Post on 30-Dec-2015
Axial and transverse stress–strain characterization of the EU dipole high
Jc RRP Nb3Sn strand
A. Nijhuis, Y. Ilyin, W. Abbas, H.J.G. Krooshoop, W.A.J. Wessel, Y. Miyoshi, L. Feng, E.P.A. van Lanen
Geneva, 20 May 2008
IntroductionIntroduction
Strain sensitivity Nb3Sn strands / ITER CICC application:evaluate sensitivity various applied strandscabled conductor design (limiting peak strains).
CICC: axial strain, periodic transverse bending strain and periodic contact stress, axial and transverse stiffness.
Besides pacman disc spring for axial Ic() measurements, we used the TARSIS test set-up with probes for bending, contact stress and stiffness (axial & transverse).
We concentrate on results of high Jc OST RRP type of strand (EU Dipole strand, EUDIPO) and make a few comparisons with ITER type strands.
Relation cabling pattern and performance degradation in CICC.
IIc (c (VIVI) and strand deformation in ) and strand deformation in TARSISTARSIS
TARSIS test set-up with probes for bending, contact stress and stiffness (axial & transverse).
Bending between contact points, various wavelengths.
Reduced Ic vs force for SMI strand for 3 wavelengths.
LMI
0
0.2
0.4
0.6
0.8
1
0 2,000 4,000 6,000 8,000 10,000 12,000
load per meter [N/m]
I c/I
c0 [-
]
Lw=5.01 mm
Lw=7.15 mm
Lw=10.01 mm
Crossing strands for contact stress characterisation.
Ic vs stress for crossing strands, 11 T and 12 T for EM-LMI strand.
Strand tensile stress-strain tests at various temperatures (participation in VAMAS).
Stress-strain curve for EM-LMI (TFMC) strand
HITX-strand
Lw=4.7 mm
0
0.2
0.4
0.6
0.8
1
0 50 100 150 200 250 300
stress [MPa]
I c/I c
0 [-
]
contour
F-release
OST RRP Nb3Sn Dipole strandOST RRP Nb3Sn Dipole strand
Jc>2060 A/mm2Ternary Nb + Nb-47Ti = 0.81 mmCu:nonCu= 191 x 84 stack designbillet number 8712
Courtesy of ENEA
A Nijhuis, Y Ilyin and W Abbas, ‘Axial and transverse stress–strain characterization of the EU dipole high current density Nb3Sn strand’Supercond. Sci. Technol. 21 No 6 (June 2008) 065001 (10pp)
Uni-axial strain & Uni-axial strain & IIc (Pacman)c (Pacman)
Sample wire
Pacman spring
Torque transfer pins
Temperature variations by placing the Pacman spring under an insulator cup, creating a helium gas volume.
With heaters and thermometers arranged symmetrically the temperature can be balanced within ±20 mK.
Strand soldered on perimeter disc shaped spring Standard procedure VI curves
I =1000 A,-appl =-0.9 to + 0.9 %B=6 to 15 TT=4.2 to 12 K.First we explore the compressive strain range, then B,T dependency and finally the tensile range for irreversibility
Uni-axial Uni-axial IIc-strain (OST-DIP)c-strain (OST-DIP)
VI curves for OST-dipole strandI > 800 A,-appl =-0.9 to + 0.9 %B=6 to 14 TT=4.2 to 10 K.
Uni-axial Uni-axial IIcc((,B,T,B,T) (OST-DIP)) (OST-DIP)
Measured Ic @ 10 V/mOST-dipole strand
Fit to Dev Strain Model,30 data points requiredfor description of entire Ic(B-T- space reversible behaviourStandard: 50 data points+ irreversible tensile.
