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

STANDARDS COMPLIANCE

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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!

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with any questions.