Modeling of elasto-plastic behaviour of granular materials using multi-particle finite element simulations

The method of multi-particle finite element involving assemblies of meshed particles interacting through finite-element contact conditions is adopted to study the plastic flow of a granular material with highly deformable elastic-plastic grains. In particular, it is investigated whether the flow rule postulate applies for such materials. Using a spherical stress probing method, the influence of incremental stress on plastic strain increment vectors was assessed for numerical samples compacted along two different loading paths up to different values of relative density. Results show that the numerical samples studied behave reasonnably well according to an associated flow rule, except in the vicinity of the loading point where the influence of the stress increment proves to be very significant. The influence of relative density and initial loading path is discussed

Research and Design of a Routing Protocol in Large-Scale Wireless Sensor Networks

无线传感器网络，作为全球未来十大技术之一，集成了传感器技术、嵌入式计算技术、分布式信息处理和自组织网技术，可实时感知、采集、处理、传输网络分布区域内的各种信息数据，在军事国防、生物医疗、环境监测、抢险救灾、防恐反恐、危险区域远程控制等领域具有十分广阔的应用前景。 本文研究分析了无线传感器网络的已有路由协议，并针对大规模的无线传感器网络设计了一种树状路由协议，它根据节点地址信息来形成路由，从而简化了复杂繁冗的路由表查找和维护，节省了不必要的开销，提高了路由效率，实现了快速有效的数据传输。 为支持此路由协议本文提出了一种自适应动态地址分配算——ADAR（AdaptiveDynamicAddre...As one of the ten high technologies in the future, wireless sensor network, which is the integration of micro-sensors, embedded computing, modern network and Ad Hoc technologies, can apperceive, collect, process and transmit various information data within the region. It can be used in military defense, biomedical, environmental monitoring, disaster relief, counter-terrorism, remote control of haz...学位：工学硕士院系专业：信息科学与技术学院通信工程系_通信与信息系统学号：2332007115216

Maximum entropy principle and texture formation

International audienceThe macro-to-micro transition in a heterogeneous material is envisaged as the selection of a probability distribution by the Principle of Maximum Entropy (MAXENT). The material is made of constituents, e.g. given crystal orientations. Each constituent is itself made of a large number of elementary constituents. The relevant probability is the volume fraction of the elementary constituents that belong to a given constituent and undergo a given stimulus. Assuming only obvious constraints in MAXENT means describing a maximally disordered material. This is proved to have the same average stimulus in each constituent. By adding a constraint in MAXENT, a new model, potentially interesting e.g. for texture prediction, is obtained

PHYSICAL MEANING AND EXPERIMENTAL CHECK OF A VARIATIONAL PRINCIPLE FOR MACRO-TO-MICRO TRANSITION

It is argued that, for strongly non-linear behaviors, a fully deterministic position can hardly be maintained in the micro-macro transitions. This is due to the lack of information on the relevant boundary conditions, and to the tendency of non-linear dynamical systems to have a "horizon of predictibility". In the variational micro-macro model proposed by us, the data of the microscopic behavior plus the overall stimulus has to be supplemented by a "heterogeneity parameter". In this model, the macro-to-micro transition depends on the validity of a "principle of minimal heterogeneity" (PMH). It is shown that the PMH has a close relation to the maximum entropy principle

ON VARIATIONAL MICRO-MACRO MODELS AND THEIR APPLICATION TO POLYCRYSTALS

International audienceSome variational micro-macro models are briefly reviewed: it is shown how, starting from the Taylor model and passing through the relaxed Taylor model, a consistent intermediate between Taylor's upper bound and the lower bound (Sachs or rather "static") model was obtained. This intermediate or "inhomogeneous" variational model (indeed, it generally predicts both strain and stress to be inhomogeneous) could offer a general alternative to self-consistent models. However, the implemented version was a rather empirical model (ARMINJON [1984]) with a less well-defined status. We present current progress in the implementation of the correct version

ON VARIATIONAL MICRO-MACRO MODELS AND THEIR APPLICATION TO POLYCRYSTALS

International audienceSome variational micro-macro models are briefly reviewed: it is shown how, starting from the Taylor model and passing through the relaxed Taylor model, a consistent intermediate between Taylor's upper bound and the lower bound (Sachs or rather "static") model was obtained. This intermediate or "inhomogeneous" variational model (indeed, it generally predicts both strain and stress to be inhomogeneous) could offer a general alternative to self-consistent models. However, the implemented version was a rather empirical model (ARMINJON [1984]) with a less well-defined status. We present current progress in the implementation of the correct version