A. Strain rate is the speed at which a material is deformed and different strain rates can have a big effect on the tensile properties of some materials.
Take silly putty as an example. If you slowly pull on a piece of silly putty, it will stretch an enormous amount before it breaks. But if you pull on it quickly, it breaks almost immediately. This is known as strain-rate sensitivity. Many plastics and polymers and some steels are strain-rate sensitive.
So it’s important to remember that stress/strain data captured at lower strain rates may not produce accurate predictions for the properties of that material at high strain rates. Using that data to analyze and design parts and structures can result in those parts and structures being perfectly able to withstand predicted day-to-day forces. However, when subject to sudden high strain rates such as those found in a collision, those parts and structures could shatter rather than absorb the energy of that collision.
For more information on various materials testing terminology, visit our online glossary.