178 research outputs found
Copper-containing bioactive glasses and glass-ceramics: From tissue regeneration to cancer therapeutic strategies
No full textCopper is one of the most used therapeutic metallic elements in biomedicine, ranging from antibacterial approaches to cancer theranostics. This element could be easily incorporated into different types of biomaterials; specifically, copper-doped bioactive glasses (BGs) provide great opportunities for biomedical engineers and clinicians as regards their excellent biocompatibility and regenerative potential. Although copper-incorporated BGs are mostly used in bone tissue engineering, accelerated soft tissue healing is achievable, too, with interesting potentials in wound treatment and skin repair. Copper can modulate the physico-chemical properties of BGs (e.g., reactivity with bio-fluids) and improve their therapeutic potential. Improving cell proliferation, promoting angiogenesis, reducing or even prohibiting bacterial growth are counted as prominent biological features of copper-doped BGs. Recent studies have also suggested the suitability of copper-doped BGs in cancer photothermal therapy (PTT). However, more research is needed to determine the extent to which copper-doped BGs are actually applicable for tissue engineering and regenerative medicine strategies in the clinic. Moreover, copper-doped BGs in combination with polymers may be considered in the future to produce relatively soft, pliable composites and printable inks for use in biofabrication
Thermo-Mechanical Fatigue of Compacted Graphite Iron in Diesel Engine Components
No full textCast iron components in combustion engines, such as cylinder blocks and heads of trucks, are exposed for long periods of time to elevated temperatures. Moreover, the engines are started and stopped frequently during their operational life, constituting a large number of heating and cooling cycles. In geometrical complex components the sudden heating (starting the engine) and cooling (stopping the engine) lead to thermal gradients and thermal mismatch within the material, resulting in the local development of high stress levels. The many start-stop operations and their associated alternating stress levels can lead to a localized cracking phenomenon known as Thermo-Mechanical Fatigue (TMF). Compacted Graphite Iron (CGI) is a common material of choice for diesel engine cylinder heads of heavy trucks and is a type of graphitic cast iron, consisting of vermicular graphite particles embedded in a metal matrix of pearlite. This material provides a suitable combination of thermal and mechanical properties, satisfying the functional requirements of these engine components. The main aim of this research is to identify and understand the damage micro-mechanisms that control thermo-mechanical fatigue phenomena in cast iron (CGI). The acquired knowledge is of relevance for predicting the lifetime, improving the properties and increasing the reliability of diesel truck cylinder heads. The work of this study can roughly be categorized into three main subjects: (i) Microstructural evolutions of CGI at elevated temperatures, (ii) TMF crack growth characterization and (iii) precise microstructural analysis of the TMF-crack path. Microstructural Evolutions of CGI at Elevated Temperatures In a first series of experiments, time and temperature induced microstructural changes in CGI were characterized, in view of their possible role in the TMF behavior of CGI. During open air annealing of CGI at 420 °C microstructural changes take place in the material, which gave rise to volume expansion and weight increase. The weight increase can be explained by considering the formation of an oxide scale whereas the volume expansion can be attributed to the decomposition of pearlite into ferrite and graphite. It was observed that the atmosphere is of crucial importance in this process. Annealing in an open-air atmosphere produced ten times less volume expansion as compared to annealing in vacuum conditions. Internal oxidation was observed during annealing under atmospheric conditions and the presence of an internal oxidation layer largely inhibited the progress of pearlite decomposition. The observed oxide layers at the internal metal/vapour interface of cavities (left behind by denuded graphite) cause the obstruction of carbon diffusion and thus the suppression of the pearlite decomposition process. In addition it was found that the depth of the oxidized zone near the surface (the oxide penetration depth) was of the same order of magnitude as the eutectic cell size, i.e. the volume in which graphite particles are interconnected. This suggests that the interconnectivity of the graphite has a dominant influence on the kinetics of the oxidation process. The microstructural dependence of tensile and fatigue properties of CGI at room temperature were evaluated by an extended annealing treatment of 720 h at 420 °C. This extended annealing treatment leads to better tensile (increase in yield strength, ductility) and dynamic properties (fatigue lifetime) at room temperature. The variations of mechanical properties were observed both after annealing under atmospheric and vacuum conditions, but were more pronounced after vacuum annealing. This can be explained by the decomposition of the pearlite phase during annealing and the formation of new ferrite at the graphite/metal interface. It is assumed that the ferrite/graphite interface exhibits a stronger bond than the pearlite/graphite interface. As this stronger bond will be better resistant to delamination, it will strengthen the material both in static and dynamic loading. Such effects were far less pronounced in the open-air annealed material, which could be associated with the fact that it was shown that internal oxidation strongly reduced the kinetics of