Influence of Loading Frequency on Fatigue Resistance of D16T Alloy

The results of experimental research on the influence of loading frequencies of 3 and 76 Hz on the durability of specimens from aluminum alloy D16T (from the appearance of fatigue cracks of 1 mm length on the surface of specimens up to their complete failure) are presented. Tests were carried out under pulsating load cycles on flat specimens with a stress raiser in the form of a central hole. It was found that at a stress level of 200 MPa, the durability of specimens tested at a loading frequency of 3 Hz exceeded that at a loading frequency of 76 Hz. At the same time, as fractographic fracture studies have shown, fractures occurred by different mechanisms. At a loading frequency of 76 Hz, the front of the main fracture was almost rectilinear. At a frequency of 3 Hz, a macrotunneling propagation of the main crack front was observed, which acquired a semi-elliptical shape in the direction of fracture development. In this case, in the axial zone, the crack grows much faster than on the specimen surface. At a stress level of 160 MPa, close to the endurance limit, the durabilities of specimens at tested at both loading frequencies coincided at the appearance of a 1-mm crack and at their complete failure.