激光金属沉积GH4169在不同应变率下的剪切特性及破坏机理研究

为了能在传统的分离式Hopkinson压杆上准确可靠地测试激光金属沉积GH4169的动态剪切特性,基于数值模拟方法对比分析了三种不同动态剪切试样形式及尺寸对剪切区应力分布的影响,结果表明:经过尺寸优化后的双剪切试样的剪切区剪应力占主导地位,可实现近似纯剪切的动态剪切实验。利用此试样形式,系统测试了不同取向（扫描方向、沉积方向）的LMD GH4169试样在不同应变率下的剪切应力应变曲线,并对破坏后试样进行了SEM分析观察。结果表明:(1) 本文中选用的试样形式剪切纯度高,应力沿剪切区宽度厚度分布均匀,可以更好地得到材料的动态剪切特性;(2) 对实验所得剪应力-剪应变曲线进行分析,发现本材料在扫描路径方向和沉积方向并没有表现出明显的各向异性,但随着应变率的增加,具有明显的应变率强化效应;将单轴压缩和动态剪切应力应变曲线同时转换为等效应力应变曲线,对比证实了试样形式能很好反应材料的剪切特性;(3) 通过对LMD GH4169剪切变形破坏试样的微观分析发现,随着应变率升高,断口韧窝尺寸和深度减小,韧性降低,在更小的变形量下容易剪切失效。初始微观缺陷容易导致材料的动态剪切破坏。

Shear characteristics and failure mechanism of laser metal deposition GH4169 at different strain rates

In order to accurately and reliably test the dynamic shear characteristics of laser metal deposition GH4169 on a traditional split Hopkinson pressure bar, this study compared the three different dynamic shear sample forms and dimensions to the shear zone stress based on numerical simulation. The influence of the distribution shows that the shear stress of the shear zone of the double shear specimen after optimization is dominant, and the dynamic shear test of approximate pure shear can be realized. Using this specimen form, the shear stress-strain curves of LMD GH4169 specimens with different orientations (scanning direction, deposition direction) at different strain rates were systematically tested, and the specimens were analyzed by SEM. The results show that: (1) the specimen used in this paper has high shear purity and uniform thickness distribution along the shear zone width, which can better obtain the dynamic shear properties of the material; (2) the shear stress-shear strain curves obtained from the experiment were analyzed. It is found that the material shows unobvious anisotropy in the scanning path direction and deposition direction. With the increase of strain rate, it has obvious strain rate strengthening effect; the uniaxial compression and dynamic shear stress-strain curves were simultaneously converted into equivalent stress-strain curves; the comparison confirms that the specimen form in this manuscript can exactly reflect the shear properties of the material; (3) through the microscopic analysis of the shear deformation of LMD GH4169, the size and depth of the fracture dimple decrease as the strain rate increases, and the toughness decreases. The shear failure is easy under a smaller deformation. Initial microscopic defects are likely to cause dynamic shear failure of the material.