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

Télescope H Alpha pour la surveillance de l'activité solaire et la météorologie spatiale

Cette étude présente un projet de télescope H alpha pour la surveillance de l'activité solaire et la météorologie spatiale: enjeux scientifiques et solutions techniques envisageable

Estudio sobre los factores que influyen en la pérdida de interés hacia las matemáticas

Este artículo presenta los resultados de una investigación sobre la pérdida gradual del interés hacia las matemáticas de 163 estudiantes del Colegio Filipense “Nuestra Señora de la Esperanza” de la ciudad de San Juan de Pasto, Nariño, Colombia. Los datos se recolectaron por medio de un cuestionario tipo Likert y entrevistas semi-estructuradas. Finalmente, se concluyó que la pérdida del interés hacia esta disciplina se debe a varios motivos: la desaparición paulatina del juego y de actividades didácticas que en la educación básica tenían una mayor presencia, la falta de actividades de motivación por parte del profesor y la poca relación que los estudiantes, de la educación media, ven con los temas tratados en clase de matemáticas con la vida diaria

Estudio acerca de los factores que influyen en la pérdida de interés hacia las matemáticas en los estudiantes del colegio Filipense de la ciudad de San Juan de Pasto, Colombia

Este artículo presenta los resultados de una investigación sobre la pérdida gradual del interés hacia las matemáticas de 163 estudiantes del Colegio Filipense “Nuestra Señora de la Esperanza” de la ciudad de San Juan de Pasto (Nariño). Los datos se recolectaron por medio de un cuestionario tipo Likert y entrevistas semiestructuradas. Finalmente, se concluyó que la pérdida del interés hacia esta disciplina se debe a varios motivos: la desaparición paulatina del juego y de actividades didácticas que en la educación básica tenían una mayor presencia, la falta de actividades de motivación por parte del profesor y la poca relación que los estudiantes de la educación media ven a los temas tratados en clase de matemáticas con la vida diaria

Elaboración de un estudio técnico de diseño para la creación de un nuevo tramo de acueducto y análisis de la situación actual del sistema con el objetivo de realizar propuestas de mejoras para el acueducto ubicado en Pénjamo de Florencia.

Proyecto de Graduación (Licenciatura en Ingeniería Agrícola) Instituto Tecnológico de Costa Rica, Escuela de Ingeniería Agrícola, 2020El presente proyecto se realizó en el acueducto rural de la comunidad de Pénjamo en Florencia de San Carlos, Alajuela. Se realizó una evaluación del sistema, el diseño de un nuevo trayecto de 408 metros de tubería y el diseño de un tanque de almacenamiento de 100 m3. El acueducto de la comunidad de Pénjamo consiste en una red de aproximadamente 15,60 km lineales de tubería y cuenta con 394 abonados para el año 2019. Se logra determinar para el acueducto, un déficit hídrico cercano a los 2 l/s para el año 2019, como también problemas de sobrepresión en tramos por debajo de los 240,00 m.s.n.m. El volumen de almacenamiento actual de 150 m3 no es el adecuado para abastecer la población futura estimada a 25 años, ya que se requiere de la implementación de otro tanque de 100 m3 que debe ser ubicado a una altura de 297,00 m.s.n.m en el sector de la tubería principal de la naciente Riggioni. Las propuestas de mejora son en sentido de regular presiones y balancear el sistema para que trabaje de manera unificada, permitiendo que el agua fluya un sentido u otro según la demanda de la población. La primera propuesta contempla la utilización de los diámetros actuales con la instalación de válvulas reguladoras de presión, la segunda propuesta incluye la modificación de los diámetros que no cumplan con el requisito mínimo estipulado por la norma técnica de diseño y de igual manera la colocación de válvulas reguladoras de presión.This project was carried out in the rural aqueduct of the community of Penjamo in Florencia of San Carlos, Alajuela. An evaluation of the system, the design of a new path of 408 meters of pipe and the design of a storage tank of 100 m3 was carried out. The aqueduct of the community of Pénjamo consists of a network of approximately 15,60 km of linear pipe and has 394 subscribers for the year 2019. It is possible to determine for the aqueduct, a water deficit close to 2 l/s for the year 2019, as well as problems of overpressure in sections below 240,00 m.a.s.l. The current storage volume of 150 m3 is not adequate to supply the future population estimated at 25 years, since it requires the implementation of another 100 m3 tank that must be located at a height of 297 meters in the sector of the main pipe of the nascent Riggioni. The proposals for improvement are in the sense of regular pressures and balance the system so that it works in a unified manner, which affects water to flow in one direction or another according to the demand of the population. The first proposal contemplates the use of the current parameters with the installation of pressure regulating valves, the second proposal includes the modification of the parameters that do not meet the minimum requirement stipulated by the technical design standard and in the same way the placement of valves pressure regulators

