확률적 열화학 점탄성 모델을 적용한 탄소섬유 강화 적층 복합재료의 가상 RTM제조 시뮬레이션

학위논문 (석사) -- 서울대학교 대학원 : 공과대학 항공우주공학과, 2020. 8. 윤군진.Composite materials undergo a shrinkage process related to the curing kinetics of the matrix. This shrinkage effect, added to the material thermal expansion, results in geometric distortions and residual interlaminar stresses that affect negatively the mechanical response of the materials. This work addresses the effects of the manufacturing process on carbon fiber reinforced composite laminates used in aerospace structures. Here, computational tools are implemented to model a viscoelastic material with degree of cure and time-dependent properties. Additionally, probabilistic modeling tools are implemented in the interest of increasing the reliability of the results by considering the random nature of curing kinetics parameters. The model consists of a multiphysics system that couples the thermochemical and mechanical processes. First, the heat transfer analysis is performed by relating Fouriers heat conduction governing equations with Kamals model of curing kinetics. Then, for the mechanical analysis, a 9-element Generalized Maxwell Model is implemented to compute the viscoelastic behavior. The representation of a cure and time-dependent viscoelastic model is possible due to the thermorheologically simple nature of the thermosetting resins. Here, a shift factor is applied to obtain stress relaxation times that change with the temperature and the degree of cure of the material. To produce the stochastic behavior of the materials, random fields were created by implementing the Karhunen-Loève Expansion method with a Monte Carlo simulation. The manufacturing method consisted of a vacuum-assisted transfer molding (VARTM) with a post-curing treatment. To emulate this process, the mechanical and thermal boundary conditions are divided into four stages. The first one refers to the curing stage. Here, the plate is constrained in the mold and subjected to thermal conduction in the surfaces. The second stage is when the plate is released from the mold and left to cool down to room temperature by natural convection. The third stage consists of placing the cooled plate into an oven (forced thermal convection). Finally, the plate is left to cool down as in the second stage. The stress and distortions that result from this manufacturing process were analyzed in six plates with different ply configurations. The results showed that the quasi-isotropic laminate [−60/−30/0/30/60/90] undergoes the highest interlaminar stresses and distortions, followed by the asymmetric cross-ply laminate[903/03] . tt also revealed that the post-curing process increases the interlaminar residual stresses in most of the laminates, especially in the case of the antisymmetric angle ply laminate. The effect of the cure dependent viscoelastic model is then compared to a basic linear elastic material response. Revealing that a viscoelastic model predicts higher stresses during the curing stage (in-mold plates) but lower stresses once the plates are released from the molds. Finally, the effects of taking into account the random nature of the curing kinetics parameters were observed in the curing stage of a cross-ply laminate. This analysis revealed that the stresses can be 23.86% higher than the values predicted from a viscoelastic model that ignores this effect. Demonstrating the importance of considering the random nature of the properties involved in the curing process.