5,815 research outputs found
Study of the behavior of a thermoplastic injection mold and prediction of fatigue failure with numerical simulation
Tese de doutoramento em Engenharia MecânicaO objetivo deste trabalho é a criação de uma metodologia de análise da resistência à fadiga de moldes de injeção de termoplásticos. Uma metodologia capaz de satisfazer o mercado atual que exige a diminuição do tempo de entrega e custos de moldes de injeção, sem comprometer a sua fiabilidade.
Para o desenvolvimento desta metodologia, foram utilizados modelos digitais. Com estes modelos é possível executar-se várias iterações sem os custos de um modelo físico. Além do menor custo dos modelos digitais, também é possível compreender o comportamento de cada molde no decorrer da fase de projeto.
Com o aumento da complexidade dos componentes injetados, o estudo da resistência à fadiga tende a ser cada vez mais importante. Neste trabalho serão apresentados cuidados a ter na preparação dos modelos digitais, de forma a obter-se resultados fiáveis.
No desenvolvimento desta metodologia, usaram-se dois softwares de simulação numérica para gerar os modelos digitais. Um deles dedica-se ao estudo reológico de peças termoplásticas e outro ao comportamento estrutural dos moldes de injeção.
A execução de simulações numéricas requer uma boa caracterização dos materiais usados. No caso dos termoplásticos, os fabricantes têm uma grande base de dados com a informação necessária para as simulações numéricas. No entanto, para as simulações estruturais, os fabricantes tendem apenas a fornecer os dados das curvas monotónicas, os quais não fornecem qualquer informação sobre o comportamento à fadiga. Portanto, neste trabalho foram estudados modelos empíricos que se adaptam aos aços usados em moldes de injeção, a partir dos quais é possível gerar as curvas S-N e e-N. De modo a avaliar qual o modelo empírico que se adaptaria melhor a esta área, foram realizados ensaios experimentais com provetes feitos em EN 1.2311. A partir destes ensaios, escolheu-se o modelo empírico mais conservador. Com base no modelo empírico escolhido, foi desenvolvida uma aplicação capaz de gerar as curvas S-N e e-N, a partir das informações fornecidas pela aciaria.
Além da caracterização dos materiais, também é importante que as condições de carregamento do modelo numérico estrutural sejam o mais aproximadas possível do que irá ocorrer no modelo físico. Como as cargas deste modelo numérico podem ser previstas a partir do modelo numérico reológico, a criação de uma ponte entre estes dois modelos numéricos é imprescindível. Logo, neste trabalho foi construída uma aplicação capaz de converter os dados gerados pelo software comercial Moldflow em ficheiros capazes de serem lidos por softwares comerciais de simulação numérica estrutural. Usando esta aplicação para a conversão dos dados, foram realizadas simulações e comparadas com os respetivos modelos físicos. Verificou-se que é possível replicar o comportamento do molde em modelos digitais. No entanto, os modelos digitais dos moldes de injeção estudados tenderam a apresentar resultados conservadores quando comparados com os modelos físicos.
Por fim, foi desenvolvida uma aplicação capaz de usar dados calculados a partir de softwares comerciais de cálculo numérico estrutural para a determinação da resistência dos moldes à fadiga. Aqui foi tido em conta o modelo para geração das curvas de fadiga dos materiais validado. Os modelos de cálculo à fadiga na aplicação baseiam-se na regra de Palmgren – Miner para a determinação dos ciclos até à nucleação da fissura. O cálculo das tensões alternadas foi realizado a partir de dois métodos, o critério da tensão de corte octaédrica e o método de Sines. Para testar a aplicação foram escolhidos cinco moldes que apresentaram falhas por fadiga. Em seguida, foi aplicada a metodologia proposta neste trabalho para a determinação da resistência dos mesmos à fadiga. A partir da aplicação desta metodologia e das ferramentas desenvolvidas para o seu emprego, foi possível verificar que esta é capaz de prever as zonas onde ocorreram as falhas, bem como outras com probabilidade de nucleação de fissuras.
Portanto, no decorrer deste trabalho foi possível criar uma metodologia e ferramentas de apoio para o cálculo de moldes à fadiga. Assim, projetistas de moldes podem ter uma boa perspetiva da resistência à fadiga de moldes de injeção ainda em projeto, tendo por base métodos científicos.The objective of this work is to create a methodology to analyze the fatigue resistance of thermoplastic injection molds. A methodology capable of satisfying the current market that demands a decrease in the delivery time and costs of injection molds, without compromising their reliability.
To develop this methodology, digital models were used. With these models it is possible to execute several iterations without the costs of a physical model. Besides the lower cost of digital models, it is also possible to understand the behavior of each mold during the design phase.
