滦县M_L=4.8地震的局部多台数字记录

据中国数字地震台网测定,2004年1月20日16时34分11.9秒在滦县发生了ML=4.8的地震,震中位于东经118.77°,北纬39.71°,震源深度H=10km。尽管地震造成的破坏轻微,但有感范围较大,在秦皇岛市、青龙县、北京市、廊坊市、天津市等地均有震感。这次地震使震中及其附近地区的5台数字强震仪触发,记录了5组3分量数字加速度记录。本文对这次地震事件、地震地质概况作了简要介绍,并就台站(阵)基本背景资料、数字强震仪主要技术指标作了详细说明。最后,对获取的15条数字加速度记录作了初步处理分析,如基线校正、加速度峰值计算、傅里叶谱及反应谱计算等

A continuum damage mechanics model for 2-D woven oxide/oxide ceramic matrix composites under cyclic thermal shocks

Oxide/oxide-ceramic matrix composites (ox/ox-CMCs) are excellent candidates for material applications in high-temperature and oxidizing environments, which exhibit complex couplings between the thermal and mechanical fields. Uniaxial tensile tests are conducted for 0 degrees/90 degrees and +/- 45 degrees fiber orientation of the thermal shocked ox/ox-CMCs. The study reveals that the anisotropy properties of the thermal shocked ox/ox-CMCs result in different degrees of thermomechanical damage, which are reflected in the degeneration of the modulus. Based on the detailed experiments and analysis, a cyclic thermal shock-induced thermomechanical damage model of the 2-D woven ox/ox-CMCs is proposed, incorporating two tensile scalar damage parameters, and one shear scalar damage parameter. The model will contribute to predicting the thermomechanical damage evolution throughout the composite structure under thermal transient conditions. In addition, the model was validated with numerical simulation to demonstrate the damage model performance, which is relatively crucial in damage tolerance analysis in the aeronautical industry

An elastic-plastic constitutive model for thermal shocked oxide/oxide ceramic-matrix composites

The oxide/oxide ceramic-matrix composites exhibits superior mechanical properties and complex nonlinear behavior in a high-temperature environment. This paper developed a constitutive model utilising an elastoplastic modeling framework to represent the nonlinear mechanical response of the thermal shocked ox/ox-CMCs under off-axis tensile loading accurately. The model captures main features such as the effects of the thermal shock temperatures on material response. The main interest of the proposed model is the ability to predict the nonlinear mechanical response for thermal shocked ox/ox-CMCs, which is of importance for industrial applications. The validity of the constitutive model is verified by analysing the mechanical behavior of an open-hole specimen and comparing the simulation result with the experimental data

基于微孔隙率作为损伤指标的陶瓷基复合材料循环热冲击引起的各向异性损伤

针对先进航空发动机/可重复使用运载系统等新型航天飞行器结构承热结构/热防护材料开展工作。氧化物/氧化物陶瓷基复合材料(Oxide/Oxide Ceramic Matrix Composites,Ox/Ox CMC)由于且耐高温、抗氧化和高比强度材料而备受关注。然而,该材料导热系数低,耐高温,对热冲击的敏感性高,在瞬态温度条件下评估Ox/Ox CMC结构完整性成为其应用的一个重要研究课题。本文以选定的工艺路线的二维编织Ox/Ox CMC为研究对象,在编织工艺分析的基础上,从微观到宏观层次,研究了循环热冲击下Ox/Ox CMC的热机械损伤与热冲击后Ox/Ox CMC的损伤力学行为。借助扫描电镜(SEM)和压汞法研究不同热冲击温度及不同累计循环周次下CMC的损伤形式,损伤萌生与演化情况,定量表征下Ox/Ox CMC在不同热冲击温度及不同累计循环周次下CMC微观结构的演化规律,获得定量描述孔隙分布与演化的参数。实验结果表明,基体裂纹密度随着累积循环次数的增加而增加,最终趋于稳定饱和状态,并证实了材料的微孔隙率是材料裂纹密度增加的宏观体现。基于详细的实验分析与研究,提出多层次孔隙的概念描述材料中两种不同尺度的孔隙对材料基体和纤维束力学性能的影响,基于Voigt混合律模型,建立了考虑多层次孔隙率影响的多孔基体CMC有效模量预测模型。提出由微孔隙率增量作为损伤变量来描述Ox/Ox CMC的各向异性损伤,并结合断裂力学方法,建立了Ox/Ox CMC微孔隙率增量与相应状态下材料应变能释放率之间的关系。最终,通过数值模拟不同状态的微孔隙率对对材料宏观弹性模量的预测,验证了所提模型的合理性

