Dynamic Mechanical Analysis of Kissing Bonds in Bonded Joints

Inspection of kissing bond defects in composite structures is a challenge for traditional nondestructive testing (NDT) methods. A kissing bond (KB) is a bondline defect where two surfaces are in intimate contact with each other but with little to no bond strength. New nondestructive testing methods need to be developed that can detect adhesive kissing bonds, and areas within a composite joint where the bondline is compromised. The primary goal of this thesis is to explore if a NDT technique based on Dynamic Mechanical Analysis (DMA) can be established which is capable of detecting kissing bonds within bondlines in composite laminates that have been bonded with epoxy film and paste adhesives. DMA as a test method has the benefit that it can be conducted quickly and is able to test the material at various temperature and frequency ranges. Thirty specimens were prepared and attempts were made to create kissing bonds by introducing different types of contaminants at the bond location. Contamination used within the adhesive joint consisted of introduction of mold release and grease lubricant. Ultrasonic inspection is first performed to demonstrate that the surfaces were in contact in the bondline and no attenuation from porosity or delamination is present. Dynamic testing was performed on each sample in an attempt to detect these kissing bonds using the DMA method. Information on changes in the sample’s stiffness, storage modulus and loss modulus over a range of temperatures is recorded and analyzed. The specimens were subsequently tested in tension to determine the maximum strength of the materials. A geometrically nonlinear, 3D finite element (FE) analysis was performed to determine the stress and strain distributions within the composite single-lap joint (SLJ). The results obtained from the study showed artificial KBs appear to have been successfully fabricated based on tension testing and optical scans of fractured surfaces. Visual inspections of the fracture surfaces showed that contaminated bonds predominately failed via adhesion failure, while the control samples failed via cohesion. The production of KBs within the joints were more successful among the paste adhesive rather than the film adhesive. Analysis of DMA parameters shows a reasonable correlation for some of the parameters and the failure load. The FE results on the tension test showed that the stresses became increasingly higher within the single-lap joint for paste adhesive compared to the film adhesive. It was seen from the FEA models that the maximum shear stress and elastic strain occur near the overlap joint corners ends, suggesting that cohesive crack initiation is most likely to occur at the corners for defect-free samples. The stiffness results obtained from the DMA showed that all the paste samples had stiffness values much larger than the film samples; this elevated stiffness could contribute to the increased stress evident in the FE models. As the stresses were higher in the paste adhesive specimens, it is interpreted to be a contributing factor in the reductions of shear strength within the SLJs when defects are present

Trade Models with Heterogeneous Firms: What About Importing?

Intermediate goods make up a large share of world trade. Yet trade models with heterogeneous firms focus almost exclusively on firms’ export decisions rather than their import decisions. We develop an analytically solvable model of a small open economy in which heterogeneous firms make endogenous import decisions. We view decisions about importing as decisions about technology adoption. In our model, firms weigh the benefit of operating a technology that uses imported intermediate goods against the fixed cost of developing trade relationships with foreign input suppliers. Similar to the selection effect in standard export-decision models, only the most efficient firms choose to import. In addition, the model features a technology upgrading effect, where importing improves a firm’s labor efficiency. The calibrated model quantifies the selection and technology upgrading effects, captures the large performance advantage associated with using imported intermediate goods, and generates large increases in trade from small decreases in tariffs.hetrogenious firms, importing, Chile, fixed costs

Web crippling strength of longitudinally stiffened steel plate girder webs subjected to concentrated loading

Currently, the AISC code provides guidance for the calculation of the ultimate strength of unstiffened plate girder webs subjected to concentric edge loads. Specifications consider three categories: local web yielding, web crippling, and sideway web buckling. Based on previous studies, the presence of longitudinal stiffeners in the web has not been considered in the calculation procedures. Longitudinal stiffeners in steel plate girders are primarily used to increase bending and shear strength. In the last two decades, a number of projects regarding the positive effect of longitudinal stiffening on the strength of plate girder webs to concentrated load have been conducted around the world. The results have shown that this type of stiffening enhances ultimate strength for web crippling depending on the position of the stiffener that modifies the slenderness of the directly loaded panel; and flexural and torsional rigidities of the stiffener. This paper presents a methodology for the consideration of longitudinal stiffening on the ultimate strength of plate girders webs subjected to concentrated loads. The methodology is based on the plastic collapse mechanism observed experimentally, in which plastic hinges are formed in the loaded flange and yield lines result in the portion of the web limited by the loaded flange and stiffener. Then, a closed-form solution accounting for the influence of the stiffener is developed following the current expression available in the AISC specifications. Theoretical predictions are compared with available test results, showing that the predicted ultimate loads are in good agreement with experimental results.Postprint (published version

Las prodigalidades del Ministerio de Instrucción Pública y la Institución Libre de Enseñanza

Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2009-201

El Partido Socialista Independiente en el gobierno de Agustín P. Justo : la gestión de Antonio de Tomaso en el Ministerio de Agricultura

El Partido Socialista Independiente fue la fuerza política de izquierdas cuyos dirigentes se comprometieron con la acción gubernamental de la restauración conservadora de los años ‟30, para instrumentar medidas económicas con el objetivo de dar respuesta a la crisis mundial. En este artículo se analiza el papel que tuvieron algunos de sus dirigentes en la gestión estatal de la economía durante el gobierno del general Agustín P. Justo, focalizando la atención en la reconstrucción de la labor que al frente del Ministerio de Agricultura de la Nación desempeñó Antonio De Tomaso, entre los años 1932 y 1933.The Independent Socialist Party was the left-wing of the political force whose leaders were committed to the government action in the conservative restoration of the '30s, in order to implement economic measures in response to the global crisis. This article analyzes the role played from some of their leaders in state management of the economy during the government of General Agustin P. Justo, focussing attention on the reconstruction work of the Ministry of Agriculture of the Nation performed by Antonio De Tomaso, between 1932 and 1933.Fil: Graciano, Osvaldo. Universidad Nacional de Quilme

Money illusion, Gorman and Lau

Any demand equation satisfying Lau’s (1982) Fundamental Theorem of Exact Aggregation and is 0 homogeneous in prices and income will have a Gorman (1981) functional form for each income term. This property does not depend on symmetry or adding up. The implications of this result are illustrated by an extensive example.Demand, exact aggregation, functional form, homogeneity

Los debates y las propuestas políticas del Partido Socialista de Argentina, entre la crisis mundial y el peronismo, 1930-1950

The objective of this work is to analyze how between the world-wide crisis of 1929 and the second postwar period, the Socialist Party of Argentina was revealed as a singular theoretical and political space of debate, able to produce a systematic diagnosis of the crisis of the liberal capitalism and the parliamentary democracies and to put in revision its ideological positions and political strategies. They are reconstructed with this aim, as much as the discussions that opposed to the Great Depression were originated in the socialism and that took it to design an economic program that gave answers to argentine capitalism like the positions that defended their adoption of revolutionary and marxist tactics, revitalized by the suppression of the democratic system, thus defining alternative ways for their political action