As more and more U.S. companies are looking to convert from ASTM to ISO standards for materials development, testing, and analysis in order to gain greater opportunities and compete more effectively in the global market, it has become increasingly important to deal with the concerns raised during the conversion process, so that the differences can be reconciled and harmonies can be brought into the two sets of standards.

This article presents our investigation on several technical issues in the ASTM and ISO standards on the tensile properties of plastics. Using polyamide (PA) 6 and polyethyleneterephthalate (PET) based thermoplastics as examples, our analysis revealed a range of similarities and differences in these two testing procedures. With either procedure — ASTM or ISO — similar results were obtained for material parameters such as tensile strength, tensile strain, and modulus of elasticity, in nonreinforced and short glass fiber reinforced plastics.

The investigation also focused on the role of the system compliance on the tensile strain and modulus measurements, and the effect of grips (wedge- and side-action grips) and gripping on the tensile behavior of the materials. Among the two types of grips, the wedge-action grip was found to cause greater measurement variability, especially in Young's modulus. The analysis of system compliance, on the other hand, reinforced the statements in both testing standards that an accurate strain and modulus measurement would require the use of extensometer. The results in this article went further to indicate how to improve the accuracy in the Young's modulus using the system compliance when the extensometer was not applied during testing. Recommendations were made on the effective use of the testing procedures in product development and design.