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: De Carlo Livio Section: 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 2

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

Devices available for the qualification of the welds (Materials section) Optical microscope (->1500x) Stéréomicroscope (->115x) Tensile machine UTS (->200 kN) Polishing machineTensile machine ZPM (1kN) 4

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 Width900 µm (>600µm) Thickness60 to 70 µm Critical section: Width110 to 170 µm Thickness30 to 45 µm Samples Maximum tensile strength (MPa) 1120,7 2127,2 3107,2 4105,4 Critical point Mechanism of failure after the tensile test: Cross section view: Stereomicroscope- 115x (left) and 80x (right) Magnification 5

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: Width300 µm (<600µm) Thickness60 to 70 µm Total width:620 to 630 µm Samples Maximum tensile strength (MPa) 1109,6 2112,4 Mechanism of failure after the tensile test: 6 => 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 7

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 02 8

Parallel study on the samples from Sefar delivered in December 2010 and from JINR delivered in January x Magnification 100x Magnification Samples Width (µm) Thickness (µm) Max-Min Proportion of the melted area (%) Sefar 1867,9 (>600µm) 67,2-59,142,6 Sefar 2860,1 (>600µm) 62,6-50,952,4 JINR 1847,4 (>600µm) 75,8-48,549,0 JINR 2551,4 (<600µm) 88,6-5833,3 9 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 1127,5Failure inside the weld Sefar 2127,6Failure outside the weld JINR 1124,2Failure outside the weld JINR 2132,6Failure outside the weld 10 JINR 2

Observations of samples from Sefar delivered in March 2011 (Straw number 23 ) Sample A A' Sample B B' 4x Section comparisons Piece of straw 2 cm Straw n◦23 Cross section A Cross section B Sample 1SM1 ASM1 B Sample 2SM2 ASM2 B Sample 3SM3 ASM3 B Sample 4SM4 ASM4 B Optical microscope analyze Tensile tests 11

Observations of samples from Sefar delivered in March 2011 SamplesSM1A-SM4B (8 samples) SD1A-SD4B (Straw number 90) (8 samples) Width (µm)635,4-719,4777,5-985,3 Thickness (µm)60,2-78,550,1-75,4 Proportion of the melted area (%) 40,0-54,136,2-53,3 Cross section view: Optical microscope- 100x Magnification Delivered in march 2011 Delivered in december

Comparison of cross section views (A and B) for samples separated from 2cm SamplesCross section A (%)Cross section B (%)Difference(%) SM148,653,95,3 SM242,940,02,9 SM354,146,08 SM451,044,5 6,6 Accuracy7 SamplesCross section A (µm)Cross section B (µm)Difference (µm) SM1681,2700,219 SM2656,4635,421 SM3710,7686,224,5 SM4710,1719,49,3 Accuracy15 Samples Cross section A (µm) Min-Max Cross section B (µm) Min-Max Biggest difference (µm) SM160,6-72,362,5-73,14,7 SM261,5-70,260,2-72,53,2 SM361,8-75,364,2-78,53,1 SM460,2-75,360,3-75,310,0 Accuracy8 MELTED AREA: WIDTH: THICKNESS: Cross section A:Cross section B: 13

Tensile test results for the samples from Sefar delivered in March: Use of the UTS machine Samplesσmax (MPa)Failure SM1A144,5In the clamps SM1B121,7In the weld SM2A138,5In the clamps SM2B147,9In the clamps SM3A146,9In the clamps SM3B147,2In the clamps SM4A109,7In the weld SM4B115,6In the weld SM5106,8In the weld Average131,1 Standard deviation17,3 Samples used for the tensile tests with the UTS machine 14

Tensile test results for the samples from Sefar delivered in March: Use of the ZPM machine Samplesσmax(MPa)Failure SM1137,2In the weld SM2163,9In the weld SM3167,2In the weld SM4103,5In the weld SM5106,6In the weld SM6173,2In the weld SM7159,4In the weld SM8118,7In the weld SM9170,7In the weld SM10111,8In the weld Average141,6 Standard deviation28,7 Graphic for SM6-SM10 15 Samples used for the tensile tests with the ZPM machine

Views of the chemical treated side of the welds SM1-50x MagnificationSM2- 50x MagnificationSM4- 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 MPaσt= 163,9 MPaσt= 103,5 MPa 16

Correlation between the tensile strength of the sample and the corresponded elongation in the weld σ t (MPa) 17 Cross 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 18 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 P int => Hoop stress Hoop stress (σ c ): With: -p=1bar ou 0,101 N/mm² - r = 9,75/2 = 4,875 mm -t = 0,036 mm => σ c = 13,68 MPa Pre-tensioned of 15 N Axial tension => Longitudinal stress Longitudinal stress (σ l ): => σ l = 13,60 MPa 19

Security factor Security factor by following the critera of the Maximum Normal Stress Theory σ ys = 100 MPa (Minimum tensile strength) σ max = σ c = 13,68 MPa Determination of the maximum pressure: Avec : σ ys = 100 MPa 20 =>

Deformations of the straws for the conditions inside the chamber Variation of the diameter : Variation of the length: With: - E= 5600 MPa - ν = 0,37 - d= 9,75 mm - L= 2300 mm 21

Buckling phenomena P With: -l= 2300 mm -E= 5600 N/mm 2 -d= 9,75 mm -t= 0,036 mm -ν= 0,37 Compressive force= Tensile force => Resultant: =>Critical load of buckling: Paille 22

Buckling phenomena Consideration of the spacers: Spacers With: Consideration of the pre-tensioned of 15N: 23

Particles 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 coatingWith coating Average (MPa)169,3162,1 Standard deviation (MPa) 4,33,1 25

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 26

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 weld  Elongation 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

SM4

DM1

35