Fracture Mechanics Interaction of MicroーFlaws with Ceramic Grain Boundaries.

目前研究的主要目标是通过测试强度之间的微力学相互作用--控制小花朵和谷物边界-通过测试微力学在陶瓷材料中的作用....实验详细情况对氧化物陶瓷的机械强度和断裂特性的测量方法包括MgO和Al 2 MgO 4，与不同的颗粒尺寸相似，如多晶体管图形材料一样，我们主要关注这些颗粒参数的影响（交错颗粒尺寸） / （强度控制颗粒尺寸）的影响。结果和讨论的简要大纲（1）在实验中确定的分形困难值中，存在着从一个宏观缺口或一个宏观裂缝和一个微观闪光中获得的微小差异。“在谷物边界结合力的减少中，多晶林陶瓷增强了这种差异。”（2）宏观结构的影响 ... More 当显微镜断裂的时候，当显微镜断裂的智力在IM方法中增加时，用谷物边界绑定力来退化。这个在较弱的谷物边界的IM方法中增加了一个可以从裂缝的微观局部分离的尖端压力场通过压力诱导的微裂纹沿着谷物边界进行的一个IM方法。在添加中，它已经在当前的研究中被披露，该研究表明这个分形的差异在宏观和微裂纹的特异性之间是封闭的与R-curve行为的多晶体管陶瓷相关的。（3） Critically reviewed was the conventional concept of the "microstructural R-curve effect" which has been introduced to plain the apparent decrease of fracture toughnss with the progressive decrease of the strManagement flaw size。它已经被放大并包含在过渡（切换） of the strength-controlling fracture Origin from the artificially induced flaws to the intrinsic flaws and vice versa是最重要的，用于定义fracture strength and fracture tue toughness of polycrystalline ceramics with defects/cracks/flaws whose dimensions are in the same order of the magnitude of sintered grains. Less（低）

The main objective of the present study is to elucidate the role of ceramic grain boundaries in toughening polycrystalline ceramic materials by examining the micromechanics interaction between the strengthーcontrolling small flaws and the grain boundaries of ceramics.1. Experimental detailsConducted were the measurements of the mechanical strength and the fracture toughness of oxide ceramics including MgO and Al2MgO4 with different grain sizes, as well as polycrystalline graphite materials, where we focused mainly on the influence of the ratio of (sintered grain size) / (strength-controlling flaw size) on these fracture parameters.2. Brief outline of the results and discussion(1) There exists a finite difference in the experimentally determined fracture toughness values obtained from test specimens with a macro-notch or a macro-crack and with a micro-flaw. The decrease in the grain boundary bonding forces of polycrystalline ceramics enhances this difference.(2) The macroscopic fracture … More toughness decreases, while the microscopic fracture toughness in the IM-method increases, with decreasing grain boundary bonding forces. This toughness increment in the IM-method for weak grain boundaries may result from the microscopic local relaxation of the crackーtip stress field through stress-induced microcracking along the grain boundaries.In addition, it has been disclosed in the present study that this fracture toughness difference between macro- and micro-cracked specimens is closely related to the R-curve behavior of the polycrystalline ceramic.(3) Critically reviewed was the conventional concept of the "microstructural R-curve effect" which has been introduced to explain the apparent decrease of fracture toughnss with the progressive decrease of the strength-controlling flaw size. It has been emphasized and concluded that the transition (switching) of the strength-controlling fracture origin from the artificially induced flaws to the intrinsic flaws and vice versa is most essential to dictate the fracture strength and fractue toughness of polycrystalline ceramics with defects/cracks/flaws whose dimensions are in the same order of the magnitude of sintered grains. Less