A Procedure for the Experimental Determination of the Fatigue Strength of Sheet Materials Under Uniaxial Tension–Compression

Abstract

Structural sheet metal materials are widely used in machine, aircraft, and rocketry building. Their strength under static tension (compression) is the primary characteristic and attribute in selecting materials for design developments. However, it is necessary to prioritize tension–compression fatigue tests for correct strength comparison under static and variable loads. The methodological difficulties associated with the need for the excitation of longitudinal vibrations in thin strip specimens with low stiffness limit the possibility of studying their fatigue strength under cyclic uniaxial tension– compression. The paper proposes a procedure for experimentally determining the fatigue strength of sheet materials under cyclic tension–compression under high-frequency loading. A special advantage of the procedure is the ability to ensure the proper stiffness of specimens without predeformation, which distorts the true experimental data inherent in the undeformed material. An algorithm was developed, and corresponding calculations were performed for a vibrating system, of which the specimen is a constituent part. The practical calculations are based on solving the problem of free longitudinal vibrations of a system of three dissimilar rods joined together at the free ends by common masses. Formulas for determining the rupture stress in specimens were obtained. Test trials of specimens of D16T and VT1-0 alloys confirmed the practical efficiency of the procedure. A resonant vibrating system was used, which was manufactured based on the results of the above theoretical calculations. In the design of this system, specimens with a cross-section of (0.5×5)×10–3 m had an active length of 48.2×10–3 m. The fatigue failure of specimens that occurred in the computational zone was controlled by the magnitude of the working stresses and the time of their occurrence. For example, a specimen of D16T alloy failed at a stress of 220 ×106 Pa after 8 ×106 loading cycles.