Information on the most widely used ASTM standards within the materials testing industry
ISO 178 Plastics - Determination of flexural properties
ISO 178 specifies a method for determining the flexural properties of rigid and semi-rigid plastics under defined conditions. A standard test specimen is defined, but parameters are included for alternative specimen sizes for use where appropriate. A range of test speeds is included.
ISO 178 test method is used to investigate the flexural behaviour of the test specimens and to determine the flexural strength, flexural modulus and other aspects of the flexural stress/strain relationship under the conditions defined. It applies to a freely supported beam, loaded at midspan (three-point loading test).
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The method is suitable for use with the following range of materials:
thermoplastic moulding, extrusion and casting materials, including filled and reinforced compounds in addition to unfilled types; rigid thermoplastics sheets;
thermosetting moulding materials, including filled and reinforced compounds; thermosetting sheets.
ISO 178:2010 applies to fibre-reinforced compounds with fibre lengths less than or equal to 7,5 mm prior to processing. For long-fibre-reinforced materials (laminates) with fibre lengths greater than 7,5 mm, see ISO 14125.
Test Procedure:
Most commonly the specimen lies on a support span and the load is applied to the center by the loading nose producing three point bending at a specified rate. The parameters for this test are the support span, the speed of the loading, and the maximum deflection for the test. These parameters are based on the test specimen thickness and are defined differently by ASTM and ISO. For ASTM D790, the test is stopped when the specimen reaches 5% deflection or the specimen breaks before 5%. For ISO 178, the test is stopped when the specimen breaks. Of the specimen does not break, the test is continued as far a possible and the stress at 3.5% (conventional deflection) is reported.
Specimen size:
A variety of specimen shapes can be used for this test, but the most commonly used specimen size for ASTM is 3.2mm x 12.7mm x 125mm (0.125" x 0.5" x 5.0") and for ISO is 10mm x 4mm x 80mm.

Die cut, saw, or injection mold your samples to a shape specified in the ISO/ASTM Specification.
If you have a standard shape then you do not need to enter the depth, width, and span length for each test.
If you have specimens that vary in width and depth then you will need to adjust the span length for each test as well as enter in the new width, depth, and span length as these values are used in the calculations.
Place the test bar on the 3 point bend fixture and begin the test and end after bending to 5% deflection or until the sample breaks.
Data:
Flexural stress at yield, flexural strain at yield, flexural stress at break, flexural strain at break, flexural stress at 3.5% (ISO) or 5.0% (ASTM) deflection, flexural modulus. Stress/Strain curves and raw data can be provided.
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