How do I select the test methods I need?

The selection of the various test methods required is heavily dependent on the nature of the work. For analysis, basic directional properties are required. For identifying generic structural response, laminate response to load and environment are required. For selecting materials for fitness for purpose and environmental durability, physical tests are required. While the tests for composites may be based on any other materials tests, their inherent orthotropy, moisture sensitivity and low ductility often lead to significant differences in testing requirements, not least the need to measure material response in different directions. Other features of composite performance make test method selection non-trivial such as the lower strength in compression to tension for most composites.

Composite materials tend to have a high sensitivity to testing parameters and this is measured by a precision and bias statement. The precision statements identify how reproducible the data generated is with regard to material, operator, or test laboratory. Bias statements generally do not exist as very few similar standard test methods exist. Hence bias is only qualitatively assessed.

Composite materials are also sensitive to size and geometry variation. A physically larger specimen can be expected to be more representative of the material microstructure including flaws. Hence, the larger specimen is more likely to contain significant flaws than a smaller specimen. Therefore, the test method should be chosen to correlate as closely as possible with structural response.