The rigid-flexible coupling model of axle gear case in tunnel traction locomotive which included the flexible axle and case body was established using Romax. Inventor and Hypermesh software. Tooth profile modification. gear-tooth fatigue strength. https://www.roneverhart.com/Western-Digital-Ultrastar-DC-HC570-WUH722222ALE6L4-0F48155-22TB-7-2K-RPM-SATA-6Gb-s-512e-SE-3-5in-Refurbished-HDD/