mechanical properties of the ncsx modular coil conductor 14 january 2004 leonard myatt myatt...

Mechanical Properties Mechanical Properties of the NCSX of the NCSX

Modular Coil ConductorModular Coil Conductor

14 January 200414 January 2004

Leonard MyattLeonard Myatt

Myatt Consulting, Inc.Myatt Consulting, Inc.

14 January 200414 January 2004 Myatt Consulting, Inc.Myatt Consulting, Inc. 22

Q: What is the Modular Coil Q: What is the Modular Coil Conductor Elastic Modulus?Conductor Elastic Modulus?

CTD Mechanical Testsof Insulated Single Modular Coil (ISMC)

ANSYS Twisted Cable Model (GlassWrap and Impregnating Epoxy not shown)


A: Detailed in the memos…A: Detailed in the memos…• “Princeton Plasma Physics Laboratory Test

Program to Determine the Mechanical and Thermal Properties of the Epoxy/Insulation System for the NCSX Modular Coils,” Composite Technology Development, Inc., Lafayette, CO, 11/21/03.

• Leonard Myatt, “Mechanical Properties of the Modular Coil Conductor, Test Data & Modeling,” January 6, 2004.

• Or…see the highlights that follow.


Compression Test Data by CTD Compression Test Data by CTD

• Lots of test data provided on a CD.– Forces from MTS machine.– Strains from strain gages.– Deflections from LVDT (used to calc strain).

• Average Room Temp (RT) moduli:– 37 Mpsi from strain gage data – 2.9 Mpsi from LVDT


Compression Specimen #14Compression Specimen #14Strain Gage Data and RT ModulusStrain Gage Data and RT Modulus

Fig. 3.1.1-1 RT Compressive Stress vs. Strain1 & Strain2Specimen #14

0

5000

10000

15000

20000

25000

30000

-0.015 -0.01 -0.005 0 0.005 0.01 0.015

Strain

Av

e. S

tre

ss

, ps

i

Strain1

Strain2

Fig. 3.1.1-2 RT Compressive Modulus, Average of Stress/Strain1 & Stress/Strain2, Specimen #14

-180

-160

-140

-120

-100

-80

-60

-40

-20

0

-0.004 -0.0035 -0.003 -0.0025 -0.002 -0.0015 -0.001 -0.0005 0

Strain

Mo

du

lus

, Mp

si

Strange looking data……not unique to Specimen #14.

CTD report lists a modulus of 62.6 Mpsi

Average the strains and take a derivative.


RT LVDT Strain and ModulusRT LVDT Strain and Modulus(Many Compression Specimens)(Many Compression Specimens)

Stress vs. LVDT Strain looks OKModulus vs. LVDT Strain looks OK

With Max. values at ~1.1 Mpsi

Fig. 3.1.1-5 RT Compressive Stress vs LVDT StrainAll Specimens

0

5

10

15

20

25

30

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Strain

Str

es

s, k

si

1.dat

14.dat

15.dat

16.dat

20.dat

21.dat

Fig. 3.1.1-6 RT Compressive Modulus vs LVDT StrainInstantaneous, All Specimens but #20

0.0

0.5

1.0

1.5

2.0

0 0.01 0.02 0.03 0.04

StrainM

od

ulu

s, M

ps

i

1.dat

14.dat

15.dat

16.dat

21.dat

Numerical derivative of data typically noisy.Ultimate Stress: ~26 ksiOnset of yield: ~10 ksi


76K LVDT Strain and Modulus76K LVDT Strain and Modulus(Many Compression Specimens)(Many Compression Specimens)

Fig. 3.1.1-9 76K Compressive Stress vs LVDT StrainAll Specimens

0

10

20

30

40

50

0 0.05 0.1 0.15

Strain

Str

es

s, k

si

3.dat

4.dat

9.dat

11.dat

23.dat

24.dat

Fig. 3.1.1-10 76K Compressive Modulus vs LVDT StrainInstantaneous, All Specimens but #9

0.0

0.5

1.0

1.5

2.0

0 0.01 0.02 0.03 0.04

Strain

Mo

du

lus

, Mp

si

3.dat

4.dat

11.dat

23.dat

24.dat

Curves look reasonable.Cold specimens fail at higher stress.

Modulus vs. LVDT Strain looks OK…but little change from RT values.

Ultimate Stress: ~45 ksiOnset of yield: ~15 ksi


Misc. ObservationsMisc. Observations• Rule of Mixtures Modulus: 85 GPa (12 Mpsi)• LVDT Compression Modulus: ~8 GPa (1.1 Mpsi)• Compression Yield/Ultimate: ~0.40• Q: At what stress level is the current-carrying

capacity of the conductor affected?• Q: What are the effects of cyclic loading?

• OK…let’s look at some tension test data.


Tension Test Data by CTD Tension Test Data by CTD

• Lots of test data provided on a CD.– Forces from MTS machine.– Strains from strain gages.– Deflections from LVDT (used to calc strain).

