BRITTLENESS,TOUGHNESS AND DUCTILITY OF CERAMICS -THE MICROSCOPIC PROCESSES AND CHARACTERIZATION.

1)根据压痕接触力学的能量原理，定义并推导了脆性和延性这两个材料特征参数。脆性/延性参数为脆性材料的可加工性提供了一个定量的表征手段。2）设计了一套表征脆性/延性参数和压痕损伤程度的装置，400立方厘米.3）对高温下脆性材料的粘弹性压痕接触变形进行了理论分析和实验研究。温度利用压痕滞后能表征了材料表面变形的粘弹性行为。4）利用声显微镜研究了压痕接触引起的材料表面损伤。5）考虑高温下晶界熔融多晶陶瓷的晶界滑移和晶粒互锁，建立了非线性流变本构方程设计了一种实验装置，用于在高达1600 ℃的高温下检查多晶材料的粘弹性行为。在压缩加载模式下的双剪切几何形状（双剪切几何形状）使得在简单剪切变形下进行流变测试成为可能。实验研究证实，第5项中提出的本构方程定量地预测了与晶界滑动和晶粒互锁相关的非线性粘弹性行为。7）通过对几种陶瓷的混合型断裂和R曲线行为的实验和理论研究，研究了增韧过程和机理。提出了一种新的测试技术和基于断裂力学的尺寸效应定律来估计过程区/尾流区尺寸。

1) The brittleness and the ductility as characteristic material parameters were defind and derived based on an energry principle of indentation contact mechanics. The brittleness/ductility parameter gives a quantitative measure for characterizing the machinability of brittle materials.2) An apparatus was designed for characterizing the brittleness/ductility parameter and the degree of indentation-induced damage in a wide range of temperatures ranging from room temperature to 1,400ﾟC.3) Conducted were the theoretical consideration and experimental work of viscoelatic indentation contact deformation of brittle materials at elevated temperatures. The indentation hysteresis energy was successfully utilized to characterize the viscoelastic behavior of surface deformation.4) An acoustic microscopy was applied to the surface damage introduced by indentation contact. An analytical method for characterizing the damage evolution has been established.5) A nonlinear rheological constitutive equation was proposed based on considerations of the grain-boundary sliding and grain interlocking of polycrystalline ceramics with grain-boundary melt at elevated temperatures.6) An experimental apparatus was designed for examining viscoelastic behavior of polycrystalline materials at elevated temperatures up to 1600ﾟC.A novel test specimen geometry (double shear geometry) under compressive loading mode makes possible to conduct rheological testing under simple shear deformation. An experimental scrutiny confirmed that the constituteve equation proposed in Item 5) quantitatively predicts the nonlinear viscoelastic behavior associated with grain-boundary sliding and grain interlocking.7) Toughening processes and mechanisms have been examined via experimental as well as theoretical studies on the mixed-mode fracture and R-curve behavior of several types of ceramics. A novel test technique and a fracture mechanics-based size-effect law were proposed to estimate process zone/wake zone sizes.