Update on straw creep · PDF file 8/31/2015  · Straw end position vs time (ref:...

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Transcript of Update on straw creep · PDF file 8/31/2015  · Straw end position vs time (ref:...

  • Update on straw creep

    measurements

    Chiho Wang, Seog Oh

    Duke University

    (doc 2484)

  • “Fixed Tension” Creep Measurement

    • PPG straws: 155cm long, 5mm ID, 18 um wall (6μm Al

    coated Mylar outer layer + 6μm Al+Au coated Mylar inner

    layer + 6um polyester adhesive).

    • Straw properties:

     Spring constant k=1.4cm/kg

     Mylar thermal expansion = 1.7E-05/°C (DuPont)

     Mylar humidity expansion = 6.0E-6/%(RH) (DuPont)

    • Initial condition: 550gm weight + 18 psi ~ 800gm tension.

    • After 120 days: changed to 550gm weight + 0 psi.

    • After 1150 days: changed to 50gm weight

    08/31/15 Chiho Wang, Seog Oh 2

  • Straw end position vs time (ref: doc#2277 & 2084 for setup)

    St ra

    w e

    n d

    P o

    si ti

    o n

    St ra

    w le

    n gt

    h en

    in g

    d ir

    ec ti

    o n

    08/31/15

    550 gm tension on 155 cm straw, Creep rate ~ 1.6 μm/day

    Chiho Wang, Seog Oh 3

    When tension is removed (reduced to 50 gm) it also takes a long time to creep back

  • “Fixed Length” Creep Measurement

    • Glue straws on a support frame (120cm) with tensions:

     300gm, 400gm, 500gm, 600gm.

    • Measure straw tension by resonant frequency as a

    function of time.

    08/31/15

    Precision Function generator

    Frequency Counter

    Weight

    Speaker Magnet Support Frame

    Straw

    Chiho Wang, Seog Oh 4

  • Tension change vs time

    Linear Fit (150 days and later)

    08/31/15 (corrected for temperature & humidity variation)

    Chiho Wang, Seog Oh 5

  • Temperature & Humidity variation

    08/31/15 Chiho Wang, Seog Oh 6

  • Corrections due to T & H variation

    08/31/15

    Humidity expansion coefficient = 7.6E-6/% Thermal expansion coefficient = 1.7E-5 (Mylar) – 2.35E-5 (Al Frame) = -6.5E-6/°C

    Chiho Wang, Seog Oh 7

  • Fractional Tension change vs time

    Linear Fit (150 days and later)

    08/31/15 (corrected for temperature & humidity variation)

    Chiho Wang, Seog Oh 8

  • Slope

    • Fractional tension change is almost the same irrespective

    of their initial tensions.

    08/31/15

    Initial Tension (T0) ∆T/T0/day-

    300 g - 8.8E-5 ± 0.1E-5

    400 - 9.5E-5 ± 0.1E-5

    500 - 9.8E-5 ± 0.1E-5

    600 - 9.8E-5 ± 0.1E-5

    Chiho Wang, Seog Oh 9

  • Fractional Tension change vs time

    Exp Fit (c0*e-c1*t+c2) (50 days and later)

    08/31/15 (corrected for temperature & humidity variation)

    Chiho Wang, Seog Oh 10

  • C2 in Exp Fit (c0*e-c1*t+c2)

    08/31/15

    Initial Tension (T0) C2

    300 g 0.556 ± 0.001

    400 0.539 ± 0.001

    500 0.543 ± 0.001

    600 0.536 ± 0.001

    Chiho Wang, Seog Oh 11

  • Fractional Tension change vs time

    Exp Fit (c0*e-c1*t+0) (150 days and later)

    08/31/15 (corrected for temperature & humidity variation)

    Chiho Wang, Seog Oh 12

  • C1 in Exp Fit (c0*e-c1*t+0)

    08/31/15

    Initial Tension (T0) C1 (day-1)

    300 g 15E-5 ± 0.2E-5

    400 17E-5 ± 0.1E-5

    500 17E-5 ± 0.1E-5

    600 17E-5 ± 0.1E-5

    Chiho Wang, Seog Oh 13

  • Exp Fit (c0*e-c1*t+c2) 6-year projection

    08/31/15 (corrected for temperature & humidity variation)

    Chiho Wang, Seog Oh 14

  • Exp Fit (c0*e-c1*t+0) 6-year projection

    08/31/15 (corrected for temperature & humidity variation)

    Chiho Wang, Seog Oh 15

  • Fractional Tension

    Exp Fit (c0*e-c1*t+0) 6-year projection

    08/31/15 (corrected for temperature & humidity variation)

    Chiho Wang, Seog Oh 16

  • Linear Fit 6-year projection

    08/31/15 (corrected for temperature & humidity variation)

    Chiho Wang, Seog Oh 17

  • Fractional Tension

    Linear Fit 6-year projection

    08/31/15 (corrected for temperature & humidity variation)

    Chiho Wang, Seog Oh 18

  • Assuming (c0*e-c1*t+0)

    Equivalent time shift by initial tension

    08/31/15 Chiho Wang, Seog Oh 19

  • Summary

    • Summary:

     Extrapolation for fractional tension after 6 years is:

    o ~0.45 from a linear fit

    o ~0.47 from an exponential to 0 fit (c0*e-c1*t+0).

    o ~0.54 from an exponential to const. fit (c0*e-c1*t+c2)

     No significant change in results since last report. However,

    extrapolations are consistently getting better over time.

     Fractional tensions continue to scale well and can be used to

    estimate creep at other initial tensions.

     Weather effect seems averaging out after a long period of time.

    Extrapolated results are very similar with or without temperature &

    humidity correction.

     Will stop taking data, but can resume in the future as needed.

    08/31/15 Chiho Wang, Seog Oh 20

  • Backup slides

     10-year fractional tensions extrapolation.

     Raw data without temperature/humidity corrections.

    08/31/15 Chiho Wang, Seog Oh 21

  • Fractional Tension

    Exp Fit (c0*e-c1*t+0) extrapolation

    08/31/15 (corrected for temperature & humidity variation)

    Chiho Wang, Seog Oh 22

  • Raw data Fractional Tension

    Exp Fit (c0*e-c1*t+0) extrapolation

    08/31/15 (Without correction for temperature & humidity variation)

    Chiho Wang, Seog Oh 23

  • Fractional Tension

    Linear Fit extrapolation

    08/31/15 (corrected for temperature & humidity variation)

    Chiho Wang, Seog Oh 24

  • Raw data Fractional Tension

    Linear Fit extrapolation

    08/31/15 (Without correction for temperature & humidity variation)

    Chiho Wang, Seog Oh 25

  • Tension change vs time

    Linear Fit (after 100 days)

    08/31/15 (without correction for temperature & humidity variation)

    Chiho Wang, Seog Oh 26