Qualification of the longitudinal weld of thin wall PET tubes of the straw tracker of the NA62 experiment Master thesis presented 28 th of june 2011 by:

Qualification of the longitudinal weld of thin wall PET tubes of the

straw tracker of the NA62 experiment

Master thesis presented 28th of june 2011 by: De Carlo LivioSection: Materials (EN/MME-MM)Supervisor: Scheubel Maud

1

Sommaire

Objective of my work Observations, Tensile tests and Analysis Calculations (Stresses, Security factor,…) Conclusions

Discussion about the qualification by the observations Discussion about the elongation Some pictures with the digital microscope

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Objective of my work: Qualification of the welds of the

straws for the straw tracker To observe the aspect of the welds

To list their dimensions (width, thickness,…)

To determine their tensile strength

To understand their mechanism of failure

To compare the quality of the welds between Sefar and JINR

3

Observations of 6 samples from Sefar delivered in September 2010

Aspect of the weld for 4 out of the 6 samples:

Cross Section view: Optical microscope-100x Magnification

Chemical treated side: Stereomicroscope – 40x Magnification

Coating side: Stereomicroscope-50x Magnification

Dimensions

Width 900 µm (>600µm)

Thickness 60 to 70 µm

Critical section:Width 110 to 170 µmThickness 30 to 45 µm

Samples Maximum tensile strength (MPa)

1 120,7

2 127,2

3 107,2

4 105,4

Critical point

Mechanism of failure after the tensile test:

Cross section view: Stereomicroscope- 115x (left) and 80x (right) Magnification

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Observations of 6 samples from Sefar delivered in September 2010

Aspect of the weld for 2 out of the 6 samples:

Cross section view: Optical microscope-100x Magnification

Dimensions

Welded width:Width 300 µm (<600µm)

Thickness 60 to 70 µm

Total width: 620 to 630 µm

Samples Maximum tensile strength (MPa)

1 109,6

2 112,4

Mechanism of failure after the tensile test:

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=> Shear phenomenon

Observations of 2 samples from Sefar delivered in December 2010 (Straw number 89)

Cross section view: Optical microscope-100x Magnification

Chemical treated side: Stereomicroscope - 40x Magnification

Coating side: Stereomicroscope- 40x Magnification

Mechanism of failure after the tensile test:

Cross section view: Optical Microscope- 200x(left) and 100x(right) Magnification

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Observations of 2 samples from JINR delivered in January 2011 (Straw number 47&02)

Cross section view: Optical microscope-100x Magnification

Chemical treated side: Stereomicroscope - 40x Magnification

Coating side: Stereomicroscope-40x Magnification

STRAW 47 STRAW 47 STRAW 47

STRAW 02 STRAW 02 STRAW 02

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Parallel study on the samples from Sefar delivered in December 2010 and from JINR

delivered in January 2011

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3

200x Magnification 100x Magnification 100x Magnification

Samples Width

(µm)

Thickness (µm)

Max-Min

Proportion of the melted

area (%)

Sefar 1 867,9 (>600µm) 67,2-59,1 42,6Sefar 2 860,1 (>600µm) 62,6-50,9 52,4JINR 1 847,4 (>600µm) 75,8-48,5 49,0JINR 2 551,4 (<600µm) 88,6-58 33,3

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Cross section views (Optical microscope):

Parallel study on the samples from Sefar delivered in December 2010 and from JINR delivered in

January 2011

Samples Maximum tensile strength(MPa)

Failure

Sefar 1 127,5 Failure inside the weld

Sefar 2 127,6 Failure outside the weld

JINR 1 124,2 Failure outside the weld

JINR 2 132,6 Failure outside the weld

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JINR 2

Observations of samples from Sefar delivered in March 2011 (Straw number 23 )

