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UPDATES TO METALS
STANDARDS 2017
22
Questions We Want to Answer
What is important?
• Which metals testing standards have changed recently?
• Why and how ha...
33
Evolution of Testing Standards
How did they evolve?
BS18
ISO 6892-1:2009DIN 50145
EN10002
ISO6892
1904 1970 20091990 20...
44
Notable Changes
What are the key changes?
• In 2009: ISO 6892-1
• Added a strain rate method – “Method A”
• Separated M...
55
EN vs ISO?
What are the differences between EN & ISO?
EN 10002 ISO 6892-1
Method A: Strain Rate Control
Method B: Stres...
66
“Method B” Rates
How is Method B applied?
• Method B – Stress Control
• Stress control during elastic region, then “set...
77
Changes in Method B?
Added a new note into Method B
"It is not the intent of Method B to maintain constant stress rate ...
88
“Method A” Rates
How is Method A applied?
• Method A – allowed strain rates
• Range 1 – 0.00007 s−1 ±20%
• Range 2 – 0....
99
Rates on Logarithmic Scale
Simpler way of displaying rates and calculations
1010
Strain Rate?
What is Strain Rate?
• Change in specimen length/original gauge length/time
• Change in strain per unit ...
1111
Strain Rate?
Why is strain rate important?
• Some metals mechanical properties are strain-rate dependent
• Extract fr...
1212
Strain Rate?
Why is strain rate important?
• From ASTM E8/E8M-11:
• In strain control, “the reproducibility of yield ...
1313
Strain Rate?
Testing on different systems
When testing on different systems at the same speed, you can get different ...
1414
Strain Rate?
Testing on the same system at different rates
• Upper Plot controlled at
Maximum Stress Rate per
Method ...
1515
So What’s New?
What changed in 2016?
• Method A was commonly confused and has been clarified
• It was assumed that Me...
1616
ISO 6892:2016
What has changed?
Strain Control (Extensometer)
Stress Control (Load/Force)
Extension Control (Crosshea...
1717
ISO6892-1:2016
Method A1 – Closed
Loop Strain Rate
Method A2 -
Estimated Strain Rate
Method B – Stress
Rate
How Does ...
1818
ASTM E8/E8M-2015 Testing Rates
What are ASTM E8 rates?
• The following control methods can be used “in the absence of...
1919
ISO 6892-1:2016 Method A1 & A2
It is important to remember the required rates and the +/-20% Tolerance is the
SAME fo...
2020
Method A2
Estimated Strain Rate
2121
Method A2 “Estimated Strain Rate”
Did it exist before?
Extract from ISO 6892-1:2009:
“Two different types of strain r...
2222
Method A2 “Estimated Strain Rate”
How do you do it?
Wording within ISO 6892-1:2016 Method A2 notes the ‘estimated str...
2323
Method A2 “Estimated Strain Rate”
How do you do it?
Example:
For a specimen with 80 mm Lc (parallel length), the requ...
2424
Method A2 “Estimated Strain Rate”
Why would it be different?
Experiment: Same testing speed, two different machines. ...
2525
ISO 6892-1 Annex F
How can you get the correct estimated strain rate?
Estimation of the crosshead separation rate in ...
2626
ISO 6892-1 Annex F
How can you get the correct estimated strain rate?
Using powerful Bluehill® Universal Software, ut...
2727
Method A2 “Estimated Strain Rate”
Test performed in extension control
What does this look like?
±20% Error
bounds
Con...
2828
Method A2 “Estimated Strain Rate”
Why would it be different?
Positives to using ‘estimated rate’:
• Simpler control m...
2929
Method A1
Closed Loop Strain Rate Control
3030
Method A1 “Closed Loop Strain Control”
System Requirements
• Load Frame
• Precise and stable drive system
• Grips
• A...
3131
Method A1 “Closed Loop Strain Control”
What is the feedback “loop”?
Extensometer
Feedback
Control Error
(Extension)
M...
3232
Method A1 “Closed Loop Strain Control”
Gain Adjustment
• Gain adjustment is what will dictate the performance of the ...
3333
Method A1 “Closed Loop Strain Control”
The effect of stiffness or “compliance”
Zero Load Under Load
Deflection
L
o
Ze...
3434
Method A1 “Closed Loop Strain Control”
What does this look like?
±20% Error
bounds
0.2% Offset yield
Strain control s...
3535
Method A1 “Closed Loop Strain Control”
Why would you want to do this?
