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)

Stra

w e

nd

Po

siti

on

Stra

w le

ngt

hen

ing

dir

ecti

on

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

PrecisionFunction generator

Frequency Counter

Weight

SpeakerMagnet 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