石家庄铁道大学工程力学系主任冯文杰教授和北京理工大学宇航学院苏煜教授访问力学系并做学术报告

应力学系郭翔老师邀请，石家庄铁道大学工程力学系主任冯文杰教授和北京理工大学宇航学院苏煜教授将于12月29日（本周六）访问力学系并做学术报告，欢迎各位老师和同学们积极参加。

报告题目：

1.The transient response analysis of interfacial crack in piezoelectric-piezomagnetic bi-layered composites by the extended finite element method(下午2点-3点)

2.Theory of thermal conductivity of graphene-polymer nanocomposites with interfacial Kapitza resistance and graphene-graphene contact resistance(下午3点-4点)。

报告时间：2018年12月29日（周六）下午

报告地点：北洋园机械工程学院第36教学楼316室

第一位报告人简介

冯文杰，男，67年出生。国务院特贴专家，国家百千万人才／国家级有突出贡献的中青年专家。先后在香港大学进行合作研究或访问12次，累计2年8个月（其中访问教授累计12个月），在美国阿克伦大学做高级访问学者1年，在德国锡根大学做高级研究学者半年。现为石家庄铁道大学教授、博士生导师，工程力学系主任。主要研究方向包括智能材料和结构（压电、电磁、功能梯度、超导材料）断裂力学、应用力学与工程中的先进计算方法和弹性波动力学。主持国家自然科学基金面上项目5项，省部级项目9项（包括河北省杰出青年基金、河北省高校领军人才等人才项目4项）；发表学术论文140多篇，其中SCI收录115篇，SCI他引800多次；相关研究成果获省部级自然科学一等奖一项（排名第二），二等奖两项（分别排名第一和第二），军队科技进步三等奖1项（排名第三）。

第一个报告摘要

Both the static and dynamic fracture problems of interfacial cracks in piezoelectric-piezomagnetic bi-layered composite structures (PE-PMBLCSs) under in-plane coupled electro-magneto-mechanical loadings are systematically analysed by means of the extended finite element method (X-FEM). The novel and more suitable crack-tip enrichment functions for interfacial cracks in PE-PMBLCSs are derived and the corresponding J-integral is evaluated using the domain-form of the path-independent contour integral. For the static analysis of interfacial cracks in PE-PMBLCSs, the validity of numerical solutions provided by X-FEM is verified by comparing with the analytical results obtained by solving the corresponding singular integral equations. The effects of X-FEM meshes, enrichment functions and enrichment domain on the computational accuracy, efficiency and robustness are studied, roundly. Using the Newmark method, the X-FEM scheme for interfacial cracks in PE-PMBLCSs under impact loadings is further outlined, where absorbing layers based on the Sarma absorbing boundary conditions (ABCs) are adopted and applied to avoid the unphysical wave reflections at the artificially introduced boundaries in the FEM meshes. And the validity of the proposed scheme for transient response problems is also verified by analyzing the possible stationary values obtained by introducing the corresponding absorbing layers. Finally, by some typical examples, the effects of the applied dynamic loadings, time variable and structural geometries on the dynamic fracture behaviors are discussed in detail. Some conclusions drawn in present study should be helpful for the design and applications of the PE-PM layered composite structures.

Keywords: Extended finite element method, piezoelectric-piezomagneticlayered structures, interfacial crack, dynamic fracture, J-integral

第二位报告人简介

苏煜，教授，博导。1998年获北京大学力学专业学士学位，2003获美国Rutger University固体力学专业博士学位。2008 年入选北京理工大学“百名人才引进计划”，2010 年入选教育部“新世纪优秀人才支持计划”。研究方向为多物理场耦合环境下智能材料与结构的动态力学行为。是国家自然科学基金创新型研究群体骨干成员。近5 年主持国家自然科学基金项目2 项、教育部科研项目2 项，爆炸科学与技术国家重点实验室项目1 项。参与国家自然科学基金重点项目、重大专项各1 项。研究成果在国际学术刊物发表SCI 检索论文近50篇，SCI 引用近千次。是国际力学刊物《Acta Mechanica》编委。

第二个报告摘要

Due to the extremely thin aspect ratio of graphene fillers, graphene-graphene contact could easily develop and this would introduce a new contact resistance to thermal transport in the graphene-polymer nanocomposites. The effect of this contact resistance has never been considered before. In this lecture, we present a new theory of thermal conductivity that includes both interfacial Kapitza resistance (filler-matrix type) and the graphene-graphene contact resistance (filler-filler type). To account for the effect of graphene-graphene contact, we treat the development of filler networks as a statistical process that can be described by Cauchy’s cumulative probabilistic function. With it, a new effective medium theory with a percolation threshold, Kapitza resistance, and graphene-graphene contact resistance is presented. We highlight this new theory by comparing it to four sets of latest experiments on the conductivity of graphene/epoxy nanocomposites, and demonstrate that both Kapitza resistance and graphene-graphene contact resistance are essential factors, with the latter gaining increasing importance as graphene loading increases. Several other interesting features of the theory, including the issue of percolation phenomenon and the dependence of filler shape, are also addressed.