From Selection of Polymeric Materials: How to Select Design Properties from Different Standards

2.6 Molecular Orientation Effects

Molecular orientation affects the tensile strength values. A load applied parallel to the direction of molecular orientation may yield higher values than the load applied perpendicular to the orientation. The opposite is true for elongation.

The process employed to prepare the specimens also has a significant effect. For example, an injection molded specimen generally yields higher strength values when it is subjected to flexural or compression loads rather than tensile or shear loads. Another important factor affecting the test results is the number, location, and size of the gate on the molded specimen. This is especially true for glass fiber reinforced tensile test specimens. A large gate located on top of the tensile specimen will orient the fiberglass parallel to the applied load, yielding higher tensile strength. A gate located on one side of the tensile test specimen will disperse the fiberglass in different directions.

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