Abstract

Abstract

El Doctor Oswaldo Valdivia nació en 1937 en Arequipa, Perú. En 1958 inició sus estudios en la carrera de medicina, en el primer año nació el amor por la neuroanatomía y en el cuarto año inicio su labor como docente. Se graduó como médico en 1964 y de anatomopatólogo en 1966. Contrajo matrimonio en 1962 con Zulema Valdivia con quien tuvo 3 hijos, en 1968 fue becado para entrenamiento de microscopia electrónica en la universidad de Wisconsin. En 1973 decidió emigrar hacia Venezuela debido a la situación del Perú y por una oferta laboral de parte de la Universidad Centroccidental Lisandro Alvarado (UCLA), donde se desenvolvió como profesor de anatomía microscópica a dedicación exclusiva, ampliadas contribuciones como la incorporación de la microscopia electrónica en la región centroccidental del país en 1980. Realizó diversos trabajos de investigación, principalmente sobre leishmaniasis, fue profesor jubilado activo de la UCLA hasta sus últimos días. En su ejercicio profesional dio grandes aportes a la salud pública, participando en jornadas de pesquisa de patológica cervical y formando profesionales de la salud. Fallece el 18 de noviembre de 2019 en Perú, su tierra natal.

Abstract

Abstract

Abstract

Porosity and voids are a type of defect that may appear during the manufacturing of composite structures. Its possible presence is checked in production parts by different non-destructive techniques based on ultrasonic inspection. It is important to perform this evaluation  considering that a high content of these defects decrease the mechanical properties compared to the original design. In recent years, optical microscopy of composite materials has become a very powerful tool, which is  available for the industry to inspect and look at the internal structure and help to reach conclusions in the field of quality, failure analysis and I+D+I. In addition, the use of automatic scanning techniques of wide cross sections has opened the possibility of quantifying the percentage of porosity/voids, as well as become an alternative to more laborious testing procedures such as acid digestion of the resins. This study contributes to existing test standards within the aeronautical sector, in the sample preparation strategy. For this purpose, samples of epoxy matrices with carbon fibers, both unidirectional and fabric tapes have been analyzed to evaluate the influence of the quality of sample preparation, the stacking sequence and the initial porosity levels, the repeatability of the measurements and the quality of the results. An attempt has been made to correlate the results with standar physical / chemical analysis.

Abstract

In this paper we have studied some physical characteristics of gypsum composites incorporated with two different tire rubber granulometry. The experimental program was formed by the following tests: consistency (mini-slump), compressive strength and scanning electron microscopy (SEM). The rubber used in the composites came from the retreading of tires with 5 and 10% incorporation in relation to the plaster mass and the two different granulometry used were denominated thicknesses (# 0.6 mm) and thick (# 1.19 mm ). The results were compared with the control paste, in which there was no incorporation of rubber. The rubbers of different granulometry stood out in different points. The thin rubber presented a compressive strength close to the value observed in the control, with an addition of 5% by mass, which may be due to its adherence to gypsum paste, which occurred in a less porous manner and with a closer interface between the rubber particles and pulp, observed through the SEM. The thick rubber presented the best results in consistency, contributing to the workability of the pulp, which was also observed in SEM, where the thick rubber presents less adherence to the gypsum plaster, compared to the composite with incorporation of fine rubber. It was possible to affirm, then, that rubber as residual material presented interesting characteristics in applications in plaster composites.