Stanstead花岗岩动态断裂性能

RESEARCH ON DYNAMIC FRACTURE BEHAVIORS OF STANSTEAD GRANITE

采用一种新的方法研究Stanstead花岗岩的动态断裂性能,包括起裂韧度、断裂能、传播韧度和裂纹传播速度。该方法采用分离式霍普金森压杆加载的带预制裂纹的半圆盘三点弯试样,同时采用激光位移计监测试样的裂纹面张开位移。在动态力平衡的条件下,起裂韧度由准静态公式计算得到。通过裂纹面张开位移数据推算出2个碎片的残余动能,从而计算出平均传播断裂能和传播韧度。裂纹传播平均速度由黏接在试样上的一系列裂缝计测量得到。试验结果表明,该花岗岩的起裂韧度和传播韧度都与加载速率有关,传播韧度大于起裂韧度,传播韧度随着裂纹传播速度的提高而提高。通过裂纹传播速度和传播韧度的关系拟合得到材料的止裂韧度及裂纹传播极限速度。得到的Stanstead花岗岩与Laurentian花岗岩结果对比表明,Stanstead花岗岩颗粒较大,起裂、止裂韧度较小;Laurentian花岗岩颗粒较小,传播韧度较小,裂纹传播极限速度较大,裂纹容易传播。

A recently proposed method is used to measure dynamic fracture parameters of Stanstead granite（SG）, such as fracture initiation toughness, fracture energy, fracture propagation toughness, and fracture propagation velocity. With the method, a notched semicircular bend specimen is loaded by the split Hopkinson pressure bar（SHPB） system： and a laser gap gauge system is employed to monitor the crack surface opening displacement （CSOD） of the specimen. The dynamic initiation toughness is subsequently calculated by using a quasi-static formula, for the dynamic force balance is achieved in the test. Based on the CSOD data, residual kinetic energies of the two fragments are estimated. The average propagation fracture energy and thus the propagation toughness are calculated. The average fracture propagation velocity is estimated with a series of crack gauges glued on the specimen. It is shown from the results of the experiments that both the initiation and propagation toughnesses of this brittle solid are loading-dependent. The propagation toughness is larger than the initiation toughness. The propagation fracture toughness is shown to increase with the fracture propagation velocity. The fracture arrest toughness and the limiting fracture propagation velocity are obtained by a literature model of this relationship. The results of SG in this work are compared with the ones of Laurentian granite（LG）. The grain size of SG is much larger than the one of LG, so that the fracture is easy to be generated and arrested but difficult to propagate. On the contract, the LG has smaller dynamic propagation toughness and the larger limit fracture propagation velocity.