107 軟質発泡材料の圧縮特性解析手法の開発(OS9 オーガナイズドセッション《計算力学と数値シミュレーション》)

Composite with nanometric particles have been used as a structural reinforcement to improve the mechanical properties in polymeric materials. The use of graphene has shown excellent results such as Young's modulus of 1 TPa, tensile strength of about 130 GPa, thermal conductivity of 5000 W/mK, electrical conductivity of up to 6000 S/cm, in addition to presenting great carrier mobility of loads of 2x105 cm2.V-1.s-1. Thus, the mechanical properties in the epoxy resin based on diglycidyl ether of bisphenol A were evaluated with the addition of increasing percentages of graphene oxide (GO) in order to evaluate the mechanical properties in this material. The synthesis of GO was made from natural graphite by the Hummers method. The nanostructured composites were manufactured with a mixture of 0.1%, 0.2%, 0.5% and 1% by weight of GO. The characterizations of the materials were made by FTIR-ATR, DRX, RAMAN, MEV and TGA. The mechanical properties were evaluated by increasing the impact energy Izod absorbed in composites with lower GO content. The results showed that with the increase in the amount of graphene oxide there was an increase in the mechanical properties and that the increase in the OG charge in the matrix generated agglomerations, impairing the impact absorption in the mechanical properties of the material making it necessary a rigorous process of dispersion of these nanometric materials in the polymeric matrix.

Polymeric materials are used in several parts because their flexibility, low cost and excellent in processing. It is important to understand the some properties of polymeric materials for optimized design. The properties of polymeric materials are strongly influenced by meso-scale (10-9 10-3 m) structure such as entanglement, molecular weight distribution, and orientation, etc. But it is difficult to investigate the relationship by experimental methods because the structures are micro scale. For this reason, the detail relationship between the properties and meso-scale structure is not clear. Recently, computing power increases and increases, therefore it is possible to calculate behaviors of molecular chains. In this study, it is aimed to clear this relationship by the simulation. Mechanical properties are one of the important properties of polymeric materials. Therefore, the relationship between the mechanical properties and meso-scale properties has been investigated. But optical property is also important as well as mechanical property. In this study, we propose simulation method to investigate the relationship between the optical property and meso-scale structure. Polymeric materials are modeled by networks of molecular chain considered the meso-scale structure. In addition, polymeric materials are birefringence material. When the polymeric materials are elongated, refraction indexes of several directions become different values. A modeling of this change of refraction index is proposed. From these modeling, the light intensity distribution in a cross-section of square optical-waveguide is obtained. Then, the relationship between the change of structure of molecular chain scale and light intensity is investigated.

In order to improve the mechanical properties of the polymer materials, three kinds of samples with the same size were manufactured by the 3D printing equipment. And the materials were polycarbonate, ABS and polypropylene, respectively. After -190°C+8h cryogenic treatment, the mechanical properties such as wear resistance and hardness were tested and the functional groups and internal molecule chain changes were observed by Fourier transform infrard spectrometer. The results showed that the mechanical properties of polymer materials can be improved effectively after the cryogenic treatment. Compared with the untreated samples, the hardness of the PC, ABS and PP samples increased by 27.6%, 10.8% and 20.3% respectively. Among the three materials, the wear resistance of ABS material was improved obviously.

Custom mouthguards are used in various sports disciplines as a protection for teeth, temporomandibular joints, and soft tissues of the oral cavity from impact forces. The purpose of this research was to evaluate the mechanical properties of flexible polymeric 3D-printable materials and to select a material with the most favourable physical properties for making intraoral protectors. Four 3D-printable polymeric materials were selected for the evaluation: IMPRIMO LC IBT (Scheu-Dental, Iserlohn, Germany), Keyortho IBT (EnvisionTEC, Gladbeck, Germany), IBT (Formlabs, Somerville, MA, USA), and Ortho IBT (NextDent, Utrecht, Netherlands). A total of 176 samples (44 from each material) was 3D-printed using the stereolitography (SLA) technique. Tensile strength, flexural strength, notch-toughness, Shore hardness, sorption, and solubility tests were conducted. The materials were compared using a series of analyses of variance (one-way ANOVA) with Bonferroni post hoc tests. Statistical analyses were performed with the use of IBM SPSS Statistics 28.0.0 software (IBM, New York, NY, USA). Each material was assigned a score from 1 to 4 depending on the individual test results, and tests were given indexes according to the significance of the parameter in the mouthguard protective function. The number of points obtained by each material in each test was then multiplied by the test index, and the results were tabulated. The material with the highest result among the ones studied-most suitable for the application in mouthguard fabrication-was Keyortho IBT from EnvisionTEC.