0
100
200
300
400
500
600
700
0 5 10 15 20 25 3...
3636
Method A1 “Closed Loop Strain Control”
Summary of why you should care
• Repeatable and comparable results
• As some m...
3737
ISO 6892-1:2016 Control Modes Summary
Simple Comparison between the methods
3838
Which Instron Systems Meet What?
Testing Systems 5900 Series vs 3300 Series
3939
Conclusions
When looking into new testing machines or accessories, ask:
• Can this achieve requirements for ISO 6892-...
4040
Please contact Instron® with any questions
Thank You
Watch our webinar recording
Visit www.instron.com for more infor...
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Metals Tensile Testing Standards: ISO 6892-1 ASTM E8/8M for Strain Control

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Brief introduction into some of the changes and updates to both the ISO 6892-1 and ASTM E8/8M tensile testing standards for metals and ambient temperature, importantly strain control

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Metals Tensile Testing Standards: ISO 6892-1 ASTM E8/8M for Strain Control

  1. 1. UPDATES TO METALS STANDARDS 2017
  2. 2. 22 Questions We Want to Answer What is important? • Which metals testing standards have changed recently? • Why and how have the standards changed? • How does this affect you? • How can you ensure your testing machine is compliant with these latest standards?
  3. 3. 33 Evolution of Testing Standards How did they evolve? BS18 ISO 6892-1:2009DIN 50145 EN10002 ISO6892 1904 1970 20091990 2016 ISO 6892-1:2016 ASTM E8-24T ASTM E8 ASTM E8M ASTM E8/E8M
  4. 4. 44 Notable Changes What are the key changes? • In 2009: ISO 6892-1 • Added a strain rate method – “Method A” • Separated Method A, strain rate, and Method B, stress rate • ASTM E8/E8M-11 • The two separate standards have been combined into one standard for imperial and metric • Clarified testing speeds and added tolerances for strain rate Prior to this, defined strain rates mostly found in product standards such as aerospace (Nadcap/EN 2002)
  5. 5. 55 EN vs ISO? What are the differences between EN & ISO? EN 10002 ISO 6892-1 Method A: Strain Rate Control Method B: Stress Rate Control Stress Rate Control Stress Rate Control
  6. 6. 66 “Method B” Rates How is Method B applied? • Method B – Stress Control • Stress control during elastic region, then “sets” constant crosshead speed • Stress = Force/Area – Accurate Load Measurement and Specimen Dimensions Required • Two Different Ranges • Aluminum samples: 2 – 20 MPa/Second • Steel samples: 6 – 60 MPa/Second (Huge variation!)
  7. 7. 77 Changes in Method B? Added a new note into Method B "It is not the intent of Method B to maintain constant stress rate or to control stress rate with closed loop force control while determining yield properties, but only to set the crosshead speed to achieve the target stress rate in the elastic region. When a specimen being tested begins to yield, the stressing rate decreases and may even become negative in the case of a specimen with discontinuous yielding. The attempt to maintain a constant stressing rate through the yielding process requires the testing machine to operate at extremely high speeds and, in most cases, this is neither practical nor desirable." Stress Control Stress Strain Crosshead Speed Control
  8. 8. 88 “Method A” Rates How is Method A applied? • Method A – allowed strain rates • Range 1 – 0.00007 s−1 ±20% • Range 2 – 0.00025 s−1 ±20% (recommended) • Range 3 – 0.002 s−1 ±20% • Range 4 – 0.0067 s−1 ±20% (recommended) • Range(s) chosen are determined by material properties being sought • Either in strain control or ‘estimated rate’ • ISO 6892-1 Method A • MOST restrictive of metals standards
  9. 9. 99 Rates on Logarithmic Scale Simpler way of displaying rates and calculations
  10. 10. 1010 Strain Rate? What is Strain Rate? • Change in specimen length/original gauge length/time • Change in strain per unit of time (in/in/min, mm/mm/s, %/s, s-1) • Typically measured with an extensometer on metals specimens ∆𝑙 𝑙 𝑙 Typically measured with an extensometer for metals specimens
  11. 11. 1111 Strain Rate? Why is strain rate important? • Some metals mechanical properties are strain-rate dependent • Extract from ISO 6892-1: “Method A is intended to minimize the variation of the test rates during the moment when strain rate sensitive parameters are determined and to minimize the measurement uncertainty of the test results.”
