Alkali activation of waste materials: sustainability and innovation in processing traditional ceramics

Environmental issues linked both to OPC production and waste management brought researchers to find new solutionsfor the production of more eco-efficient binders. In this frame, alkali-activated materials are receiving increasing attention. They are obtained by reaction of an alkali metal source, generally sodium or potassium, with amorphous calcium-aluminosilicate precursors. More recently, also the reuse of mining wastes was investigated due to the impressive production of sludges and muds which do not have practical applications and shall be landfilled. The aim of our researches was to investigate the use of semi-crystalline/high-crystalline by-products in the production of alkali-activated materials. Thus, two different powders were used: an alumino silicate mud, composed by quartz, feldspars, biotite and dolomite; and a carbonatic one, composed of calcite and small amounts of dolomite. Both powders were alkali-activated using a solution of NaOH and Na2SiO3. Pastes were produced mixing the activating solution and the powder in different liquid/solid ratiosandinvestigatingthe use of waste glass powder as further source of amorphous silica. Samples were oven-cured for 24h at 60-80 °C and then cured in different environments (dry, humid and immersed in water) for other 27 days before testing physical and mechanical properties. Very promising results were obtained in terms of compressive strength (about 30 MPa for the aluminosilicate sludge and up to 45 MPa for the carbonatic one), showing their potential as innovative building products

Auxetic response of additive manufactured cubic chiral lattices at large plastic strains

Auxetic lattices exhibit a negative Poisson’s ratio and excellent energy absorption capability. Here, we investigate the compressive performance of auxetic cubic chiral structures. By utilising finite element analysis (FEA) verified by interrupted mechanical testing and x-ray computed tomography, the auxeticity and failure mechanisms at the large strain deformation have been evaluated. The FEA results show that the initial elastic–plastic response agrees with the prediction of the classic scaling laws of bending-dominated lattices. At increasing plastic deformation, the energy absorption and auxeticity are dependent on relative density, i.e., the slenderness ratio, of the constitutive struts. In the plastic regime, the auxeticity decreases with relative density. Ductile fracture precedes densification in relative densities above 1.2%, thus dictating a new scaling law for the variation of the maximum energy absorbed with density. The numerical model predicts the scaling of mechanical properties, fracture strains, and energy absorption of the constitutive unit cell and finite-sized specimens in the relative density ranging from 0.3% to 6.5%. However, to accurately model the failure mechanism, geometrical imperfections should be included. The scaling laws derived from this work may aid the design of next generation auxetic lattices with tailored mechanical properties

Mechanical behavior of PA12 lattice structures produced by SLS

Dissertação de mestrado integrado em Engenharia de PolímerosTaking into account the rapid technological evolution and the growing demand, for the industrial sector to meet the most diverse needs of the market, Additive Manufacturing (AM) technology appears as a transformative approach to industrial production that enables the creation of lighter, stronger parts and systems. The versatility of this type of technology allows a reduction in production time and energy consumption, as well as, reducing material waste in the production of a product. It is in this last point that the technologies of AM stand out when comparing to the technologies of conventional manufacture. In AM technologies, it is possible to carry out the deposition of material in a controlled manner, where it is really necessary and, at the same time, ensure the necessary mechanical properties to meet the product requirements. Due to its versatility and rapid technological advances, it has become possible to implement typological optimization in AM. In this context, this study aims to investigate the mechanical behavior of lattice structures to support further investigations based on Topology Optimization (TO). The study of the mechanical behavior of these structures allows an intelligent distribution of these structures along a given structure in order to absorb the amount of energy needed for the impact, presenting competitive manufacturing times and costs. In the course of this research, the manufacturing technique to be used will focus on the Powder Bed Fusion (PBF) process, more specifically in the EOS P396 equipment with the polymeric material polyamide 12 (PA12), that will shape the desired lattice structures, which are constituted by different topologies and volume fractions. The purpose of this development is focused on obtaining the experimental mechanical properties of certain types of cellular structures in order to compare them with the properties obtained from the simulations. Thus, strut-based (BCC) and Triply Periodic Minimal Surfaces (Schwarz-P and Neovius) lattice structures were defined based on different independent variables, such as, cell size, strut diameter/ surface thickness and shell thickness. The defined structures were evaluated by compression and impact mechanical tests. It was found that beside geometrical design, the relative densities of the unit cells could also significantly influence the impact energy absorption performance.Tendo em conta a rápida evolução tecnológica e a crescente procura do sector industrial para satisfazer as mais diversas necessidades do mercado, as tecnologias de Fabrico Aditivo (FA) aparece como uma abordagem transformadora da produção industrial que permite a criação de peças e sistemas mais leves e fortes. A versatilidade deste tipo de tecnologia permite uma redução do tempo de produção e do consumo de energia, bem como a eliminação do desperdício de material na produção de um produto. É neste último ponto que as tecnologias de FA se destacam no que diz respeito às tecnologias de fabrico convencional. Nas tecnologias FA, é possível realizar a deposição de material de forma controlada, onde é realmente necessário, e ao mesmo tempo, garantir as propriedades mecânicas necessárias para satisfazer os requisitos do produto. Neste contexto, este estudo destina-se a investigar o comportamento mecânico de lattice structures para apoiar investigações posteriores que têm por base a Otimização Topológica (OT). O estudo do comportamento mecânico destas estruturas permite uma distribuição inteligente destas mesmas ao longo de uma determinada estrutura de forma a absorverem a quantidade de energia necessária ao impacto, apresentando tempos e custos de fabrico competitivos. No decurso desta investigação, a técnica de fabrico a ser utilizada centrou-se no processo de Powder Bed Fusion (PBF), mais especificamente no equipamento EOS P396 com o material polimérico poliamida 12 (PA12), que dará forma às lattice structures, constituídas por diferentes células unitárias e frações de volume. O objetivo deste desenvolvimento focou-se na obtenção das propriedades mecânicas experimentais das estruturas celulares de maneira a compará-las com as propriedades obtidas a partir das simulações. Assim, as lattice structures baseadas em strut-based (BCC) e Triply Periodic Minimal Surface (TPMS) (Schwarz-P e Neovius) foram definidas com base em diferentes variáveis independentes, tais como, tamanho da célula unitária, diâmetro da viga/ espessura da superfície e espessura da casca. As estruturas definidas foram avaliadas mecanicamente através de testes de compressão e impacto. Verificou-se assim que, para além do desenho geométrico, as densidades relativas das células unitárias também podiam influenciar significativamente o desempenho de absorção de energia de impacto