Sample A A' Sample BB' 4x

Section comparisons

Piece of straw2 cm

Straw n◦23 Cross section A

Cross section B

Sample 1 SM1 A SM1 BSample 2 SM2 A SM2 BSample 3 SM3 A SM3 BSample 4 SM4 A SM4 B

Optical microscope analyze

Optical microscope analyze

Tensile tests

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Observations of samples from Sefar delivered in March 2011

Samples SM1A-SM4B(8 samples)

SD1A-SD4B(Straw number 90)

(8 samples)

Width (µm) 635,4-719,4 777,5-985,3

Thickness (µm) 60,2-78,5 50,1-75,4

Proportion of the melted area (%)

40,0-54,1 36,2-53,3

Cross section view: Optical microscope- 100x Magnification

Delivered in march 2011

Delivered in december 2010

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Comparison of cross section views (A and B) for samples separated from 2cm

Samples Cross section A (%) Cross section B (%) Difference(%)

SM1 48,6 53,9 5,3SM2 42,9 40,0 2,9SM3 54,1 46,0 8SM4 51,0 44,5 6,6

Accuracy 7

Samples Cross section A (µm) Cross section B (µm) Difference (µm)

SM1 681,2 700,2 19SM2 656,4 635,4 21SM3 710,7 686,2 24,5SM4 710,1 719,4 9,3

Accuracy 15

Samples Cross section A (µm)Min-Max

Cross section B (µm)Min-Max

Biggest difference (µm)

SM1 60,6-72,3 62,5-73,1 4,7SM2 61,5-70,2 60,2-72,5 3,2SM3 61,8-75,3 64,2-78,5 3,1SM4 60,2-75,3 60,3-75,3 10,0

Accuracy 8

MELTED AREA:

WIDTH:

THICKNESS:

Cross section A: Cross section B:

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Tensile test results for the samples from Sefar delivered in March: Use of the UTS machine

Samples σmax (MPa) Failure

SM1A 144,5 In the clamps

SM1B 121,7 In the weld

SM2A 138,5 In the clamps

SM2B 147,9 In the clamps

SM3A 146,9 In the clamps

SM3B 147,2 In the clamps

SM4A 109,7 In the weld

SM4B 115,6 In the weld

SM5 106,8 In the weld

Average 131,1Standard deviation 17,3

Samples used for the tensile tests with the UTS machine

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Tensile test results for the samples from Sefar delivered in March: Use of the ZPM machine

Samples σmax(MPa) FailureSM1 137,2 In the weldSM2 163,9 In the weldSM3 167,2 In the weldSM4 103,5 In the weldSM5 106,6 In the weldSM6 173,2 In the weldSM7 159,4 In the weldSM8 118,7 In the weldSM9 170,7 In the weld

SM10 111,8 In the weld

Average 141,6Standard deviation 28,7

Graphic for SM6-SM1015

Samples used for the tensile tests with the ZPM machine

Views of the chemical treated side of the welds

SM1-50x Magnification SM2- 50x Magnification SM4- 50x Magnification

Marks generated by the path of the sonotrode <=> Possible explanation which can justify the dispersion of the values of the tensile strength obtained for the samples extracted from a same straw from Sefar delivered in march 2011

σt=137,2 MPa σt= 163,9 MPa σt= 103,5 MPa

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Correlation between the tensile strength of the sample and the corresponded elongation in the

weld σt (MPa)

17Cross section view: Optical microscope-200x Magnification

◦

◦

◦

◦

◦

*

*

*

Caption:

◦ Failure in the clamps

* Failure in the weld

Tensile strength for samples extracted from a roll of PET film with copper coating

Samples without weld

Average (MPa) 184,7

Standard deviation (MPa)

6,9

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Samples with weld

Results of tensile strength for samples from Sefar delivered in March 2011

Calculation of the stresses generated in the straws by the conditions inside the chamber

Internal pressure of 1 bar

Pint => Hoop stress

Hoop stress (σc):

