フォーム材の力学特性への気泡構造の影響

Effects of carboxymethyl cellulose concentration on mechanical, viscoelastic properties, and thermal properties of starch/plant fiber foaming tableware materials with foam structure

The objective of this study is to develop an analytical approach for evaluating mechanical properties of polymeric foam material by the two-dimensional finite element analysis using homogenization method. From observation of cross-section structure, porosity, mean cell diameter and dispersion of cell diameter were investigated using one foam material. Those characteristics were similar in any cross-sections. As a result of the investigation, it is possible to consider one cross-section as a representative cross-section of foam material. Then, a unit cell model for numerical simulation of microscopic structure was created. Two-dimensional finite element analysis based on a formulation of homogenization theory was performed, and the analysis results were compared with a uniaxial compression test result. As a result of the comparison, the effect of foam material structure on mechanical properties was evaluated.

Artificial cartilage foam (ACF) is a novel polyurethane foam, characterized by a pore structure that is partially connected and partially closed. The present study proposes a novel mesoscale model with mixed cellular pores, and investigates the effects of parameters such as strain rate of the soft matrix, air, and interconnectivity between pores on the mechanical properties of foam materials. The research reveals that the strain rate effect of the cellular foam matrix significantly enhances the plateau stress of the foam material under high‐speed compression. Additionally, it is demonstrated that the connectivity and pore size parameters have a noticeable influence on the mechanical performance of the matrix mixed cellular foam materials. Furthermore, the investigation extends to the internal development of the material under both high‐speed and static compression, a phenomenon that is difficult to observe experimentally. The study finds that the different stress plateau regions caused by dynamic and static compression are primarily due to pore deformation, and the deformation sequence of the pores is related to their spatial positions, with pores located in the damage zone being more likely to deform. Finally, under high‐density conditions, the soft matrix results in increased lateral deformation, forming a horizontal densification zone. The methods and conclusions of this study can be applied to material design in the materials industry, providing guidance for the production of polymer foam materials.

Low density polyethylene, expanded polystyrene and expanded polypropylene: Strain rate and size effects on mechanical properties

Mechanical characterization and numerical modeling on the yield and fracture behaviors of polymethacrylimide (PMI) foam materials

Application of Cellular Material in Crashworthiness Applications: An Overview

It is necessary to evaluate the mechanical properties of foam materials at wide range of strain rates, since these materials have the strain rate dependence of strength. In this study, we evaluated the dynamic compressive behaviour of the closed-cell foam materials using the load-measuring apparatus with opposite load-cells, which is applying the drop-weight testing machine. In order to measure large deformation at dynamic strain rate range, universal rate range load-cell, which can reduce the influence of the reflected stress wave, was used. In addition, load equilibrium can evaluate using opposite load-cells which consist of movable (drop-weight) and stationary load-cells. In this study, the commercially available ALPORAS closed-cell aluminum foam was used. From the results of quasi-static tests, three deformation processes of elastic response, plateau deformation and densification were confirmed in stress-strain relation. Within the set of experiments, the closed-cell aluminum foam was locally deformed from cells with low strength and the stress variation occurred during plateau deformation, regardless of the strain rate. In addition, it was clarified that the stress equilibrium was not achieved at the dynamic strain rate. This is thought to be a phenomenon caused by local deformation of cell structure.

Foam shock-absorbing structures such as cushioned packages are often utilized to protect various products from mechanical shock and vibration during transportation. The goal of packaging design engineers is to design a cushioned package structure that improves the shock-absorbing performance and minimizes the volume of the package. Some optimization techniques, combined with computational simulation, provide engineers with a way to design an optimal structure. In this paper, we propose a modified topology optimization method suitable for a polymeric foam shock-absorbing structure under dynamic drop loads in multiple directions. Our approach uses a heuristic topology optimization method, known as the Hybrid Cellular Automata (HCA). The HCA algorithm uniformly distributes internal energy density and controls the relative density of Cellular Automata (CAs) making up the design space. This allows the algorithm to maintain or increase the performance of shock absorption and to decrease the amount of material. In particular, this paper presents a modified Solid IsotropicMaterial with Penalization (SIMP) model for foam materials, which parameterizes the design region and interpolates the material properties. We attempt to optimize a simple bottom-cushioned package for a refrigerator by using the proposed foam SIMP model with commercial software: LS-DYNA for drop dynamic simulation and LS-OPT/Topology for the HCA algorithm. Drop simulation and topology optimization are performed considering multiple drop-directions. As a result, our method removes elements that are not related to the shock-absorption performance and provide an optimal cushioning structure using foam material.

