Hidetake Yamamoto

Two-dimensional modelling of solid-fluid composites

The purpose of this paper is to apply biomimetic-designed composites to artificial structures. From the results of numeric modelling analysis in biomechanics, we have learned the bone structures optimized to lighten weight and understood that the solid-fluid composite structure of the cancellous bone at the joint part works to distribute the joint load perfectly. In this paper, the two-dimensional honeycomb structure filled with fluid was investigated by way of a simplified solid-fluid composite material model of the cancellous bone. Hybrid finite element analyses illustrated that the solid-fluid phase interaction is effective in dispersing compressive load. In-plane indentation tests were carried out and in-plane deformation distributions of the solid-fluid composite specimens were measured. Consequently, as for the solid-fluid composite specimens whose cells were filled up with glycerine, a good enough cell deformation mode was obtained.

Development of solid–fluid biomimetic composites: Load dispersion effect of controlled hydrostatic pressure

Abstract The purpose of this research project is to apply biomimetic-designed composites to artificial structures. The natural bone is an optimum-designed structural system to support the living body. So, it is very useful in developing original optimum designs of the composite materials to study composite structures of the bone. Looking at the bio-joint mechanism, the solid–fluid composite structure of the cancellous bone has likely important effect in the load transmission. In this study, the solid–fluid composite model of the cancellous bone was made by using honeycomb structure. Static-indentation tests were carried out, and in-plane deformation conditions of the specimens were measured quantitatively. At first, the load dispersion effect of two kinds of fluid was examined by using small cell size Al honeycombs. Air and glycerine were sealed in each hexagonal cell of the specimens with thin films, respectively. But the film adhesion did not affect the deformation of honeycomb structures. Even the hydrostatic pressure of air greatly affects the in-plane deformation condition of the solid phase. Next, the load dispersion effect of the controlled hydrostatic pressure was examined by using large cell size Al honeycombs. The propagation of air hydrostatic pressure in the specimens was controlled by making a small hole in the specific cell walls of the honeycomb structure. Consequently, as for the solid–fluid composite models, the possibility of the optimum control of the compressive load dispersion was expected.

Optimum design of artificial joints considering initial fixation of prosthesis

Living bone is a stratified structural system which is functionally built of many substructures. Loads applied on the articular surface are transmitted through the articular cartilage, the subchondral bone and the cancellous bone to the shaft bone. The prosthesis for the artificial joint is a material replacing the articular cartilage and the subchondral bone. So, it is important for an effective design of the artificial joint possessing the mechano-compatibility to living bones to understand the mechanical behavior of them sufficiently. The purpose of this paper is to investigate the optimum design of the artificial joint by considering the better plate shapes of the prosthesis for the fixation on the cancellous bone under compressive loading based on the mechanical behavior of the subchondral bone. Consequently, the effectiveness of the optimum designs of the artificial joints using the arched plate prostheses is shown numerically.

Optimum Structure of Knee Prosthesis Using Laminate Composites Considering the Stress Dispersion at Prosthesis/Bone Interface

Composite materials are useful as replacement materials for human bone, signifying complicated mechanical characteristics because of many degrees of freedom of design. In the previous work, the authors indicated a numerical approach to force transmission from artificial knee joint (prosthesis) to cancellous bone by finite element analysis and verified the usefulness of composite materials for knee prosthesis. This paper describes a design procedure of replacement materials for the prosthesis based on the theoretical model of cancellous bone structure. Optimum ply construction and configuration of laminate composites for the prosthesis are analysed by considering stress dispersion at the prosthesis/bone interface.

Static Load Dispersion Analysis of Solid-Air Composites-Effect of Adhesive Film on the Load Dispersion-

In order to propose a new movement of the composite material design, the load dispersion of the solid-air composites caused by the hydrostatic pressures is investigated by applying numerical analysis. To simplify the evaluation of the load dispersion, the admissible stress field is supposed, where each stress field of closed cell is independent and that two different fields being in both sides of a cell wall satisfy the equilibrium of forces through the cell wall. The non-linear deformation under indentation was incrementally simulated by using the finite element formulation based on displacement method. The effect of adhesive film on the load dispersion is considered in the numerical model. It was shown that the assumption of admissible stress field on the interfacial load transmission is useful in evaluating the static load dispersion because the numerical results were well in agreement with the experimental ones. And it was clarified that a few structural design parameters become effective for the load dispersion.

LOAD SUPPORT OF FRC CYLINDERS UNDER COMPRESSION

ABSTRACT The purpose of this research is to look for the optimum structure applied FRC for load support by considering the biomimetic design. For example, cortical bone is made of FRC structures for load support in living bones. Making a start of analysis, the osteon being an structural unit of cortical bone was modelled in filament-wound (FW) cylinder. The first approximation of cortical bone was represented by the densest arrangement of the cylinders to focus on compressive behaviour of osteons. E-glass/epoxy cylinders were applied to specimens. Static compression tests were carried out to evaluate these models. On the osteon model, the smaller ply angle to the longitudinal direction gave the larger compressive strength. The larger ply angle was the more effective in hoop tension of axial compressed cylinders. On trial model for the cortical bone, compressive strength was largest when ply angle was 60 degrees. Interference force between compressed cylinders had a great influence on compressive fracture of the model.

Mechanical Behavior of Cortical Bone Under Static and Substatic Compressive Loading

Elucidation of the deformation mechanism of cortical bone is essential to estimating the biomechanical strength of long bones. Cortical bone consists of osteon and interstitial lamellae; the osteon has a composite multilayer structure consisting of collagen fibers such as helical structures and hydroxyapatite crystals. In this article, the deformation mechanism of cortical bone as a composite is clarified. A typical model of cortical bone is as a unidirectional, fiber-reinforced composite, assuming that the osteon is the reinforcing material and the interstitial lamella is the matrix. Cylindrical cortical bone specimens at angles of both 0° and 90° to the axis were obtained from bovine tibias. Static and substatic compression tests were carried out using an acoustic emission technique, and the elastic index of work done was measured in each strain step under the static test condition to estimate microfracture of the specimens. It appeared that microfracture of the specimens occurred as delamination at the interface between the osteons and interstitial lamellae or as debonding in the lamellae by deflective deformation of osteons. For static tests, the modulus of 0° direction specimens was higher than that of 90° direction samples. This was explained by the large shear force occurring in osteons of 0° direction. For substatic tests, the relationship was the inverse.