OST-DIP strand degrades immediately, actually before passing zero strain (peak), red markers are after irreversible degradation
General conductor scaling parameters:Deviatoric strain (~2nd inv.: slope) Ca1 49.05Deviatoric strain (~3rd inv.: asymmetry) Ca2 13.05Hydrostatic strain (~1st inv.: peak rounding) eps_0a 0.374%Thermal pre-strain (axial) eps_m -0.143%Maximum upper critical field Bc2m(0) 29.40 TMaximum critical temperature Tcm 15.97 KPre-constant [ =(constant*Bc2m(0)^2)/kappa_1m(0) ] C 47095 AT
EFDA DipoleOST strand
Pacman
0
100
200
300
400
500
600
700
800
900
-1 -0.8 -0.6 -0.4 -0.2 0 0.2
strain, [%]
criti
cal c
urr
en
t, I c
[A]
measured
dev strain model
after eps-applied > 0.1 %
IIcc((B,TB,T) () (applappl=0)=0)
Measured Ic @ 10 V/mOST-dipole strand
Fit to Dev Strain Model
OST Dipole strandPacman
T=constant
0
100
200
300
400
500
600
700
800
900
5 7 9 11 13 15
B [T]cr
itica
l cu
rre
nt,
I c [A
]
T=6 K, measT=8 K, measT=4.2 K, measT=4.2 K, modelT=8 K, modelT=6 K, modelT=10 K, measT=10 K, model
OST Dipole strandPacman
0
100
200
300
400
500
600
700
800
900
1000
4 5 6 7 8 9 10 11
T [K]
criti
cal c
urr
en
t, I c
[A]
B=12 T, meas B=12 T, modelB=6 T, meas B=6 T, modelB=8 T, meas B=8 T, modelB=10 T, meas B=10 T, modelB=14 T, meas B=14 T, model
nn-value (OST-DIP)-value (OST-DIP)
n-value 10-100 V/mOST-dipole strand
OST-DIP strand degrades immediately when passing zero (peak) strain, the n-value is good indicator (red markers)
OST-DipoleB=12 T
0
10
20
30
40
50
60
-1 -0.8 -0.6 -0.4 -0.2 0 0.2
strain [%]
n-v
alu
e [-
]
T=4.2 KT=6 KT=8 KT=10 KT=4.2 K, e-appl > 0.1 %
OST-Dipole
y = 2.1684x0.456
0
10
20
30
40
50
60
0 200 400 600 800 1000
I c [A]
n-v
alu
e [-
]
n-value (10-100uV/m)
after eps-applied > 0.1 %
all n-values eps-appl < 0.1 %Power (n-value (10-100uV/m))
Axial strain irreversibility limitAxial strain irreversibility limit
Hitachi bronze strand with irr=0.63 %
HitachiBronze
Pacman
0
50
100
150
200
250
-0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
strain, [%]
Ic [
A]
0
10
20
30
40
50
60
70
80
90
100
n-v
alu
e [-
]Ic reversiblen reversiblen-value, irreversibility limit
Ic
OST-I
0
50
100
150
200
250
300
-0.1 0 0.1 0.2 0.3 0.4 0.5
strain [%]
Ic [A
]0
5
10
15
20
25
30
35
40
45
50
n-v
alu
e [-
]
Ic, reversibleIc, irreversiblen-value, reversiblen-value, irreversiblen-value, irreversibility limit
Irreversibility strain limit determined by intersection of two lines through n-values vs. strain for two ITER type of strands (Ic criterion 10 V/m, n- value between 10 and 100 V/m)
OST internal tin strand with irr=0.25 %
Strain irreversibility limit OST-DIPStrain irreversibility limit OST-DIP
Ic & n-valueOST-dipole strandB=12 TT=4.2 K.
Determine irreversibility strain limit by intersection of two lines through n-values vs. strain.For ODT-DIP irr=-0.03 %, so irreversibility appears already before intrinsic zero axial strain is reached
EFDA DipoleOST strand
Pacman
0
100
200
300
400
500
600
700
-0.2 -0.1 0 0.1 0.2
strain, [%]
criti
cal c
urr
en
t, I c
[A]
0
10
20
30
40
50
60
70
n-v
alu
e [-
]
Ic
n-value
n-value, irreversibility limit
Uni-axial Uni-axial IIcc((,B,T,B,T) (OST-DIP & ) (OST-DIP &
HEP prototype DIP)HEP prototype DIP)
Other high Jc OST-RRP (HEP prototype DIP) strand (127 filaments) also degrades immediately when passing zero strain (peak), two samples tested.
normalised I c
T =4.2 K, B=12 T
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-1 -0.8 -0.6 -0.4 -0.2 0 0.2
strain, [%]
I c/ c
I max
[-]
OST Dipole
OST prototype HEP Dipole
prototype HEP Dipole2 samples on Pacman
0
100
200
300
400
500
600
700
800
900
-1 -0.8 -0.6 -0.4 -0.2 0 0.2
strain, [%]
criti
cal c
urre
nt, I
c [A
]
#1, measured, 12 T
#2, measured, 11 T
Both types high Jc OST-RRP strands, HEP prototype and Dipole (91 filaments) degrade around zero strain (peak).Different strain sensitivity, DIP strand less sensitive (materials not analysed).
