基于3D-ILC含偏心内裂纹半圆弯拉断裂特性研究

断裂力学是各行业的基础学科之一。半圆弯拉(SCB)试验为该领域经典试验，目前含裂纹的SCB研究多为底部切口等表面裂纹或穿透型裂纹研究。内裂纹和内部类裂纹缺陷是材料的固有属性，但是对于SCB内裂纹扩展规律研究较少。基于3D-ILC（三维激光疲劳内裂纹）技术，分析了表面无任何影响的情况下凭空生成任意参数的纯内裂纹，在SCB试样中生成内裂纹，对含内裂纹试样进行SCB试验，分析了裂纹生长过程、应力双折射规律、I-II-III型裂纹扩展面、破坏形态、宏微观断口特征，开展数值模拟，得到裂纹尖端应力强度因子分布规律及扩展路径，与物理试验一致。结果表明：（1）基于3D-ILC的SCB内裂纹及I-II-III型扩展断裂规律明显，3D-ILC为断裂力学中的内裂纹问题研究提供了有力工具；（2）应力云纹在内裂纹处显示应力集中，SCB整体云纹在内裂纹处发生明显变异；（3）SCB试样从预制裂纹处发生压剪型起裂，发生I-II-III型裂纹扩展，分为光滑区和撕裂区，持续生长转变为动态断裂进而破坏，动态断口存在裂纹分叉出现雾化区、羽毛区特征；（4）根据M积分和最大周向应力准则，对试样进行了数值模拟，得到了试样内裂纹尖端应力强度因子分布规律及扩展路径，与试验结果一致。结论与成果对断裂力学领域的SCB试验、内裂纹、I-II-III型断裂问题、裂纹扩展路径模拟问题的研究，具有重要意义。

Study of fracture characteristics of semi-circular bending with internal crack based on 3D-ILC

Fracture mechanics is one of the basic disciplines in various industries. The semi-circular bending (SCB) test is a classic test used in the study of solid mechanics. At present, the research on SCB mainly focuses on surface cracks such as bottom notch or penetrating cracks. Whereas the internal cracks and internal defects that are the intrinsic properties of material have been seldomly researched employing the SCB test. Based on the 3D-ILC (3D-internal laser-engraved crack) method, an analysis was performed on the pure internal cracks with arbitrary parameters generated randomly given that surface had no influence on crack generation, internal cracks were created in SCB specimens and the specimens were assessed by the SCB test. Numerical simulation was performed to analyze the crack growth process, stress birefringence, I-II-III crack growth surface, failure pattern, and macro to micro fractography characteristics. Moreover, the distribution law of stress intensity factor and extension path were obtained that agreed with the physical test. The results show that: 1)The 3D-ILC method is useful for solving the problem of internal cracks in fracture mechanics. 2) Stress concentration is shown at the internal crack of stress nephogram, and significant variation occurs at the internal crack of SCB stress nephogram. 3) The compression-shear crack initiation occurs at the prefabricated crack of the SCB and develop into I-II-III mix-mode crack. The crack growth surfaces are divided into smooth zone and tear zone. The continuous growth is transformed into dynamic fracture and then failure, along with the mist zone and the hackle zone. 4) Based on the M-integral and maximum tensile-stress (MTS) theory, the numerical simulation of the specimens is carried out. The distribution of the stress intensity factor at the crack tip is given, and the crack growth path is simulated. The numerical simulation agrees with the experimental results. It provides experimental and theoretical basis for the study of SCB testing, internal cracks, I-II-III mix-mode fracture, simulation of crack propagation paths in the field of fracture mechanics.