The paper gives an overview of issues relating to the characterisation of the progressive collapse of core cellular materials used in sandwich construction. The specific structural application addressed is foreign object impact, and in this case the core cellular material is subject to multi axial stresses, progressive collapse and possible rupture. Crushable foams have been used for many years as core materials. Possible foam materials are based on polymers (e.g. Divinycell, Rohacell), metals (e.g. Alporas) and graphite. It has been shown that the mechanical properties of cellular materials, e.g. elastic behaviour, uniaxial crush and densification, are dependent on the cell geometry, on the cell size (foam density) and on the parent material.

Micro and meso‑scale modelling of the response of transversely isotropic foam to impact — a structural cell-assembly approach

<div class="htmlview paragraph">Various foam models are developed using LS-DYNA3D and the model predictions were validated against experiments. Dynamic and static stress-strain relations are obtained experimentally for crushable and resilient foam materials and used as inputs to the finite element analyses. Numerous simulations were carried out for foams subjected to different loading conditions including static compression and indentation, and dynamic impacts with a rigid featureless and a rigid spherical headform. Comparisons of the results obtained from different foam models with test data show appropriate correlations for all the cases studied. Parametric studies of the effects of tensile properties of foam material and the interface parameters on foam performance are also presented.</div>

Water plays an important role in the physicochemical and mechanical properties of Nafion (poly tetrafluorosulfonic acid) and cellulosic materials. Due to the strong influence of hydration on the properties of these materials, the mechanism and molecular-level understanding of hydration processes are the subject of ongoing interest in food, environmental and energy science. Nafion is a sulfonated tetrafluoroethylene polymer that represents a prototypical polymer electrolyte membrane (PEM) material. PEMs are often composed of a hydrophobic backbone with a strongly hydrophilic region (e.g., sulfonic acid moieties), which are directly attached to the backbone or through a pendant group. The application of Nafion in fuel cells as PEMs necessitate that the hydration properties of the membrane play an important role for maintaining high proton conductivity and mechanical properties. Cellulose on the other hand is one of the most abundant and low-cost renewable biopolymers with unique hydration properties. The hydration of cellulose impacts its biodegradability, recyclability and tunable physicochemical properties for various applications employing composite materials, pharmaceutical delivery systems, paper production, fibers and biofuel production. One of the challenges in the development and valorization of cellulose-based materials relates to its insolubility in aqueous media and conventional solvents. Therefore, evaluation of the hydration properties of Nafion and cellulose materials is required in order to characterize their physicochemical properties. Studies of the hydration properties of these materials include dielectric, spectroscopic techniques (NMR and IR), dynamic vapor sorption, differential scanning calorimetry (DSC), viscometry and computer simulations to determine the structural, kinetic and thermodynamic properties associated with such hydration processes. DSC is a sensitive and versatile thermal analysis method for the study of hydration phenomena, thermal behavior and thermodynamic state of water in hydrated macromolecular systems. The aim of this mini-review is to provide an overview of recent DSC studies relevant to aspects of hydration phenomena for Nafion and cellulose. This overview will contribute to an improved understanding of the hydration properties of Nafion and cellulose materials for applications that involve hydration phenomena.

