The fracture is mainly caused by the lower hardness and strength which resulted from the Widmanstatten structure existing in the structure of the spline shaft. 花键轴的显微组织中存在魏氏组织，导致其硬度和强度低于技术要求，是造成花键轴断裂的根本原因。
The splinted shaft is made of alloy and the surface is specially treated, its abrasion performance and fatigue strength is enhanced. 花键轴采用合金材料进行特殊表面处理，提高了耐磨性及疲劳强度。
