1. Constant rate of extension (CRE): The rate of elongation of the test specimen is kept constant and the load is applied accordingly.
2. Constant rate of loading (CRL): Here, the rate of increase of the load is kept uniform with time, and the rate of extension is dependent on the load elongation characteristics of the specimen.
3. Constant rate of traverse (CRT): Here, one of the clamps is pulled at a uniform rate and the load is applied through the other clamp that moves to actuate a load-measuring mechanism so that the rate of increase of either load or elongation is usually not constant.
Reference: A Practical Guide to Textile Testing by K. Amutha (Woodhead Publishing)