Integración de elementos para una aproximación sostenible en el diseño conceptual de transportadores continuos de sólidos a granel

Se integran elementos en la estructura de diseño conceptual de transportadores continuos de sólidos a granel para que el proceso de diseño conduzca a soluciones satisfactorias en términos operacionales y con un desempeño adecuado a nivel de sostenibilidad. La integración de estos elementos implica modificaciones a métodos existentes y el desarrollo de nuevos modelos para estimar el desempeño de los transportadores continuos desde una perspectiva ambiental, económica y social en una etapa conceptual. En el proceso de diseño se considera desde lo ambiental el consumo de energía, la intensidad de recursos en fabricación, las emisiones en operación y el potencial de reciclaje y reúso de los sistemas; desde lo social se considera los riesgos a la salud y la seguridad por la operación del equipo y desde lo económico se tiene en cuenta el costo de compra e instalación del equipo y todos los costos operacionales significativos. El diseño conceptual con integración de elementos para la aproximación sostenible como el listado de referencia, base de conocimiento para definición de alternativas, métodos de priorización multi-criterio y modelos de desempeño sostenible, condujo a resultados significativamente más atractivos que los obtenidos a través de estructuras tradicionales de diseño conceptual de transportadores al definir soluciones a problemas de transporte con menor costo de propiedad y menor consumo de energía.MaestríaMagister en Ingeniería Mecánic

Evaluación de la degradación de la tierra usando la entropía de shannon sobre imágenes polarimétricas en desiertos costeros Patagónicos

En esta investigación se focalizó en la Entropía de Shannon (ES) para la caracterización de imágenes polarimétricas de apertura sintética. Este parámetro analiza la contribución de la información por pixeles individuales para toda la imagen en la evaluación de la degradación de la tierra en imágenes ALOS PALSAR. Escenas de polarización dual y cuádruple fueron adquiridas bajo el proyecto SAOCOM (Satélite Argentino de Observación con Microondas) en 2010 y 2011, del desierto costero noreste patagónico, Argentina. Los mapas fueron verificados con información de alta verosimilitud para la misma área de estudio. Los resultados muestran que la ES puede describir y precisar las características de las imágenes de manera obvia, de tal manera que representa un valor de referencia para la detección de la degradación de la tierra y la extracción de las características de los diferentes estados y transiciones.We focus on Shannon Entropy (SE) for the characterization of polarimetric Synthetic Aperture Radar (PolSAR) images. This approach analyzes the information contribution made by individual pixels to the whole image for assessment of land degradation in the information content of ALOS PALSAR images. Additionally, the performance of other polarization parameters, and polarization decomposition is illustrated and discussed. Dual-Pol and Quad-Pol scenes have been acquired under the SAOCOM (Satélite Argentino de Observación con Microondas, Spanish for Argentine Microwaves Observation Satellite) project in 2010 and 2011, from northeastern Patagonian coastal desert, Argentina. The accuracy of the SE map was assessed using a set of ground observations based on remotely sensed data that have higher accuracy. The results show that the SE can describe and determine the image features more obviously in the study area, so that it represents an important reference value for land degradation detection and land status characteristics extraction .Fil: del Valle, Hector Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagonico; ArgentinaFil: Hardtke, Leonardo Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagonico; ArgentinaFil: Blanco, Paula Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagonico; ArgentinaFil: Sione, Walter Fabian. Universidad Autónoma de Entre Ríos. Fac de Ciencia y Tecnologia. Centro Regional de Geomatica; Argentina. Universidad Nacional de Luján; Argentin

Fecal carriage of Escherichia coli O157:H7 and carcass contamination in cattle at slaughter in northern Italy