Bio-inspired design for engineering applications: empirical and finite element studies of biomechanically adapted porous bone architectures

Includes bibliographical references.2020 Summer.Trabecular bone is a porous, lightweight material structure found in the bones of mammals, birds, and reptiles. Trabecular bone continually remodels itself to maintain lightweight, mechanical competence, and to repair accumulated damage. The remodeling process can adjust trabecular bone architecture to meet the changing mechanical demands of a bone due to changes in physical activity such as running, walking, etc. It has previously been suggested that bone adapted to extreme mechanical environments, with unique trabecular architectures, could have implications for various bioinspired engineering applications. The present study investigated porous bone architecture for two examples of extreme mechanical loading. Dinosaurs were exceptionally large animals whose body mass placed massive gravitational loads on their skeleton. Previous studies investigated dinosaurian bone strength and biomechanics, but the relationships between dinosaurian trabecular bone architecture and mechanical behavior has not been studied. In this study, trabecular bone samples from the distal femur and proximal tibia of dinosaurs ranging in body mass from 23-8,000 kg were investigated. The trabecular architecture was quantified from micro-computed tomography scans and allometric scaling relationships were used to determine how the trabecular bone architectural indices changed with body mass. Trabecular bone mechanical behavior was investigated by finite element modeling. It was found that dinosaurian trabecular bone volume fraction is positively correlated with body mass like what is observed for extant mammalian species, while trabecular spacing, number, and connectivity density in dinosaurs is negatively correlated with body mass, exhibiting opposite behavior from extant mammals. Furthermore, it was found that trabecular bone apparent modulus is positively correlated with body mass in dinosaurian species, while no correlation was observed for mammalian species. Additionally, trabecular bone tensile and compressive principal strains were not correlated with body mass in mammalian or dinosaurian species. Trabecular bone apparent modulus was positively correlated with trabecular spacing in mammals and positively correlated with connectivity density in dinosaurs, but these differential architectural effects on trabecular bone apparent modulus limit average trabecular bone tissue strains to below 3,000 microstrain for estimated high levels of physiological loading in both mammals and dinosaurs. Rocky Mountain bighorn sheep rams (Ovis canadensis canadensis) routinely conduct intraspecific combat where high energy cranial impacts are experienced. Previous studies have estimated cranial impact forces up to 3,400 N and yet the rams observationally experience no long-term damage. Prior finite element studies of bighorn sheep ramming have shown that the horn reduces brain cavity translational accelerations and the bony horncore stores 3x more strain energy than the horn during impact. These previous findings have yet to be applied to applications where impact force reduction is needed, such as helmets and athletic footwear. In this study, the velar architecture was mimicked and tested to determine suitability as novel material architecture for running shoe midsoles. It was found that velar bone mimics reduce impact force (p < 0.001) and higher energy storage during impact (p < 0.001) and compression (p < 0.001) as compared to traditional midsole architectures. Furthermore, a quadratic relationship (p < 0.001) was discovered between impact force and stiffness in the velar bone mimics. These findings have implications for the design of novel material architectures with optimal stiffness for minimizing impact force

Clinical, industrial, and research perspectives on powder bed fusion additively manufactured metal implants

