Understanding Changes to Key Plastics Testing Standards: ISO 527- 1, 2, ASTM D638, and ISO 178

1. Understanding Changes to Key Plastics Testing Standards
ISO 527- 1, 2; ASTM D638; and ISO 178
STANDARDS COMPLIANCE

2. The following slides are provided as a brief summary
of changes in the most common plastics
testing standards, and are designed to enlighten
users on a selection of the key changes that have taken
place in the past several years that they may not be
aware of. Users should obtain a copy of the international
testing standards prior to testing for a full understanding
of specifications and requirements.

3. 1993 (1st Edition) 1993/COR 1:1994
1993/AMD 1:2005 2012
MODULUS
TENSILE STRENGTH
DEFINITION
NOMINAL STRAIN
SPEED
GAUGE LENGTH
(multipurpose)
Specific Young’s
Modulus
Max Tensile Stress
During Test
Based off
Grip Separation
One speed allowed
50 mm
Newly defined Modulus
Newly defined Tensile Strength
New alternative
preferred method
Two speeds allowed
Now 75 mm
(50 mm okay for QC)
EVOLUTION OF ISO 527 – 1, 2
= read on!

4. THE IMPACT
MODULUS
New definition
TENSILE STRENGTH
New definition
NOMINAL STRAIN
New method
SPEED
Two now allowed
GAUGE LENGTH
Now 75 mm
RESULTS METHOD EFFICIENCY PRODUCT

5. NEW TENSILE STRENGTH DEFINITION
ɛ
σ
Tensile strength
1993 versionTensile strength
2012 version

6. A REVIEW OF STRAIN TERMS
ɛ
σ
(0) (-)
or
ASTM D638Uniform deformation Non-uniform deformation (necking)
ISO 527-1 Inhomogeneous strain distribution
(yielding or necking)
Homogeneous strain distribution
ɛ
σ

7. STRAIN TERMS
Elongation and Strain
Measured from an extensometer
Nominal Strain
Calculated from grip separation
(With the exception of ISO 527-1, Method B)
ε = ΔL/L0
L0
L0

8. WHY DOES NOMINAL STRAIN EXIST?
When specimen necking
occurs outside of the gauge
length, strain captured by the
extensometer is useless
Nominal strain is
based off the entire
specimen straining

9. EXTENSOMETER REMOVAL POINT
Some labs incorrectly calculate Percent Elongation at Break with their
extensometers, particularly when automatic extensometers are used.
Extensometers are not an
acceptable strain source for
materials that neck or have
a yield point
Using an extensometer for strain
at break is OK only if strain is
homogeneous within the GL
(no necking or yield)
ɛ
σ
ɛ
σ
Remove extensometer at yield Leave extensometer on through failure

10. WHAT TO REPORT?
Both ASTM D638 and ISO 527 specify Nominal Strain
for materials that exhibit inhomogeneous strain
It is important to understand what Type of Strain to report
because they all produce different results
Example: PP
ɛ
σ
ɛ
σ
100% 66.3% 63.6%
PERCENT STRAIN
Extensometer Only
NOMINAL STRAIN
D638 & 527-1, Method A
NOMINAL STRAIN
527-1, Method B

11. KEY TAKEAWAYS
NOMINAL STRAIN
• Used only for materials that neck or have zero-slope yield points
• D638: measured entirely based off crosshead displacement
• ISO 527 two methods:
• Method A: ~D638
• Method B: combination of extensometer and crosshead displacement
• Nominal Strain ≠ Percent Elongation
… so make sure you are comparing apples to apples when
investigating differences in results!

12. 1993
1997
2001
2004 (AMD)
2003 2010 2012 + A1:2013
DEFLECTION
ACCURACY
MICROMETER/
CALIPER ANVILS
SPEED
Error should not exceed
1% of value
No specification
1%/min
(2 mm/min)
ISO 178
Extensometer required
(ISO 9513 Class 1)
Width: 1 mm diameter
(flat) or 1 mm
rectangular
Thickness:
4 mm diameter (flat) and
50 mm radius (spherical)
Method B (New):
Allows 2 speeds in 1 test
Width: 4-6.4 mm
rectangular faces
Thickness: 1.5 to 6.4 mm
diameter (flat) or ≥ 50 mm
radius (spherical)

13. DEFLECTION
ACCURACY
MICROMETER/
CALIPER ANVILS
SPEED
THE IMPACT
RESULTS METHOD EFFICIENCY PRODUCT

14. ASTM D638 vs. ISO 527 – 1, 2
Key differences related to producing different results include:
• Different specimen sizes
• Different test speeds
• Multiple speeds vs. single speed
• Different Tensile Strength calculations
• Different Nominal Strain calculations
• Micrometer anvil shapes vary – difference directly
linked to how much plastic “sink” exists
Expect different results even when testing the same material

15. CONFIDENCE IN RESULTS
 Procedure reflects the latest standard
 Equipment meets the latest requirements
 Requirements are all interpreted correctly
NOW WHAT?
Based on this information, it is recommended
that you check your lab for the following

16. THANK YOU FOR YOUR TIME!
Please contact your local
Instron® Sales Representative
with any questions.