복합 재료는 매트릭스(matrix)의 경화 속도에 관련된 수축 과정을 거친다. 재료 열팽창에 더해지는 이러한 수축 효과는 재료의 기계적 성능에 부정적인 영향을 미치는 기하학적 비틀림과 잔류 층간 응력을 초래한다. 본 연구는 항공 우주 구조물에 사용되는 탄소 섬유 강화 복합재료 라미네이트(laminate)에 제조 공정이 미치는 영향을 분석한다. 여기서, 경화 정도 및 시간 의존적 특성을 갖는 점탄성 재료를 모델링하는 컴퓨터 시뮬레이션 툴이 구현된다. 또한, 결과의 신뢰성을 높이기 위해 경화 동역학 파라미터의 랜덤 특성을 고려하는 확률론적 모델이 구현된다. 이 모델은 열화학 및 기계 공정을 결합하는 다중 물리 시스템으로 구성된다. 먼저, 열전달 해석은 FourierFourier의 열전도 지배 방정식과 Kamal의 경화 동역학 모델을 통해 수행된다. 그런 다음 점탄성 거동을 나타내기 위해 아홉개의 요소(9-element)로 일반화 된 Maxwell 모델이 구현된다. 재료모델이 경화 모델과 점탄성 모델 만으로 표현될 수 있는 이유는 열경화성 수지가 열/유동학적으로 간단한 성질을 가지기 때문이다. 여기서, 재료의 온도 및 경화 정도에 따라 변화하는 응력 완화 시간을 얻기 위해 환산 인자(shift factor)가 적용된다. 재료의 확률론적 거동을 나타내는 랜덤 필드(random field)는 Monte Carlo 시뮬레이션으로 Karhunen-Loève Expansion 방법을 구현하여 만들어진다. 이번 연구에서 모델링하는 제조 공정은 진공 레진 전달 몰딩(vacuumvacuum--assisted transfer molding, assisted transfer molding, VARTM)과 그 후처리 과정으로 구성되었다. 이 공정을 모방하기 위한 열기계적 경계 조건은 4 단계로 나뉜다. 첫 번째는 경화 단계이다. 여기서 플레이트는 몰드(mold)에 구속되고 몰드 표면에서 열 전도가 일어난다. 두 번째 단계는 플레이트가 몰드에서 분리되어 대류에 의해 상온으로 냉각되는 상태이다. 세 번째 단계는 냉각된 플레이트를 오븐(강제 열 대류)에 넣는 것이다. 마지막으로, 플레이트는 두 번째 단계에서와 같이 냉각되도록 방치된다. 이 제조 공정에서 발생하는 응력과 비틀림은 플라이 구성이 다른 6 개의 플레이트에 대해 분석되었다. 시뮬레이션 결과 준 등방성 라미네이트 [-60 / -30 / 0 / 30 / 60 / 90]가 가장 높은 층간 응력과 비틀림을 겪었고 그 다음으로는 비대칭 크로스-플라이(cross-ply) 라미네이트[903/03] 가 높은 층간 응력과 비틀림을 기록했다. 또한, 후처리 공정은 대부분의 비대칭 앵글 플라이(angle ply) 라미네이트에서 층간 잔류 응력을 증가시키는 것으로 밝혀졌다. 경화 의존 점탄성 모델의 타당성은 선형 탄성 재료모델과의 비교를 통해 검증된다. 점탄성 모델은 선형 탄성 모델에 비해 경화 단계에서는 더 높은 응력을 예측하지만 플레이트가 몰드에서 분리되면 더 낮은 응력을 보여준다. 마지막으로, 경화 동역학 파라미터의 랜덤 특성을 고려함에 따른 효과는 크로스-플라이 라미네이트의 경화 단계에서 관찰되었다. 랜덤 특성을 고려한 모델은 이 효과를 고려하지 않은 모델에 비해서 최대 23.86% 더 높은 응력을 가질 수 있음이 관측되었다. 이는 경화 공정과 관련된 랜덤 특성을 고려하는 것이 복합재료 경화 공정을 해석하는 데에 매우 중요 함을 보여준다.Chapter 1. Introduction 1 1.1 Aerospace Industry Materials 2 1.2 Composite Materials 4 1.3 Manufacture of Composite Materials 6 1.4 Previous Research 9 1.5 Thesis Structure 10 Chapter 2. Literature Review 11 2.1 Thermochemical Model 11 2.2 Viscoelastic Model 14 2.2.1 Analog Mechanical Models 15 2.2.2 Multiple Element Models 20 2.2.3 Generalized Kelvin Model 21 2.2.4 Generalized Maxwell Model 22 2.3 Cure and temperature dependence 24 2.4 Random Field Modeling 28 2.4.1 Orthogonal Series Expansion 29 2.4.2 Karhunen-Loève Expansion 31 2.4.3 Parameters to be randomized 33 2.5 Classical Lamination Theory 34 Chapter 3. Materials and Methodology 36 3.1 Materials 36 3.2 Methodology 40 3.3 Experimental Setup 44 Chapter 4. Model Verification 46 Chapter 5. Results 50 5.1 Residual stress comparison 50 5.2 Cure-induced distortion 53 5.3 Curing-induced distortions coupling effects 58 5.4 Post curing-induced stress and distortion 64 5.5 Viscoelasticity Effects 66 5.6 Random Field Distribution 68 5.7 Experimental Results 73 6. Conclusions 78 Bibliography 81 Appendix 91 Appendix A. Laminate Stiffness Matrix 91 Appendix B. Thermochemical analysis code 93Maste

