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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.
This study is concerned with the linear elasticity theory for bodies with a dipolar structure. In this context, we approach transient elastic processes and the steady state in a cylinder consisting of such kind of body which is only subjected to some boundary restrictions at a plane end. We will show that at a certain distance d=d(t), which can be calculated, from the loaded plan, the deformation of the body vanishes. For the points of the cylinder located at a distance less than d, we will use an appropriate measure to assess the decreasing of the deformation relative to the distance from the loaded plane end. The fact that the measure, that assess the deformation, decays with respect to the distance at the loaded end is the essence of the principle of Saint-Venant.
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.
Additive manufacturing offers unique possibilities to produce complex components, which would not be possible or only very difficult to be realizable with conventional manufacturing processes. The potential of additive manufacturing of aluminum alloys has already been realized in prototyping, but still offers potential in the establishment of series applications. For enabling the establishment of additive manufacturing in series applications, comprehensive knowledge about the material behavior is necessary. This study examines the torsional behavior of additive manufactured AlSi10Mg samples and shows the correlation between tensile and torsional strength. Comprehensive torsion tests with strain gauges were performed and significant directional dependencies were shown. The correlation factor in the area of torsional yield strength/tensile yield strength and torsional strength/tensile strength was determined and was compared with the yield/failure conditions according to Tresca and von Mises.
Advanced LaTeX in Academia
(2021)
Herein, the general constitutive equation of bi-phasic materials equipped with orientation tensor is presented in direct notation. The formulation is refined by some correction factors specific to natural fibre-reinforced composites; then, a planar case is derived. The necessity of local information is emphasised through the introduction of auxiliary maps, which included volume fraction and orientation data. A semi-analytical homogenisation method is introduced through finite element analysis. Auxiliary maps are shown to be a better alternative to the overall orientation of fibres. Global calculations are insensitive to local variations whilst appropriate auxiliary maps offer refined results. Considering the multidisciplinary application of orientation tensors, the proposed scheme can be used in all areas where local information cannot be disregarded.
An optimal control problem for equations with p-structure and its finite element discretization
(2022)
Application and machine learning methods for dynamic load point controls of electric vehicles (xEVs)
(2020)
From the customer's perspective, the appeal of electric vehicles depends on the simplicity and ease of their use, such as flexible access to electric power from the grid to recharge the batteries of their vehicles. Therefore, the expansion of charging infrastructure will be an important part of electric mobility. The related charging infrastructure is a big challenge for the load capacity of the grid connection without additional intelligent charge management: if the control of the charging process is not implemented, it is necessary to ensure the total of the maximum output of all xEVs at the grid connection point, which requires huge costs. This paper proposes to build a prediction module for forecasting dynamic charging load using machine learning (ML) techniques. The module will be integrated into a real charge management concept with optimization procedures for controlling the dynamic load point. The value of load forecasting through practical load data of a car park were taken to illustrate the proposed methods. The prediction performance of different ML methods under the same data condition (e.g., holiday data) are compared and evaluated.
Application of Induction Thermography for Detection of Near Surface Defects in Steel Products
(2020)
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 thesis deals with the analysis of the family policies in Finland, Sweden and Norway. The focus is on policies for families with children below the age of three years concerning day care and social services and benefits for parents. Thus, child benefit, child-related leave and home care allowance are in the centre of this thesis. The aspects of the welfare development, facts about their societies, as well as current challenges, complement this thesis. Eventually, the final analysis of the Nordic family policies is considered in an international comparison, focusing on Germany’s contextual issues.
Comparing multidimensional sensor data from vehicle fleets with methods of sequential data mining
(2020)
Composite Mechanics
(2023)
This book is the second edition of an introduction to modern computational mechanics based on the finite element method. It includes more details on the theory, more exercises, and more consistent notation; in addition, all pictures have been revised. Featuring more than 100 pages of new material, the new edition will help students succeed in mechanics courses by showing them how to apply the fundamental knowledge they gained in the first years of their engineering education to more advanced topics.
In order to deepen readers’ understanding of the equations and theories discussed, each chapter also includes supplementary problems. These problems start with fundamental knowledge questions on the theory presented in the respective chapter, followed by calculation problems. In total, over 80 such calculation problems are provided, along with brief solutions for each.
This book is especially designed to meet the needs of Australian students, reviewing the mathematics covered in their first two years at university. The 13-week course comprises three hours of lectures and two hours of tutorials per week.