Feedlot cattle slaughtered at a large abattoir in northern Italy during 2002 were examined for intestinal carriage and carcass contamination with Escherichia coli O157:H7. Carcass samples were taken following the excision method described in the Decision 471/2001/EC, and fecal material was taken from the colon of the calves after evisceration. Bacteria were isolated and identified according to the MFLP-80 and MFLP-90 procedures (Food Directorate’s Health Canada’s). Eighty-eight non-sorbitol-fermenting E. coli O157:H7 isolates were obtained from 12 of the 45 calves examined. In particular, E. coli O157:H7 isolates were found in 11 (24%) fecal and five (11%) carcass samples. PCR analysis showed that all 11 fecal samples and five carcass samples carried eae-γ1-positive E. coli O157:H7 isolates. In addition, genes encoding Shigatoxins were detected in O157:H7 isolates from nine and two of those 11 fecal and five carcasses, respectively. A representative group of 32 E. coli O157:H7 isolates was analyzed by phage typing and DNA macrorestriction fragment analysis (PFGE). Five phage types (PT8, PT32v, PT32, PT54, and PT not typable) and seven (I–VII) distinct restriction patterns of similarity > 85% were detected. Up to three different O157:H7 strains in an individual fecal sample and up to four from the same animal could be isolated. These findings provide evidence of the epidemiological importance of subtyping more than one isolate from the same sample. Phage typing together with PFGE proved to be very useful tools to detect cross-contamination among carcasses and should therefore be included in HACCP programs at abattoirs. The results showed that the same PFGE-phage type E. coli O157:H7 profile was detected in the fecal and carcass samples from an animal, and also in two more carcasses corresponding to two animals slaughtered the same day. [Int Microbiol 2007; 10(2):109-116

Análisis de las actitudes del profesional gallego ante la prevención escolar de las drogodependencias.

Sin resume

Baja endemicidad de parásitos intestinalesen tres distritos de Puriscal

Artículo científico -- Universidad de Costa Rica. Instituto de Investigaciones en Salud, 1985A study of the prevalence of intestinal parasites among 44 family units (198 individuals) in three Costa Rican rural districts was conducted by the Institute for Health Research (INISA). A very low prevalence of all parasites investigated was demonstrated in comparison with two surveys conducted in 1966 and 1982 in similar rural and urban areas. Giardia was the most frequently encountered parasite (12,17o), followed by Entamoeba histolytica (5%), Ancylostoma-Necator (4%), Trichuris (1.5%), Ascaris (1%) and Hymenolepis nana (0.5%). Strongyloides, Taenia, Dientamoeba, Balantidium and Cryptosporidium were not found. The low prevalence of intestinal parasites seems to correlate with the availability of water supply (in 76% of homes), the disposal of feces in latrines (90,4%) or water toilets (9.6%), the common wearing of shoes and the periodic deworming of the population. The improvement of other socioeconomic indicators such as income and education, and the marked dispersion of dwelligns explain the drastic reduction in parasites in recent yearsDe noviembre de 1983 a junio de 1984, se realizó un estudio transversal en el INISA para investigar la prevalencia de parásitos intestinales en 44 familias (198 individuos) de los distritos de Barbacoas, Grifo Alto y Candelarita del cantón de Puriscal. Se encontraron parásitos patógenos en el 24,7% de los individuos. Giardia fue el parásito más frecuente (12,1%), seguido por Entamoeba histolytica (5%), Ancylostoma-Necator (4%), Trichuris (1,5%), Ascaris (1%) e Hymenolepis nana (0,5%). No se encontré, Strongyloides, Taenia, Dientamoeba, Balantidium ni Cryptosporidium. La investigación mostró que el 76% de los hogares se abastecían de agua de cañería propia, comunal o del Instituto Costarricense de Acueductos y Alcantarillados, y que el 100% de las familias disponen las excretas adecuadamente (90% en letrina y 10% en otro tipo de servicio sanitario). Esta investigación mostró una muy baja prevalencia de parásitos intestinales patógenos lo cual indica que las tres comunidades presentan: alto nivel educativo y de tecnología familiar, cobertura por lo programas de medicina preventiva y curativa, y un nivel socioeconómico adecuado.Universidad de Costa Rica. Instituto de Investigaciones en SaludUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias de la Salud::Instituto de Investigaciones en Salud (INISA