ISO 178 is a test method for determining the flexural properties of rigid and semi-rigid plastics by performing a three-point bend test on a universal testing system. A three-point bend test applies force at the midpoint of a rectangular specimen, which is freely supported at either end. The applied force is measured by a load cell, and the resulting deflection is measured by either the system’s crosshead displacement (with results corrected for system compliance) or by a direct strain measurement device. There are four test types outlined in ISO 178, each specifying a deflection measurement method (i.e. via crosshead or direct strain transducer) and an associated calibration accuracy requirement.

The type of ISO 178 test a lab performs is prescribed by the requirements of its customers, whether they are internal, such as an R&D lab, or external, such as a third party testing lab. It is important to ensure that the specific requirements for your lab are identified and agreed upon by your customers prior to purchasing test equipment and performing testing.