Can you speak ISO?

If not, you might want to learn, as resin suppliers and OEMs are driving the conversion from ASTM.

By James J. Beauregard and R. James Galipeau

Is the change to ISO (International Standards Organization) testing procedures coming? It might already be here. After years of controversy, some major modifications are suddenly occurring in the way materials are characterized and compared.

While the majority of testing requests are still for ASTM (American Society for Testing and Materials) evaluations, trends suggest a major move to the new ISO test procedures replacing ASTM tests.

For decades the large resin suppliers in North America have characterized their products in American units by American test procedures, namely ASTM. The advent of engineering materials further solidified this approach as marketing and sales representatives compared their materials to competitors in terms of superior Heat Deflection Temperature or better Izod.

Design engineers could be heard saying, "I need a stiff material with a modulus of at least a million," and production managers might call for a touch impact-resistant grade with an Izod in the 16 range.

In that provincial world a strong material had Tensile Strength of 15,000, and reference to units like psi or ft. lb/inch were assumed and not required in conversation. With even the units of measurement assumed, ASTM test methods were all but taken for granted.

While that approach worked well in the past, the fact is the advent of a second testing language in the form of ISO is here and the North American plastics industry is learning to speak it and possibly preparing to make it their only form of communication .

Driven by users
For years, the Federal Government and plastics trade groups such as SPI have politely pointed to a need for American companies to convert to more internationally accepted procedures and metric units.

However many of these efforts in testing procedure consolidation have been to no avail. Instead, development of metric procedures such as ASTM D638M Tensile Properties were attempted.

Despite ASTM's switch to metric units as the sole unit of measurement for new standards, to be completed by 1997, the vast majority of the industry still conversed in units of psi and equivalence to ISO was nonexistent.

What's different now is that the changes are being driven by large end users themselves under the influence of global business needs that cannot be ignored.

USCAR (United States Council for Automotive Research) is driving thermoplastic suppliers to a full conversion to ISO test methods by June 1, 1998.

In addition, SAE material specifications such as J1639, which calls for characterization of thermoplastics largely by ISO procedures, is being used extensively to specify materials in Detroit. And resin manufacturers are faced with the option of characterizing their materials by these standards or loosing supplier recognition.

Similar end user driven influences are occurring in the he electronics industry with major electronics firms instituting Worldwide Specifications that combine both ISO test procedures with IEC (International Electrotechnical Commission) international standards. At the same time, CAMPUS (Computer Aided Materials Preselection by Uniform Standards), the worldwide materials data base is listing only ISO 10350 data.

Recent developments at ASTM D20 meetings further point to these changes, and in 1996 ASTM published a nearly 400-page volume entitled "ISO and IEC Selected Standards for the Plastics Industry."

Additionally, at the most recent meeting of the ASTM D20 Executive Committee, an extensive plan was unveiled to evaluate every ASTM plastics procedure line by line for comparison and harmonization with ISO and IEC standards, based on which, each procedure will be classified as either Identical, Equivalent or Not Equivalent.

While some of the specifics are still being worked out, Identical procedures will be provided with ASTM numbers, while some Equivalent procedures may be incorporated into existing ASTM procedures with identifiers like Part B.

Procedures determined to be Not Equivalent will probably receive an interim ASTM number until full ASTM recognition is obtained. Many hurdles, such as the absence of Precision and Bias Statements in ISO procedures and the conservatism of ASTM procedure writing still exist, but genuine progress is being made and ASTM seems committed to establishing equivalency to ISO.

Are these changes actually going to happen this time? While no one is absolutely sure, one way to gauge this is the volume of ISO testing at an independent testing lab like Plastics Technology Laboratories, Pittsfield, Mass. Over the past year PTLI has experienced major growth in the number of requests for ISO testing, and the requesters have mostly been major resin suppliers to the automotive industry.

As a result of these growing trends, the laboratories have modified their equipment and trained employees to be able to perform nearly all ISO tests. The new procedures not only call for new measurement units but require new specimen geometries, sometime s changes in procedures and even minor test equipment modifications.

With the changes in place, the new language of ISO can now be heard in the lab as technicians discuss HDT testing not in terms of 66 or 264 psi but referring to 80mm bars at 0.45 and 1.8 MPa tested flatwise.

While this entire subject is complex, it is time for North American plastics users to increase their familiarization with this new ISO language.

In any typical data sheet or plastics commercial database, resin purchasers can find a laundry list of properties, some common like tensile strength or noted Izod impact, others more exotic like electrical Dissipation Factor at 10 MHz.

In most cases however, first comparisons will hinge on a few basic properties including Tensile and Flexural results as a measure of strength, Modulus data to characterize stiffness, HDT for heat resistance comparisons and some form of impact test to monitor toughness.

With this in mind lets take a more detailed look at ISO vs. ASTM testing and to simplify things lets focus only on Specimen Preparation for four primary tests, namely Tensile, Flexural, Izod and HDT for thermoplastics.

Specimen Preparation:
Tensile, Flexural, Izod and HDT specimens are used for ISO testing vs. ASTM test. Accordingly, new tooling will be required to produce the ISO specimens. ISO/DIS294 9-1:1995 is quite specific in terms of the requirements for injection molding of specimens, even recommending transducers in the molding cavities to monitor cavity pressure and clearly outlines what types of runner systems are acceptable. Additionally, ISO 3167-1993 on Multipurpose Specimens allows for the use of the ISO multi-purpose test specimen cut down in length to produce all four required specimens for Flexural, Izod and HDT, thus simplifying the number of specimen geometries required.

ASTM methods clearly outline specimen geometries required but in general are far less specific on sample preparation and does not provide for multi-purpose specimens.

