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The moisture absorption behavior of flax fiber-reinforced epoxy composites is deliberated to be a serious issue. This property restricts their usage as outdoor engineering structures. Therefore, this study provides an investigation of moisture in flax fibers on the performance of the flax/epoxy composite materials based on their shear responses. The ±45° aligned flax fibers exposed to different relative humidities (RH) and the vacuum infusion process was used to manufacture the composite specimens. The optimum shear strength (40.25 ± 0.75 MPa) was found for the composites manufactured with 35% RH-conditioned flax fibers, but the shear modulus was reduced consistently with increasing RH values. Although shear strength was increased because of fiber swelling with increased moisture absorption rate until 35% RH environments with good microstructures, nonetheless, strength and modulus both started to decrease after this range. A very poor microstructure has been affirmed by the SEM images of the composite samples conditioned at 90% RH environments.
Development of environment-friendly natural fiber composites has been a recent trend. However, due to the fact that natural fibers permit high level of moisture absorption from the surroundings, it can lead to weak bindings and degradation of composite properties. This paper presents an experimental study on the dynamic performance of flax fiber composite beams manufactured at different relative humidity (RH) levels. Five types of flax fiber-reinforced composite materials were made under different RH values, i.e., dry, 35%, 50%, 70%, and 95% RH, and beam samples were prepared using the composite. Impact hammer testing was conducted to measure the natural frequencies and damping of the beams. It was found that for the first three modes, while the resonant frequencies are very close for most samples, there is a clear drop of frequencies for the composite fabricated at 95% RH. Along with an increase of the RH level, the damping ratios for all the three modes have reported a slight increase, but the variation is not significant.
The characteristics and atomic mechanisms (physics) of processes of thermal desorption of deuterium from isotropic graphite at temperatures 700–1700 K are considered.
The aim of the current work was to illustrate the effect of the fibre area correction factor on the results of modelling natural fibre-reinforced composites. A mesoscopic approach is adopted to represent the stochastic heterogeneity of the composite, i.e. a meso-structural numerical model was prototyped using the finite element method including quasi-unidirectional discrete fibre elements embedded in a matrix. The model was verified by the experimental results from previous work on jute fibres but is extendable to every natural fibre with cross-sectional non-uniformity. A correction factor was suggested to fine-tune both the analytical and numerical models. Moreover, a model updating technique for considering the size-effect of fibres is introduced and its implementation was automated by means of FORTRAN subroutines and Python scripts. It was shown that correcting and updating the fibre strength is critical to obtain accurate macroscopic response of the composite when discrete modelling of fibres is intended. Based on the current study, it is found that consideration of the effect of flaws on the strength of natural fibres and inclusion of the fibre area correction factor are crucial to obtain realistic results.
The methodology of the approximation and interpretation of thermal desorption spectra (TDS) of hydrogen in some carbon nanostructures and graphite has been developed and applied for such materials.
The methodology is based on a definite approximation by the symmetrical Gaussians of the hydrogen thermal desorption spectra, obtained by using one single heating rate, for carbon materials and nanomaterials, and a definite processing of the Gaussians, in the approximation of the first-order reactions and the second-order ones. It results in determining (with a satisfactory accuracy, for the further physical analysis), from TDS data of one single heating rate, the activation energies and pre-exponential factors of the rate constants of desorption processes corresponding to the main TDS peaks with different temperatures of the maximum desorption rate. The developed methodology contains several successive steps of its implementation, including the use of several “criterions of truth” and the final verification and/or modification of the results, with the help of numerical modeling methods. This technique is not less informative, but much less time-consuming in experimental terms compared to the generally accepted classical Kissinger method, which demands using of several heating rates, and has strict limits of applicability. Furthermore, the methodology allows one to reveal physics and atomic mechanisms of the main desorption processes through thermodynamic analysis of the obtained peak characteristics and comparison with the corresponding independent experimental and theoretical data.