Coverage Probability of Methods for Steady-State Availability Inference with a Confidence Interval
(2021)
Designing the OR cockpit
(2021)
A number of planetary boundaries, including climate change as a result of greenhouse gas emissions, has already been exceeded. This situation has deleterious consequences for public health. Paradoxically, 4.4% of these emissions are attributable to the healthcare sector. These problems have not been sufficiently acknowledged in health professions curricula. This paper addresses two main issues, humanistic learning and the application of knowledge acquisition to clinical practice. Humanistic learning principles can be used to emphasize learner-centered approaches, including knowledge acquisition and reflection to increase self-awareness. Applying humanistic principles in everyday life and clinical practice can encourage stewardship, assisting students to become agents for change. In terms of knowledge and skills application to clinical practice, an overview of varied and novel approaches of how sustainable education can be integrated at different stages of training across several health care professions is provided. The Health and Environment Adaptive Response Taskforce (HEART) platform as an example of creating empowered learners, the NurSusTOOLKIT, a multi-disciplinary collaboration offering free adaptable educational resources for educators and the Greener Anaesthesia and Sustainability Project (GASP), an example of bridging the transition to clinical practice, are described.
Effect of voids in a heat-flux dependent theory for thermoelastic bodies with dipolar structure
(2020)
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.
Effects of Reusing Polyamide 12 Powder on the Mechanical Properties of Additively Manufactured Parts
(2022)
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.
This book provides an update on recent advances in various areas of modern engineering design, such as mechanical, materials, computer, and process engineering, which provide the foundation for the development of improved structures, materials, and processes. The modern design cycle is characterized by the interaction of different disciplines and a strong shift toward computer-based approaches involving only a small number of experiments for verification purposes. A major driver for this development is the increased demand for cost reduction, which is also connected to environmental demands. In the transportation industry (e.g. automotive or aerospace), where there is a demand for greater fuel efficiency, one solution 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.
For an efficient operation of a low voltage PMSM an optimized voltage usage is very important. Because of the relation between the low voltage and the high currents in this type of machine, a large voltage reserve is needed to compensate the influence of parameter mismatches and to guarantee a stable current control. As the power is limited by the low voltage in this type of hybrid drive systems, optimizing the voltage usage is also required to maximize the power and the torque availability. This paper describes a closed loop flux control to maximize the voltage usage. The controller feedback is used to estimate and maximize the available torque for each operating point.
Das Interesse der Industrie an additiv gefertigten Bauteilen steigt z unehmend, wobei mit zunehmendem Verständnis der statischen Kennwerte nunmehr der Fokus in Richtung der dynamischen Festigkeiten wandert. Deswegen werden Einflussparameter auf die Lebensdauer und potenzielle Nachbearbeitungsmethoden untersucht und analysiert. Ein großer Einfluss ist dabei der Oberflächengüte und den durch Rautiefen initiierten Kerbeffekten zuzuschreiben. Deswegen werden unterschiedliche Methoden zur Verbesserung der Oberflächengüte untersucht. Dabei werden die Verfahren Laserpolieren, elektrochemisches Polieren und Hartmetallkugelstrahlen und deren Auswirkung auf Oberflächengüte sowie Härte untersucht. Für das elektrochemische Polieren werden die Proben in einer Perchlorsäure für 90 s bei 32 V und maximal 10 A poliert. Das Hartmetallkugelstrahlen wird mit einem UFS 100 Strahlmittel bei einem Druck von 4 bar und einer Strahldauer von 10 s ausgeführt. Anschließend werden Wöhlerlinien für die unterschiedlichen Zustände mittels Umlaufbiegeversuch ermittelt, welche mit Referenzwerten analysierter konventioneller Proben verglichen werden. Des Weiteren werden die Bruchflächen analysiert. Die Untersuchungen ergaben ein hohes Optimierungspotenzial der additiv gefertigten Proben bei einer Verdichtung der Oberfläche sowie einer Entfernung der Randschicht durch eine spanende Bearbeitung. Dadurch wurden höhere Zeitfestigkeiten als mit konventionell gefertigten Proben erreicht.
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.
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.
Laser powder bed fusion has become one of the major techniques within metal additive manufacturing, especially when delicate structures and high geometric accuracy are concerned. Lately, the awareness of the material-specific macroscopic anisotropy has risen and led to widespread investigations on the static mechanical strength. However, little is known about the fracture behavior of the layer-wise fabricated metal components and their affinity of crack propagation between consecutive layers, which is particularly important for aluminium–silicon alloys containing embrittled zones in double-irradiated areas. A recent study indicated that there is a significant drop in fracture toughness in case the crack growth direction is parallel to the layering. To investigate this matter further and to shed light on the fracture toughness behavior in the range of a 0°–45° angle offset between the crack growth direction relative to the layering, notched samples with varying polar angles were subjected to mode I fracture toughness testing. Our results indicate that the fracture toughness is an almost-stable characteristic up to a mismatch of about 20° between the crack propagation path and the layering, at which point the fracture toughness decreases by up to 10%.
