基于DIC的含3D打印起伏节理试样破裂特性及损伤本构

受地质构造的影响，岩体工程中经常赋存起伏结构面(如扭转皱褶)，由于形态复杂，目前起伏节理岩体的破裂及损伤本构研究仍不充分. 采用3D打印技术制作不同倾角的起伏节理模型，通过单轴压缩试验和数字图像相关技术(DIC)对起伏节理试样的力学及破裂特性进行研究，并基于断裂力学原理，首次提出采用DIC位移场求解节理尖端应力强度因子(SIF:一型SIF，K_I；二型SIF，K_II)进而探究损伤本构特性的思路. 结果表明:通过分析最小强度确定了起伏节理对试样的损伤上限为46.6%，起伏节理试样单轴强度对倾角的敏感性大于平直节理试样；起裂发生在峰值应力附近，破裂过程可分为破裂路径上微裂隙的产生和同步贯通，破裂模式表现为多条裂隙张剪组合模式；峰前SIF随荷载增加而增加，峰后同一荷载下K_II>K_I，节理左右两端均匀以剪切裂隙形式扩展；起伏节理对试样的损伤与倾角呈正弦关系，节理和荷载对试样的总损伤与应变均大致呈“S”型曲线. 

Fracture characteristics and the damage constitutive model of 3D printing undulating joint samples based on DIC

Due to the influence of geological structures, various forms of joint structural planes are present in rock mass engineering. The undulating structural planes, such as a torsional fold surface, are unique geological structures. These structures affect the stability of rock masses and cause potential hazards to rock mass engineering. Because of their shape complexity, the research on the fracture and damage constitutive law of rock mass with undulating joints is not thoroughly conducted. Undulating joints with various dip angles were fabricated using three-dimensional printing technology. The uniaxial compression test and digital image correlation (DIC) technology were used to study the mechanical and fracture characteristics of undulating joint specimens. Based on the principle of fracture mechanics, an idea was proposed to use the DIC displacement field for solving the stress intensity factor (SIF: type one K_I and type two K_II) at the joint tips and to study the damage constitutive law. The results show that the upper limit of undulating joint damage to specimens is determined with 46.6% through the minimum strength analysis. The sensitivity of uniaxial strength to a joint dip angle of undulating joint specimen is greater than that of a straight joint specimen. The fracture initiation occurs near peak stress. The fracture process can be divided into the initiation and synchronous penetration of microcracks on the fracture path. Additionally, the fracture mode shows a combination of multiple tension and shear fractures. The SIF increases with loading at the prepeak stage, and the cracks propagate in shear fracture at the joint left and right tips in the postpeak stage because K_II>K_I under the same stress. The undulating joint damage to the specimen with the dip angle is in a sinusoidal curve form. The relationships between the total damage coupled by joint and load with strain are all “S” curves.