For over ten years, metallic skeletal endoprostheses have been produced in select cases by additive manufacturing (AM) and increasing awareness is driving demand for wider access to the technology. This review brings together key stakeholder perspectives on the translation of AM research; clinical application, ongoing research in the field of powder bed fusion, and the current regulatory framework. The current clinical use of AM is assessed, both on a mass-manufactured scale and bespoke application for patient specific implants. To illuminate the benefits to clinicians, a case study on the provision of custom cranioplasty is provided based on prosthetist testimony. Current progress in research is discussed, with immediate gains to be made through increased design freedom described at both meso- and macro-scale, as well as long-term goals in alloy development including bioactive materials. In all cases, focus is given to specific clinical challenges such as stress shielding and osseointegration. Outstanding challenges in industrialisation of AM are openly raised, with possible solutions assessed. Finally, overarching context is given with a review of the regulatory framework involved in translating AM implants, with particular emphasis placed on customisation within an orthopaedic remit. A viable future for AM of metal implants is presented, and it is suggested that continuing collaboration between all stakeholders will enable acceleration of the translation process

Advances on Mechanics, Design Engineering and Manufacturing III

This open access book gathers contributions presented at the International Joint Conference on Mechanics, Design Engineering and Advanced Manufacturing (JCM 2020), held as a web conference on June 2–4, 2020. It reports on cutting-edge topics in product design and manufacturing, such as industrial methods for integrated product and process design; innovative design; and computer-aided design. Further topics covered include virtual simulation and reverse engineering; additive manufacturing; product manufacturing; engineering methods in medicine and education; representation techniques; and nautical, aeronautics and aerospace design and modeling. The book is organized into four main parts, reflecting the focus and primary themes of the conference. The contributions presented here not only provide researchers, engineers and experts in a range of industrial engineering subfields with extensive information to support their daily work; they are also intended to stimulate new research directions, advanced applications of the methods discussed and future interdisciplinary collaborations

X-ray computed tomography for additive manufacturing: a review

In this review, the use of x-ray computed tomography (XCT) is examined, identifying the requirement for volumetric dimensional measurements in industrial verification of additively manufactured (AM) parts. The XCT technology and AM processes are summarised, and their historical use is documented. The use of XCT and AM as tools for medical reverse engineering is discussed, and the transition of XCT from a tool used solely for imaging to a vital metrological instrument is documented. The current states of the combined technologies are then examined in detail, separated into porosity measurements and general dimensional measurements. In the conclusions of this review, the limitation of resolution on improvement of porosity measurements and the lack of research regarding the measurement of surface texture are identified as the primary barriers to ongoing adoption of XCT in AM. The limitations of both AM and XCT regarding slow speeds and high costs, when compared to other manufacturing and measurement techniques, are also noted as general barriers to continued adoption of XCT and AM

Design and Topology Optimisation of Tissue Scaffolds

Tissue restoration by tissue scaffolding is an emerging technique with many potential applications. While it is well-known that the structural properties of tissue scaffolds play a critical role in cell regrowth, it is usually unclear how optimal tissue regeneration can be achieved. This thesis hereby presents a computational investigation of tissue scaffold design and optimisation. This study proposes an isosurface-based characterisation and optimisation technique for the design of microscopic architecture, and a porosity-based approach for the design of macroscopic structure. The goal of this study is to physically define the optimal tissue scaffold construct, and to establish any link between cell viability and scaffold architecture. Single-objective and multi-objective topology optimisation was conducted at both microscopic and macroscopic scales to determine the ideal scaffold design. A high quality isosurface modelling technique was formulated and automated to define the microstructure in stereolithography format. Periodic structures with maximised permeability, and theoretically maximum diffusivity and bulk modulus were found using a modified level set method. Microstructures with specific effective diffusivity were also created by means of inverse homogenisation. Cell viability simulation was subsequently conducted to show that the optimised microstructures offered a more viable environment than those with random microstructure. The cell proliferation outcome in terms of cell number and survival rate was also improved through the optimisation of the macroscopic porosity profile. Additionally artificial vascular systems were created and optimised to enhance diffusive nutrient transport. The formation of vasculature in the optimisation process suggests that natural vascular systems acquire their fractal shapes through self-optimisation

Design and Topology Optimisation of Tissue Scaffolds

Tissue restoration by tissue scaffolding is an emerging technique with many potential applications. While it is well-known that the structural properties of tissue scaffolds play a critical role in cell regrowth, it is usually unclear how optimal tissue regeneration can be achieved. This thesis hereby presents a computational investigation of tissue scaffold design and optimisation. This study proposes an isosurface-based characterisation and optimisation technique for the design of microscopic architecture, and a porosity-based approach for the design of macroscopic structure. The goal of this study is to physically define the optimal tissue scaffold construct, and to establish any link between cell viability and scaffold architecture. Single-objective and multi-objective topology optimisation was conducted at both microscopic and macroscopic scales to determine the ideal scaffold design. A high quality isosurface modelling technique was formulated and automated to define the microstructure in stereolithography format. Periodic structures with maximised permeability, and theoretically maximum diffusivity and bulk modulus were found using a modified level set method. Microstructures with specific effective diffusivity were also created by means of inverse homogenisation. Cell viability simulation was subsequently conducted to show that the optimised microstructures offered a more viable environment than those with random microstructure. The cell proliferation outcome in terms of cell number and survival rate was also improved through the optimisation of the macroscopic porosity profile. Additionally artificial vascular systems were created and optimised to enhance diffusive nutrient transport. The formation of vasculature in the optimisation process suggests that natural vascular systems acquire their fractal shapes through self-optimisation