The effect of thickness of Nylon 6,6 nanofibrous mat on Modes I-II fracture mechanics of UD and woven composite laminates

This paper presents an experimental investigation on epoxy resin-carbon bers composites interleaved with Nylon 6,6 nanobers. In particular, the paper focuses on the eect of the thickness of the nanoreinforce into two types of laminae: unidirectional (UD) and plain wave (PW). The eectiveness of the nanoreinforce has been addressed by comparing critical and propagation energy release rates, calculated by testing samples under Mode I and Mode II fracture mechanic loads. Experiments show a general improvement in delamination resistance when the nanobers are interleaved. Nevertheless slightly dierent behaviour has been found between the two types of lamina: micrographs of crack paths have been used to explain the reinforce mechanisms and such dierences, suggest- ing a strong interaction between the nature of the fabric and the thickness of the nanointerlayer

Ultra-High-Molecular-Weight Polyethylene Rods as an Effective Design Solution for the Suspensions of a Cruiser-Class Solar Vehicle

Ultra-high-molecular-weight polyethylene (UHMWPE) is a subgroup of the thermoplastic polyethylene characterized by extremely long chains and, as result, in a very tough and resistant material. Due to remarkable specific mechanical properties, its use is gradually being extended to multiple fields of application. This study describes, perhaps for the first time, how the UHMWPE can represent a valid material solution in the design and optimization of suspensions for automotive use, especially in the case of extremely lightweight vehicles, such as solar cars. In particular, in this design study, UHMWPE rods permitted to assure specific kinematic trajectories, functionalities, and overall performance in an exceptionally light suspension systems, developed for an innovative multioccupant solar vehicle. These rods reduced the weight by 88% with respect to the classic design solutions with similar functions, offering, at the same time, high stiffness and accuracy in the movements. An experimental campaign was conducted to evaluate the ratcheting behaviour and other mechanical properties needed for a proper design and use

Modelado discreto de tasas de interés

Tesis (Lic. en Matemática)--Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía, Física y Computación, 2022.Fil: Brugo, María Pía. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.En el mercado financiero se comercializan contratos en los cuáles uno podría encontrar desequilibrio y lograr un arbitraje. Las opciones son un tipo de contrato basado en un subyacente, como por ejemplo una tasa de interés. El objetivo del trabajo es determinar el precio de algunas opciones sobre tasas de interés aleatorias, para que no exista oportunidad de arbitraje. Para esto se desarrollan distintos modelos matemáticos discretos que parametrizan el desarrollo de la tasa de interés; mostraremos su implementación algorítmica, ejemplos de los mismos y como calibrar sus coeficientes de acuerdo a los precios observados en el mercado.In the financial market, contracts are traded, in which one could find an imbalance and achieve arbitration. Options are a type of contract based on an underlying, such as an interest rate. The objective of this work is determinate the price of some options on random interest rates so that there is not arbitrage opportunity. For this, different discrete mathematical models are developed. These parameterize the development of the interest rate; We will show their algorithmic implementation, examples of them and how to calibrate their coefficients according to the prices observed in the market.Fil: Brugo, María Pía. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina

Rubbery nanofibers by co-electrospinning of almost immiscible NBR and PCL blends

The paper presents a simple method for producing rubbery nanofibers without additional crosslinking required. Electrospinning's fast solvent evaporation is able to induce in liquid NBR/PCL pairs thermoplastic elastomeric (TPE) structure that holds stable over time without any further processing. The slight relative solubility of the polymers pair promotes a homogeneous blend formation with low Tg regions of blended NBR/PCL, avoiding phase separation. Such nanofibers show also a PCL-like crystal phase that is surprisingly higher than plain PCL nanofibrous counterpart and seemingly promoted by NBR/PCL interaction at molecular scale. The obtained nanofibrous-TPE morphology is reproducible, stable with time up to at least two years and is detected in a wide range of blend compositions (up to 80%wt NBR). Such a morphology reflects in good mechanical properties, which are analysed with a fitting model taking into account nanofibrous structure. Its impressive fitting ability helps interpretation of tensile tests behavior, carried out via normalization of force data with respect to sample mass, highlighting the contribution of liquid rubber in improving both elastic modulus and properties at failure. Such rubbery nanofibers represent a cost-effective powerful tool for the production of advanced self-damping composite materials with improved overall mechanical properties

Selected regional forces of the land use system of the Upper Napa Valley of California since 1950

The Upper Napa Valley land use system is presently agricultural and epitomized by vineyards of quality wine grapes. As the San Francisco Bay Urban Area continues to expand the Upper Napa Valley is brought into closer proximity to the urban margin, and its agricultural usefulness is being threatened. Whether the upper valley will remain agricultural or succumb to urbanization depends upon the implementation of controls which can produce a compatible combination of both agricultural and urban design