• Average RT moduli:– 13.2 Mpsi from strain gage data (sounds high)– LVDT modulus not reported


Tension Specimen #9 Strain Gage Tension Specimen #9 Strain Gage Data and RT ModulusData and RT Modulus

• CTD memo reports a modulus of 13.9 Mpsi.

• Derivative of Stress vs. Strain gage data curve indicates similar result.

Fig. 3.1.2-1 RT Tensile Modulus vs Ave. Strains 1&3Average & Instantaneous, Specimen #9

0

5

10

15

20

25

30

0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004

Strain

Mo

du

lus

, Mp

si

Ave Mod1&Mod3

Inst. Mod

Poly. (Inst. Mod)


RT LVDT Strain and ModulusRT LVDT Strain and Modulus(Many Tension Specimens)(Many Tension Specimens)

All specimens have “steep” initial slope.Some stay “stiff” and failure at low strains.

Some soften at 4-7 ksi and fail at high strains.

Modulus vs. LVDT Strain shows these two different characteristics.

Fig. 3.1.2-2 RT Tensile Stress vs LVDT StrainMultiple Test Specimens

0

5

10

15

20

25

30

0 0.02 0.04 0.06 0.08 0.1

Strain

Str

es

s, k

si

9.dat

7.dat

12.dat

9B.dat

6A.dat

3F.dat

3E.dat

Fig. 3.1.2-3 RT Tensile Modulus vs. LVDT StrainInstantaneous, Multiple Test Specimens

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 0.005 0.01 0.015 0.02

Strain

Mo

du

lus

, Mp

si

9.dat

7.dat

12.dat

9B.dat

6A.dat

3F.dat

3E.dat


What would a 3D ANSYS ModelWhat would a 3D ANSYS Modelof a Strand Cable Predict?of a Strand Cable Predict?

• Modeling the entire 44x5x9 Cu stranded cable would be crazy (computer resource issue).

• Modeling an 8-strand cable is relatively easy.

• With linear materials and Large-Deflection theory, the modulus is only a weak function of axial load direction & magnitude.

• ~8 Mpsi which matches Rule of Mixtures.

Fig. 3.2-1 Ave. Stress and Instantaneous Modulus from 3D ANSYS(8) 6.3 mil Cu wires, 0.63" twist-pitch, 4 mils Epoxy-Glass Insulation

-1500

-1000

-500

0

500

1000

1500

-0.03 -0.02 -0.01 0 0.01 0.02 0.03

Strain

Str

es

s, M

Pa

0

2

4

6

8

10

12

Ins

t. M

od

ulu

s, M

ps

i

Stress-Strain curve (black) Local derivative indicates modulus (blue)


Remove the Epoxy & Glass, and the Remove the Epoxy & Glass, and the Cable gets very soft (0.3 Mpsi @ -0.2%)Cable gets very soft (0.3 Mpsi @ -0.2%)

• The model is compressed without the impregnating epoxy or glass.

• This allows the Cu strands to move more freely.

• The bare cable modulus is a strong function of strain.

• The modulus is 0.3 Mpsi or 1.0 Mpsi at -0.2% strain, depending on the definition of Area in the average stress calculation.


Remove the Cu, and the Epoxy & Remove the Cu, and the Epoxy & Glass get moderately softGlass get moderately soft

• The model is compressed without the Cu Strands.

• The composite modulus of the glass-epoxy drops to 2.2 Mpsi.

• Could it be that the actual impregnated cable behaves more like this than a Cu-Epoxy-Glass monolith?

Stress-Strain and Modulus, ANSYS 3D Model ofEpoxy and Glass Wrap Only (8 Cu Wires removed)

0

100

200

300

400

500

600

0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035

Compressive Strain

Co

mp

res.

Str

ess,

MP

a

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Inst

. Mo

du

lus,

Mp

si

Ave. Stress, MPa

Inst. Modulus, Mpsi


Summary and CommentsSummary and Comments

• Strain Gage data is suspicious.– CTD admits this, but has not yet explained.– Stress-Strain plots & reported E values (+13 & -37 Mpsi) confirm this.

• Moduli based on LVDT data looks reasonable:– 1.1 Mpsi in compression (RT and 76K)– 2-3 Mpsi in Tension initially, with scatter above ~5 ksi

• Some specimens soften abruptly.

• Non-Linear ANSYS model of 8-stranded cable:– Matches Rule of Mixtures hand-calc, which is stiffer than test results.– Shows importance of epoxy to stabilize the Cu strands.– Shows that conductor behaves like epoxy-glass composite without Cu.


Summary and CommentsSummary and Comments• These inconsistencies raise the question of:

– Impregnation quality or monolithic assumption of conductor composite.– LVTD data (although the Auburn data from CDR shows 1.2-1.7 Mpsi).– Modeling accuracy.

• Although a small yield-to-ultimate ratio is generally a good characteristic for a structural material, there is no test data which describes the electrical performance of the conductor as a function of stress or cyclic loading.

• Are expected loads Primary (must be carried by the structure, like EM) which could produce large deflections, or Secondary (self-limiting, like thermal) which produce essentially no deflections and lower stresses?

mechanical properties of the ncsx modular coil conductor 14 january 2004 leonard myatt myatt...

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