  12. 12. 1212 Strain Rate? Why is strain rate important? • From ASTM E8/E8M-11: • In strain control, “the reproducibility of yield strength test results from machine to machine and laboratory to laboratory is good.” • “In order to reproduce yield test results, for strain-rate sensitive materials, it is important that strain rates during the determination of yield are similar.” • “The yield strength of some materials can change by more than 10% when tested with the slowest and then the highest speeds permitted by E8/E8M.”
  13. 13. 1313 Strain Rate? Testing on different systems When testing on different systems at the same speed, you can get different results • Upper Plot controlled at constant crosshead speed on ‘stiff’ system • Lower Plot controlled at same constant crosshead speed but on weaker system
  14. 14. 1414 Strain Rate? Testing on the same system at different rates • Upper Plot controlled at Maximum Stress Rate per Method B • Lower Plot controlled at Minimum Stress Rate per Method B When testing on the same system at different speeds, you can get different results
  15. 15. 1515 So What’s New? What changed in 2016? • Method A was commonly confused and has been clarified • It was assumed that Method A required ‘closed loop strain control’ to be able to conform. This is NOT true. • You can achieve the strain rate with a constant crosshead speed • Calculated by multiplying the required strain rate by the parallel length
  16. 16. 1616 ISO 6892:2016 What has changed? Strain Control (Extensometer) Stress Control (Load/Force) Extension Control (Crosshead/Position)
  17. 17. 1717 ISO6892-1:2016 Method A1 – Closed Loop Strain Rate Method A2 - Estimated Strain Rate Method B – Stress Rate How Does This Compare with ASTM E8? What are the differences? ASTME8M-15 Method A – Rate of Stressing Method B - Rate of Straining Method C – Crosshead Speed Control Strain Control (Extensometer) Stress Control (Load) Extension Control (Crosshead)
  18. 18. 1818 ASTM E8/E8M-2015 Testing Rates What are ASTM E8 rates? • The following control methods can be used “in the absence of any specified limitations”: • Method A – Rate of Stressing 1.15–11.5 Mpa/s (10-100 ksi/min) • More restrictive than ISO 6892-1 Method B (6-60 MPa/S) • Method B – Rate of Straining 0.00025 s−1 ± 40% • Less restrictive than ISO 6892-1 Method A (± 20%) • Method C – Crosshead Speed 0.015 ±.003 (+/-20%) mm/mm/min of specimen gauge length • Similar to ISO 6892-1 Method A ‘estimated rate’ • Similar recommendations and control modes as ISO 6892-1:2009, but less restrictive tolerance for strain rate and more restrictive for stress rate
  19. 19. 1919 ISO 6892-1:2016 Method A1 & A2 It is important to remember the required rates and the +/-20% Tolerance is the SAME for BOTH methods. What is important? So, how can you conform?
  20. 20. 2020 Method A2 Estimated Strain Rate
  21. 21. 2121 Method A2 “Estimated Strain Rate” Did it exist before? Extract from ISO 6892-1:2009: “Two different types of strain rate control are described in this section. The first is the control of the strain rate itself, that is based on the feedback obtained from an extensometer. The second is the control of the estimated strain rate over the parallel length, which is achieved by controlling the crosshead separation rate at a velocity equal to the desired strain rate multiplied by the parallel length.” Method A1 and A2 were already there!
  22. 22. 2222 Method A2 “Estimated Strain Rate” How do you do it? Wording within ISO 6892-1:2016 Method A2 notes the ‘estimated strain rate over the parallel length’ • This is achieved by controlling the crosshead separation rate at a velocity equal to the desired strain rate multiplied by the parallel length
  23. 23. 2323 Method A2 “Estimated Strain Rate” How do you do it? Example: For a specimen with 80 mm Lc (parallel length), the required crosshead separation rate would be: • Range 2: (0.00025 mm/mm/s) 0.00025 mm/mm/s X 80 mm = 0.02 mm/s (or 1.2 mm/min) • Range 4: (0.0067 mm/mm/s) 0.0067 mm/mm/s X 80 mm = 0.536 mm/s (or 32.16 mm/min) This would suggest that the speeds above will mean you are compliant. However, NOT NECESSARILY! The strain rate still needs to be within the +/-20% tolerance. Annex F?
  24. 24. 2424 Method A2 “Estimated Strain Rate” Why would it be different? Experiment: Same testing speed, two different machines. Results the same?
  25. 25. 2525 ISO 6892-1 Annex F How can you get the correct estimated strain rate? Estimation of the crosshead separation rate in consideration of the stiffness (or compliance) of the testing equipment. This equation it takes into account the full machine compliance and will give a more accurate constant crosshead speed to achieve the target strain rate. This is particularly helpful for systems that are not able to perform closed loop strain control.
