基于3D-ILC三点弯脆性固体内裂纹扩展规律及破坏特征研究

Three-point bending test study on the propagation law of internal cracks and failure characteristics of brittle solids based on 3D-ILC technology

岩石内裂纹扩展问题是岩土工程学科的重要问题之一。基于3D-ILC技术,选用理想脆性材料,在对试样表面无影响的前提下,生成任意参数的真实内裂纹,进行含内裂纹试样三点弯试验,并与完整试样进行对比。开展试样破坏过程、特征荷载、破坏形态、断口特征、动态分叉、应力云纹分析,通过数值模拟得到裂纹尖端K分布规律及扩展路径,与试验对比。结果表明:(1)内裂纹的存在极大的降低试样的起裂与破坏荷载;(2)应力双折射技术可与3D-ILC联合应用进行内裂纹应力信息监测,内裂纹尖端呈现"花瓣"状应力云纹;(3)三点弯下空白试样发生动态断裂,断口呈现雾化、羽毛区特征,由动态裂纹分叉引起。含裂纹试样,从内裂纹下尖端到上尖端逐渐起裂,呈现水滴状,为纯I型破坏,断口呈现交汇Wallner线特征;(4)基于M积分的裂纹尖端K分布与试验起裂规律一致;基于MTS的内裂纹扩展路径模拟与试验一致。3D-ILC相对于目前透明类岩石研究中主流方法,在脆性度、裂纹真实性、应力场可视化、断口特征等方面具备一定进步性,试验与数值模拟成果将为岩石等脆性材料的三维断裂、内裂纹扩展等问题的研究,提供试验和理论参考。

Crack propagation in rocks is one of the important issues in geotechnical engineering. Based on 3 D-ILC technology,an ideal brittle material is selected,and the actual internal crack with arbitrary parameter is generated without affecting the surface of the sample. The three-point bending test of ideal brittle material samples containing actual random internal cracks generated without changing the sample surface was carried out and compared with the complete samples. Failure process,characteristic load,failure mode,fracture characteristics,dynamic bifurcation and stress moire were analyzed,and the K-distribution and extension path of the crack tip were obtained by numerical simulation. The results show that the cracking and breaking loads of the specimen are reduced greatly due to the existence of internal cracks,and that the internal crack tip presents petal-like strain moire which can be monitored by the stress birefringence technology combined with 3 D-ILC. Under three-point bending,the blank specimens occur dynamic fractures with atomization,feather zone characteristics caused by dynamic crack bifurcation,while the crack-containing specimens gradually crack from the lower tip to the upper tip of the internal crack of a pure type–I failure in a drop-like shape with characteristics of the intersection Wallner line. It is also indicated that both the K-distribution at the crack tip based on M-integral and MTS-based internal crack propagation path simulation are consistent with the test results. Compared with the current mainstream methods in the study of transparent rock,3 D-ILC has certain advancement in brittleness,crack authenticity,stress field visualization and fracture characteristics. The test and numerical simulation results will provide experimental and theoretical references for research on problems including internal crack propagation and three-dimensional fracture of brittle materials such as rock.