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

1)基于压痕接触力学的能量原理，定义并推导了脆性和延性作为特征材料参数。脆性/延性参数是表征脆性材料可加工性的定量指标。2)设计了在室温~ 1400℃范围内的脆性/延展性参数和压痕损伤程度的表征装置。3)对脆性材料在高温下的粘弹性压痕接触变形进行了理论思考和实验工作。成功地利用压痕滞回能表征了表面变形的粘弹性行为。4)应用声学显微镜对压痕接触引起的表面损伤进行了研究。建立了一种表征损伤演化的解析方法。5)考虑晶界熔体在高温下的晶界滑动和晶粒互锁，建立了多晶陶瓷的非线性流变本构方程。6)设计了一种实验装置，用于测试多晶材料在高达1600℃的高温下的粘弹性行为。压缩加载模式下的新型试样几何形状（双剪切几何形状）使简单剪切变形下的流变试验成为可能。实验验证了第5项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)通过对几种陶瓷混合模式断裂和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.