Ever wonder why the speed of a tensile test after yield varies from material specification to material specification? Does that produce a significant difference in results?

Engineers at Instron Corp. Norwood, Mass., (instron.com) say most materials are sensitive to the rate at which they are stretched, meaning some of properties are dependent on the strain rate. The effect is most noticeable after plastic flow occurs, although some properties can be affected while in the elastic region. There is no intrinsically correct strain rate for a given material, but to allow comparison of test results it is important to do all tests within a range of rates. Test standards define the range over which results will be consistent and comparable. The company answers other testing questions in its online TechNotes.