Physical cues, such as extracellular matrix stiffness, direct cell differentiation and support tissue-specific function. Perturbation of these cues underlies diverse pathologies, including osteoarthritis, cardiovascular disease and cancer. However, the molecular mechanisms that establish tissue-specific material properties and link them to healthy tissue function are unknown. We show that Runx2, a key lineage-specific transcription factor, regulates the material properties of bone matrix through the same transforming growth factor-β (TGFβ)-responsive pathway that controls osteoblast differentiation. Deregulated TGFβ or Runx2 function compromises the distinctly hard cochlear bone matrix and causes hearing loss, as seen in human cleidocranial dysplasia. In Runx2+/⁻ mice, inhibition of TGFβ signalling rescues both the material properties of the defective matrix, and hearing. This study elucidates the unknown cause of hearing loss in cleidocranial dysplasia, and demonstrates that a molecular pathway controlling cell differentiation also defines material properties of extracellular matrix. Furthermore, our results suggest that the careful regulation of these properties is essential for healthy tissue function.

1. Rigid polyurethane foams are feasible for encapsulation of intermediate voltage low-energy networks. From the knowledge of the dielectric system, design packaging voltages in 3 to S kv RMS range appear to be practical. This type of packaging would require careful attention to exposed electrode design so as to reduce dielectric stress levels to acceptable values adjacent to terminals. 2. Foam materials with an adequate closed cell structure will provide elevated insulation in a varying atmospheric environment. This includes changes caused by elevated temperatures and high altitudes as well as prolonged operation while passing through the atmosphere and in the vacuum of space. Thus the advantages of a solid encapsulant or a hermetic sealed container can be achieved by foams. 3. The length of time for which foams may be serviceable has not yet been determined quantitatively at room temperatures. At elevated temperatures in a vacuum environment gas diffusion will increase and a shorter effective life is expected. 4. The foam dielectric provides a design advantage over rigid and elastomeric insulating materials in that it has a unique combination of properties. It is light weight, mechanically and chemically stable, insulates in the intermediate voltage range and is suitable for use with many phases of network packaging for aerospace vehicles. 5. The ease of repairability further enhances the desirability of foam packaging for aerospace applications since complex network packages are seldom made in duplicate. In addition, with the advent of short-delivery schedules for most of today's space vehicles and the lag of component reliability data, part or electronic component replacement in existing hardware is becoming more common. 6. The designer must also consider the need for dissipation of thermal energy when using foam. Thermal profiles should be established under operating conditions to determine if the energy dissipation will cause excessive heating of the components. High energy dissipation with foam materials will be a problem in both the atmosphere as well as in space. Contrary to this problem, foam will offer thermal insulation which quite often is desirable with spacecraft.

It is indeed a pleasure to have the opportunity to discuss some aspects of education in materials. The subject of this symposium is not new, for education in materials has received the attention of many individuals. One of the first of whom we have a record is Vitrivius, a builder who lived in Rome in the first century. His writings are contained in a publication, Ten Books of Architecture. In them he describes and discusses the properties and the utilization of building materials. Much of what he has to say is almost identical with what can be found in certain college textbooks now being used in materials courses. Not only the same information but also the same methods of approach to problems are being given some of our engineering students today in their instruction in materials that was being given 2000 years ago. Of course, the physical and mechanical properties of certain natural building materials have not changed appreciably since the days of Vitrivius. Granites and limestones are about as they were in the first century, and the botanical processes influencing the properties of oak and cedar have not altered in 20 centuries. During the 2000-year interval the properties of some man-made materials have not been improved much either. The strength of concrete, for example, has changed less than an order of magnitude, although potentially the change could be four orders of magnitude. Until only a few years ago the same comment was true for metals. However, the uses to which the materials are put, the demands upon them in modern design, and our understanding of their properties have altered greatly. As one example, our understanding of metals has now progressed to the point where fibers having strengths nearly equivalent to their theoretical maximum strength of a few million pounds per square inch can be produced. In other instances, new materials have been designed and produced to meet desired specifications. Revolutionary developments of this type have directed attention to the need for reconsideration of instruction in materials. At the outset, it should be recognized that programs in materials include not only the formal courses in college, but also on-the-job training and informal self-study after graduation. Our question is whether or not present-day education in materials is well adapted to adjust the outlook of the engineer to the current revolutionary developments that will greatly affect the utilization of materials a few decades hence.