decomposition. TMF Crack Growth Characterization An important part of this study was to measure and analyze the TMF lifetime of CGI. For smooth and notched specimens, the TMF lifetime was measured in TMF tests under total-constraint conditions, with temperatures cycling between 50 °C and 420 °C. By considering the notch depth as the initial crack length, TMF lifetimes were reproduced numerically using the Paris equation for fatigue crack growth (da/dN = C (?K)m). The calculated lifetimes were found to be in good agreement with all experimental results, covering a wide range of TMF lifetimes from 30 to 1400 cycles. Also for smooth specimens the Paris model worked well by considering the typical graphite particle size as notch depth. It is one of the main conclusions of this work that graphite particles act as internal notches from which a TMF crack almost immediately starts to grow during the first TMF cycles. Hence, it was established that TMF lifetime in CGI is governed by crack growth and not by crack initiation. The relevance of the Paris growth law was further confirmed by meticulously measuring the actual crack growth rates for three typical values of the stress intensity factor. The resulting crack growth rates proved to be in reasonable agreement with the predicted values according to the Paris model. It was further shown that the cyclic plasticity of the bulk material, accumulated during TMF cycles, does not have a noticeable effect on TMF lifetime (i.e. crack growth rates are not affected). The notched dog-bone specimen geometry is proposed in this work as a valid alternative for monitoring the TMF behavior of CGI. By applying standard TMF tests with notched specimens, it was possible to significantly reduce both testing time and experimental data scatter, whilst preserving a realistic estimation of the lifetime of the smooth sample. The effect of prolonged holding times (HT) on TMF lifetime was studied by using notched specimens and a clear effect was observed. Extended holding times were accompanied by an increased relaxation of compressive stresses, causing higher tensile stresses to develop in the subsequent low temperature stages of the TMF cycles. So, extended HTs had an adverse effect on the sample lifetime with a saturating effect for HTs above 1800 s. The Paris fatigue-crack-growth model was used also to estimate the impact of extended HTs. According to the Paris growth law, using a fixed value of tensile stress at low temperature, it was estimated that an increase of holding time from 30 s to 18000 s (5 h) produced a drop of 45% in lifetime. In reality a 60% drop in lifetime was measured, though, which implies that a combined effect of (tensile) stress and microstructural evolution during TMF is responsible for the reduction of lifetime. Precise Microstructural Analysis of the TMF Crack Path To the purpose of precise characterization of the complex TMF-crack-path morphology in CGI in relation to local microstructural features and to find out how and by which mechanisms the cracks predominantly develop, 2D and 3D orientation contrast imaging was carried out on wide field sample volumes, covering several mm3 of imaged material. The data analysis revealed that the crystal planes that are parallel to the (local) crack plane are essentially of a random orientation. Conversely, it was found that graphite particles do not only play a crucial role in the crack initiation, but also are of primary significance for crack propagation. Quantitative analysis of the EBSD data in 2D and 3D showed that the distribution of graphite particles is very important for the crack propagation, as it was revealed that graphite particles enhance crack growth. It was statistically proven that the density of graphite particles in the crack plane is more than double of the density in an arbitrary plane. Our materials knowledge, based on the interpretation of test results in terms of quantifiable microstructural data functions, is of crucial importance to develop a microstructurally based TMF model.Materials Science & EngineeringMechanical, Maritime and Materials Engineerin
A transient simulation for a novel solar-geothermal cogeneration system with a selection of heat transfer fluids using thermodynamics analysis and ANN intelligent (AI) modeling
No full textToday, due to the reduction of fossil resources and on the other hand the high environmental pollution of these resources, it is necessary to pay attention to alternative resources, including clean and available renewable resources. In this study, solar and geothermal energy sources are combined, generating electricity, cooling, freshwater, and hydrogen, along with selecting a suitable heat transfer fluid for parabolic trough solar collectors. This system consists of parabolic trough solar collectors, a steam Rankine cycle, a steam Rankine cycle with an organic Rankine cycle, a proton exchange membrane electrolyzer, and a reverse osmosis desalination unit. To analyze the performance of solar collectors, Therminol 59, Marlotherm SH, Syltherm 800, and Therminol VP1 heat transfer fluids are selected. Solar radiation intensity, solar collector mass flow rate, turbine and pump efficiency, evaporator pinch-point temperature, and organic Rankine cycle turbine inlet temperature were investigated as design parameters affecting system performance. Maximizing energy efficiency and reducing cost rate were selected as two objective functions and determined using a multi-objective sorting genetic algorithm (NSGA-II). The results showed that Therminol 59 has the highest energy efficiency and net power output compared to other heat transfer fluids. Also, the proposed system produces 1140 kW of electricity in the optimal state, and in the best state, it has an energy efficiency of 32.39% and a cost of 36.32 $/GJ
Narrative Metalepsis in Persian Stories