With the increasing complexity of injected components, the study of fatigue resistance tends to be more and more important. In this work, care will be presented in the preparation of the digital models, in order to obtain reliable results.
In the development of this methodology, two numerical simulation software’s were used to generate the digital models. One of them is dedicated to the rheological study of thermoplastic parts and the other to the structural behavior of injection molds.
The execution of numerical simulations requires a good characterization of the materials used. In the case of thermoplastics, manufacturers have a large database with the information needed for numerical simulations. However, for structural simulations, manufacturers tend to provide only monotonic curve data, which do not provide any information about fatigue behavior. Therefore, in this work, empirical models that fit the steels used in injection molds were studied, from which it is possible to generate the S-N and e-N curves. In order to evaluate which empirical model would best fit this area, experimental tests were performed with specimens made in EN 1.2311. From these tests, the most conservative empirical model was chosen. Based on the chosen empirical model, an application capable of generating the S-N and e-N curves from the information provided by the steel mill was developed.
Besides the characterization of the materials, it is also important that the loading conditions of the numerical structural model are as close as possible to what will occur in the physical model. Since the loads of this numerical model can be predicted from the rheological numerical model, the creation of a bridge between these two numerical models is essential. Therefore, in this work was built an application capable of converting the data generated by the commercial software Moldflow into files capable of being read by commercial structural numerical simulation software. Using this application for data conversion, simulations were performed and compared with the respective physical models. It was found that it is possible to replicate the mold behavior in digital models. However, the digital models of the injection molds studied tended to present conservative results when compared to the physical models. Finally, an application capable of using data calculated from commercial numerical structural calculation software was developed for determining the fatigue resistance of molds. Here the validated model for generating the fatigue curves of the materials was taken into account. The fatigue calculation models in the application are based on the Palmgren - Miner rule for the determination of the cycles until crack nucleation. The alternating stresses calculation was performed from two methods, the octahedral shear stress criterion and the Sines method. To test the application, five molds that presented fatigue failures were chosen. Then, the methodology proposed in this work was applied to determine their fatigue resistance. From the application of this methodology and the tools developed for its use, it was possible to verify that it is able to predict the areas where the failures occurred, as well as others with a probability of crack nucleation.
Therefore, during this work it was possible to create a methodology and support tools for the calculation of fatigue molds. Thus, mold designers can have a good perspective of the fatigue resistance of injection molds still in project, based on scientific methods
Genetic Conditions Affecting the Skeleton
In this Special Issue of Genes entitled “Genetic Conditions Affecting the Skeleton: Congenital, Idiopathic Scoliosis and Arthrogryposis”, evidence is presented that suggests that congenital, idiopathic scoliosis, and arthrogryposis share similar overlapping, but also distinct, etiopathogenic mechanisms, including connective tissue and neuromuscular mechanisms. Congenital scoliosis (CS) is defined by the presence of an abnormal spinal curvature, due to an underlying vertebral bony malformation (VM). Idiopathic scoliosis (IS) is defined by the presence of an abnormal structural spinal curvature of ≥10 degrees in the sagittal plane, in the absence of an underlying VM. Arthrogryposis is defined by the presence of congenital contractures in two or more joints of the appendicular skeleton. All three conditions have complex genetic causes. This Special Issue highlights the complex nature of these conditions and current concepts in our approach to better understand their genetics
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Self-Limiting Morphologies in Geometrically Frustrated Assemblies
Geometrically frustrated assembly, where locally preferred motifs are incompatible with constraints on global ordering of the assembly, may result in a super-extensive energy penalty to assembly growth and self-limitation of the assembly size. Using theory and simulation, we study how this mechanism may also shape the assembly\u27s boundary and its interior packing, which are distinct morphological changes. In Chapter 1, we provide some background and a theoretical framework for understanding self-limiting behavior due to geometric frustration. Three distinct projects are detailed in the subsequent chapters: original numerical results are presented on competing responses to frustration in helical bundles made of chiral filaments in Chapter 2, a novel tilt-curvature coupling and its consequences in microphase separated chiral rod membranes are illustrated by both numerical and theoretical results in Chapter 3, and a new particle model for simulation of saddle-wedge membrane assemblies with new theoretical advancement of a continuum model and new numerical results are presented in Chapter 4. In Chapter 5, we conclude by considering lessons from this work for future engineering of self-limiting materials
Determining the Mechanisms and Applications of Covalent Bonding Between Atmospheric Pressure Plasma Jet Activated Surfaces and Biomolecules
3D bioprinting, where cells, hydrogels and structural polymers can be printed layer by layer into complex designs, holds great promise for advances in medicine and the biomedical sciences. The immobilisation of biomolecules on the surfaces of structures is a powerful way to introduce bioactivity to perform useful functions. Functions include minimising the foreign body response, and directing the differentiation of cells. Covalent immobilisation is the gold standard. However, existing approaches for covalent immobilisation are unsuitable for 3D bioprinting, with shortcomings such as reagent toxicity, long reaction times, and limited patterning capabilities.