Strain irreversibility limit OST-DIPStrain irreversibility limit OST-DIP
For OST-DIP irr=-0.03 % (just before reaching peak) and prototype HEP DIP irr= ~0.07 %
EFDA DipoleOST strand
Pacman
0
100
200
300
400
500
600
700
-0.2 -0.1 0 0.1 0.2
strain, [%]
criti
cal c
urr
en
t, I c
[A]
0
10
20
30
40
50
60
70
n-v
alu
e [-
]
Ic
n-value
n-value, irreversibility limit prototype HEP Dipole
0
100
200
300
400
500
600
700
800
-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2
strain, [%]cr
itica
l cu
rre
nt,
I c [A
]
0
10
20
30
40
50
60
70
80
90
100
n-v
alu
e [-
]
Ic-meas
n-value
Uni-axial Uni-axial IIc-strain, overviewc-strain, overview
Ic() @ 12 T & 4.2 K of 16 Nb3Sn strands
High Jc OST RRP: 600 AITER Advanced: 200-300 AITER Model Coil: 150 A
measused I c
T=4.2 K, B=12 T
0
100
200
300
400
500
600
700
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
strain, [%]
I c/ c
I max
[-]
OST DipoleOST-I, 2nd sampleOST-II, scaled B=11 TEASNIN&WST, 0.77 mmVAC (CSMC) DUEM-LMI (TFMC) DUSMI-PIT 504 (binary)OST prototype HEP DipoleMitsubishiHitachiRF IntTin CuNbLuvata Pori (TFAS)OCSI (TFAS)KOR-1NIN-WST 45-5
Uni-axial Uni-axial IIc-strain sensitivity, c-strain sensitivity, overviewoverview
Normalised Ic @ 12 T & 4.2 K
High Jc OST RRP: 600 AITER Advanced: 200-300 AITER Model Coil: 150 A
normalised I c
T=4.2 K, B=12 T
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
strain, [%]
I c/ c
I max
[-]
OST Dipole
OST prototype HEP DipoleThe relative strain sensitivity for strands is defined as the slope of the reduced Ic (Ic/Ico) vs. the strain between -0.7 % < < -0.3 %.
Relative Relative IIc-strain sensitivityc-strain sensitivity
The average relative strain sensitivity of all strands is 1.01 and the stdev is 0.08.
OST RRP DIP strand is least sensitive int. tin strand while the HEP prototype is one of the most sensitive.(Materials not analysed).
Recent bronze is least sensitive except (VAC-CSMC)
0.80
0.85
0.90
0.95
1.00
1.05
1.10
1.15
Hitach
iEAS
OST-D
IP
ITER-IT
ITER-IT
ITER-IT
ITER-IT
ITER-IT
ITER-IT
ITER-IT
VAC (CSM
C)
ITER-IT
ITER-IT
ITER-IT
OST-p
roto
HEP D
IP
ITER-IT
rel.
Ic s
en
sitiv
ity Ic
vs
stra
in [-
]
Irreversibility strain limitIrreversibility strain limit
Irreversibility strain limit for tested strandsLow limit for high Jc OST RRP type of strands (near peak) and bronze high limit.ITER internal tin mostly between 0.2 % and 0.4 % (average 0.33 % stdev 0.11 %).(EAS strand to be measured, here based on micrography from Matt Jewell on Twente samples)
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
OST-D
IP
OST-p
roto
HEP D
IP
ITER-IT
ITER-IT
ITER-IT
ITER-IT
ITER-IT
ITER-IT
ITER-IT
ITER-IT
ITER-IT
ITER-IT
ITER-IT
VAC (CSM
C)
Hitach
iEAS
irre
vers
ibili
ty s
tra
in li
mit
[%]
HitachiBronze
Pacman
0
50
100
150
200
250
-0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
strain, [%]
Ic [
A]
0
10
20
30
40
50
60
70
80
90
100
n-v
alu
e [-
]
Ic reversiblen reversiblen-value, irreversibility limit
Ic
TARSIS stress-strain results, 4.2 KTARSIS stress-strain results, 4.2 K
Stress-strain curves on ITER and Model Coil strands at 4.2 K: racture: 0.9 % - 1.2 % strain
TARSIS 4.2 K stress-strain test TARSIS 4.2 K stress-strain test OST-DipoleOST-Dipole
OST-Dip stress-strain4.2 K tests
0
50
100
150
200
250
300
0 0.005 0.01 0.015
strain [%]
stre
ss [M
Pa
]He_noCr_bht 1
He_noCr_bht 3
He_Cr 1
He_Cr 2
He_noCr_aht 1
Strand failure just beyond 0.5 % strain (T=4.2 K).
