Barre花岗岩动态压缩破坏特性研究

ANALYSIS OF FAILURE FEATURE OF BARRE GRANITE UNDER DYNAMIC COMPRESSION

利用修正的分离式Hopkinson压杆(SHPB)系统,对Barre花岗岩(Barregranite,BG)圆柱形试样进行高应变率单轴压缩试验。根据各向异性BG试样3个主轴方向将试样分为X向(P波速度中等),Y向(P波速度最低)和Z向(P波速度最高)。试验过程中,采用组合型整形器(黄铜+橡皮)保证加载中的应力平衡,实现对试样的常应变率加载;利用单脉冲加载技术确保试样在试验过程中只受到1次动态载荷。得到试样3种破坏状态形态:未破坏、表面开裂以及完全破碎。对回收试样切片后的微观裂纹分布研究发现,裂纹随着加载应变率的提高而增多。试验测得BG三个方向不同加载应变率(70,100,130s-1)下的应力–应变关系,分析不同破坏状态下的应力–应变曲线形式。3个方向的试样均表现出应变率相关,最大承受应力随着应变率的增加。在较低和较高的加载应变率下,试样的最大承受应力与初始裂纹方向无关,呈现出各向同性。而在中间加载应变率下Y试样承受应力最大,这是因为BG初始裂纹面平行与XZ平面,在临界加载条件下裂纹扩张比较困难。

High strain rate uniaxial compressive loading tests on disk Barre granite（BG） samples were conducted by modified split Hopkinson pressure bar（SHPB） system with pulse shaping and momentum-trap technique. The samples were tested under X（intermediate P-wave velocity）, Y（lowest P-wave velocity）, and Z （highest P-wave velocity） directions. The dynamic stress equilibrium on both ends of the sample and constant strain rate was achieved during loading with help of pulse shaper（copper ＋ rubber） technique. The momentum-trap technique was adopted to protect the sample from multi-loading by the incident bar. Corresponding to three loading levels, three damage levels of the rock samples were identified according to the extents of damage, namely, quaso-elastic, cracked, and fragmented samples. The damage assessment of recovered sample was investigated after cut to thin sections, and the microcrack increased with the loading rate. The stress-strain curves of samples at different strain rates（70, 100, 130 s^-1） under three directions were obtained. The correlation between the failure modes and shape of the stress-strain curves was discussed. The maximum stress increased with the loading rate. The dynamic strength was isotropic at low and high strain rates, but Y-samples had the highest dynamic strength under middle loading rate. The XZ plane was considered to be parallel to the rift plane, thus it was difficult to split the cracks with the critical loading level.