Fracture Toughening and Self-Healing of Composite Laminates by Nanofibrous Mats Interleaving

Composite laminates present important advantages compared to conventional monolithic materials, mainly because for equal stiffness and strength they have a weight up to four times lower. However, due to their ply-by-ply nature, they are susceptible to delamination, whose propagation can bring the structure to a rapid catastrophic failure. In this thesis, in order to increase the service life of composite materials, two different approaches were explored: increase the intrinsic resistance of the material or confer to them the capability of self-repair. The delamination has been hindered through interleaving the composite laminates with polymeric nanofibers, which completed the hierarchical reinforcement scale of the composite. The manufacturing process for the integration of the nanofibrous mat in the laminate was optimized, resulting in an enhancement of mode I fracture toughness up to 250%. The effect of the geometrical dimensions of the nano-reinforcement on the architecture of the micro one (UD and woven laminates) was studied on mode I and II. Moreover, different polymeric materials were employed as nanofibrous reinforcement (Nylon 66 and polyvinylidene fluoride). The nano toughening mechanism was studied by micrograph analysis of the crack path and SEM analysis of the fracture surface. The fatigue behavior to the onset of the delamination and the crack growth rate for woven laminates interleaved with Nylon 66 nanofibers was investigated. Furthermore, the impact behavior of GLARE aluminum-glass epoxy laminates, toughened with Nylon 66 nanofibers was investigated. Finally, the possibility of confer to the composite material the capability of self-repair was explored. An extrinsic self-healing-system, based on core-shell nanofibers filled with a two-component epoxy system, was developed by co-electrospinning technique. The healing potential of the nano vascular system has been proved by microscope electron observation of the healing agent release as result of the vessels rupture and the crosslinking reaction was verified by thermal analysis

Aplicación de buenas prácticas ganaderas y sus efectos sobre la calidad de la leche obtenida en el Tambo Escuela

Trabajo Final Integrador. (Área de Consolidación Gestión de la Producción de Agroalimentos - Ingeniería Agronómica) -- UNC- Facultad de Ciencias Agropecuarias, 2019En estos últimos años, la implementación de Buenas Prácticas en los sistemas agrícolas ganaderos viene cobrando mucha importancia. Esto se debe a las exigencias cada vez mayores de los consumidores en cuanto a la calidad de los productos de consumo masivo. El presente trabajo se desarrolló en el Tambo Escuela de la Universidad Nacional de Córdoba, donde se evaluó cómo influyen las Buenas Prácticas Ganaderas en la calidad higiénico-sanitaria de la leche. Para relevar datos se utilizó la “Guía de Buenas Prácticas para tambos” y también se realizaron análisis microbiológicos de muestras de agua, leche y efluentes. Los datos fueron digitalizados con la aplicación CheqTambo. Los ejes que presentaron mayor incumplimiento de las Buenas Prácticas fueron: Ordeño e Higiene, Sanidad Animal y Ambiente. Se propusieron mejoras para los ejes Sanidad Animal y Ordeño e Higiene teniendo en cuenta los parámetros de calidad del producto que se quieren alcanzar. Para el eje Ambiente se planteó un sistema de tratamiento del efluente que cumpliría con las exigencias del decreto de la legislación provincial N°847/16 y la Ley N°9306 (SICPA). A través de un análisis de inversión se demostró que, con las mejoras propuestas, se obtendría un mayor ingreso por bonificaciones de calidad y número de litros de leche. Además, este nuevo ingreso permitiría cubrir los costos de las inversiones en un año

A Thermoplastic Elastomeric Nanofibrous Membrane as CFRP Modifier to Boost Both Delamination and Damping Performance

In the present work, thermoplastic elastomeric nanofibers made up of a homogenous blend of nitrile butadiene rubber (NBR) and Ppolycaprolactone (CL), with 80% wt of rubbery component, are used to modify a carbon fiber reinforced polymer (CFRP) laminate with the aim of improving its delamination and damping behavior at the same time. Since the nanofibrous membrane is not chemically cross-linked, the fibrous morphology is lost during composite curing owing to its melting. Nonetheless, the nanomodified CFRP displays an impressive ability to improve the delamination resistance in mode I and also an enhanced damping capacity at low temperature. The use of nanofibrous membranes allows for modification of specifically selected areas, thus maximizing the toughening and damping behavior where most required, without necessarily affecting the whole bulk of the resin. Both PCL and NBR components contribute to the final performance; however, the very high amount of rubber leads to a membrane difficult to handle whose final performance in CFRP modification is not superior to membranes up to 60% wt NBR that are instead more stable and easier to deal with. Overall, the proposed results are nonetheless very promising, taking into account also that the improved delamination resistance in mode I and enhanced damping are obtained without significantly sacrificing the weight and overall dimension of the obtained composite