棱锥压入断裂测试中裂纹萌生和扩展机制的研究

Pyramidal indentation fracture test is an important probing technique for determination of fracture toughness on local test area or small speciments. Compared with conventional fracture test, it requires much simpler and smaller specimens, which awards itself a great advantage when testing ceramics and MEMS parts. The mechanism of crack initiation and propagation is the key problem in both research and application of pyramidal indentation fracture test because it plays a key role in establishing analyzing models, choosing experimental parameters and define test methods' scopes of application. This proposed project is aimed to research on the mechanism of crack initiation and propagation for pyramidal indentation on brittle materials which consists of radial crack initiation model, evolution of crack geometry and the work-energy conversion during the indentation fracture. In this project a radial crack initiation model will be theoretically established to unveil the influence of indenter's geometric features and specimen's mechanical properties on critical indentation load for radial crack initiation, and numerical calculations will be carried out to simulate the cracking process during indentation fracture to investigate the crack geometry evolution and the work-energy conversion. Finally, Experiments will be carried out to verify above investigations on radial crack initation model, final crack geometries and work-energy conversion. The success of this project will help advance the understanding of mechanical mechanism of pyramidal indentation fracture test by investigating the crack initiation and propagation, and improve the applicability of indentation fracture test by predicting experimental parameters and defining scopes of application for test methods.

棱锥压入断裂是一种重要的试样微区和微尺度试样断裂韧度测试技术，与传统断裂力学测试相比，制样简单、测试尺度小，适用于陶瓷材料和微机电系统部件的测试。棱锥压入断裂中的裂纹萌生和扩展机制，是影响测试方法所用分析模型建立的基础理论问题，也是影响测试方法中实验条件选择和适用范围确定的关键技术问题。本项目旨在研究，棱锥压头压入脆性材料过程中的裂纹萌生和扩展机制，包括径向裂纹临界载荷模型、裂纹构形演变过程和压入断裂中的功-能转化关系。本项目拟通过理论分析建立径向裂纹临界载荷模型，以预测压头几何形状和材料力学性能对临界载荷的影响趋势；通过数值计算模拟裂纹的萌生和扩展，以总结裂纹构形演变过程和功-能转化关系；通过实验验证临界载荷模型、最终裂纹构形和功-能转化关系。本项目的完成，将可深入认识裂纹萌生和扩展的规律，理解棱锥压入断裂的力学机制；并将据此预测实验条件和明确适用范围，改善棱锥压入断裂测试技术的实用性。

棱锥压入断裂是一种重要的试样微区和微尺度试样断裂韧度测试技术，与传统断裂力学测试相比，制样简单、测试尺度小，适用于陶瓷材料和微机电系统部件的测试。棱锥压入断裂中的裂纹萌生和扩展机制，是影响测试方法所用分析模型建立的基础理论问题，也是影响测试方法中实验条件选择和适用范围确定的关键技术问题。本项目通过理论分析，建立了棱锥压入径向裂纹萌生的近似模型，得到了临界压入载荷的显式表达式，有助于理解和预测棱锥压入的裂纹萌生和扩展；通过对棱锥压入应力场的有限元数值模拟，发现等效半锥角越小的压头越容易制造径向裂纹，侧棱数越多的压头越容易制造径向裂纹；通过实验观测，验证了理论模型预测和数值模拟的结果，总结了三种典型棱锥压头的适用情况：cube-corner压头更适用于试样尺度小、显微观测能力高的压入断裂测试，Vickers和Berkovich压头更适用于试样尺度相对较大、显微观测能力不高的压入断裂测试。通过本项目的研究，有助于加深对棱锥压入断裂的力学机制的理解，总结典型棱锥压头适用范围，改善棱锥压入断裂测试技术的实用性。