For the execution of high-cycle fatigue tests in a low frequency range Hegewald & Peschke uses a newly developed hydraulic clamping device. By the special construction of the clamping device alternating load tests with zero crossing are possible without the appearance of load reversal slackness. When using grips with a too high mechanical slackness a way is recorded in the phase of the zero crossing (at the change between tensile and compression load), however no load is carried out on the specimen since the specimen for a start only moves in the grip. The problem is solved with the new hydraulic grip because the pistons of the both-way parallel closing system itself are fixed circulating free of play by means of a clamping piston detent. Thereby it is made sure that at the change of the load direction from tensile to compression and reversed a direct closed linkage is carried out.
Another advantage of this hydraulic grip is the mechanical synchronization control of the clamping pistons. The synchronization control guarantees an exact parallel closing of the clamping pistons. This is primarily essential for an exact determination of the material characteristics of extremely cross force sensitive specimens, such as carbon fiber compounds.