With: -p=1bar ou 0,101 N/mm² -r = 9,75/2 = 4,875 mm -t = 0,036 mm

=> σc= 13,68 MPa

Pre-tensioned of 15 N

Axial tension => Longitudinal stress

Longitudinal stress (σl):

=> σl = 13,60 MPa

tr

Fl

2t

rpc

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Security factor

Security factor by following the critera of the Maximum Normal Stress Theory

σys = 100 MPa (Minimum tensile strength)

σmax = σc = 13,68 MPa

31,768,13

100min FS

Determination of the maximum pressure:

barbarr

tp ys 129,7max

Avec : σys= 100 MPa

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t

rpc

=>

Deformations of the straws for the conditions inside the chamber

Variation of the diameter: mmmmdE

lcd 05,0015,0]

)([

Variation of the length: mmmmlE

cll 23005,3]

)([

With:

- E= 5600 MPa- ν = 0,37- d= 9,75 mm- L= 2300 mm

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Buckling phenomena

P

With:-l= 2300 mm -E= 5600 N/mm2

-d= 9,75 mm-t= 0,036 mm-ν= 0,37

barl

tdEpcrit 028,0

²)21(

²2

Compressive force= Tensile force => Resultant:

=>Critical load of buckling:

)21(²4

pd

²

]8³

[²4

l

tdE

Paille

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Buckling phenomena

Consideration of the spacers:

Spacers barl

tdEpcrit 51,2

'²)21(

²2

3'l

l With:

Consideration of the pre-tensioned of 15N:

barbarbar

d

T

l

tdEpcrit

129,71,1062,751,2

)21(²4/'²)21(

²2

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Particles from the coatingParticles from the coating

Tensile tests for samples extracted from a straw with coating and from a straw without coating

coming from a same batch

Without coating With coating

Average (MPa) 169,3 162,1

Standard deviation (MPa)

4,3 3,1

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Conclusions Improvement in the aspect of the welds by Sefar (September->March)

Samples of straw tested from JINR delivered in December 2010 presented similar tensile strength in comparison with the samples of straw tested from Sefar delivered in January 2011

Samples of welds from Sefar delivered in March 2011:

- Present values in width close to the requirement of 600 µm

- Dispersion in the results of tensile strength from 100 MPa to170 MPa (for a same straw)

Marks generated by the path of the sonotrode should have an influence on the strength of the welds

Security factor of minimum 7

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Discussion about the qualification by using the

observations

Difficulty for the qualification of the welds

Sefar delivered in September 2010 Sample 1: σt =121 MPa

Sefar delivered in September 2010 Sample 3: σt = 110 MPa

JINR delivered in January 2011 Sample 2: σt = 132 MPa

Sefar delivered in March 2011 Sample SM4 A: σt =110 MPa

Sefar delivered in March 2011 Sample SM3 A: σt = 147 MPa

JINR delivered in May 2011 Sample DM2: σt = 60 MPa

Difficulty for the qualification of the welds

My assumptions:

•The proportion of the melted area in the weld and their shape => No correlation observed

•The aspect of the weld for the cross section view => Not sufficient

•The aspect of the weld for the chemical treated side => Not sufficient

•The aspect of the weld for the cross section view AND the chemical treated side => Destructive test for the observation of the cross section of the weld

• The aspect of the weld for the chemical treated side AND the coating side => To find a way to observe the coating side inside the straws

• The tensile test=> Destructive test

Propositions in order to find a process control for the qualification of the weld :

Elongation determination

Elongation in the samples:

Graphic for SM1-SM5 Graphic for S1-R2

Presumably relation between the elongation for the samples and their tensile strength Elongation included in a range of values of about 10 to 40% ( PET film 25 to 40% for Hostaphan RNK 2600)

Elongation in the welds:

No relation between the tensile strength and the elongation in the weldElongation in the weld included in a range of values of about 1 to 18%

Digital microscope:Analyze of the

topography of the chemical treated side

SM3

SM4SM4

DM1

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