No full textThis study aimed at defining and classifying types of metalepsis, and analyzing its status in Persian stories. Narrative metalepsis refers to the combination of various narrative levels, whereby the author could descend to the story level and communicate with the characters or ascend to the discourse level which is the world of author, narrator and reader. This narrative technique which is also called meta-fictional narration is commonly used in postmodern stories. There are four important types of metalepsis: 1) Descending Metalepsis, whereby the author descends to the story level or the fictional world, 2) Ascending Metalepsis which refers to the movement of the characters out of the fictional world to the real world to encounter the author or readers, 3) Ontological Metalepsis occurs when the author, narrator or character moves across the narrative levels to the fictional or real world, finally 4) Rhetorical Metalepsis happens when the author or character only have a glance at other narrative levels. This narrative device had been used in some Persian stories before it was introduced into Persian sources on narratology and criticism. All the four types of metalepsis have been used in some modern and postmodern Persian novels and short stories. The novel ‘The Gipsy by the Fire’ and the short stories ‘The Last Night, the Last Stairway’ and ‘Bat’ are built upon descending and ontological metalepsis. Other works built upon ascending and ontological metalepsis are the novel ‘Steel-Hearted’, and the short story ‘Again in the Same Streets’. Finally, the short stories ‘The Man Who Didn’t Return’ and ‘Selection’, and the novel ‘The Narrator River’ are built upon rhetorical metalepsis
Integrating shape memory materials in haptic technology as an aid for the visually impaired
No full textThere are approximately 285 million people worldwide living with a visual impairment and the rate of acquired blindness is expected to continue increasing. Assistive technology for them is progressively being developed in order to enable independent living. For the blind and visually impaired, the tactile sense is the primary source of understanding non-audible information. Therefore, haptic technology is being incorporated more in assistive devices meant for situations in which one cannot rely on sight to manipulate objects and conduct various activities.An issue with currently available haptic solutions is that they typically use electromechanical systems that are heavy with large, obtrusive forms, produce sounds that hinder their usability and sometimes even provide unpleasant haptic feedback. A way to mitigate these problems is by incorporating soft, flexible and lightweight smart materials as actuators into these systems. Shape memory materials are a specific category of smart materials that have the ability to recover their original shapes from a deformation when certain stimuli are applied. They have the potential to bring hedonic characteristics to haptic technology such as providing organic sensations. Consequently, the haptic assistive devices become effective and comfortable interventions for the visually impaired.This project demonstrates how these materials can successfully be incorporated to produce different types of tactile feedback as a form of an assistive-wearable and enrich the lives of the blind and visually impaired. The end demonstrator provides two types of sensations- dragging and squeezing.Integrated Product Desig
Shape memory origami for haptics: Exploring the potential of a material system based on SMAs to generate haptic feedback for visually impaired people
No full textThis project explores the potential of a material system based on SMAs that generates haptic feedback for Visually Impaired People (VIPs). Since VIPs rely more than others on tactile information, there is a need for more natural and unintrusive haptic devices as the commonly used electromechanical actuations are often perceived as intrusive and less acceptable than non-vibrating feedback. SMAs emerge as a promising solution to address these challenges effectively, due to their inherent ability to create silent, organic sensations, while being lightweight, thin, and flexible (Cruz et al., 2018). The aim of this project is to investigate the unique characteristics of SMAs and translate this into an integrated material system that could inspire designers to adopt these materials and revolutionize tactile experiences. The process had an explorative nature and included a research, form configuration and embodiment phase. Most current haptic systems based on SMAs have the limitation of small actuation ranges and/or difficulties in integrating them in soft material systems. Therefore, in this project, a soft integrated material system is designed that shows the potential of incorporating SMA and SE flat springs into an origami-paper textile to create haptic feedback. By using the combination of the SMA-SE flat springs, an easy integration of the wires in the paper-textile is enabled and a two-way actuation is created with a displacement of around 16%. Through the use of the origami structure, the two-dimensional shape change of the SMA spring is transformed in a three-dimensional shape change creating rich tactile feedback that can be perceived passively as well as actively. The sensations generated by the material system were easily perceived with the hands and the movement was characterized as natural, calm and gentle by sighted participants. This demonstrates that there is a potential for creating an integrated material system based on flat springs SMAs that generated haptic feedback for VIPs in a natural and new way. Additionally, based on all these findings, a guideline was developed for SMA wires with the aim to give an overview of all steps involved when designing a material system based on SMAs.Integrated Product Desig
