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

２１世紀ＣＯＥプログラム
「動的機能機械システムの数理モデルと設計論」‐「環境調和型エネルギーの研究教育拠点形成（水素G）」

共催講演会

開催概要

プログラム

講演要旨

講演１-Part1: Dr. Tong-Earn TAY, Progressive Damage Modeling with Element-Failure Method

It is recognized that in order to develop more rational design and damage tolerance approaches, there is a great need for accurate, realistic and practical modeling of damage progression in composite structures at the component and not just laboratory specimen levels. Experimental and analytical results at the specimen level do not always translate to observations of damage at the component or structural levels. In this presentation, we propose a novel element-failure method (EFM) with a failure criterion (SIFT, recently proposed by Boeing) for composite materials. The new approach involves nodal force modifications while leaving the material stiffness matrix unchanged. This has a number of important advantages compared to conventional material property degradation and fracture models, including computational robustness, versatility and efficiency. Damage in a three-point bend composite specimen is predicted and found to be consistent with experimental observation when the EFM is used with SIFT. Other methods of modeling damage such as element removal or material property degradation are also studied, but the correlation with experimental results in these cases is not as good. Some preliminary results for damage around open holes in laminates under tension are demonstrated and discussed.

講演１-Part2: Dr. Tong-Earn TAY, A Novel Biodegradable Nano-Scaffold for Tendon/Ligament Tissue Engineering

This talk will present a novel biodegradable nano-scaffold for tissue engineering, developed at the Tissue Repair Laboratory at the Division of Bioengineering, National University of Singapore. The research is motivated by the search for a mechanically strong but biodegradable and biocompatible scaffold for tissue engineering of tendons and ligaments. Additionally, the scaffold should be porous to enable good penetration of nutrients, and has sufficient surface area for cell adhesion, proliferation and growth. By depositing nano-fibers onto knitted scaffolds, it is possible to create a hybrid nano-scaffold that has the advantage of reducing the pore size and increasing the surface area for cell attachment, while retaining the strength of the parent knitted structure. In this way, it is possible to eliminate the need to use fibrin gel for cell delivery. It is also shown that the increased surface area and improved hydrophilicity of the nano-fibers facilitates new tissue formation and extracellular matrix synthesis.

講演２: Dr. Zihui XIA, On Selection of Repeated Unit Cell Model (RUC) and Application of Unified Periodic Boundary Conditions for Composites

Many laminated or textile composites can be seen as a periodic structure of a representative volume element. The micro-mechanical approach is commonly based on analysis of the representative volume element or so-called repeated unit cell model (RUC). In the analysis, two continuity requirements must be satisfied at the boundaries of the RUC. One is that after deformation the neighboring RUCs must satisfy continuity in geometry, i.e. they cannot be separated or interfered into each other at the boundaries. The second is that the tractions at the boundaries must also satisfy the continuity condition, i.e. those neighboring RUCs can be assembled as a not only geometrically but also mechanically continuous body after the deformation. Due to neglection of the second requirement, inappropriate RUCs and boundary conditions were applied in some previous publications. In this presentation, displacement-based unified periodic boundary conditions for the RUCs are derived. They meet strictly the above two continuity requirements and can be applied for any multiaxial loading cases. Through a 2-D illustrative example, results based on errant RUC and boundary conditions are compared with the correct ones. Subsequently, the proposed unified boundary conditions are applied to several laminated or textile composites. The results obtained are compared with available experimental or analytical data and they are in very good agreement.

講演３: Dr. Hongneng CAI, Prediction of Long-Term Strength of CFRP Laminates by Accelerating Testing Methodology (ATM) and Strain Invariant Failure Theory (SIFT)

In this presentation, Accelerating Testing Methodology (ATM) and Strain Invariant Failure Theory (SIFT) combined method will be introduced. The strain invariant failure theory (SIFT) was proposed by Gosse and others to predict the strength of CFRP laminates based on fiber and polymer matrix failure mechanism. The accelerated testing methodology (ATM) was also proposed by Miyano and others to predict the long term strength of CFRP laminates using the short term strength based on time-temperature superposition principle. The master curves of these SIFT critical parameters were constructed according to the tension and compression tests for longitudinal and transverse direction of unidirectional CFRP under various temperatures and the measuring of the time-temperature shift factor for the storage modulus of matrix resin. The long term compressive strength of CFRP quasi-isotropic laminates was predicted using the master curves of SIFT critical parameters based on ATM/SIFT combined method.

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