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，提出并推导了以脆性和延性为特征的材料参数。脆性/延性参数是表征脆性材料可加工性的定量指标。2)设计了一套表征脆性/延性参数和压痕损伤程度的装置，从室温到1,400ﾟ进行了高温下脆性材料粘弹性压痕接触变形的理论研究和实验工作。利用压痕滞后能表征了表面变形的粘弹性行为。4)利用声学显微镜对压痕接触引起的表面损伤进行了研究。建立了表征损伤演化的分析方法。5)在考虑高温下多晶陶瓷与晶界熔体的晶界滑移和晶界互锁效应的基础上，提出了一种非线性流变本构方程。6)设计了一种测试多晶材料在1600ﾟC高温下的粘弹行为的实验装置。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界互锁有关的非线性粘弹性行为。7)通过对几种类型陶瓷的混合型断裂和R曲线行为的实验和理论研究，研究了增韧过程和增韧机理。提出了一种新的试验技术和基于断裂力学的尺寸效应定律来估算过程区/尾流区的尺寸。

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.