FE calculations for the bolted helium vessel 1106/05/15
CavityStress from the submodel (2)
Pressure ONLYStress due to pre-tuning (secondary stress) not presentONLY primary stress
FE calculations for the bolted helium vessel 1206/05/15
CavityStress Linearization
LINEARIZATION on primary stress (only pressure)
FE calculations for the bolted helium vessel
• Red: membrane stress• Green: bending stress• Blue: membrane + bending stress VERIFIED
06/05/15
CavityElastic-plastic analysis (1)
THIS IS NOT A STRENGHT ASSESSMENT.Analysis performed only to have an idea about the plastic
behaviour
Equivalent stress
FE calculations for the bolted helium vessel 1406/05/15
CavityElastic-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-06Total principal structural strain 2: 0.000694 / -0.000378Total principal structural strain 3: 3.6e-06 / -0.00519
FE calculations for the bolted helium vessel 1506/05/15
CavityBuckling
Load multiplier = 48 wrt to p = 0.18 MPa
FE calculations for the bolted helium vessel 1606/05/15
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 platesModel
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
Fixed surface
Surface where the loads are applied
Weld seams for platesStrength 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
BoltsModel
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
BoltsVDI 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 NMaximum 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
BoltsOpen 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
BoltsContact between plates
The joints don’t open.
Contact between plates to be improved (in some cases)
FE calculations for the bolted helium vessel 2506/05/15
FE calculations for the bolted helium vessel 26
Thermal effects
06/05/15
OptimizationThe 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