understanding changes to key plastics testing standards
DESCRIPTION
Understanding Changes to Key Plastics Testing Standards: ISO 527- 1, 2, ASTM D638, and ISO 178TRANSCRIPT
Understanding Changes to Key Plastics Testing StandardsISO 527- 1, 2; ASTM D638; and ISO 178
STANDARDS COMPLIANCE
Click icon to add picture
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.
1993 (1st Edition) 1993/COR 1:19941993/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!
THE IMPACT
MODULUSNew definition
TENSILE STRENGTH
New definition
NOMINAL STRAINNew method
SPEEDTwo now allowed
GAUGE LENGTH Now 75 mm
RESULTS METHOD EFFICIENCY PRODUCT
0
10
20
30
40
50
60
70
0 1 2 3
Tensi
le s
tress
[M
Pa]
Tensile strain (AutoX) [%]
Specimen 1 to 5
Specimen #
12345
NEW TENSILE STRENGTH DEFINITION
ɛ
σ
Tensile strength 1993 versionTensile strength
2012 version
A REVIEW OF STRAIN TERMS
ɛ
σ
(0) (-)or
ASTM D638 Uniform deformation Non-uniform deformation (necking)
ISO 527-1 Inhomogeneous strain distribution (yielding or necking)
Homogeneous strain distribution
ɛ
σ
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
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
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
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 STRAINExtensometer Only
NOMINAL STRAIN D638 & 527-1, Method A
NOMINAL STRAIN 527-1, Method B
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!
1993 19972001
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)
DEFLECTION ACCURACY
MICROMETER/ CALIPER ANVILS
SPEED
THE IMPACT
RESULTS METHOD EFFICIENCY PRODUCT
0
10
20
30
40
50
60
70
0 1 2 3
Tensi
le s
tress
[M
Pa]
Tensile strain (AutoX) [%]
Specimen 1 to 5
Specimen #
12345
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
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
THANK YOU FOR YOUR TIME!
Please contact your local Instron® Sales Representative
with any questions.