法国LAMPA实验室Amine Ammar教授和 Saber EL AREM课题组招CSC全职博士
LAMPA实验室隶属于法国国立高等工程技术学校（Arts et Métiers ParisTech），致力于在先进制造工艺以及材料和结构的耐久性领域开展基础和应用研究。法国国立高等工程技术学校为法国最负盛名的工程师院校之一，也是巴黎高科集团（ParisTech）的创办成员之一，与CSC有多个合作项目。Amine Ammar和Saber EL AREM均为LAMPA实验室全职教授，希望招收2023年秋季入学的CSC全职博士，学制为3-4年，目前可选择的课题有《Seismic cycle characteristics and dependence on rock rheology and friction》和《Failure modeling of cementitious composites in the framework of gradient damage approach》，详细描述见下文，感兴趣的同学可以直接发送邮件至Amine.AMMAR@ensam.eu，Saber.ELAREM@ensam.eu，尤其欢迎具有地球物理、地质工程、岩土工程、固体力学、土木工程、材料等专业背景的申请者。
1-《Seismic cycle characteristics and dependence on rock rheology and friction》
该课题由Amine Ammar教授, Saber EL AREM教授和 Soumaya Latour教授（图卢兹三大）联合指导。
Understanding how earthquakes initiate on active faults and whether this initiation could be detected is an issue of foremost importance in seismology. However, because the physical process of co-seismic rupture corresponds to the development of an instability, its physics is highly non-linear, and involves many scale-dependent processes. This leads to fundamental challenges in studying rupture initiation and propagation whether it be theoretically, numerically or experimentally.
An experimental setup has allowed interesting observations of rupture nucleation, in this study we aim to reproduce numerically the experimental results. Nucleation on a heterogeneous interface with a periodic friction heterogeneity has been considered. It was shown experimentally that a large scale globally accelerating nucleation process can develop on a heterogeneous fault, while the details of the rupture propagation are controlled at smaller scale by the friction heterogeneity.
The numerical model will help in better understanding of the rupture process by comparing with the experimental results and discussing their relevance with respect to recent theoretical developments and to earthquakes preparatory processes. We want to derive a reliable friction law to be used in numerical exploration of seismic cycle characteristics and dependence on rock rheology and friction.
2-《Failure modeling of cementitious composites in the framework of gradient damage approach》
The degradation of quasi-brittle materials such as concrete and cementitious composites are generally brittle at the microscopic scale and ductile at the macroscopic scale (damage). Moreover, this quasi-brittleness is depending on the heterogeneous microstructure of the material (volume fraction, shape and size of the inclusions as well as their nature and the contrast in rigidity between the cementitious matrix and the inclusions), which often generates a different failure modes. This often results in a transition from a brittle failure mode to a more ductile mode or vice versa, and generates a size effect on the compressive strength of cementitious materials whose apprehension and modeling are complex. Indeed, several types of inclusions with different physical and mechanical properties can be incorporated into a cementitious matrix depending on the desired application. In ordinary concrete of common density, these inclusions are natural aggregates of sand and gravel which are more rigid than hardened cement paste.
On the other hand, in a light concrete, the inclusions are very flexible light aggregates or even air bubbles assimilated to pores. Furthermore, these inclusions can have different shapes and sizes and can be regularly or randomly distributed in the cementitious matrix.
Despite the abundance of scientific literature on the subject of compressive failure of quasi-brittle cementitious materials, this subject remains topical. In fact, there are several ways to model it. Some are purely empirical since they are based on tests on real materials in which the microstructure is varied. This approach is costly because it requires a very large number of tests to be able to correctly understand the failure mechanisms and predict all the effects of the microstructure of the material studied on its compressive strength.
Other approaches are purely numerical and are based first on the modeling of the real or idealized microstructure of these materials and then on the adoption of a nonlinear constitutive law modeling the behavior of the cementitious matrix placed between the inclusions which are generally assumed to be elastic or perfectly rigid. This approach is efficient but costly in terms of numerical implementation and computation time. Moreover, certain local numerical models exhibit problems of pathological localization of the damage or concentration of the stresses in points of the cracks leading to problems of nonconvergence of computation or mesh dependence of the results. Recently, alternative methods for the numerical simulation of brittle fracture phenomena have appeared and where discontinuities are not explicitly introduced into the solid. The major advantage of using a phase field is that the evolution of the fracture surfaces stems from the resolution of a coupled system of PDE. It is not necessary to explicitly follow the topology of the crack nor to constrain its path a priori. Thus, this approach will be adopted in the PhD proposal to simulate the complete failure process of cementitious composites containing different types of inclusions.
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