高强度金属棒料高速与应力集中复合剪切断裂行为

High-Speed Shearing with Stress Concentration and Fracture Behavior of High-Strength Metal Bars

针对传统剪切工艺不适用于高强度金属棒料高效精密切断的难题,提出了高速与应力集中复合的精密剪切新原理工艺,分析了环形槽几何参数对理论应力集中系数的影响,建立了42CrMo高强度棒料的高速剪切断裂有限元模型,研究了铣削和激光旋切环形槽对槽根等效应力应变场、应力三轴度、损伤起裂及三维裂纹扩展断裂行为的影响,并通过高速剪切试验,获得了不同环形槽对棒料剪切断面质量的影响规律。研究结果表明:对于表面不带环形槽的棒料,损伤起裂需要较大程度的塑性变形累积,切断后的棒料存在压塌及飞边缺陷;所提工艺方法有效约束了槽根附近材料的塑性变形,提高了高速剪切断面质量,圆度误差由11.2%减少到2.3%~4.7%,平面度误差由1.08 mm降低为0.58~0.65 mm,最大弯曲变形度由1.5 mm降低为0.4~0.5 mm,最大剪切载荷和断裂能量也得到了显著降低;相比铣削环形槽,激光旋切获得的尖角窄槽进一步降低了剪切载荷和断裂能量。新工艺方法可为高强度金属棒料的高效、精密及低能耗剪切行为提供参考。

Due to the deficiencies of low efficiency and precision in traditional shearing methods,a new high-speed precise shearing method with stress concentration is proposed for high-strength metal bars.The influence of geometric parameters of circumferential notches is analyzed on theoretical stress concentration coefficient.High-speed shearing finite element models are established for 42CrMo bars with notches processed by milling cutter or laser,and the effects of notches on fracture behavior,such as damage initiation and three-dimensional crack propagation,are revealed based on distribution of equivalent stress,plastic strain and stress triaxiality.Besides,comparative experimental tests are conducted,and section quality is evaluated for notched and unnotched 42CrMo bars.The results show that for unnotched bars,the damage initiation needs more accumulation of plastic deformation,and squeezed flashes are left on the fracture section.As contrast,the new method effectively restrains the plastic deformation near the notch and improves the section quality,with roundness error from 11.2% to 2.3%—4.7%,flatness error from 1.08 mm to 0.58—0.65 mm,and the maximum bending deformation from 1.5 mm to 0.4—0.5 mm.The maximum shear load and fracture energy also decrease significantly.In addition,compared with milled notches,the narrow and sharp notches by laser further reduce the shear load and fracture energy.The new method shows advantages of high efficiency and precision,and low energy consumption.