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

微缺陷与陶瓷晶界的断裂力学相互作用。

基本信息

批准号：
01550598
负责人：
SAKAI Mototsugu
金额：
$ 1.34万
依托单位：
Toyohashi University of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1990
项目状态：
已结题

项目摘要

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

本研究的主要目的是通过研究控制强度的小缺陷和陶瓷晶界之间的微观力学相互作用来阐明陶瓷晶界在增韧多晶陶瓷材料中的作用。 1．研究了不同晶粒尺寸的MgO、Al2MgO4等氧化物陶瓷以及多晶石墨材料的强度和断裂韧性，重点研究了其影响（烧结晶粒尺寸）/（强度控制缺陷尺寸）之比对这些断裂参数的影响。 2. 结果和讨论的简要概述（1）实验测定的断裂韧性值存在有限差异具有宏观缺口或宏观裂纹以及微观缺陷的试样，多晶陶瓷晶界结合力的降低增强了这种差异。(2) 宏观断裂韧性降低，而。随着晶界结合力的降低，IM 方法中的微观断裂韧性增加。对于弱晶界，IM 方法中的这种韧性增加可能是由于应力诱导的微裂纹导致裂纹尖端应力场的微观局部松弛所致。此外，本研究还揭示了宏观和微观裂纹样品之间的断裂韧性差异与多晶陶瓷的 R 曲线行为密切相关。(3)批判性地审查了“微观结构 R 曲线效应”的传统概念，该概念被引入来解释断裂韧性随着强度控制缺陷尺寸的逐渐减小而明显下降。）从人为缺陷到内在缺陷的强度控制断裂起源（反之亦然）对于决定具有缺陷/裂纹/瑕疵的多晶陶瓷的断裂强度和断裂韧性至关重要其尺寸与烧结晶粒的数量级相同。