ISO 178 Plastics - Standard Test for Determination of Flexural Properties

This standard specifies a method for determining the bending properties of solid and semi-rigid plastics under defined conditions. A preferred test sample is defined, but parameters for alternative sample sizes are included for use where appropriate.

The method is used to investigate the flexural behavior of test specimens and determine the flexural strength, flexural modulus, and other aspects of the flexural stress/strain relationship under defined conditions. Applies to a freely supported beam loaded in the middle of the span.

The method is suitable for use with the following range of materials:

• Thermoplastic molding, extrusion and casting materials, rigid thermoplastic sheets, including filled and reinforced compounds, in addition to unfilled types;
• Thermosetting molding materials, thermoset sheets, including filled and reinforced compounds.

The method is performed using specimens that can be molded to specified dimensions, processed from the middle section of a standard multi-purpose test specimen, or processed from finished or semi-finished products such as moulds, laminates or extruded products.

The method specifies the preferred dimensions for the test specimen. Testing on samples of different sizes or on samples prepared under different conditions may yield non-comparable results. Other factors such as test speed and conditioning of samples can also affect results.

Particularly for injection molded semicrystalline polymers, the thickness of the oriented surface layer, which depends on the molding conditions, also affects the bending properties.

The method is not suitable for determining design parameters, but can be used in materials testing and as a quality control test.

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