This thesis demonstrates that atmospheric pressure plasma jets (APPJs) are capable of activating polymers for single-step, reagent-free immobilisation with a range of biomolecules, hydrogels and polymers. This capability has been shown on 2D & 3D printed structures, and with hydrogels and biomolecules co-immobilised. Furthermore, immobilised biomolecules induced increased rates of chondrogenic differentiation compared to a standard protein-in-medium approach. This is evidence that biomolecules immobilised by APPJ treatment are bioactive, cytocompatible and can guide stem cell differentiation. Moreover, it was determined that reactive oxygen species alone are the mechanism of covalent immobilisation on APPJ treated surfaces, and that any macromolecule presenting amine or thiol should be able to immobilise.
This thesis has established the potential for APPJ as a general purpose surface modification tool within 3D bioprinters. With the ability to immobilise biomolecules in such a way, these new bioprinters will be in a far stronger position to mimic and interact with biological systems, paving the way for a range of emerging healthcare technologies
Feature Papers in Compounds
This book represents a collection of contributions in the field of the synthesis and characterization of chemical compounds, natural products, chemical reactivity, and computational chemistry. Among its contents, the reader will find high-quality, peer-reviewed research and review articles that were published in the open access journal Compounds by members of the Editorial Board and the authors invited by the Editorial Office and Editor-in-Chief
Identification and Quantification of Sperm Head Plasma Membrane Proteins Associated with Male Fertility
The major objective was to characterize proteins in head plasma membrane (HPM) of sperm from animals of two species to identify species’ and proteins’ differences related to fertility. HPM’s sodium/potassium-ATPase (Na+⁄K+-ATPase) acts as a receptor, inducing capacitation when bound by its hormone ouabain. Na+/K+-ATPase is an α/β dimer, each with several isoforms (α1, α2, α3, α4, β1, β2, β3) whose exact relationship to in vivo fertility and capacitation is unknown. In the first study, specific Na+/K+-ATPase isoforms in sperm HPM of boars with different Direct Boar Effects (DBEs) for farrowing rate (FR) and litter size, differed between low and high fertility boars (LF, HF, n=6/each; DBE-based). SDS-PAGE and immunoblotting detected more α3 (P or <100; Semex evaluated). Statistical analysis identified 67 differential abundance proteins (DAPs) between HF and LF (n=3/group; P<0.05), which associated by meta-analysis to BFI. Gene ontology assigned 48 up-regulated HF proteins to sperm fertilization, and 19 down-regulated to catalytic and transporter activity. 38-up-regulated DAPs (HF and LF, n=16) correlated positively (r2=0.29 to 0.66; P≤0.05) and 6 down-regulated negatively (r2=0.26 to 0.44; P≤0.05) to BFI. The third study characterized HPM Na+/K+-ATPase in 16 bulls with differing BFI but similar sperm motility kinetics. Normalized Spectral Abundance Factor (NSAF) of α1 was significantly greater in 8 higher- vs 8 lower-fertility bulls. Linear regression positively correlated BFI to NSAF of α1 and β2 (r2=0.42 and 0.47, respectively; P≤0.05), and negatively correlated BFI to α4 (r2=0.37; P≤0.05), confirmed by bioinformatics predictions. These results suggest involvement of α1 and β2 in fertilization as potential fertility biomarkers. Overall, specific Na+/K+-ATPase isoforms identified in boar and bull sperm HPM significantly correlate with in vivo fertility, as do other specific bull HPM proteins. Elucidating potential fertility biomarkers in two species improves understanding of key proteins and their roles in various, complex mechanisms that enable successful sperm fertilization
Bionic Lid Implant for Natural Closure (BLINC)
Facial nerve palsy (FNP) leads to an inability to blink. The exposed eye is at risk of developing corneal keratopathy and currently there is a lack of solution to active eye closure that is immediate and reliable. Bionic Lid Implant for Natural Closure (BLINC) proposes the use of an implantable actuator combined with the effects of an eyelid sling for dynamic eye closure. The aims of this thesis are to 1) explore the clinical need for BLINC, 2) describe the BLINC technology, and 3) present the results of its application in cadaveric and live models.