Tensile Properties:
Table 1 provides a summary comparison of ISO 527-93 vs. ASTM D638-94b for tensile evaluations. Most laboratories will find conversion to the ISO procedure quite easy because the new sophisticated universal testers allow setting test speeds in metric with automated software. At Plastics Technology Laboratories, a new Instron Model 5569 Universal Tester with Series IX and Merlin Software changes speeds and units in a Windows Environment with the click of a mouse.


Table 1
Tensile Properties:
ASTM D638-94b vs. ISO 527-93E
  ASTM ISO
Prefered Specimen Type: Type I Type 1A (ISO 3167)
 
Specimen Dimensions (mm):
Overall Length: 165 (min) 150 (min)
Length of Narrow Section: 570.5 802
Radius (tab to gage): 761 20-25
Width @ ends: 196.4 200.2
Width of narrow portion: 130.5 100.2
Preferred thickness: 3.20.4 40.2
Gauge Length: 500.25 50.5
Initial grip distance: 1155 1
 
Test Speed (mm/min) 5, 50, 500mm/min as specified by the material spec. or based on time to rupture 50mm/min for ductile materials. 5mm/min for brittle materials (Per ISO 10350)

Laboratories with older equipment that provides set American unit crosshead speeds like 0.2 and 2.0 inches per minute may find that major and expensive equipment modification will be required to accomplish the ISO 527-93 procedure.

Flexural Tests:
(ISO 178-93E vs. ASTM D790-92) Table 2 outlines comparison of the two methods. Again, we see that once specimen preparation is accomplished the conversion to ISO is quite simple.


Table 2
Flexural Properties:
ASTM D790-92 vs. ISO 178-93E
  ASTM ISO
Preferred Specimen: length: 127mm
width: 12.7mm
thickness: 3.2mm
length: 80mm2mm
width: 10mm0.2mm
thickness: 4mm0.2mm
 
Support Span: Span to depth ratio of 16 Span to depth ratio of 16
 
Support Radius 50.1mm or 3.2mm minimum up to 1.5 times the depth for 3.2mm or greater specimen thickness 50.1
 
Loading Nose Radius 50.1mm or 3.2mm minimum up to 4 times the specimen depth 50.1mm
 
Test Speed: 1.3mm/min50% for the preferred specimen 2mm/min20% for the preferred specimen
 
Maximum allowable strain: 5% 3.5% (at conventional deflection of 1.5 x height)

New fixturing may be required, since some Flex fixtures are permanently set at American span widths like 2.0 and 4.0 inches and new radius on bending noses are required but these should require only minor fixturing expenses provided the universal tester c an be adjusted for metric speeds as addressed above.

Izod Impact:
(ISO 180-93E vs. ASTM D256-93a) Table 3 outlines the major specific differences. Conversion to this method generally requires the purchase of a new impact hammer (the pendulum that swings through to sample to break it on impact.) Again, at PTLI the presence of a digital Monitor Izod Sys tem from TMI, Inc. made the conversion easier since the microprocessor did all the metric calculations.


Table 3
Izod Impact:
ASTM D256-93a vs. ISO 180-93E
  ASTM ISO
Preferred Specimens: length: 60.5mm-63.5mm
width: 12.7mm
thickness: 3 to 13mm
length: 80mm2mm
width: 10mm0.2mm
thickness: 4mm0.2mm
(Type 1)
 
Notch Dimensions: Radius: 0.250.05mm 45 Radius: 0.250.05mm 45
    (Type A notch)
 
Width Remaining under notch: 10.160.05mm 80.2mm
 
Striking Edge Radius: 0.790.12mm 0.80.2mm
 
Impact Velocity: ~3.46m/s 3.5m/s10%
 
Reporting Units: J/m kJ/m2

Older or dial type Izod apparatus may require had calculations since the dials are permanently marked with American units.

Heat Deflection Temperature:
(ISO 75-93E vs. ASTM 648-88) An inspection of Table 4 demonstrates that two test procedures are available under the ISO procedure.


Table 4
Deflection Temperature Under Load:
ASTM D648-88 vs. ISO 75-93E
  ASTM ISO
Edgewise Test:    
Preferred Specimens: length: 120mm10mm
width: 12.7mm0.3mm
thickness: 3 to 13mm
length: 110mm10mm
width: 9.8mm to 15mm
thickness: 3 to 4.2mm
 
Loads: 1.82 MPa and 0.455 MPa 1.8 MPa or 8.0 MPa
 
Support Span: 100mm 100mm2mm
Load Noise Radius: 3mm 3mm0.2mm
Temperature Rate: 20.2C/min 120C/h10C
Standard Deflection:
(@ which temp. is taken)
0.25mm Based on test specimen height (width), nominal is 0.32mm for 10mm specimen
 
Flatwise Test:    
Preferred Specimens: na
na
na
Length: 802mm
Width: 100.2mm
Thickness: 40.2mm
 
Loads: na 1.8 MPa, 0.45 MPa or 8.0 MPa
 
Support Span: na 641mm
Standard Deflection: na Based on test specimen height (thickness--nominal is 0.34 for 4mm specimen)
 

Most testing personnel believe that Flatwise testing will become the only method in the future and Plastics Technology Labs confirms that nearly 100% of the requests for ISO 75 tests call out the Flatwise variety.

From an equipment standpoint most HDT baths such as the Tinius Olsen variety at PTLI can be inexpensively modified to accomplish the new span and force requirements of the ISO procedure.

Data
To conclude, SPI comparisons have shown, that for some materials, ASTM data can easily vary by 10% vs. International Data counterparts, but by using the new ISO procedures, North American engineers of the future can say: "I need a stiff material with a modulus of at least 7000 MPa," fully confident that they are speaking a globally accepted technical language with no apparent accent. PW


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