Determinación del potencial y los requerimientos para aplicar la tecnología de gasificación por plasma en el tratamiento de desechos y la producción de energía eléctrica en el país

Proyecto de Investigación. Instituto Tecnológico de Costa Rica. Vicerrectoría de Investigación y Extensión (VIE). Escuela de Física, 2012Este informe se enfoca en la implementación de tratamientos con plasmas térmicos como una alternativa o complemento para métodos existentes para el manejo de desechos en Costa Rica. Se tomó en cuenta varios desechos posibles y se evaluó la factibilidad de comprar sistemas existentes o crear versiones locales de estas tecnologías

Proyecto de ejecución y repavimentación de casco céntrico en la ciudad de Villa Allende

Práctica Supervisada (IC)--FCEFN-UNC, 2017Describe el proceso de planificación y ejecución de la repavimentación de casco céntrico en la ciudad de Villa Allende. Identifica los principales aspectos que hacen al control de gestión y certificación de obra y describe principalmente aspectos de control de calida

A randomized controlled trial comparing nerve block and mandibular infiltration techniques in posterior mandible implant surgeries

To compare global surgical pain under nerve block and mandibular infiltration anesthesia techniques, and to evaluate pain during drilling and the distance to the mandibular canal in posterior mandible implant surgeries. A prospective, randomized, controlled, double-blind, clinical trial was conducted to compare nerve block (Group A) to mandibular infiltration (Group B) techniques for dental implant placement. Global surgical pain (VAS = visual analogue scale), pain during drilling or implant placement (MPQ = McGill pain questionnaire) and distance to the mandibular canal (Image J) were statically analyzed. Age, gender, anxiety levels, tooth to be replaced, implant size, adjacent teeth and duration of surgery were also analyzed. 172 patients were included and 283 dental implants were analyzed. VAS values were significantly higher in Group B (p<0.05). In Group A, 99% of the surgeries were performed painlessly during drilling and implant placement, but in Group B, 11.6% of implant placements (17 implants) felt pain during these surgical steps. Mean distance to mandibular canal (3.8 mm, range: 0.0 to 7.0) in those 17 implants placed under mandibular infiltration was clinically and statistically similar to the mean distance (3.0 mm, range: 0.0 to 9.0) of 130 implants placed painless (p=0.10). Pain during drilling under mandibular infiltration was significantly associated with the duration of surgery (p<0.05) and to both adjacent teeth being present (p<0.05). Although both techniques are safe and effective for placing implants in the posterior mandible, nerve block provides a more profound analgesia than mandibular infiltration. When placing implants under mandibular infiltration, as getting closer to the canal does not increase the feeling of pain, it is not recommended to use the presence of pain as a preventive resource to avoid inferior alveolar nerve injuries

Activation of iNKT Cells Prevents Salmonella-Enterocolitis and Salmonella-Induced Reactive Arthritis by Downregulating IL-17-Producing γδT Cells