Negotiations are a relevant and highly complex business skill. Therefore, extensive training is required to become a good negotiator. Such training is offered by universities for their students and by companies for their employees. The present paper designs gamified feedback features in electronic negotiation training and evaluates their potential and their effects. Following a design science research method, feedback mechanisms in electronic negotiation training are derived from literature. An assessment regarding their relevance for e-negotiation training shows a preparation quiz, set and track goals and expert reviews to be the most useful gamified feedback mechanisms. Dedicated mock-ups implementing these feedback mechanisms are designed and evaluated in semi-structured interviews showing their capability to improve relevant negotiation skills, as well as motivation and competence of the learners. Out of the three mock-ups, the interviewees prefer the feedback mechanisms “expert review” and “set and track goals”; both mechanisms provide a competence-confirming learning experience and an autonomous learning experience.
Recently the production of electric cars is increasing worldwide. The main target is to lower the greenhouse gas emissions. Even if an electrified vehicle is locally emission-free the manufacturing of lithium ion batteries are producing significant amounts of CO2. In order to decrease the air pollution governments are considering recycling programs to extend battery life and usage of important raw materials. A new approach to recover LiNixMnyCozO2 (NMC) particles while saving the chemical and morphological properties using water was presented by Tim Sieber et al. [1]. With the presented study, we are focusing on the analysis of the effects on the Global Warming Potential (GWP) for the water based recycling process based on a reuse of NMC material in new batteries.
It is possible to reduce the ecological damage of the manufacturing process of Li-Ion battery cells even with little amounts of recovered cathode material that is used for the production of new battery cells. Based on the suggestion that 95% of the NMC cathode material can be recovered by the hydrometallurgical recovery and the reuse of 10% within the production of new batteries a reduction of the GWP by 7% ,can be identified for the cathode materials. For other impact categories such as Acidification Potential (AP), Eutrophication Potential (EP), and Photochemical Ozone Creation Potential (POCP), savings of 10%, 11%, and 8 % can be achieved respectively.
The studied water based recycling process can be quoted as environment-friendly and leads to a reduction of all impact categories by a re-use of 10% recovered NMC material. Based on this knowledge an additional recycling on substance level is recommended.
Laser powder-bed fusion (LPBF) has significantly gained in importance and has become one of the major fabrication techniques within metal additive manufacturing. The fast cooling rates achieved in LPBF due to a relatively small melt pool on a much larger component or substrate, acting as heat sink, result in fine-grained microstructures and high oversaturation of alloying elements in the α-aluminum. Al-Si-Mg alloys thus can be effectively precipitation hardened. Moreover, the solidified material undergoes an intrinsic heat treatment, whilst the layers above are irradiated and the elevated temperature in the built chamber starts the clustering process of alloying elements directly after a scan track is fabricated. These silicon-magnesium clusters were observed with atom probe tomography in as-built samples. Similar beneficial clustering behavior at higher temperatures is known from the direct-aging approach in cast samples, whereby the artificial aging is performed immediately after solution annealing and quenching. Transferring this approach to LPBF samples as a possible post-heat treatment revealed that even after direct aging, the outstanding hardness of the as-built condition could, at best, be met, but for most instances it was significantly lower. Our investigations showed that LPBF Al-Si-Mg exhibited a high dependency on the quenching rate, which is significantly more pronounced than in cast reference samples, requiring two to three times higher quenching rate after solution annealing to yield similar hardness results. This suggests that due to the finer microstructure and the shorter diffusion path in Al-Si-Mg fabricated by LPBF, it is more challenging to achieve a metastable oversaturation necessary for precipitation hardening. This may be especially problematic in larger components.
Hot isostatic pressing can be utilized to reduce the anisotropic mechanical properties of Al–Si–Mg alloys fabricated by laser powder-bed fusion (L-PBF). The implementation of post processing densification processes can open up new fields of application by meeting high quality requirements defined by aircraft and automotive industries. A gas pressure of 75 MPa during hot isostatic pressing lowers the critical cooling rate required to achieve a supersaturated solid solution. Direct aging uses this pressure related effect during heat treatment in modern hot isostatic presses, which offer advanced cooling capabilities, thereby avoiding the necessity of a separate solution annealing step for Al–Si–Mg cast alloys. Hot isostatic pressing, followed by rapid quenching, was applied to both sand cast as well as laser powder-bed fused Al–Si–Mg aluminum alloys. It was shown that the critical cooling rate required to achieve a supersaturated solid solution is significantly higher for additively manufactured, age-hardenable aluminum alloys than it is for comparable sand cast material. The application of hot isostatic pressing can be combined with heat treatment, consisting of solution annealing, quenching and direct aging, in order to achieve both a dense material with a small number of preferred locations for the initiation of fatigue cracks and a high material strength.