基于DIC技术的3D打印节理试件破裂机制研究

Study on the fracture mechanism of 3D-printed-joint specimens based on DIC technology

为了准确表征不同角度预制节理岩石在单轴压缩下的变形破坏模式,基于3D打印技术制作了节理模型用于模拟岩体中的结构面,通过水泥砂浆的浇筑得到含不同角度预制节理的岩石试件并进行单轴压缩试验,同时采用数字图像相关技术(DIC)观测、分析试验过程中试件裂纹产生、扩展以及贯通过程。结果表明:随着预制节理从0°增加到90°,试件强度与峰值应变均呈现先降低后升高的变化趋势,0°和45°试件弹性模量相对于完整试件有所降低。基于DIC检测结果,0°、30°、45°及60°试件裂纹皆从预制节理尖端部位起裂,各角度试件的起裂应力与试件强度变化规律一致。各角度试样起裂时在剪应力控制下以剪切翼型裂纹形式起裂,0°与45°试件裂纹在扩展过程由剪切发展为张拉型裂纹,30°和60°试件以剪切裂纹形式贯穿始终,90°试件从底部起裂并最终表现为张拉破坏。研究还发现,下翼起裂角θ2和上翼起裂角θ1之间存在明显的线性正相关关系,关系式为θ2=0.828 6θ1+12.185,且起裂应力大小变化与峰值应力变化一致,皆随节理角度的增加先减小后增大。

In order to accurately characterize the deformation and failure modes of prefabricated jointed rocks with different angles under uniaxial compression, a joint model based on 3D printing technology was used to simulate the structural surface in the rock mass. Rock specimens with precast joints with different angles were obtained by pouring cement mortar, and a uniaxial compression test was performed. At the same time, digital image correlation(DIC) technology was used to observe and analyze the process of crack formation, propagation, and penetration in the test specimen. The results showed that as the angle of prefabricated joints increased from 0° to 90°, a decrease followed by an increase in the strength and peak strain of the test piece was observed. Additionally, the elastic modulus of the test piece with angles of 0° and 45° decreased compared to the complete test piece. Based on the DIC test results, the cracks of specimens with angles of 0°, 30°, 45°, and 60° all started from the tip of the prefabricated joint. The crack initiation stress of the specimens with different angles was all consistent with the strength change of the specimens. Under shear stress, the cracks started in the form of shear wing cracks. The cracks of 0° and 45° specimens changed from shear to tensile cracks during the propagation process, and the shear cracks were observed in the specimens of 30° and 60° throughout this process. The crack of the specimen of 90° started from the bottom and tensile failure was eventually witnessed. In this study, an obvious linear positive correlation was found between the cracking angle θ2 of the lower wing and the cracking angle θ1 of the upper wing, and it can be expressed as θ2= 0.828 6θ1 +12.185. As the joint angle increased, the cracking stress decreased first and then increased, which was consistent with the peak stress.