Body Over Wedge Operating Principle
Wedge grips operating on this principle apply a greater preloading force when the specimen is inserted. The preload applied to the specimen is transmitted to the jaws via the body of the grips using a lead screw. In this case also the main gripping force is not attained until during tensile loading (via the wedge effect). Grips of this type have two additional advantages: Specimens inclined to slippage are gripped more firmly right from the beginning and the gripping length remains constant, even if thickness varies from specimen to specimen. In addition, strain-rate control to ISO 6892-1 (2009) Method A (closed loop) and ASTM E 8 (2009) Method B can be applied with greater precision.