Abstract: A device for subjecting n (n .gtoreq. 1) test specimens to alternate tensile and compressive stresses comprises an excitation source having a horizontal axis of displacement and a guide rod which is capable of free translational displacement along a horizontal axis. The guide rod is rigidly fixed at one end to the exciter and provided at the other end with means for clamping the ends of n test specimens. A massive part is provided with nozzles for the injection of a gas under pressure and with n horizontal bearing blocks constituting gas bearings for n cylindrical and horizontal masses to which the other ends of the test specimens are secured.