Method of cyclic testing of sample-models of the crankshaft of a marine internal combustion engine for bending with torsion

Abstract

It is proposed to consider the bending fatigue strength of the crankshaft as the main criterion of its operability during operation. It is noted that thermomechanical straightening with heating by stress relaxation method is most acceptable for straightening critical shafts that have received a curvature of the longitudinal axis during operation. Bending fatigue tests of round samples with a diameter of 20 mm in a dangerous section were carried out to substantiate the correction technology, test modes and evaluate the results of the correction. It was found that an increase in diameter leads to a decrease in the endurance limit of structural steels. The loading scheme of the experimental sample is adopted – transverse bending with torsion. A semicircular notch in the sample was used to focus the fracture site, and the radius of the notch was calculated. The size of the sample tuck is determined by the formula based on the similarity criterion adopted in the statistical theory of similarity of fatigue failure of parts, proposed by V. P. Kogaev. The requirements for the roughness of the surface of a circular groove of at least Ra 0.16 are established. The need for control of the manufacturing technology of the experimental sample is noted. An experimental installation for testing flexural fatigue strength is proposed. A cone cartridge was used to securely fasten and prevent the sample from turning during the experiment. Experimental samples were used-models with deflection arrows of 1, 2, 3, 4 and 5 mm. The method and equipment for obtaining samples with the necessary deflection arrows have been determined. Diagrams of a model sample for testing cantilever bending with torsion, an experimental installation for testing model samples, bending to a given deflection arrow, and a model sample with a curved longitudinal axis are presented.