一种用于材料高应变率剪切性能测试的新型加载技术

高应变率下的冲击剪切实验技术是材料动态力学行为及其微观机理研究的重要基础.采用分离式霍普金森压杆(split Hopkinson pressure bar)装置一般可以获得材料在10~4s~(-1)以内应变率的动态力学性能.在超过10~4s~(-1)的应变率下对材料进行冲击剪切测试时,通常需要采用高速压剪飞片技术或由气炮发射子弹对试样进行直接加载.本文提出一种可用于传统霍普金森压杆技术的新型双剪切试样,可以在103～10~5s~(-1)剪应变率范围实现对材料剪切性能的精确测量;同时,可以对材料的变形及失效过程进行直接观测.试样与压杆之间避免了复杂的界面或连接装置,通过转接头可以保证试样与压杆直接接触,提高测试精度,同时可以防止因试样的横向位移而导致的非均匀变形.获得了紫铜在1 400～75 000 s~(-1)应变率下的剪应力-剪应变曲线,并采用计算软件"ABAQUS/Explicit"对双剪切试样的动态加载过程进行了数值模拟和结果验证.分析表明,剪切区的主要区域内剪切成分占主导地位,其应力应变场沿厚度及宽度方向基本呈均匀分布.实验得到的剪应力-剪应变曲线与模拟结果吻合较好,说明所提出的基于分离式霍普金森压杆系统的双剪切试样可以为材料的高应变率力学性能测试提供一种方便有效的加载技术.

A NEW LOADING TECHNIQUE FOR MEASURING SHEARING PROPERTIES OF MATERIALS UNDER HIGH STRAIN RATES

Impact shearing loading technique at high strain rates is an important foundation for studying of dynamic behaviors and micromechanism of materials. Using the split Hopkinson pressure bar (SHPB) technique, material behaviours can usually be investigated under strain rates up to 104s^-1. To obtain strain rates that exceed 104s^-1 under dynamic shearing, however, pressure-shear plate impact technique or direct impact method with an air-gun launched projectile has to be used. In this paper, a new double-shear specimen that can be used under the SHPB technique is proposed. With this method, dynamic shear properties of materials can be tested precisely under strain rates ranging from 103 to 105s^-1. Complex interfaces or connectors are not needed between the specimen and the bars. With the aid of a simple fixture, the specimen can contact with the bars directly, with its transverse movements limited. In this work, shear stress-shear strain curves of pure copper were acquired at strain rates between 1 400 and 75 000 s^-1. The dynamic loading processes were modeled by ABAQUS/Explicit to check the validity of this testing method. The results show that the shear component dominates the stress and strain fields, which are distributed uniformly in the central part of the shear zone. The measured shear stress-shear strain curves agree very well with the simulation results. It shows that the new double-shear specimen provides a convenient and e ective way to test dynamic shear properties of materials under high strain rates.