• Industry: Plastics industry

The tensile test according to ISO 527-1 or ASTM D638 can be used to determine key mechanical properties of plastics such as tensile strength, yield strength and modulus of elasticity.

With its various test area extension options, the inspekt duo 10 kN tensile testing machine is the ideal choice for numerous testing applications on plastics and other materials with high elongation. Equipped with pneumatic grips and a control unit, the clamping pressure can be controlled and regulated over the entire tensile test. This ensures the reproducibility of the tensile test and also enables thin plastic films to be tested.

The machine also has a force-holding mode that minimizes compressive stresses that occur due to clamping, for example. This prevents pre-damage, especially to force-sensitive samples. This is recommended for materials such as fiber-reinforced plastics or films in order to avoid undesirable influences on material characteristics. Axial clamping of the tensile specimens is ensured by means of specimen depth stops so that no transverse forces impair the test results.

The testing machine and clamping fixtures can be controlled directly at the machine using manual operation, which makes the operator's work easier and optimizes work processes when testing large quantities. Alternatively, operation via the LabMaster testing software is also possible. Here, for example, the test parameters for different sample shapes and materials can be entered.

Another component of the testing system is the MFE910-1 long distance extensometer, which determines elastic parameters such as the tensile modulus using an inductive fine measuring range in accordance with method B as per ISO 527-1. Due to the high measuring path, the other measured values such as the equivalent yield point or yield strength and the elongation at break for plastics/elastomers with high elongation can be determined.

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Overview of plastic tensile tests according to ISO 527 – Tensile properties of plastics

ISO 527 describes the determination of the tensile properties of plastics and plastic composites under specified conditions. It is divided into five parts, with Part 1 specifying the general principles for determining the tensile properties. In the following parts 2 to 5, the test conditions are specified for specific materials:

• Part 2 - for moulding and extrusion compounds
• Part 3 - for films and sheets
• Part 4 - for isotropic and anisotropic fibre-reinforced plastic composites
• Part 5 - for unidirectional fibre-reinforced plastic composites

The methods specified in ISO 527 can be used to determine the following characteristic values with the specific test specimens:

• Tensile strength: maximum mechanical tensile stress that a material can withstand
• Modulus of elasticity (modulus of elasticity): Material characteristic value that describes the proportional relationship between stress and strain in linear elastic behaviour, which occurs when a solid body is deformed.
• Yield stress: first local stress maximum in the stress-strain diagram – increase in strain without increase in stress
• Tensile stress: tensile stress that occurs when the test specimen breaks
• Elongation at fracture: percentage of permanent elongation of the tensile test specimen (relative to the initial measured length) after the test specimen breaks
• Poisson's ratio (transverse contraction ratio): Material characteristic describing the ratio of the relative change in thickness to the relative change in length in a uniaxial tensile test.

The types of test specimens and their manufacture are described in the relevant section of ISO 527 for the respective material.

Plastic tensile test according to ASTM D638

The tensile test according to ASTM D638 is, alongside ISO 527, one of the most important test methods for determining the mechanical properties of plastics. Among other things, tensile strength, elongation at fracture, modulus of elasticity and yield strength are measured.

The ASTM D638 standard specifies precise requirements for specimen geometry, test speed and evaluation, ensuring that the results are comparable worldwide. The method is particularly suitable for fixed and semi-fixed plastics and provides fundamental characteristic values for material development, quality control and standard testing.

Both standards - ASTM D638 and ISO 527 - deliver comparable results, but are not directly exchangeable, as the specimen geometry and test parameters differ. For international projects, it is recommended that testing be carried out in accordance with both ASTM D638 and ISO 527.