Characterizing Interwoven: Testing and Modeling Root-Textiles
No full textInterwoven refers to material structures made by growing plant roots into man-made patterns. Originally developed as an art piece to demonstrate root intelligence and bring attention to human-nature relations, Interwoven shows the potential to disrupt various commercial industries, especially as textile-based natural fiber reinforcements for composite materials. The artist that created Interwoven, Amsterdam-based Diana Scherer, started a collaboration with the TU Delft Faculty of Industrial Design Engineering to help further develop Interwoven from an art piece to a sustainable material for products design. Following the Material Driven Design method (Karana, et al., 2015), two students have identified materials experience opportunities created by Interwoven materials, the mechanical properties and internal structure of Interwoven are still not fully understood. This study tackles the challenge of performing a technical characterization on Interwoven structures in an effort to correlate processing parameters to its structure, properties, and performance. It is known from past works that Interwoven is fragile and “weak”, but a quantified value for these terms serves as a point of comparison with other materials in the market. To determine these values, a series of tensile tests were performed on grids with a simple square pattern. Dynamic Mechanical Analysis (DMA) tests performed on single roots proved that the amalgamation of roots that make up an Interwoven structure do not efficiently transfer tensile loads since the tensile strength and elastic moduli of Interwoven samples were nearly two orders of magnitude lower than those of a single root. Load transfer between roots was improved through the design of natural fiber-reinforced composites (NFRCs). The (bio)-polymer matrix used for these NFRCs was made up of agar gel, which improved the tensile properties of Interwoven samples, but was still lower than the single root.A full characterization of a material correlates the observed properties to the structure of the material, which is done through the use of microscopy. Microscopic analyses were performed on all the tested samples to find any correlation between the observed tensile properties and the structure of Interwoven samples. In addition to providing insight about the complex interactions of roots as they form the patterns that they grow into, the microscopy also revealed that there is a direct correlation between the number of root tips (root endings) present at the intersection of squares in the grid and the mechanical properties of the sample. With further research, this result can be tied to a parameter that the designer has direct control of, giving them better control of the properties of their Interwoven structures. Varying cell size in square patterns also allows designers to create structures with locally varying properties. The correlations between design parameters and material strength are summarized in the Guidelines to Designing with Interwoven booklet. A material demonstrator was also designed to showcase the locally variable mechanical properties in one structure while summarizing the test results in a way that is accessible and easy to understand.Integrated Product Desig
Designing 3d-Printed Deployable Structures With Shape Memory Polymers
No full textThe aim of this project was to get a better understanding of the shape memory behaviour of 3D-printed polymers, and the different parameters which affect this, with the ultimate goal to apply shape memory in product design. This project started with a literature study on shape memory polymers and 3D-printing. The material properties, different types of shape memory and different actuation methods were investigated, as well as different 3D-printing techniques and using shape memory polymers in 3D-printing. Existing applications and concepts using shape memory polymers, as well as recent studies in applying these materials were also investigated. In parallel to the literature study, testing was done on the influence of different parameters on the shape memory behaviour of one of the most common FDM 3D-printing materials: PLA. Through an iterative process, a test sample was designed which was used to test parameters related to material (different types of PLA), manufacturing (printing settings), and design (geometry and orientation of models). Knowledge gained through the literature research and testing was combined to create design guidelines for manufacturing shape memory objects using 3D-printing. To demonstrate how the shape memory capabilities of 3D-printed PLA could be applied in product design, A product concept was developed. With a vision as a starting point, ideation and concept development was started by first having a brainstorm session with different people to learn how people not involved with the project envisioned shape memory in product design. Moving on from this, useful results from this session were taken into an ideation phase, where a multitude of different ideas were thought up. From these ideas, four were chosen to be developed into concepts, of which one was chosen to be further developed into a physical prototype. The chosen concept was a wake-up light which uses the heat of the lightbulb inside the lamp to heat the shape memory material and initiate shape recovery, which resulted in the lamp gradually giving off more light. This would wake up the user in a natural way. The concept, which was given the name ‘’DAWN’’, was developed into a physical demonstrator, and the shape memory parts were printed based on the established guidelines. This also served as a test for the guidelines to see how they could be applied in the design process. After testing several printed prototype parts, a final design for the demonstrator was created and produced. At the end of the project, the process and results were evaluated and recommendations were given for further research into 3D-printing shape memory objects.Integrated Product Desig
