Made available in DSpace on 2014-12-17T14:58:20Z (GMT). No. of bitstreams: 1 AnaCMCB_DISSERT.pdf: 5204946 bytes, checksum: 70bedde30acbc8578034105c8c4fc24e (MD5) Previous issue date: 2013-07-25 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / The utilization of synthetic fibers for plastic reinforcement is more and more frequent and this growing interest requires that their mechanic behavior under the most variable conditions of structural applications be known. The use of such materials in the open and exposed to the elements is one of them. In this case, it becomes extremely necessary to study their mechanical properties (strength, stiffness) and the mechanism of fracture by which the environment aging them out. In order to do that, the material must be submitted to hot steam and ultraviolet radiation exposure cycles, according to periods of time determined by the norms. This study proposal deals with the investigation of accelerated environmental aging in two laminated polymeric composites reinforced by hybrid woven made up of synthetic fibers. The configurations of the laminated composites are defined as: one laminate reinforced with hybrid woven of glass fibers/E and Kevlar fibers/49 (LHVK) and the other laminate is reinforced with hybrid tissue of glass fibers/E and of carbon fibers AS4 (LHVC). The woven are plane and bidirectional. Both laminates are impregnated with a thermofix resin called Derakane 470-300 Epoxy Vinyl-Ester and they form a total of four layers. The laminates were industrially manufactured and were made through the process of hand-lay-up. Comparative analyses were carried out between their mechanical properties by submitting specimen to uniaxial loading tractions and three-point flexion. The specimen were tested both from their original state, that is, without being environmentally aging out, and after environmental aging. This last state was reached by using the environmental aging chamber / O interesse na utiliza??o dos pl?sticos refor?ados por fibras sint?ticas ? cada vez mais crescente e esse grande interesse na utiliza??o dos mesmos faz com que seja necess?rio o conhecimento do comportamento mec?nico desses materiais sob as mais variadas condi??es de aplica??o estrutural. Dentre estas pode ser destacada a aplica??o desses materiais em situa??es em o elemento encontra-se exposto ? intemp?rie, e nesse caso os estudos das propriedades mec?nicas (resist?ncia, rigidez) al?m do mecanismo fratura frente ao envelhecimento ambiental s?o de extrema necessidade. Para tanto, submeter o material ? per?odos c?clicos de exposi??o ao vapor aquecido e ? de radia??o ultravioleta, por tempo definido em norma, se faz necess?rio. A presente proposta de trabalho de investiga??o consiste no estudo do envelhecimento ambiental acelerado em dois laminados comp?sitos polim?ricos refor?ados por tecidos h?bridos ? base de fibras sint?ticas. As configura??es dos laminados comp?sitos s?o definidas como: um laminado refor?ado com tecido h?brido de fibras de vidro/E e de fibras kevlar/49 (LHVK) e outro laminado refor?ado com tecido h?brido de fibras de vidro/E e de fibras de carbono AS4 (LHVC). Os tecidos s?o dos tipos planos e bidirecionais. Ambos os laminados foram impregnados a base de resina termofixa Derakane 470-300 Ep?xi Vinil-Ester e constitu?dos com quatro camadas no total. Os laminados t?m fabrica??o industrial e foram obtidos atrav?s do processo de lamina??o manual (Hand-lay-up). Foram realizados estudos comparativos entre as propriedades mec?nicas sob a a??o dos carregamentos de tra??o uniaxial e flex?o em tr?s pontos, nas condi??es dos corpos de prova sem o efeito do envelhecimento ambiental (estado original) e sob o efeito desse envelhecimento (estado envelhecido). O envelhecimento ambiental foi acelerado atrav?s do uso da c?mara de envelhecimento

Master´s thesis deals with some problems associated with utilisation of lightweight concrete from the porous aggregates in the load – carrying structures. The thesis focuses on the possibilities of the increase of the cement composites toughness using dispersed reinforcement. Lightweight concretes were reinforced with a combination of different lengths of polypropylene fibers Forta Ferro. There were used polypropylene fibers of three lengths 19, 38, 54 mm. The thesis is divided into theoretical, experimental and static part.