Reactive arthritis (ReA) is an inflammatory condition of the joints that arises following an infection. Salmonella enterocolitis is one of the most common infections leading to ReA. Although the pathogenesis remains unclear, it is known that IL-17 plays a pivotal role in the development of ReA. IL-17-producers cells are mainly Th17, iNKT, and γδT lymphocytes. It is known that iNKT cells regulate the development of Th17 lineage. Whether iNKT cells also regulate γδT lymphocytes differentiation is unknown. We found that iNKT cells play a protective role in ReA. BALB/c Jα18−/− mice suffered a severe Salmonella enterocolitis, a 3.5-fold increase in IL-17 expression and aggravated inflammation of the synovial membrane. On the other hand, activation of iNKT cells with α-GalCer abrogated IL-17 response to Salmonella enterocolitis and prevented intestinal and joint tissue damage. Moreover, the anti-inflammatory effect of α-GalCer was related to a drop in the proportion of IL-17-producing γδT lymphocytes (IL17-γδTcells) rather than to a decrease in Th17 cells. In summary, we here show that iNKT cells play a protective role against Salmonella-enterocolitis and Salmonella-induced ReA by downregulating IL17-γδTcells.Fil: Noto Llana, Mariangeles. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones en Microbiología y Parasitología Médica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en Microbiología y Parasitología Médica; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Microbiología; ArgentinaFil: Sarnacki, Sebastian Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones en Microbiología y Parasitología Médica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en Microbiología y Parasitología Médica; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Microbiología; ArgentinaFil: Morales, Andrea Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones en Microbiología y Parasitología Médica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en Microbiología y Parasitología Médica; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Microbiología; ArgentinaFil: Aya Castañeda, Maria del Rosario. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones en Microbiología y Parasitología Médica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en Microbiología y Parasitología Médica; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Microbiología; ArgentinaFil: Giacomodonato, Mónica Nancy. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones en Microbiología y Parasitología Médica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en Microbiología y Parasitología Médica; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Microbiología; ArgentinaFil: Blanco, Guillermo Armando C.. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni; ArgentinaFil: Cerquetti, Maria Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones en Microbiología y Parasitología Médica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en Microbiología y Parasitología Médica; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Microbiología; Argentin

Romeo y Julián, representaciones de las parejas homosexuales en la televisión Colombiana, una perspectiva desde el diseño gráfico.

En los últimos años ha existido una considerable representación de personajes LGBT en producciones colombianas, el propósito de esta investigación es analizar una de las más recientes en la novela Hermanos y Hermanas, para conocer cómo sus elementos visuales naturalizan unas representaciones de parejas homosexuales, por medio de un análisis de contenido de la serie, un taller a una muestra de 30 personas y una serie de entrevistas a hombres y parejas homosexuales, evidenciando la importancia de ese mensaje visual en la consolidación de estereotipos y una nueva propuesta que apoye la visibilidad de múltiples realidades del colectivo, posicionando a Hermanos y Hermanas como un enfoque nuevo, alejado de los clichés del pasado pero aun con mucho que mejorar, todo esto desde una perspectiva del diseño gráfico.In recent years there has been a considerable representation of LGBT characters in Colombian productions, the purpose of this research is to analyze one of the most recent in the novel Hermanos y Hermanas, to know how its visual elements naturalize representations of homosexual couples, through from an analysis of the content of the series, a workshop with a sample of 30 people and a series of interviews with men and homosexual couples, showing the importance of this visual message in the consolidation of stereotypes and a new proposal that supports the visibility of multiple collective realities, positioning Brothers and Sisters as a new approach, away from the clichés of the past but still with much to improve, all from a graphic design perspective

Optimal monetary policy with non-homothetic preferences

This paper explores the optimal design of monetary policy in a multisector model where agents' preferences are non-homothetic. Non-homotheticity derives from the existence of a minimum consumption requirement for food, which households need to satisfy for subsistence. We find that the introduction of a minimum consumption requirement reduces the weight on food inflation in the optimal index that the monetary authority should target. We identify three motives for such prescription. First, non-homothetic preferences turn the stabilization of food inflation more costly, as it requires larger deviations of output from the efficient level. Second, proximity to the subsistence level turns the demand for food insensitive to monetary policy. Inflation in this sector thus becomes difficult to control. Third, non-homothetic preferences imply that households spend only a small share of any additional income on food. This means that prices in this sector have a reduced impact on aggregate consumption demand. Hence, responding to inflation in this sector becomes less relevant. Importantly, our results provide a rationale for targeting an index that excludes (or attaches a limited weight to) food inflation, a usual practice amongst central bankers

Uniminuto second semester student´s perceptions about a series of tasks based on song in the pronuncuation clubs.