Methods
The aims of this project are addressed in three parts. In part one, the current therapies addressing key clinical end points in FNP from an ocular perspective and the setting where BLINC may first be used are explored. In part two the science behind BLINC is outlined. Finally in part three application of BLINC in cadaveric and live models are studied followed by a discussion on future steps preceding a pilot study in humans.
Results
Patients with FNP consistently identify issues related to the eye a primary concern. Current reanimation strategies offer the possibility of dynamic eye closure but the results are delayed and often unpredictable. BLINC reliably achieves active eye closure in cadaveric models by means of a wireless-powered, implantable electromagnetic actuator in conjunction with an eyelid sling. BLINC closes the eye in a similar fashion to natural closure
for a symmetrical blink in FNP. Successful application of an inactive device in its complete form is achieved in a live animal without significant morbidity.
Conclusion
BLINC offers the possibility of restoring active eye closure with use of an implantable actuator. The concept has been successfully demonstrated in cadaveric models with successful device implantation in a live model. Future live trials are needed to address the remaining biocompatibility issues in preparation for human application
Towards the Development of Flexible Substrate Materials for Label-free Surface Enhanced Raman Spectroscopy (SERS) and Photo-induced Enhanced Raman Spectroscopy (PIERS)
This thesis is concerned with the label-free detection of small molecules and
macromolecules using enhanced Raman spectroscopic techniques: Surfaceenhanced Raman Spectroscopy (SERS) and photo-induced enhanced Raman
spectroscopy (PIERS). The work focuses on the development of reproducible
and stable plasmonic nanoparticles (NPs) incorporated into flexible substrates
to realise their SERS potential. The materials have been designed to fulfil the
criteria of flexible and sensitive substrates in many applications with an
emphasis in the biomedical field, especially within wound healing. A number of
measurements on varying molecules were conducted to assess the SERS
efficacy of the substrates. Most of the novel research presented in this thesis is
proof-of-concept, laying the framework for further work.
Chapter I highlights the importance of SERS and potential of PIERS with a
thorough evaluation of the literature. Motivations behind the research as well as
the aims of this work are addressed. Theoretical concepts are introduced with a
touch on the mathematical background. Key principles and parameters
influencing SERS and considerations are all covered to give a complete outline
of the topic.
The next few chapters focus on the results of this thesis. Chapter II provides
synthetic routes for gold nanoparticles and includes a comparative study on the
influence on nanoparticle shape on their subsequent SERS function. The
effects of capping agents on the shape, size and stability of the NPs are
examined. These are fully characterised and functional SERS testing is carried
out using a range of molecules to fully evaluate their SERS ability. Surface
modification is also attempted in this work with great concern given to
overpowering solvent effects. Several biomarkers are introduced with qualitative
SERS analysis. Duplex testing was performed to determine the specificity and
sensitivity of the gold NPs.
Chapter III starts investigating flexible materials as SERS substrates. These are
readily available, low cost and biocompatible materials with gold NPs
incorporated into them to become SERS active. Simple methods for synthesis
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and data collection are presented as well as their SERS results. Paper and
PDMS, whilst having some advantages lack clear Raman enhancement with
inherent material signals dominating the spectra. Gelatine based hydrogels are
chosen as an ideal candidate for SERS substrates. Many gelatine/polymer
blends are synthesised and characterised to find the optimum gel regarding
both mechanical and chemical permanence as well as SERS capability. Studies
looking into cross-linking agents to establish the best synthetic protocol are
executed. There is always a trade-off between highest functional efficiency and
a more ‘green’ and sustainable approach. The PVA/hydrogel nanocomposite
material exhibits valuable SERS whilst maintaining a facile methodology for
synthesis and data acquisition.
Chapter IV extends the SERS studies to biological macromolecules such as
proteins and wound biomarkers. Both colloidal NPs and hydrogels are used as
substrates. Concentration studies are conducted and attempts at correlating
intensity with concentration are made, to limited realization. Real samples from
patients are probed with patterns and trends hypothesised. These are
corroborated against photographic evidence of the wound. Preliminary machine
learning is employed to help classify the data with suggestive, positive results.
Chapter V inspects PIERS on biomolecules with varying degrees of
enhancements, but low concentration detection of glucose is reported. Different
TiO2 substrates are investigated for their influence in the PIERS effect and are
characterised appropriately. The preparation method, film thickness and wetting
behaviour of the property are likely parameters that can impact the PIERS
property of the substrate. Comparisons between SERS and PIERS reveal
complex mechanistic considerations between the two phenomena. As a novel
technique the possibilities to fully realise the potential of PIERS is yet to be
explored, but there is a lot more research to be done to fully understand the
effect.
This thesis concludes with a summary of the key findings from the experimental
work and presents possible avenues for further research to consolidate and
advance the current work
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