The purpose of such a methodology is to further reveal the weakly studied physics of the main states of hydrogen in carbon materials and nanomaterials, and not the thorough detailed mathematical description of the spectra. For this case, both the large difference and the large spread of the known experimental and theoretical values of the thermodynamic characteristics of the main desorption processes, important for hydrogen storage problems, are also taken into account.
In our present paper, we approach the mixed problem with initial and boundary conditions, in the context of thermoelasticity without energy dissipation of bodies with a dipolar structure. Our first result is a reciprocal relation for the mixed problem which is reformulated by including the initial data into the field equations. Then, we deduce a generalization of Gurtin’s variational principle, which covers our generalized theory for bodies with a dipolar structure. It is important to emphasize that both results are obtained in a very general context, namely that of anisotropic and inhomogeneous environments, having a center of symmetry at each point.
Bone Cement
(2020)
This book provides an overview of the composition of polymeric and ceramic bone cements. It also discusses complex, biomimetic structures based on biomaterials, such as cells and bioactive molecules, which more closely resemble natural bone
The first chapter describes the main concepts of the cementation process and the parameters affecting it, while the second chapter focuses on the composition and structure of candidate biomaterials. Lastly, the third and fourth chapters present recent research aimed at improving the ability of naked biomaterials to enhance bone healing by adding cells and bioactive agents.
This study aid on numerical optimization techniques is intended for university undergraduate and postgraduate mechanical engineering students. Optimization procedures are becoming more and more important for lightweight design, where weight reduction can, for example in the case of automotive or aerospace industry, lead to lower fuel consumption and a corresponding reduction in operational costs as well as beneficial effects on the environment. Based on the free computer algebra system Maxima, the authors present procedures for numerically solving problems in engineering mathematics as well as applications taken from traditional courses on the strength of materials. The mechanical theories focus on the typical one-dimensional structural elements, i.e., springs, bars, and Euler–Bernoulli beams, in order to reduce the complexity of the numerical framework and limit the resulting design to a low number of variables. The use of a computer algebra system and the incorporated functions, e.g., for derivatives or equation solving, allows a greater focus on the methodology of the optimization methods and not on standard procedures.
The book also provides numerous examples, including some that can be solved using a graphical approach to help readers gain a better understanding of the computer implementation.
A Review on Dental Materials
(2020)
This book discusses the current biomaterials used for dental applications and the basic sciences underpinning their application. The most critical structures in the oral cavity are the teeth, which play a central role in speaking, biting, chewing, tasting and swallowing. Teeth consist of three types of tissue: the cementum, enamel and dentin, with bone and gingival tissue serving as supporting structures. Caries, tooth wear, trauma and mechanical defects can lead to severe facial conditions; however, correcting these defects remains a challenge for scientists and dentists. Presenting insights form a broad range of disciplines, including materials science, biology, physiology and clinical science, this book provides a timely review of the principles, processing and application of dental materials.
Stoff- und Formleichtbau
(2020)
Dieses Lehrbuch stellt die unterschiedlichen Leichtbaukonzepte anhand einfacher eindimensionaler Strukturen in sehr verständlicher Weise dar und ermöglicht einen leichten Einstieg in das Thema. Es werden nachvollziehbare Informationen und Hinweise zur Werkstoffauswahl und geometrischen Gestaltung von Bauteilen gegeben.
Der Grundgedanke dieser Einführung in die Methode der Finiten Elemente wird von dem Konzept getragen, die komplexe Methode nur anhand eindimensionaler Elemente zu erläutern. Somit bleibt die mathematische Beschreibung weitgehend einfach und überschaubar. Das Augenmerk liegt in jedem Kapitel auf der Erläuterung der Methode und deren Verständnis selbst. Der Leser lernt die Annahmen und Ableitungen bei verschiedenen physikalischen Problemstellungen in der Strukturmechanik zu verstehen und Möglichkeiten und Grenzen der Methode der Finiten Elemente kritisch zu beurteilen.
