live webinar, september 2013 composites fatigue testing using specimen self-heating control for...
TRANSCRIPT
Live Webinar, September 2013
Composites Fatigue Testing using
Specimen Self-Heating Control for WaveMatrix
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Overview
• Composites Fatigue
• Problems with current methods
• A solution
• Rewards vs Concerns
• Case Study
• SSHC live demonstration
• Questions
• Temperature measurement / monitoring
• Options and set-up demonstration
• More questions ?
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Composites Fatigue
• Cyclic loading tests on coupons
• Roughly equivalent to HCF for metals
- No consistent methodology yet for crack growth
• Highly sensitive to structure in the same “type” of material
• Rapid commercial uptake by wind energy sector
• Cost vs lifecycle is of critical importance
• System qualification is less complex than aerospace
• Other sectors gradually catching up
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Industry Interest
• Turbine manufacturers
• Vestas, Siemens, GE
• Composite materials producers
• Resins - Hexcel, DSM
• Fibres - LM Glasfiber, Teijin, Sabic
• Aerospace & automotive are deciding what to do…
• Boeing, Airbus, Fokker, BMW, Jaguar, and others
• Test houses
• Researchers
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Current Standards
• Standards include:
• ASTM D 3479
• ISO 13003
• Similar AITM, Boeing and SACMA
• These standards specify:
• Fixed frequency
• Temperature monitoring
• They also recommend:
• Frequency < 5 Hz
• Temperature rise < 10°C during test
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An easy opportunity?Growing industry with international standards….
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A Major Problem
• Composite specimens heat significantly under cyclic loading
• Composites fatigue tests are slow
• 8 weeks for a reasonable S-N curve
• Run at higher frequency ?
• Test temperature fluctuates severely
• Room temperature at low load
• >20° C rise at high load
• Run at even lower frequency ?
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Cyclic Heating Effect
• Woven CFRE – thermal imaging• 80% UTS, R = 0.1, 5 Hz
t = 0 1 min 2 min 4 min 8 min
16 min30°C 35°C 40°C
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Customers’ Current Methods
• General practise:• Pick a frequency based on 1 or 2 materials
• Use it for everything
• Not worry too much about temperature rise, because they can’t control it.
• Result:• Very slow test; > 4 weeks for reasonable S-N curve
• Often exceeds 10 °C temperature rise
• Unpredictable specimen temperature
• Temperature varies for different loading
• Temperature varies during test
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Not quite so easy after all !
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Specimen Self-Heating Control
• New WaveMatrix module to improve specimen throughput
• Automatically adjusts frequency to balance the heating and cooling rates at a user selected specimen temperature
• Faster tests where cycles-to-failure is high
• Maintains stable temperature for all tests
• Patent pending – our competitors cannot do this
• Good comparability with fixed frequency tests
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Simple Control Tab
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Optimising Frequency
Stable temperature by reducing frequency
tan δ → Increasing heating rate
* GFRE loaded to 40% UTS at R = 0.1, target temperature 21.0 ± 0.5 °C
~3x higher frequency
Acceptable temperature
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Preventing Over-Heating
Stable temperature by reducing frequency
tan δ → Increasing heating rate
* GFRE loaded to 60% UTS at R = 0.1, target temperature 28.0 ± 0.5 °C
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How do we sell it ?Neat technology
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System Requirements
• Specimen Self-Heating Control Module for WaveMatrix
• Available from WaveMatrix version 1.8• Requires Console 8.2.149 or later
• Requires temperature sensor
• either a Thermocouple interface • National Instruments USB DAQ supported in WaveMatrix
• Does not need SCM
• Supports multiple channels
• or an IR camera/probe input via strain channel• Tested with Optris camera and spot sensors
• Need to allow a spare SCM (+ CP to interface?)
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Does the customer even know they have
a problem?
• Customers already working on composites fatigue
• Have an idea of the problem
• Often do not continuously monitor temperature
• Don’t know how badly it affects their results
• Customers new to the field
• Have probably read the standards
• Don’t know how badly it affects results
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Rewards and Concerns
• Not mentioned in ASTM or ISO standards
• But many do not work strictly to standards anyway!