Cr layer removed before HT: slightly weaker stiffness. Confirmed with other strand types.All TARSIS tests are done with Cr layer removed before HT.
necking
fracture
yielding
TARSIS bendingTARSIS bending
TARSIS bending test OST-DipoleTARSIS bending test OST-Dipole
OST-DipoleBending
Lw=7 & 10 mm
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1 1.2 1.4
peak bending strain [%]
I c/I
c0 [-
]
V1, 10mm
V3, 7mm
LRL
HRL
OST-DipoleBending
Lw=7 & 10 mm
0
5
10
15
20
25
30
35
40
45
50
0 0.2 0.4 0.6 0.8 1 1.2 1.4
peak bending strain [ ]
n-v
alu
e [-
]
ext1
ext2
ext3
V3, 7mm
V1, 7mm
EFDA Dipole strand:Initially following the LRL (good IF redistribution).Failure at 0.5 % strain.
Correlation between fracture strain and deviation from bending-LRL:
OST-Dip stress-strain4.2 K tests
0
50
100
150
200
250
300
0 0.005 0.01 0.015
strain [%]st
ress
[MP
a]
He_noCr_bht 1
He_noCr_bht 3
He_Cr 1
He_Cr 2
He_noCr_aht 1
TARSIS bending, resultsTARSIS bending, results
Reduced Ic vs peak bending strain for several tested strands illustrating the spread in sensitivity but in particular the high sensitivity for OST-DIP (> 0.5 %).
Bending
0
0.2
0.4
0.6
0.8
1
0 0.5 1 1.5 2 2.5
peak bending strain [%]
I c /
I c0
[-]
OST Dipole
TARSIS crossing strands test: TARSIS crossing strands test: IIcc
Probe for X-strands test with periodicity 4.7 mm and 90 angle.Reacted straight X-strands, are pressed by top plate (not visible).
Ic() for OST-DIP strand also showing Ic release of load and irreversibility up to 50 MPa () transverse stiffness
OST-DipoleX-strand
Lw=4.7 mm
0
0.2
0.4
0.6
0.8
1
0 50 100 150 200 250
stress [MPa]
I c/I c
0 [-
]
contour
released load
OST-DipoleX-strand
Lw=4.7 mm
0.8
0.85
0.9
0.95
1
0 10 20 30 40 50 60 70 80
stress [MPa]
I c/I c
0 [-
]
contour
released load
OST-DipoleX-strands
Lw=4.7 mm
0
50
100
150
200
250
300
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
strain [-]
stre
ss [M
Pa
]
stress [MPa]
TARSIS crossing strands:TARSIS crossing strands:IIc and n-valuec and n-value
OST-II strand most sensitive to transverse contact stress (and binary SMI-PIT) followed by EM-LMI, OST-DIP, MIT and less sensitive HIT and EAS bronze strands.n-value OST-II degrades rapidly between 10 and 30 MPa.
0
0.2
0.4
0.6
0.8
1
0 50 100 150 200 250 300stress [MPa]
I c/I c
0 [-
]
EASOST-IOST-IIHitachiEM-LMIMitsubishiOST-DipSMI-504, binaryKOR-1
0
0.2
0.4
0.6
0.8
1
1.2
0 50 100 150 200 250 300
stress [MPa]
n/n
0 [-
]
EASOST-IOST-IIHitachiMitsubishiOST-DipEM-LMISMI-504, binaryKOR-1
Is it possible to use strain sensitive strands like the high Jc OST RRP for CICC??
Influence of cabling in CICCInfluence of cabling in CICC
April 2006 (Barcelona), a priori TEMLOP prediction postulating influence characteristic bending wavelength (Lw), no experimental data available at that time to prove it.
Influence of cabling in CICCInfluence of cabling in CICC
vf =0.36E // = 29 Gpa
IxB =750 kN/m
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
0 0.005 0.01 0.015 0.02
bending wavelength, L w [m]
red
uce
d I
c [-
]
0.0%
0.2%
0.4%
0.6%
0.8%
1.0%
1.2%
1.4%
1.6%
1.8%
2.0%
pe
ak
be
nd
ing
str
ain
[%]
reduced Ic @ peak load
peak strain
`
August 2007: relation for Lw and Lp (1st stage twist pitch) ]1[
21
21
1
m
L
N
LL p
Lp
pw
A. Nijhuis and Y. Ilyin, ‘Transverse Load Optimisation in Nb3Sn CICC Design; Influence of Cabling, Void Fraction and Strand Stiffness’, Supercond. Sci. Technol. 19 (2006) 945-962.