Designing a locomotive device driven by a shape memory alloy composite: a mimicry of the caterpillar movement
No full textThe materials we encounter in our every day lives already extend beyond the traditional materials of wood, metal, ceramics and glass. The characteristics and behavior of materials and material composites are continuously being tweaked. The introduction of new materials that can respond to inputs from the environment has brought about a new movement for material development and interaction design: computational composites. A computational composite is capable of sensing inputs from the environment, processing and controlling the consequent expression or formation of the material.The aim of the thesis was two-fold: to design and develop a soft bodied mechanism inspired by the movement of a caterpillar, using a Shape Memory Alloy-based (SMAs) composite, and to design material concepts based on the qualities of the composite.This was an explorative project, investigating the application of a bio-inspired approach and the Material Driven Design (MDD) approach to the development of a moving material.The first phase of the project focused on uncovering the technical aspects of a SMA-based composites and its relation to a computational composite. To understand caterpillar locomotion, a thorough study on its anatomy and locomotion strategies was performed. A qualitative study on howdesigners interpret caterpillar-like motion lead to four interesting movements, which were further developed in moving SMA-based composites from silicone and 4D printed textile.One SMA-based composite was selected for further improvement of the mechanism to be capable of translational caterpillar-like motion.The mechanism can also be interpreted and applied in other ways, and thus the experiential characteristics of the material were uncovered to define a material experience vision for further applications. Through a creative session and ideation phase three material concepts were proposed, suited for three types of user input on the computational composite: none, indirect and direct.The ultimate purpose for the material would be to sensitize people to the idea of a world where materials move from passive objects to active elements in our daily lives. It is recommended to do more research on the composite and to apply the materials experience vision to applications beyond every day objects and into the more innovative field of computer interface design and human-material interaction.Integrated Product Desig
Designing a recyclable impact resistant tablet cover
No full textThis thesis looks into the application of self-reinforced polypropylene (SRPP) in a tablet cover for the company Gecko Covers. Gecko Covers is a company that provides protection for devices in the form of covers and sleeves. They are performing at their best in the tablet market. They would like to enter the impact resistant tablet cover market using an impact cover that is both impact resistant and stylish. Their product style is characterized by the usage of contrast in both material texture and color, simple shapes and an attention to detail. Based on a market analysis, the tablet user on the go is selected as target group. These people carry their tablets with them wherever they go. To differentiate from the current competitors in this tablet market segment, Gecko has to focus on reducing the environmental impact of the new cover by e.g. making it recyclable. The most important material properties for the impact cover are high toughness, low density and a minimum ductile-to-brittle temperature of -20 °C. Not only does SRPP meet these requirements, it is also recyclable as it is only made out of a single type of thermoplastic. The manufacturing process of producing laminates out of woven SRPP influences the material properties such as impact resistance. Literature research shows that a combination of hot compaction and film stacking improves the impact resistance of the SRPP laminate the most. The values of the other parameters which influence the material properties of the laminates were determined through trial and error. To evaluate the SRPP laminates, a bending fatigue test and an alternative Izod impact test were conducted. In the end, the laminates with a compaction temperature of 170 °C, a pressure of 1,73 bar, an active heating time of 5 min and 1 PP film layer in between the SRPP fiber layer are the toughest and ductile. The focus of the design was on a minimum viable product. A back structure inspired by those of suitcases, the screen edge and the regular corners and edges of the cover were all taken into account. To validate that the shape is manufacturable from SRPP, a proof of concept was made with a mold. Furthermore, this proof of concept was tested via a drop test to get more information about the actual performance of the SRPP layer and to determine which orientation would have the highest impact resistance. The drop test showed the importance of the screen edge, which was missing from the proof of concept as it cannot be made out of SRPP. The test also showed that the SRPP lacked damping. To add the screen edge and the damping to the product, additional injection molded PP was used in order to add the screen edge and damping elements to the product. The final design was inspired by natural Voronoi structures and also creates a contrast in material texture and color, matching the current style of Gecko Covers.Integrated Product Desig
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