Die Beschränkung auf eindimensionale Elemente ermöglicht somit das methodische Verständnis wichtiger Themenbereiche (z.B. Plastizität oder Verbundwerkstoffe), die einem angehenden Berechnungsingenieur in der Berufspraxis begegnen, jedoch in dieser Form nur selten an Hochschulen behandelt werden. Somit ist ein einfacher Einstieg – auch in weiterführende Anwendungsgebiete – durch das Konzept (a) Einführung in die Grundlagen (b) exakte Ableitung bei Beschränkung auf eindimensionale Elemente (und in vielen Fällen auch auf eindimensionale Probleme) (c) Umfangreiche Beispiele und weiterführende Aufgaben (mit Kurzlösung im Anhang) gewährleistet.
Zur Veranschaulichung wird jedes Kapitel sowohl mit ausführlich durchgerechneten und kommentierten Beispielen als auch mit weiterführenden Aufgaben inklusive Kurzlösungen vertieft.
This Encyclopedia covers the entire science of continuum mechanics including the mechanics of materials and fluids. The encyclopedia comprises mathematical definitions for continuum mechanical modeling, fundamental physical concepts, mechanical modeling methodology, numerical approaches and many fundamental applications. The modelling and analytical techniques are powerful tools in mechanical civil and areospsace engineering, plus in related fields of plasticity, viscoelasticity and rheology. Tensor-based and reference-frame-independent, continuum mechanics has recently found applications in geophysics and materials.
This book offers an update on recent developments in modern engineering design. Different engineering disciplines, such as mechanical, materials, computer and process engineering, provide the foundation for the design and development of improved structures, materials and processes. The modern design cycle is characterized by the interaction between various disciplines and a strong shift to computer-based approaches where only a few experiments are conducted for verification purposes. A major driver for this development is the increased demand for cost reduction, which is also linked to environmental demands. In the transportation industry (e.g. automotive or aerospace), the demand for higher fuel efficiency is related to reduced operational costs and less environmental damage. One way to fulfil such requirements is lighter structures and/or improved processes for energy conversion. Another emerging area is the interaction of classical engineering with the health and medical sector.
In this chapter, to investigate the tensile behavior of CNTs, finite element models of single-walled carbon nanotubes (SWCNTs) in perfect and doped modes for common types of carbon nanotube (CNT) configuration, i.e., the armchair, zigzag, and chiral models, were generated using a commercial finite element software (MSC Marc). To create the computational models, nodes were placed at the locations of carbon atoms and the bonds between them were modeled using three-dimensional elastic generalized beam elements. Doped models were simulated by three different heteroatoms including silicon, nitrogen, and boron separately with the doping concentration ranging from 0 to 5%. Young’s moduli of all models were obtained and compared with the perfect structures. The results indicated that Young’s modulus of chiral SWCNTs is larger than the moduli of the armchair and zigzag SWCNTs in all models and incorporating the silicon and boron atoms into CNT led to a linear reduction in Young’s modulus which was most significant for silicon and less noticeable for boron. Regarding nitrogen doping, a different trend was observed that was a negligible and less conspicuous increment in the value of Young’s modulus by increasing the percentage of doping. Besides, this behavior was the same for all armchair, zigzag, and chiral configurations with the same dopant atom. The investigations also revealed that the structural irregularity and ripples, which are induced by dopant atoms, are a key factor which influences the tensile behavior of CNTs. Our results for Young’s modulus of doped CNTs are in good agreement with recent investigations.
This paper aims to analyze the stress and strain states appearing in the elbow of a tube, such as those commonly used in a city’s water supply network. The stress field is characterized by the fact that there is a significant stress increase when compared to a straight tube. As a result, the strength of such an elbow must be investigated and guaranteed for such a network to be well designed. A practical solution used is to anchor the elbow in a massive concrete block. The paper compares the stress field that occurs in the elbow when it is free, buried in the ground, and when it is anchored in a massive concrete block. Furthermore, we investigate how a crack appears and propagates in the elbow. This happens especially for the elbow buried in the ground where the stress and strain are higher than when the elbow is anchored in concrete. The results obtained can be used in the current practice in the case of water supply networks made by high-density polyethylene pipes.