A. Nijhuis, ‘A solution for transverse load degradation in ITER Nb3Sn CICCs, effect of cabling on Lorentz forces response’ Supercond. Sci. Technol. 21 (2008) 054011 (15pp)
April 2007 SULTAN test first verification of a priori prediction influence bending wavelength for long pitches.
Influence of cabling in CICCInfluence of cabling in CICC
TFPRO-2 SULTAN sample: two legs, one reference ITER cabling pattern gave Tcs= 5.5 K and very low n-value, other leg with roughly twice longer pitches gave best performance ever of Tcs=7.3 K and high n-value.
TFPRO-2 ITER reference cabling pattern
0 200 400 600 800 10005.0
5.5
6.0
6.5
7.0
7.5
Tcs
, K
Cycle
OST2 OST1
TFPRO2
TFPRO-2 long pitches
Required:Influence current non-uniformity induced at joints and terminations must be excludedRoughly similar cable design (relevant # strand layers / ratio of copper strands)
Influence of cabling in CICCInfluence of cabling in CICC
Sample PITSAM2 (LF2)PITSAM5
Short pitchesPITSAM5
Long pitches
EDIPO LF2 LF2 LF2
Cable pattern (3x3)x3x4 3x3x3x4 3x3x3x4
Sc strand number 48 48 48
Sc strand Cr plated OST dipole 0.81 mm
Cr plated OST dipole 0.81 mm
Cr plated OST dipole 0.81 mm
Cu strand number 60 60 60
Twist pitch 58/95/139/213 34/95/139/213 83/140/192/213
Outer conductor dimensions (mm)
12.6 x 12.6 12.6 x 12.6 12.6 x 12.6
vf (%)(calculated)
30 30 30
PITSAM SULTAN test of similar CICC shape but different cabling patternPITSAM 2, 5L & 5SFully soldered joints
Dipole PITSAM 2 & 5, and ITER TFPRO2 (long pitches) Lw has been determined by:
Influence of cabling in CICCInfluence of cabling in CICC
]1[
21
21
1
m
L
N
LL p
Lp
pw
Conductor type 1st stage Lp Lw [m]
PITSAM1, 2, 3, 4 0.058 0.0098
PITSAM5 Long = ITER Option II 0.083 0.0161
PITSAM5 Short 0.033 0.0048
TFPRO2/OST1 = ITER Option I * 0.045 0.007
TFPRO2/OST2, Long Lp 0.116 0.0263
USTF1 (alternate 6x1)* 0.025 0.0011
* For USTF1 the strand properties are not available so the virgin performance, and thus the degradation can not be determined. For TFPRO2/OST1 Option I influence of the joint non-uniformity can not be excluded.
PITSAM and TFPRO2 (long pitches) performance for (virgin) zero load condition is determined by Jackpot Model (Jacket Potential) for =0.6 %.
Influence of cabling in CICCInfluence of cabling in CICC
JackPot model:PITSAM 2, 548 SC strands60 Cu strands
Good agreement with TEMLOP prediction.
Measured degradation:
Tcs/Tcs0 vs Lw
with Tcs0 computed for =-0.6 %
0.6
0.7
0.8
0.9
1.0
1.1
0 0.005 0.01 0.015 0.02 0.025 0.03
characteristic bending wavelength L w [m]
Tcs
/Tcs
0 [-
]
PITSAM LF2 (2 & 5)
TFPRO2/OST2, Long Lp
polyn. fit
SummarySummary
Ic vs. uni-axial strain, bending, contact stress and stiffness is characterised on OST RRP high Jc Nb3Sn strands.
Strain sensitivity I/ in the range of ITER Int tin. Irreversibility strain limits: ~ 0% for OST-DIP, from +0.2% to
+0.4% for ITER Int tin and > +0.6% for (recent) bronze. Bending behaviour follows the LRL until failure strain is
reached: 0.5% peak bending strain for OST DIP. Intermediate twist pitch length in CICC causes degraded
performance: TEMLOP prediction influence pitches further confirmed.