“2023年广东省土木工程研究生学术论坛”系列讲座
报告一：
报告主题：防热复合材料细观烧蚀理论研究
报告人：梁军 教授（北京理工大学）
邀请人：曾涛 教授
报告时间：12月1日上午8：00-10：15
报告地点：科技楼521室（会议室）
个人简介：
梁军，北京理工大学先进结构技术研究院教授、博士生导师，国家杰出青年科学基金获得者、“国家百千万人才工程”有突出贡献中青年专家。从事飞行器防热材料与结构性能表征与评价、轻量化多功能复合材料结构设计及仿真等方面研究，已发表学术论文200余篇，授权发明专利10项，出版专著1部，参编著作3部，并获得多项国家及省部级奖励。兼任中国复合材料学会副秘书长、奖励工作委员会主任委员，SAMPE北京分会常务理事、通讯委员会主任委员。
内容简介：
高超声速飞行是人类拓展时空运用能力的重要手段，临近空间飞行器面临高温/长时/有氧的极端气动热环境，热防护技术是决定飞行器成败的关键。报告针对临近空间飞行器大面积热防护材料表面烧蚀和体积烧蚀条件下多孔介质的传热传质特性、介绍课题组近年来在炭化复合材料细观烧蚀理论、特别是烧/剥蚀耦合作用判据和模型等方面取得的研究进展。
报告二：
报告主题：非均质材料各向异性及失效研究
报告人：刘彬 教授（清华大学）
邀请人：曾涛 教授
报告时间：12月1日上午10：15-12：30
报告地点：科技楼521室（会议室）
个人简介：
刘彬，清华大学工程力学系教授、博士生导师，国家杰出青年科学基金获得者。主要从事固体力学的理论和计算研究，研究兴趣包括超大规模多尺度多物理场计算方法，断裂力学和复合材料力学。主持国家杰出青年科学基金、国家自然科学基金等多项国家级科研计划项目；发表SCI论文140余篇，出版英文书章3篇。获国家自然科学二等奖，中国力学学会自然科学一等奖，中国力学学会青年科技奖，教育部新世纪人才计划，德国洪堡奖学金。任国际期刊《Forces in Mechanics》主编，《International Journal of Plasticity》和《Journal of Computational and Theoretical Nanoscience》编委及《力学学报》副主编。
内容简介：
Obtaining intergranular and transgranular fractures through grain boundary engineering has been considered an efficient technique that improves the effective fracture toughness of polycrystalline aggregates. In this paper, the idealized hexagonal microstructure, random microstructures, and microstructures of grains with large aspect ratios are analyzed through a semi-analytical approach and the cohesive finite element method. The results indicate that when the aspect ratio of grains is not too large, the crack paths consisting of intergranular and transgranular fractures are approximately Mode I fracture morphologies among these microstructures. As the ratio of toughness between grain boundaries and grains varies, the effective fracture toughness of the microstructure can be increased more than the grain boundary fracture toughness but cannot exceed the inner grain fracture toughness. In contrast, the microstructure of grains with a large aspect ratio leads to deflected crack paths that are unexpectedly obtained, which implies that the approximate Mode-I intergranular fracture along transverse direction is almost impossible. The results demonstrate that the projected energy dissipation rate along the direction perpendicular to the loading axis can be significantly improved beyond the inner grain fracture toughness by enlarging the aspect ratio of the grains. Nevertheless, the mixed-mode effective fracture toughness is still limited to the grain fracture toughness. Corresponding experiments are also carried out to qualitatively verify the numerical results. The underlying mechanism for this deflection of fracture path is due to the strong anisotropy of fracture toughness. The higher the grain aspect ratio, the greater the anisotropy of the macroscopic effective fracture toughness. The energy favored fracture path is determined by the largest ratio between the driving force and the toughness of fracture over all directions. Therefore, cracks cannot propagate in the direction of the maximum fracture toughness when the aspect ratio of the grain is sufficiently large. The fracture diagrams that vary with the aspect ratio of grain and the ratio of fracture toughness between the grain and grain boundary are provided. The results can provide valuable guidance for designing microstructures and improving fracture toughness in materials.
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2023年11月30日
