Abstract: The traditional separation processes of metal tubes had some disadvantages，such as low productive efficiency, high energy-consumption and waste of raw materials.A new method for separating tubes was adopted.The eccentric loading technology and stress concentration effect were used to promote the rapid initiation of fatigue cracks at the bottom tip of V-shaped groove and control the steady propagation of fatigue cracks.The working principles of fatigue fracture separation device under eccentric cyclic loadings were described.The judgment formula of crack initiation at the root of V-shaped groove of tubes under fatigue loadings was deduced.The four experimental control curves including linear decrement control curve, multi-step decrement control curve, 1/4 convex arc decrement and 1/4 concave arc decrement control curve were designed.The 304 stainless steel tubes were studied by experiments under the control curves, finally the tube precision separation was achieved.The experimental results show that using the stress concentration effect of V-shaped groove and the continuous action of eccentric loading forces, the loading frequencies are gradually reduced from high to low by using multi-step decrement control curve, then the rapid initiation and stable propagation of cracks at the root of V-shaped groove of tubes may be ensured.Finally, tube fast fracture is realized and good cross-section quality is obtained.

Key words: tube, precision separation, fatigue crack, stress concentration

摘要： 针对传统的金属管材分离技术存在生产效率低、能耗高以及浪费原材料等问题，采用了一种新的管材分离方法，利用偏心加载工艺和应力集中效应促使管材表面环状V形槽底尖端处快速萌生疲劳裂纹并控制疲劳裂纹的稳定扩展。描述了管材的偏心循环加载疲劳断裂分离装置的工作原理，推导出了疲劳加载下管材V形槽根部裂纹是否起裂的判断公式。设计了线性递减、多层阶梯递减、1/4凸弧递减和1/4凹弧递减四种实验控制曲线，针对304不锈钢管材进行实验研究，实现了管材的精密分离。实验结果表明，利用V形槽的应力集中效应，在偏心加载力的持续作用下，加载频率采用多层阶梯递减控制曲线由高到低地逐渐降低加载频率，能够保证管材V形槽根部裂纹的快速萌生和稳定扩展，并可实现管材快速断裂，获得良好的断面质量。

关键词: 管材, 精密分离, 疲劳裂纹, 应力集中