210116 2 Mechanical Measurement Lab ENMME M Guinchard m ichaelguinchardcernch TEMSC Technical Meeting Lab workflow 210116 TEMSC Technical Meeting 3 Thermal Conductivity and Diffusivity ID: 806812
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Slide1
Slide2Mechanical measurements in Superconducting magnets
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Mechanical Measurement LabEN/MME M. Guinchardmichael.guinchard@cern.ch
TE-MSC Technical Meeting
Slide3Lab
workflow
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Thermal Conductivity and Diffusivity
Specific Heat
Density and CTE
Experimental modal analysis
Vibration monitoring
Operating deflection shape
Experimental stress
Analysis
Dynamic behaviour of structure
Ground motion / Seismic measurements
Development of home-made sensors
Thermo-physical analysis
Mechanical properties analysis
CERN Wide Support
EDMS – TEST REPORTS
Impact testing method
Flexural tests 3 or 4 points
Compression tests
Stress / strain analysis
Dynamic strain measurements
Residual stress measurements
Transfer function analysis
Transfer path analysisCoherence length measurements
Load cell based on strain gauges
Displacement sensorsCapacitive gauges
Slide4Accuracy according ISO5725 :
Accuracy determination in practice:
Definition
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Precision
Accuracy = Repeat. + Repro. + Trueness
Slide5Outline
Mechanical measurements in superconducting magnets :Comparison of tools for mechanical measurements
Electrical strain gaugesDisturbance effects on the gaugesCompensation of disturbance effects
Validation testsThermo-mechanical characterization :Mechanical testing machineThermal Expansion measurementsResidual stress measurementsDigital image correlation system
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Slide6Application : Mechanical measurements in superconducting magnets
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Slide7Why mechanical measurements in
magnets ?
Goal : Finite Element Analysis (FEA) validation and integrity control of the structure during assembly phases
Mechanical measurements during assembly, cryogenic cool down to 1.9 K and powering tests
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Slide8Tools for mechanical measurements
Electrical strain gauges
Capacitive gauges
Optical
fiber sensors
Non contact
video systems
Principle
Resistive
Capacitive
BraggImage processingLoading
casesAllCompressionAllAll
Magnetic effectsAffectedNon affectedNon affected-
Cryogenic temp.AffectedAffectedAffected
Only RTResolution
0,1 μm/m1 MPa
0,5 μm/m5 μm (3)
Repeatability0,6 %3% (>10 MPa)1,5 %
-Reproducibility0,7 %5
%2,5 %-Trueness
< 3,7 % (1)
9 %Under evaluation (2)-Accuracy
< 5% (1)
17 % (4)Under evaluation (2)0,5 % (3)
EDMS1073153: Caractérisation des mesures de déformation par jauges d'extensomètrie à temp. cryogénique
Collaboration agreement KN2480/KT/EN/223Chttp://www.imetrum.comhttps://accelconf.web.cern.ch/accelconf/IPAC10/papers/mopeb043.pdf
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Slide9Strain gauges : Introduction
1856 : Lord Kelvin first reported on a relationship between strain and the resistance of wire conductors.
1938 : E. Simmons and Arthur C.
Ruge invented the strain gaugeAfter 1952 : Optimisation period and strain gauges are now used by many industry.
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Slide10Strain gauges : Basic principles
with k : Gauge factor
The resistance of a wire (R) is a function of three parameters :
F (N)
F (N)
with R (
Ω
), Length (m), Section (m²) and
ρ
(
Ω
/m)
With an external force, the resistance value increases.
A strain gauge is a long length of conductor arranged in a zigzag pattern on a membrane. When it is stretched, its resistance increases.
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Resistance values : 120, 350, 700
For 2000 m/m,
R is equal to 11
Wheatstone bridge !
Wheatstone
bridge equation :
If
R
1
=R
2
=R
3
=R
4
, Vs= 0
Application with strain gauges :
+
R
1
+
R
4
+
R
2
+
R
3
Configuration :
- ¼ bridge
-
Half bridge
-
Full bridge
V
0
V
s
R
1
R
4
R
2
R
3
Strain Gauges : Wheatstone bridge
Slide12Strain Gauges : Wheatstone bridge
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Wheatstone
bridge configuration :
¼ Bridge :
Half bridge :
Full bridge :
Sensitivity
Slide13Strain Gauges : External disturbances
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13Main external disturbances : temperature, magnetic field, …
Two types of disturbances :
strain gauge disturbances
electrical circuit disturbances
Slide14Strain gauges d
isturbances
Temperature :
1) K factor variation
2) Apparent
strain :
10 % of variation between RT and 1.9 K
Correction must be applied !