A methodology for determining the local mechanical properties of model atomistic glassy polymeric nanostructured materials

Therapeutic mouthwashes are commonly used in dentistry to support mechanical plaque removal. Their interaction with orthodontic materials is increasingly studied due to potential effects on biocompatibility and biomechanics. To investigate in a systematic manner and evaluate the quality of the available evidence from randomized clinical trials regarding the effects of various mouthwashes on the morphology, structure, and mechanical properties of polymeric and metallic orthodontic materials. Comprehensive electronic and manual searches were conducted in seven databases from inception until August 2024. We analysed randomized controlled clinical studies that examined the impact of mouthwashes on the morphology, structure, and mechanical properties of both polymeric and metallic orthodontic materials. Data eligibility, data extraction, and risk of bias (RoB-2 tool) were performed independently. Ten studies were included, with most of them presenting some concerns in terms of bias. Chlorhexidine mouthrinse use did not affect the shear bond strength of polycarbonate brackets, the soldering alloys, as well as the stainless-steel bracket surfaces, but increased the roughness and friction of stainless-steel wires. The corrosion and mechanical properties of NiTi wires were not significantly affected by chlorhexidine. Rinsing with fluoride solutions increased surface roughness of NiTi wires, with more pronounced effects seen in acidulated fluoride solutions. While yield strength increased, no significant impacts on unloading force or modulus of elasticity was observed. Mouthwashes containing Salvadora persica did not significantly alter the surface topography of stainless-steel brackets and the roughness of stainless-steel archwires. The evidence from randomized clinical trials suggests that chlorhexidine- and fluoride-containing mouthwashes may impact the structure and certain mechanical properties of stainless-steel and NiTi archwires. While study limitations exist, clinicians should be mindful of possible effects on orthodontic treatment. Open Science Framework: osf.io/hz6wk.

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

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

Supramolecular polymeric materials have received much attention in recent years due to the fabrication of supramolecular materials with mechanical properties and stimuli-responsive properties in response to polymeric designs based on noncovalent cross-linkers. Host–guest interactions are useful noncovalent interactions that can be employed to realize supramolecular materials. To understand the relationship between the mechanical properties of supramolecular polymeric materials based on host–guest interactions and the molecular structure of guest molecules on the polymer side chain, we prepared supramolecular hydrogels cross-linked by inclusion complexes between cyclodextrin (CD) and cationic alkyl guests on the polymer side chain. The mechanical properties were influenced by an electric barrier due to the cationic group, CD cavity size, length of the guest unit, charge number of the electric barrier, and reduction responsiveness. Although the introduction of an electric barrier to the end of the alkyl gue...

The development of a new polymer materials depends on properties and it typically involves synthesizing a lot of compounds that finally becomes a new materials. This process is very expensive and take a long time. Therefore, the accurately prediction of the mechanical properties of polymer materials are required for understanding the rationale behind those predictions would be a valuable knowledge to the material studies. This work proposed the extreme gradient boosting to predict the mechanical properties of polymer materials. The model were developed, learn and the existing mechanical properties dataset. Then, the models were used to predict the mechanical properties for polymer materials. The predicted mechanical properties values were compared with the laboratory experimental results to validate the models. The experiment results have shown that the model could significantly enhance to predict the mechanical properties of polymer materials. In which way, this work could solve the problem of the polymer material and improve the efficiency of prediction obviously. This work evaluated the model with the logarithmic loss function, and the random forest classifier is used to test the model with all the features. Furthermore, this study enhance to reduce both time and cost of polymer material development. Even though, the accuracy of the predictions are not high enough, it has caused the insufficient number of sample in the dataset and the collection of data is widely scattered.

This paper describes four aspects of the work which has been performed by individuals within my research group during the past five years. The first subject discussed is the effect of pressure and environment on the yield and fracture behaviour of plastics. Secondly, a description is given of micro deformation processes in amorphous polymers, with emphasis on the control of the transition from the crazing to the shear banding modes of irreversible deformation. The third subject discussed emphasises the importance of the adhesive bond in composite materials. In addition to the usual concern with chemical interactions at the interface, some recent work is described showing the importance of moulded‐in thermal stresses which can be controlled by process history. Finally, a more sophisticated multi‐composite system is dealt with, which is found in nature; namely, the relationships between hierarchial organisation and mechanical function in tendon. Whether, as a result of understanding biological composites of this type, innovative synthetic materials will immerge makes for interesting speculation at the present time.All of the subjects described contain many unsolved questions, and I am hopeful that these will provide us with useful and interesting territory for research in the future.

