热应力对金属棒料内部损伤的机理研究

Inner Damage Mechanism of Metal Bar with Thermal Stress

针对棒料热应力变频振动的下料方法,建立了带V型槽棒料在分段强制冷却过程中的热力耦合模型,利用ANSYS有限元软件,获得了棒料在强制循环水冷却过程中内部应力场的分布.数值模拟结果表明,棒料内部最大拉应力点位于V型槽尖端正下方0.34 mm附近,该处的轴向拉应力已超过材料的强度极限,在V型槽所在棒料断面上靠近尖端点处产生一条环形损伤带,在水流速度下,该损伤带随着绝热边界宽度的增加先增大后减小,存在一个大约2 mm宽的最佳绝热边界,可使损伤的程度达到最大.在等绝热边界宽度下,损伤带随着水流速度的增加逐渐地增大,当水流速度大于5 m/s时,对棒料的内部损伤较小.实验结果表明,有热应力作用比无热应力作用的棒料下料时间减少了15%以上,从而验证了热应力损伤对棒料下料作用的有效性.

To obtain the inner damage mechanism of a new type of thermal stress precision cropping bar. A thermal stress coupling model of the bar with an annular V-shaped notch in the course of cooling was established. The stress field in the inner of the bar was evaluated by means of ANSYS software. The numerical simulation results show that the axial tension stress gets maximum at 0. 34 mm from the bottom of the tip of the V-shaped notch on the bar cross-section. As the maximal stress and its nearby stress exceed the ultimate yield strength of the material, an annular damage strip in the bar cross-section of the V-shaped notch and close to V-shaped notch tip appears. At the same cycle cool water velocity, the damage strip increases and then decreases with the increase of width of adiabatic boundary, and reaches to the maximum when the width of adiabatic boundary is 2 mm. With the same width of adiabatic boundary, the damage strip increases with the increase of water velocity, and it changes feebly when the water velocity is greater than 5 m/s. The damage strip disappears when the water velocity is equal to 1 m/s. The cropping experimental results show that the cropping time, by heat stress prefabricating an ideal crack at V-shaped notch bottom, is reduced by 15% compared with the simplex variable-frequency vibration cropping method without the action of the heat stress, which validates the thermal stress behaviors.