Specimen shapes for tests on molding materials
The overriding goal of testing molding materials is to achieve a high degree of reproducibility. This requires limiting the number of specimen types. Specimens are usually produced by injection molding. Type 1A specimens as defined in ISO 527-2 are used; in ISO 3167 these are designated as Specimen Type A and are additionally restricted to a specified thickness of 4mm. These specimens are also designated as Type A1 in ISO 20753.
Injection molded specimens display decreasing orientation as the distance from the feed point increases, leading to non-constant mechanical property curves along the length of the specimen, and therefore frequently resulting in specimen break on the side away from the gate. The preferred gage length for the specimen is 75mm, or alternatively 50mm. Alternately, Type 1B specimens are permitted; these are designated as Type B in ISO 3167 and as Type A2 in ISO 20753. They are generally machined from pressed or injection molded sheets. The orientations of the polymer normally differ significantly from those in injection molded specimens. Comparability of results obtained using different specimen shapes is not guaranteed. A gage length of 50mm is specified for Type 1B specimens due to the larger radius resulting in a shorter parallel area.