This research project examines a series of tasks based on songs in which they were used as a key factor to deal with pronunciation problems in English inside a Task-Based Instruction (TBI) approach. This action research was carried out at Uniminuto University, a private university in Bogotá with a group of second semester students who belonged to the B.A. in English Language Teaching. The starting point was a needs analysis which revealed the perceptions that such group of students had in regards to an extracurricular space called Pronunciation Clubs offered by such Bachelor Program to its students in order to work on their pronunciation. Therefore, six lessons based on songs inside a TBI framework with communicative tasks were designed and implemented in order to allow students to put into practice the five pronunciation features selected by means of real contexts with real people in different situations. The changes in regards to students’ perceptions about the Pronunciation Clubs, their improvements in regards to their pronunciation, and the benefits of using TBI approach in such Pronunciation Clubs were recorded as the main results of this action research project

Modeling Collective Animal Behavior with a Cognitive Perspective: A Methodological Framework

The last decades have seen an increasing interest in modeling collective animal behavior. Some studies try to reproduce as accurately as possible the collective dynamics and patterns observed in several animal groups with biologically plausible, individual behavioral rules. The objective is then essentially to demonstrate that the observed collective features may be the result of self-organizing processes involving quite simple individual behaviors. Other studies concentrate on the objective of establishing or enriching links between collective behavior researches and cognitive or physiological ones, which then requires that each individual rule be carefully validated. Here we discuss the methodological consequences of this additional requirement. Using the example of corpse clustering in ants, we first illustrate that it may be impossible to discriminate among alternative individual rules by considering only observational data collected at the group level. Six individual behavioral models are described: They are clearly distinct in terms of individual behaviors, they all reproduce satisfactorily the collective dynamics and distribution patterns observed in experiments, and we show theoretically that it is strictly impossible to discriminate two of these models even in the limit of an infinite amount of data whatever the accuracy level. A set of methodological steps are then listed and discussed as practical ways to partially overcome this problem. They involve complementary experimental protocols specifically designed to address the behavioral rules successively, conserving group-level data for the overall model validation. In this context, we highlight the importance of maintaining a sharp distinction between model enunciation, with explicit references to validated biological concepts, and formal translation of these concepts in terms of quantitative state variables and fittable functional dependences. Illustrative examples are provided of the benefits expected during the often long and difficult process of refining a behavioral model, designing adapted experimental protocols and inversing model parameters

Decoration of squalenoyl-gemcitabine nanoparticles with squalenyl-hydroxybisphosphonate for the treatment of bone tumors

Therapeutic perspectives of bone tumors such as osteosarcom are main restricted due to the inefficacy of current treatments. We propose here the construction of a novel anticancers qualene-based nanomedicine with bone affinity and retention capacity. A squalenyl-hydroxybisphosphonate molecule was synthetized by chemical conjugation of a 1-hydroxyl-1,1-bi-sphosphonatemoiety to the squalenechain. This amphiphilic compound was inserted onto squalenoyl-gemcitabinenano-particles using the nanoprecipitation method. The co-assemblyled to nanoconstructsof 75 nm, with different morphology and colloidal properties. The presence of squalenyl-hydroxybi-sphosphonate enhanced the nanoparticles binding affinity for hydroxyapatite,a mineral present in the bone. Moreover, the in vitro anticancer activity was preserved when tested in commercial and patient-treated derived pedia tricoste osarcomacells. Furtherin vivo studies will shed lighton the potential of these nano medicines for the treatment of bones arcomas