Plastics, elastomers and even steel may significantly change properties with the rate of loading. Axel Products has test systems capable of testing at strain rates as high as 100 s-1 depending on the material and the conditions. Special loading systems, test frames, gripping, transducers and signal conditioning are needed as strain rates increase.
The rate sensitive properties of elastomers and plastics is typically observed at several decade changes in rate.
Typical High Strain Rate Experiments:
As with typical quasi-static tensile tests, the strain needs to be measured in the narrowed section of the test specimen. As the rate of straining increases, the rate of data collection and the rate of measuring needs to increase for both strain and force. Even at modest strain rates in the 1 1/s and 10 1/s range, special load cells and strain measuring devices may be needed to accurately capture the event. At rates in the 100 1/s range, very specialized strain measuring, force measuring and loading systems need to be employed.
The additional challenge of compression testing at high rates of straining is the material stiffness increases rapidly which may require very large amounts energy to continue compressing at a constant strain rate.
The bend test enjoys a long history in plastic testing because it is relatively easy to perform and requires no additional strain measuring. Unfortunately, the data obtained from the bend test isn't very useful in the determination of basic structural properties. The bend geometry is unknown and the neutral axis between tension and compression in the specimen is unknown. However, the experiment is a complex strain state experiment and it can provide valuable data for material model verification.