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