利用实验和数值结合的方法测量镁合金AZ91动态断裂韧性

Measuring the Dynamic Fracture Toughness of Magnesium Alloy AZ91by Combining Experimental and Numerical Methods

采用一种实验与有限元数值计算相结合的方法研究镁合金AZ91的动态断裂韧性。由Hopkinson压杆实现镁合金AZ91三点弯曲断裂试件的动态加载,基于傅里叶变换和VC++面向对象的程序设计方法修正了加载应力波在传播过程中的弥散效应,同时扣除了附加加载杆楔形头惯性效应对加载波的影响;利用ANSYS/LS-DYNA有限元软件对三点弯曲试样在冲击载荷下的动态响应进行分析,采用虚拟裂纹闭合技术求得动态应力强度因子时程曲线,依据监裂应变计测试信号,换算起裂时间,确定对应于动态应力强度因子时程曲线的值,即为镁合金AZ91的动态断裂韧性。通过调整试样跨距并监测支座脱离的状况,保证实验过程中试样的真三点弯曲加载条件。结果显示镁合金AZ91的动态断裂韧性为(6.7±1.8)MPa·m1/2。此外,该实验与数值结合的方法拓宽了Hopkinson压杆实验技术在测试材料动态断裂韧性方面的应用范围。

The dynamic fracture toughness of Magnesium alloy is the basic data for the design of the anti-impact magnesium alloy com- ponent and safety assessment of magnesium alloy structure under dynamic load. The combining method of experimental and numerical was improved to obtain the dynamic fracture toughness of magnesium alloy AZ91. The dynamic load for the three-point bending speci- men was supplied by the Hopkinson pressure bar, and the dispersion and inertia effect were considered and corrected by numerical method, simultaneously, based on the FFT and the VC ＋ ＋ object-oriented programming method. Then the response of dynamic stress intensity factor vs. time was calculated with visual crack close technique method based FEM. Finally, the crack initiation time was com- puted from the strain gauge message,and the corresponding value on the response of dynamic stress intensity factor vs. time was ob- tained as the dynamic fracture toughness. Considering that,the actual three-point bending condition, which is guaranteed by the monito- ring message during the process, was acquired through the adjusting of specimen span. The results showed that the dynamic fracture toughness of magnesium alloy AZ91 is （6.7 ±1.8） MPa. m 1/2. In addition,the method mentioned extends the application of Hopkin- son pressure bar for measurement of dynamic fracture toughness.