The 21st Century COE Program
"Center of Excellence for Research and Education on Complex Functional Mechanical Systems"

---

材料グループ特別講演会

下記の要領にて，来る9月16日（木）に21世紀COE特別講演会を開催させて頂きます．

外部環境の下で多数要素の相互作用により生み出される現象，すなわち，複雑系の観点から材料研究を捉えた場合，その対象は非常に多様となります．今回のCOE特別講演会は，原子レベルからのマルチスケール材料力学，適応・自己再生能力を有するバイオ材料工学，ミクロな材料の複合化が作り出すメゾレベルの材料挙動等について，それぞれの分野における最新の研究についてご講演いただきます．「複雑系」＋「材料研究」を考える上で，それらの多様性と共通普遍性について議論する機会となれば幸いです．ふるってご参加下さい．

北條 正樹（工学研究科機械工学専攻）

開催概要

プログラム

講演要旨

The role of ab initio electronic structure calculations in multiscale modelling of materials

Prof. Mojmir Sob (Institute of Physics of Materials, Academy of Sciences of the Czech Republic)

Most technologically important material properties and phenomena involve multiple length and/or time scales, for example elastic properties of polycrystals and other composites, plasticity, phase transformations, processing and synthesis of materials, fracture etc. We can model the problem either at different length/time scales separately and pass information between distinct simulations at the separate scales ("series multi scale modelling") or at two or more length/time scales simultaneously so that the different scales are linked within the same simulation ("parallel multiscale modelling"). In the present talk, we discuss first briefly the general aspects of multiscale modelling in materials science, including ab initio electronic structure calculations, atomistic and microstructure modelling as well as continuum mechanics. Then we concentrate on the role of ab initio claculations in particular and show how to link the ab initio and atomistic modelling. Our approach is illustrated by discussing phase transformations and magnetic properties of grain boundaries in iron, theoretical strength of materials, segregation of impurities at grain boundaries and modelling of grain boundary structure in nanocrystalline nickel.

Engineering skeletal reconstruction

Prof. Scott J. Hollister (Departments of Biomedical Engineering, Surgery, and Mechanical Engineering, The University of Michigan)

Tissue engineering utilizes a porous biomaterial scaffold together with biofactors like cells, genes and proteins to regenerate damaged tissue instead of merely replacing it. The porous scaffold must fulfill three primary functions: 1) fit complex 3D anatomic defects, 2) provide temporary function (usually mechanical) in the defect, 3) enhance tissue regeneration through biofactor delivery. In addition, the biomaterial may be degradable. These requirements present significant challenges and require a systematic approach for engineering scaffold/biofactor constructs. We have developed such a systematic approach that integrates homogenization based scaffold design, free-form scaffold fabrication, and in vitro testing utilizing both cell and gene based therapy approaches to address the challenges of tissue engineering. This talk will cover image-based scaffold design including microstructure topology optimization, scaffold fabrication using solid free-form fabrication (SFF) techniques, and the use of these scaffolds to deliver cells transduced with BMP-7 genes to regeneration bone tissue.

A micro/macro-mechanical approach of first ply failure in CFRP

Prof. Karl Schulte (Polymer Composite Section, Technical University Hamburg-Harburg)

The state of the art criteria to describe the failure of composite structures are based on homogenized properties and they cannot regard on the micromechanical level of fibre and matrix. On the micromechanical level many models exist to describe the fracture phenomena observed in composites. High performance composites are cured at higher temperatures, after curing and cooling the composite is subjected to residual stresses. The resulting tri-axial stress state has a strong effect on the mechanical performance of composites. It is revealed that the presence of residual stresses reduces the transverse strength to failure. In the past three decades numerous researchers investigated residual stresses in composite materials by using analytical, numerical and/or experimental approaches. Most analyses regard on thermal expansion mismatch between the constituents. However, analytical calculations have strong limitations concerning boundary conditions, nonlinear material behaviour, large strains etc., the finite element analysis is a suitable method to investigate the residual stresses on the micromechanical level. Fiedler, et al. studied the residual stresses by finite element and photo elastic analysis with regard to the influence on interfacial contact. In former work, the authors showed that the local fibre volume fraction (resin rich area to fibre contact) has a strong influence on the residual stress state and initial matrix failure. The failure behaviour of epoxy resins was studied and discussed in detail. Prediction of residual stresses and induced matrix failure requires knowledge of the temperature dependent mechanical and thermal properties of the constituents. The temperature dependent nonlinear matrix behaviour is one of the most important among them, because matrix plasticity and creep during curing at high temperatures lower the residual stress state predicted for the elastic case. However, transferring the results obtained on micromechanical level to the level of composite structures is difficult. The present work regards on this problem. The finite element analysis is used to link the micromechanical approach with the homogenised description of composite structures. Considering 3 point bending specimens made of CFRP with unidirectional 90° fibre orientation and cross ply laminates with varying numbers of 0° and 90° oriented layers. The results obtained by the modelling are in good agreement compared to the results from in-situ 3 point bending tests carried out in SEM.

From microstructure, morphology and properties of mesophase and crystalline interfaces to engineering-scale performance of composites

Prof. Gad Marom (Casali Institute of Applied Chemistry, The Hebrew University of Jerusalem)

Mesophase and crystalline interfaces are formed when one constituent material (phase) acts as substrate for another. The role of the substrate, which in composites is the fiber reinforcement, is to shape the crystalline structure and habit of the second phase, the matrix, both at the nano- and micro-meter dimensions. In the most common mechanism at the nano-scale level, the substrate behaves as template for epitaxial nucleation, which eventually results in ordered microcrystallinity in the over layer. In another mechanism of nano-scale (molecular) dimensions, the substrate behaves as template for self-assembly to form an ordered mesophase in the over layer. At the micro-scale level, the influence of the substrate derives from its surface topography, such as roughness patterns, which determine the crystalline morphology and habit of the over layer. In fiber reinforced composite materials, the fiber surface may act as a substrate for shaping the matrix, which will then acquire new properties that are different than those of its bulk. A number of examples of composite systems will be presented in detail, introducing state-of-the-art techniques of crystallographic and morphological analyses, including synchrotron microbeam in-situ WAXS and quantitative AFM. These examples will include crystalline interfaces in a number of composite systems based on semicrystalline thermoplastic matrices such as high density polyethylene, polypropylene and nylon 66. A concentric cylinder model will be presented for a composite material with a mesophase or crystalline interface, to account for the new properties of the matrix. The model describes the thickness and relative volume of the interfacial layer as a function of the volume fraction of the fibers. It shows that at high fiber volume fractions even with very thin interfacial layers, the full volume of the matrix is invaded by the interfacial layer. Finally, results of full-scale properties of different composites will be discussed to relate the new properties of the orientated interfacial layer to those of the composite material. Emphasis will be given to mechanical properties in the fiber direction.