  26. 26. 2626 ISO 6892-1 Annex F How can you get the correct estimated strain rate? Using powerful Bluehill® Universal Software, utilizing Expression Builder, there are now default methods built for Annex F of ISO 6892-1:2016.
  27. 27. 2727 Method A2 “Estimated Strain Rate” Test performed in extension control What does this look like? ±20% Error bounds Constant crosshead displacement 0.2% Offset yield (strain rate within ±20% at this point) Strain rate moves into ±20% error band during yield. Correct rate during Rp0.2 calculation point
  28. 28. 2828 Method A2 “Estimated Strain Rate” Why would it be different? Positives to using ‘estimated rate’: • Simpler control method – can be used on most testing machines • Still get comparable results Negatives to using ‘estimated rate’: • Test times are increased • Further calculation for machine compliance/stiffness • May need to break specimens to tune test • Different results from machine to machine if not tuned • Common misunderstanding of ‘Method A’ in ISO 6892-1
  29. 29. 2929 Method A1 Closed Loop Strain Rate Control
  30. 30. 3030 Method A1 “Closed Loop Strain Control” System Requirements • Load Frame • Precise and stable drive system • Grips • Able to securely grip the specimen during the test without slippage • Extensometer • High-precision device with stable feedback • Good gauge length to parallel length ratio • Software/Controller • Responsive control loop able to maintain +/-20% or +/-40% limits • Automatic tuning or manual tuning for yield region • Lab Environment • Free of vibration and shock *Not achievable on every system
  31. 31. 3131 Method A1 “Closed Loop Strain Control” What is the feedback “loop”? Extensometer Feedback Control Error (Extension) Machine Controller e.g. 5900 Error Signal GAIN Adjustments Set Point from Software
  32. 32. 3232 Method A1 “Closed Loop Strain Control” Gain Adjustment • Gain adjustment is what will dictate the performance of the machine control • “PID” Controller is most common. Proportional gain requires greatest adjustment, and will change throughout the test
  33. 33. 3333 Method A1 “Closed Loop Strain Control” The effect of stiffness or “compliance” Zero Load Under Load Deflection L o Zero Load Lo+ΔL Under Load Compressed Lead Screw and Drive System Deflection Load Cell Deflection Crosshead and Base Deflection Grip, Jaw Face and Adaptor Deflection Amplified deflection!
  34. 34. 3434 Method A1 “Closed Loop Strain Control” What does this look like? ±20% Error bounds 0.2% Offset yield Strain control slows the crosshead down to compensate Significant and rapid change in system stiffness during the onset of yield Test performed in closed loop strain control
  35. 35. 3535 Method A1 “Closed Loop Strain Control” Why would you want to do this? 0 100 200 300 400 500 600 700 0 5 10 15 20 25 30 35 40 45 50 55 60 65 TensileStress(MPa) Time (s) Closed Loop Estimated Rate 40% Time Saving when compared to estimated rate
  36. 36. 3636 Method A1 “Closed Loop Strain Control” Summary of why you should care • Repeatable and comparable results • As some metals are strain-rate sensitive, this reduces variance between labs and systems • Improved efficiency • Shorter testing times with a range of specimens • 5900 Automatic tuning reduces setup time • No need to use a specimen for tuning 35% Time Saving when compared to estimated rate ISO 6892-1 Method B – 10 Mpa/s ISO 6892-1 Method A – Estimated Rate 0.00025/s ISO 6892-1 Method A – Closed Loop Rate 0.00025/s Seconds 50 100 Time required to run an ISO 6892-1:2016 test on aluminium: 0 25 75
  37. 37. 3737 ISO 6892-1:2016 Control Modes Summary Simple Comparison between the methods
  38. 38. 3838 Which Instron Systems Meet What? Testing Systems 5900 Series vs 3300 Series
  39. 39. 3939 Conclusions When looking into new testing machines or accessories, ask: • Can this achieve requirements for ISO 6892-1:2016 Method A1? This will enable you to: 1. Future proof your laboratory 2. Increase repeatability 3. Ensure accurate results 4. Decrease your testing times! Using advanced 5900 controller enables: 1. Less operator training 2. Always with +/-20% tolerance 3. No setup time
  40. 40. 4040 Please contact Instron® with any questions Thank You Watch our webinar recording Visit www.instron.com for more information

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