Effect of temperature and ageing on the mechanical properties of dental polymeric composite materials

Incorporating topologically nontrivial molecules (e.g., catenanes) is an emerging strategy for tuning properties of polymer networks, but the fundamental roles of these molecules remain poorly understood. Herein, we report a unified gel system employing isomeric linkers with distinct topologies, which allows for cross-gel comparison and elucidation of how topology governs mechanical and dynamic properties in polymeric materials. Our gels feature a panel of phenanthroline-based macrocyclic molecules as linkers, which adopt structures including a large macrocycle, a flexible catenane, and, through metal coordination, a rigidified catenane and a twisted figure-eight structure. By mechanical and thermodynamic analysis and simulations, we identify topology-dependent coordination and conformational entropy as the key factors driving the gels' mechanical responses. We reveal that the toughness and energy dissipation capacity of the gels correlate directly to the conformational change allowed by each topology, proportional to the "hidden length" that can be released by the linkers. Surprisingly, metal-ligand bonds primarily tune the initial linker conformation rather than dissipate energy through bond dissociation, while they simultaneously enhance network dynamics. Our findings could guide the selection of topological molecules for engineering advanced polymer materials.

Developing innovative materials with superior properties has been a major engineering challenge. Rationally designed polymer nanocomposites represent an emerging field that offers materials with enhanced mechanical properties and added functionalities. Here, we propose a computational methodology for predicting the heterogeneous mechanical behavior of model polymer nanocomposites that combines deep learning and detailed atomistic simulations. Atomistic simulations, while crucial for unraveling the mechanical behavior of composite materials, often focus on global mechanical properties by applying macroscopic strain and calculating the overall stress response. However, exploring the distributions of mechanical properties in heterogeneous polymer systems requires the computation of stress and strain fields for each atom within the simulation box. Our approach is based on a hierarchical data-driven computational framework that involves a nano/micro/macro coupling approach to predict the mechanical properties of polymer nanocomposites. We introduce a physics-aware deep learning method to predict the distribution of mechanical properties of model nanocomposites by directly computing stress and strain at the atomic level. Incorporating a set of physics-based constraints in the loss function encourages the deep learning model to follow the physical symmetries of the underlying system and to accurately predict the values of local stress and strain data in any arbitrarily chosen domain of the model systems. The proposed framework is transferable over systems with different volume fractions of nanofiller while being computationally efficient and effectively agnostic to the underlying microscopic model.

The state of stress under tension-shear load was investigated experimentally and analytically on the single spot welded lap joint of single shear splice.Specimens were made from mild steel sheet of 1.0mm thickness. The stress distributions on the surfaces of the specimen were examined experimentally by the brittle coating and strain gage methods.According to the experimental results, the state of stress in the joint under tension-shear load appeared to be determined by the following factors.(i) Plane stress distribution near the weld nugget caused by the local transmission of load.(ii) Bending in the longitudinal direction resulted from the offset of lapped plates.(iii) Bending in the transverse direction, occured secondarily by the superposed effect of factors (i) and (ii).To clarify the state of stress owing to factor (i), the plane stress distribution was examined by the experiments on the middle plate of single spot welded double shear lap joint in tension, which was not affected by bending. Two-dimensional analysis by the finite element method was also made of the assumption of the idealized“Plane Model”.In connection with the state of stress due to longitudinal bending (factor (ii)), two-dimensional finite element analysis was employed on the“Section Model”of single spot welded single shear lap joint.Finally, the experimental stresses on the single spot welded single shear lap joint were compared with the analytical values, which were obtained by superposition of the stresses computed by Plane and Section Models.The results obtained are as follows:(1) In the stress measurement on the single spot welded single shear lap joint, the peak stress at 3mm distant above the nugget edge attained the value 3.9 or -1.3 times of the nominal tensile stress on the inner or outer surface of lapped plate, respectively.(2) The plane stress distribution computed by Plane Model agreed fairly well with the experimental result observed on the middle plate of double shear lap joint. In the finite element analysis by Plane Model, the lapped plates of the joint were doubly defined in the same plane.(3) The stress concentration factor deduced from the plane stress distribution was 2.2∼2.3 at the nugget edge of the joint, where the width of joint was 25mm and the nugget diameter was 5φ.(4) At the representative positions on the inner and outer surfaces of single shear lap joint, the superposed values of the stresses computed on the factors (i) and (ii) corresponded well with the axial stresses obtained from the experiments.