A dynamic tensile method for M-shaped specimen loaded by Hopkinson pressure bar
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摘要: 采用传统分离式Hopkinson压杆进行M型试样的动态拉伸实验，可避免试样与杆的连接问题，但该方法并未得到发展和验证。本文中，采用有限元数值分析和实验方法，对M型试样动态拉伸实验进行分析和改进。结果表明：（1）改进的封闭M型试样，可以增强试样整体刚度，有效减少试样畸变引起的附加弯矩对拉伸标段的影响，方便通过Hopkinson压杆加载实现一维拉伸变形；（2）采用试样刚度系数修正法，可消除M型试样整体结构的弹性变形对测试的影响，精确获得试样拉伸标段的塑性应变；（3）高加载率下，建议采用波形整器加载，可显著减少试样结构引起的载荷震荡现象、改善两端的应力平衡，获得准确的动态拉伸应力应变曲线，实现5 900 s−1甚至更高应变率下的动态拉伸实验。研究方法可为M型试样拉伸实验设计和应用提供参考。
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关键词:
- M型试样 /
- 动态拉伸 /
- Hopkinson压杆 /
- 高应变率 /
- 应力应变曲线
Abstract: The M-shaped specimen can be used in dynamic tensile testing only by using the conventional split Hopkinson pressure bar, which do not need the connection between specimen and bars. But the feasibility of this method has not been further verified widely. In this paper, the dynamic tensile testing of M-shaped specimen were analyzed and improved by the finite element and experimental method. The results show that: (1) the improved closed M-shaped specimen was proposed, which can enhance the total stiffness of the specimen, effectively reduce the distortion deformation of the specimen and the influence of additional bending moment in the tensile gage section, and easily realize dynamic tensile through Hopkinson pressure bar; (2) the influence of the elastic deformation of the M-specimen on the tensile displacement could be corrected by the stiffness coefficient of specimen, the plastic strain of the tensile section of the specimen can be analyzed accurately; (3) under higher loading rate, it is suggested to adopt loading through the pulse shaper of Hopkinson bar, which can significantly improve the wave oscillation and stress balance at both ends of the specimen, obtain an accurate dynamic stress-strain curve, and realize the dynamic tensile test up to 5 900 s−1 or even higher strain rate. The study provides an important reference for the design and application of tensile test of M-shaped specimen. -
图 1 M型试样的拉伸加载原理
Figure 1. Schematic of quasi-static and dynamic tensile test for M-specimen
图 3 M型试样的加载力、压缩位移和整体变形
Figure 3. Dynamic force, compression displacement and global deformation of M-specimen
图 4 拉伸标段不同位置点的应力比较和轴向应力演化
Figure 4. Stress comparison and axial stress evolution at different points of tensile section
图 7 三角波加载下的入射波、反射波和透射波
Figure 7. Incident, reflected and transmitted wave by pulse shaper
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