Splines are widely used in mechanical drive systems to transfer rotational motion from a shaft to the gear or from a gear to the shaft. The failure investigation was performed on the differential housing of three different four-wheel-drive car models with gasoline engines. Compilation of failure reports was performed by a first author as a professional car expert from the famous car repair shop in Mashhad city for 6 years. Failure zones appeared on the housing splines after an average operation of 60,000 km. Experiments were performed on two matched members, including the failed ductile cast iron housing and undamaged transfer case shaft of tempered martensite steel. For this purpose, a series of experiments including fractography using scanning electron microscopy (SEM) only for housing and chemical composition, mechanical properties, microstructure, and hardness were performed for both matched members, and finally, stress analysis was performed for two matched members numerically. The results showed that the strength and hardness of the housing material were lower than that of the shaft. Also, striations associated with the teeth flank and face surfaces of the housing using SEM imaging showed that failure was of fatigue type on housing spline teeth.

花键被广泛用于机械驱动系统中，以将旋转运动从轴传递到齿轮或从齿轮传递到轴。对三种不同的带汽油发动机的四轮驱动汽车的差速器壳进行了故障调查。失败报告的编辑由第一作者作为一位专业汽车专家从马什哈德市著名的汽车维修店进行了6年。在平均行驶60,000 km后，房屋花键上会出现故障区域。在两个匹配的构件上进行了实验，包括失效的球墨铸铁外壳和未损坏的回火马氏体钢分动箱轴。为此目的，进行了一系列实验，包括使用扫描电子显微镜（SEM）进行的断口扫描，仅针对外壳和化学成分，机械性能，对两个匹配部件进行了显微组织和硬度测试，最后，对两个匹配部件进行了应力分析。结果表明，壳体材料的强度和硬度低于轴的强度和硬度。同样，使用SEM成像发现与齿面和壳体端面相关的条纹表明，壳体花键齿的疲劳是疲劳型的。