Investigation of long-term thermal aging-induced dainage in oxide/oxide ceramic matrix composites

Long-term thermal aging is a typical factor affecting the thermo-mechanical fatigue life for hot-end components in the gas turbine. The present work focuses on the development of thermal aging-induced damage in 2-D woven oxide/oxide ceramic matrix composites from micro-mechanism and macroscopic mechanical performance. The porosity evolution and mechanical performance after long-term thermal aging were characterized through mercury intrusion measurements and uniaxial compressive tests, respectively. The results show that the decrease of micro-porosity directly reflects the irreversible evolution of material microstructure in the thermal aging process, and the decrease of compressive strength after aging is the macroscopic reflection of the microstructure variation. The porosity increment of matrix was thus used to characterize the thermal aging-induced damage, establishing a unique analysis model between the increment of micro-porosity under thermal aging and the corresponding degradation of material compressive strength. The experimental results are in good agreement with the established model

含热冲击预损伤的陶瓷基复合材料损伤本构模型

陶瓷基复合材料结构在服役过程中不可避免地经受热冲击(较高的热应力梯度)而产生热机械损伤,因此,建立含循环热冲击预损伤材料的损伤本构模型,以描述材料在热机械载荷作用下的力学行为,对材料结构损伤容限设计与结构完整性评估非常重要。本文首先对经历了循环热冲击的材料进行单调拉伸损伤实验,发现对于含循环热冲击预损伤的材料,其弹性模量的下降与所施加的应变直接相关。然后在连续介质损伤力学的框架下,基于平面应力假设,建立了含循环热冲击预损伤材料的损伤演化模型,该模型所涉及的参数可通过一个偏轴(45°)以及两个正轴(平行于两个主方向)的单调拉伸试验获得。最后,采用经典塑性理论对由基体损伤引起的非弹性应变进行了描述。本文所提出的应变损伤宏观模型可以描述陶瓷基复合材料在热机械载荷作用下的损伤演化,同时弥补了含预损伤的陶瓷基复合材料在机械载荷下损伤本构模型在理论及实验研究方面的不足

Micro-porosity as damage indicator for characterizing cyclic thermal shock-induced anisotropic damage in oxide/oxide ceramic matrix composites

Ceramic matrix composites display complex mechanical behavior under thermo-mechanical loading conditions. The present work focuses on micro-structural evolution and resultant macroscopic property representation of the composites after cyclic thermal shocks. Micro-structural investigation reveals that variations of the hierarchical porosity in the matrix characterize the collective behavior of micro-structural evolution in the material. Cyclic thermal shocks induce thermo-mechanical damage and lead to increasing matrix porosity. Material damage development is driven by elastic strain energy density which is related to the matrix porosity increment. Experiments confirm that the anisotropic damage can be represented by the porosity increment accurately. The porosity provides a meaningful model for the thermal shock damage evolution in the anisotropic composites

Damage modeling of oxide/oxide ceramic matrix composites under cyclic loading conditions

Ceramic matrix composites exhibit optimal high temperature property and complex nonlinear behaviors including irreversible deformations and stiffness degradation under different mechanical loading conditions. In the present work, the damage evolution of the material under multi-axial loads considering effects of loading-unloading cyclic was studied and a novel continuum damage constitutive model was proposed. The material de gradation was decomposed into monotonic damages and cyclic damages. The anisotropic hardening behavior of the material was considered by taking orientation dependence into account. Compared to the experimental results, the constitutive model could accurately predict the stress-strain response and stiffness degradations of the oxide/oxide ceramic matrix composites for monotonic loading and cyclic loading

Развитие идей педагогической антропологии в России: (вторая половина XIX - начало XX вв.): автореферат диссертации на соискание ученой степени кандидата педагогических наук: специальность 13.00.01 - Общая педагогика, история педагогики и образования

A particular emphasis is placed on the thermal aged oxide/oxide ceramic matrix composites under cyclic thermal shocks, which exhibit hierarchical internal structures spanning multiple volume/scales. The present work focuses on establishing thereto-mechanical loading conditions-structure-property linkages for the thermal aged oxide/oxide ceramic matrix composites under cyclic thermal shocks. Firstly, the matrix micro-cracks and delamination were identified by SEM observation, and the compressive mechanical behaviors were studied after different cyclic thermal shock numbers. The thermal aging process resulted in apparent changes in thermal shock resistance of materials. Considering the material deterioration induced by the thermal aging process, aging-related factor was introduced to predict the compress behaviors of the thermal aged oxide/oxide ceramic matrix composites under cyclic thermal shocks. The correlation between porosity and strain energy release rate was also constructed, which provided an excellent agreement with the experiments.</p