ANALYSIS OF DAMAGE EVOLUTION IN ALTERNATED WET-DRY CONTACT TESTS ON A RAILWAY WHEEL STEEL BY A VISION SYSTEM

Tests in alternated dry-wet contact were carried out by a bi-disc machine on specimens extracted from railway wheels. Some of them were cylindrical, other ones were crowned: cylindrical-cylindrical and crowned-cylindrical couplings were tested. The surface appearance was acquired by a vision system; the acquired images were elaborated to extract quantitative damage indexes. In cylindrical-cylindrical coupling, the damage increased in alternated dry-wet sessions as far as the cycle number increased, whereas it was stabilized in long dry sessions. In crowned-cylindrical couplings, the damage tended to decrease as far as the cycles increased, in all the test conditions. The contact patch width in crowned-cylindrical coupling increased as far as the cycle number increased: this led the overall stress state to decrease, this way mitigating the damage.