液压膨胀环恒应变率加载技术

Constant strain-rate loading of liquid-driving expanding ring

膨胀环实验技术主要包括爆炸膨胀环实验技术和电磁膨胀环实验技术,实验过程中膨胀环的加载应变率在达到峰值后会随着圆环的膨胀而迅速降低,给研究应变率敏感材料的拉伸碎裂带来极大的不便。在前期提出的液压膨胀环实验技术的基础上,发展了一种恒应变率加载技术。首先,从理论上获得了实现金属圆环恒应变率膨胀所需的液压加载曲线的近似表达式;然后,采用有限元流固耦合数值模拟了液压膨胀环装置中1060-O铝环的膨胀碎裂过程,在给定液压加载曲线下,膨胀环的环向应变率在应变率稳定阶段上下波动范围最大不超过20%;并进一步研究了加载曲线对碎裂过程中应变率的影响规律。在液压膨胀环实验装置上对1060-O铝环开展了膨胀环实验,验证了恒应变率加载技术的可行性。

The expanding ring experimental technology mainly refers to the explosion expanding ring and the electromagnetic expanding ring experimental technology. During the experiment, the loading strain rate of the expansion ring decreases rapidly with the expansion of the ring after reached the peak value, which creates great inconvenience to the study of tension fragmentation of strain-rate sensitive solids. In this paper, a constant strain-rate loading technology is developed on the basis of the liquid-driving expanding ring experimental technology. Since it is not possible to apply sudden loading to the expansion ring during the experiment, it is assumed that the strain rate of the expansion ring during the expansion process is divided into linear growth stage and stable stage of the strain rate. By reasonably controlling the loading velocity and loading time of the liquid, an approximate expression of the liquid-driving loading curve required to realize the constant strain-rate expansion of the metal ring is deduced theoretically. The tension fragmentation process of the 1060-O aluminum ring under liquid-driving loading is simulated by the fluid-solid coupling numerical simulation. Under the liquid-driving loading curve, the hoop strain rate of the expanding ring fluctuates within a maximum of 20% in the stable stage of the strain rate. Before occurring of the significant necking of the expansion ring, the circumferential velocity of the expansion ring is basically zero, indicating that the expansion ring is under uniform tensile loading and there is no stress wave propagation in the circumferential direction. When the expansion ring is significantly necked, an obvious sudden change in the circumferential velocity will take place, indicateing that a Mott wave from the fracture site propagates to the corresponding position. The influence of the loading curve on the strain rate during the fracture process is further studied. Then an expanding ring experiment was carried out on the 1060-O aluminum ring on the liquid-driving expanding ring experimental device to verify the feasibility of the constant strain rate loading technology.