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Effects compensated using half or full bridge
Slide15Strain gauges disturbances
- Magneto resistance effect
- Magneto
striction
effect
- Induction current
- Adhesive degradation
- Zero drift
Magnetic field :
Radiation effects :
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3)
Kondo effect
:
Kondo effect is due to
magnetic
impurities, resulting in a characteristic change in electrical resistivity with
temperature
Effects compensated using correct excitation
Effects compensated using half or full bridge
Slide16Strain gauges : Disturbances compensation
V
0
V
s
1
2
With disturbance
:
+ K
1
MF
+ K
1
Th+ K2MF
+ K2Th
If K1
K2
K (Same batch or bi-axial strain gauges)
Use Half or full bridge configuration
Bridge Configuration
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Electrical circuit : Disturbances compensation
Current
Voltage
Voltage
Slide18Electrical circuit : Disturbances compensation
Cable length compensation :
- Disadvantage comparing to current power supply ;
- Two additional wires
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Slide19Lead resistance compensation
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Electrical circuit : Disturbances compensation
DC effect compensated by AC power supply
Slide20Electrical circuit : Disturbances compensation
Cable or installation capacitances effect :
Unsymmetrical capacity in
the bridge circuit can
unbalance the bridge and affect measurement
results
.
With
the resistances the cable capacitances form
RC
networks which produce a
change of
phase with dynamic signals.
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Inductance effect :
Unsymmetrical inductance in
the bridge circuit can
unbalance the bridge and affect measurement results.
Slide21Electrical circuit : Disturbances compensation
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Capacity and inductance compensation with AC power supply
Slide22Validation tests : Magnetic field effects
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Validation tests : Cryogenic temperature
Without K factor correction !
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Validation tests with LARP collaboration
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Validation tests with LARP collaboration
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Validation tests with LARP collaboration
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Validation tests with LARP collaboration
LARP System :
Channel scanning system
Low sampling frequency : 1/10s
CERN System :
Real synchronous measurements
Sampling frequency from 1 Hz up to few kHz
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Strain gauge configuration for 11T magnet
Collars configuration
W
e assume an uniaxial loading case
1/2 bridge with Poisson ratio compensation
b
i
value
b
11
b2-νb3
0b40
b1+ν
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Strain gauge configuration for 11T magnet
b
i
value
b
1
1
b
2
0
b
30
b40B1
Shell configuration
Inner and outer shell diameter instrumentation¼
bridge with external ¼ bridge compensation
Slide30Bullet gauges configurationAxial loading monitoringFull bridge with Poisson compensation
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Strain gauge configuration for 11T magnet
b
i
value
b
1
1
b
2
-ν
b31b4
-νB2(1+ν)
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Strain gauge configuration for MQXFS magnet
Coils configuration
1
/2 bridge with thermal compensation
b
i
value
b
1
1
b20
b30b4
0B1
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Strain gauge configuration for MQXFS magnet
Shell configuration
1/2 bridge with thermal compensation
b
i
value
b
1
1
b
20
b30b4
0B1
Slide33Thermo-mechanical characterization :
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Slide34Differential Scanning Calorimeter
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Thermal properties characterization
λ
(T)= a(T) ·
Cp
(T) · ρ(T)
a
:
Thermal diffusivity
[m²/s
]cp: Specific heat capacity [J/(K·kg)]
ρ : Density [kg/m³]λ : Thermal conductivity [W/(m·K)]T : Temperature[K]
Laser Flash LFA 427
Dilatometer21/01/16
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Thermal properties characterization
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Thermal properties characterization of solids, liquids, and powders from RT up to 2000°C
Possible
upgrade at low temperature for CTE measurements under evaluation
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ZWICK Tensile machine (400kN
) – UTS Tensile Machine (200kN)
Cryostat for
tests up to
25kN – Temperature Range
: 4.2K - 293K
in the bath
Cryostat for tests up to
100kN –
Temperature Range
: 4.2K - 293K
in the
bath
Compression tools up to 400kN
– Temperature Range :
77K - 293K in the bath
Mechanical testing at RT, 77K, 4.2K
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Compression tools up to 400kN
–
Temperature Range :
77K
-293K in the bath
Mechanical testing at RT, 77K, 4.2K
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Compression tools up to 400kN
–
Temperature Range :
77K
-293K in the bath
Mechanical testing at RT, 77K, 4.2K
Results
Cable stiffness : 20 Gpa +/- 2 GPa
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Residual stress measurements
Measuring residual stresses by the hole-drilling method
Reverse strain measurements on loaded
structure
The
hole
changes
the initial strain allowing redistribution
of the residual stresses originally existing in the material
More information here : https://edms.cern.ch/document/1502506/1
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Digital image correlation system
Measurement technique was evaluated but not useful for field measurements
Slide41Slide42MML
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Slide43Thank you !Questions
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