Oriented thermoplastics offer interesting opportunities for making structural automotive components due to their higher strengths. A new process, referred to as the axial feed hot oil tube forming (AF-HOTF) process, has been developed and studied for the forming of oriented thermoplastic tubes. The starting material for AF-HOTF process is an oriented polypropylene (OPP) tube produced by the solid state extrusion process. AF-HOTF was used to study forming and fracture behaviour of OPP tubes at large strains. Mechanical properties and molecular orientation of starting and post-formed materials were investigated to gain a better understanding of structure-property-process relationships during solid state extrusion and subsequent forming of OPP tubes. The development of molecular orientation and other microstructural changes and damage development in extruded and bulged OPP tubes during solid state extrusion and AF-HOTF processes were studied with optical microscopy, wide-angle X-ray diffraction (WAXD) and field emission scanning electron microscope (FE-SEM) techniques. Also, the development of large strains during AF-HOTF of OPP samples were experimentally studied in the form of spatial strain maps, strain/stress state and forming limit strains using an on-line strain mapping method based on digital image correlation (DIC). In addition, tensile tests have been carried out at room temperature on samples machined from the extruded and bulged tubes along the axial and hoop directions. Experimental quantitative relationships amongst molecular orientation parameters and extrusion and AF-HOTF process parameters such as draw ratio, strain and strain state have been obtained. These relationships in the form of White and Spruiell biaxial orientation factors provide a useful insight into molecular reorientation that occurs during extrusion and subsequent forming of OPP tubes. Also, an analytical model for forming limit prediction that takes into account OPP tube properties, tube dimensions and AF-HOTF process parameters was developed based on existing model of tube hydroforming in the literature. In addition, a new biaxial ball stretching test (BBST) system was developed and utilized to subject the thermoplastic tube to biaxial stretching. The design of the test-rig and results were presented for polypropylene (PP) tubes subjected to BBST at various temperatures. The BBST system was combined with an available on-line imaging and strain analysis system (ARAMIS® system from GOM) to observe the development of strains in the biaxial tensile region during the test. BBST samples were studied with wide angle X-ray diffraction (WAXD) pole figures. Three different hot forming processes (Solid-state extrusion, AF-HOTF and BBST) were used in this research. The structure of the extruded samples at draw ratio 5 and higher was completely changed to fibrils structure, and the yield strength and elastic modulus increased by 50%. Also the crystallinity increased from 47% to 68% with an increase in draw ratio. An increase in axial feed during the hot forming process resulted in higher formability (strains values of 0.55 major strain and -0.25 minor strain) and delayed failure. The analytical model prediction of bursting shows good agreement with the experimental results. The results provide an understanding of the orientation development in solid state extrusion of PP tubes as well as an understanding of tube formability, flow localization and fracture characteristics of PP tube from AF-HOTF process and other related processes. / Thesis / Doctor of Philosophy (PhD)

Das Rissverhalten von Stahlbeton wird maßgeblich durch die Verbundwirkung zwischen Bewehrung und Beton beeinflusst. Aktuelle Untersuchungen befassen sich mit der Rissbreitenentwicklung und Verbundspannungsverteilung unter Langzeitbelastung. Dabei werden verschiedene Betonsorten (fcm ≈ 30–70 MPa), drei unterschiedliche Probetypen sowie faseroptische Sensoren verwendet. In diesem Artikel sind der experimentelle und messtechnische Aufbau sowie die Ergebnisse der ersten Versuchsreihen im Vergleich zu bestehenden Verbundmodellen dargestellt. Darüber hinaus werden Einflüsse des Prüfkörpers und der Verbundlänge sowie die Möglichkeiten zur Erfassung des lokalen Verbundverhaltens mit faseroptischen Sensoren aufgezeigt.