ISO 178 is used to determine the flexural properties of plastics. This test measures the flexural stress, strain, and modulus of rigid and semi-rigid plastics. The test uses a universal testing machine and a three point bend fixture to bend plastic test bars to acquire the data needed to make the calculations. Two methods are outlined in the standard: method A uses a strain rate of 1%/min, method B uses two different strain rates: 1%/min for determination of the flexural modulus and %5/min or 50%/min, depending on the ductility of material, for the determination of the remainder of the flexural stress-strain graph.
Prior to conducting ISO 178, it is important to read the entire specification in the relevant ISO publication.
Click here to read the equivalent ASTM standard method, ASTM D790.