• Data may differ from an existing method
• But may indicate longer fatigue life
- versus -
• Even a small increase in frequency on lower loading gives a big time saving.
• Don’t waste time and specimens trying out different frequencies.
• Controlled temperature can reduce spread of data.
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Convince me!Sounds good, but…
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A Case Study
• UK National Composites Certification and Evaluation Facility
• Used “standard” thermocouple temperature measurement
• ISO 13003 tension-tension test
• Complete repetition of S/N curve
• > 25% reduction in machine time
• Comparable or reduced scatter
• Comparable fit – better intercept
• < 4% difference for 10 million cycles prediction
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Comparative Case StudyWoven CFRE prepreg, Tension-Tension (R=0.1)
1,000 10,000 100,000 1,000,000 10,000,000 55
60
65
70
75
80
85
4 Hz fixed frequency
Specimen Self-Heating Control
Cycles to Failure
σm
ax
[%
UT
S]
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Case Study: Fitting and Prediction
Gradient Intercept (% UTS)
Fit quality
(“R²”)
Predicted Stress at 107 cycles (%UTS)
Predicted Stress at 108 cycles (%UTS)
4 Hz – all data 3.156 106.7 0.844 55.9 48.6
4 Hz – exclude outliers 2.886 104.4 0.931 57.9 51.2
Adaptive frequency 2.651 100.7 0.966 57.9 51.8
Logarithmic fit: σc = ‒ a ln(N) + c
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Case Study: Time Saving
Frequency variation
Total time for S/N curve
Equivalent time at 4 Hz
Time saving vs 4 Hz
< 62 % 40 days 55 days 27.5 %
Load (%UTS)
Specimen Self-Heating Control Fixed Frequency 4 Hz
Frequency * (Hz)
Time per specimen* (hours)
Equivalent time per specimen** (hours)
80% 3.6 0.93 0.84
75% 4.0 3.9 3.9
70% 4.6 22 24
65% 5.0 290 349
60% 6.5 642 946
* averaged across duration of test ** from cycles to fail
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Conclusion
• SSHC offers a unique enhancement for coupon based fatigue testing of composites
• Quick simple set-up
• Comparable results to existing methods
• Better use of machine time by automatically optimising frequency
• Reliable temperature control
• Reduced test time
• Excellent lock-out opportunity – our competitors cannot
do this due to patent pending!
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Catalogue Entry
• In catalogue for all territories
• Released and shipping since June
• Dynamic Systems: Software• 2495-915 F1 – new systems
• 2495-965 F1 or F2 – upgrades
• Dynamic Systems: Composite Testing Accessories• CP112383 – Thermocouple USB integration (4 channel)
• Basic solution from NI to allow you to specify a whole system with SSHC
• PoD, white paper, and press release available
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Questions?Technical Background and Case Study
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Specimen Self-Heating Control
Live demonstration
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Simple Control Tab
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Live test screen
* target 25°C
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Temperature MonitoringOptions and setting up for temperature measurement and SSHC
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Temperature Measurement
• Temperature measurement is important
• WaveMatrix has good capability
• Standard product is limited for now
• Integrated temperature recording is a great feature anyway especially for composites & polymers
• Even if you are not going to use SSHC
• Even if you are operating in a chamber
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Thermocouples
• Universally understood
• USB daq our preferred option
• Single point measurements
• Standardised one-shot CP112383
• Attachment to specimen can cause problems
• Measurement is taken by WaveMatrix not 8800
• Values are not available as Live Displays
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Infrared Transducer
• Single point measurement(s) • spot size 1mm to >>10mm
• Popular & established in industrial process control
• Desirable for non-contact measurement
• Connect as strain channel to 8800 or using USB daq
• No standard product or one-shot
• Good for relative monitoring but…
• Absolute measurement is difficult because it depends on the specimen
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Infrared Camera
• Full thermal imaging
• Similar benefits to IR spot sensor
• Useful features such as averaging and hot-spot detection
• Observe/capture localisation
• Connect as strain channel to 8800
• Strongly recommend customer source directly
• x10 more expensive than thermocouples and IR spot
• Response still depends on specimen
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Questions?Temperature Measurement and Monitoring