A study has been made of the respective performance of cubic boron nitride (CBN) and polycrystalline diamond (PCD) cutting tool materials and compared to various coated and uncoated tungsten carbide grades when cutting titanium alloy workpieces. Two important experimental techniques were employed during the course of this work, firstly a quasi-static contact method was employed to establish the workpiece/tool interfacial temperature above which strongly adherent layers may be formed. This technique revealed that the critical temperatures which marked adhesion and welding, were 740, 820 and 800 °C for coated and uncoated carbides, and 760 and 900 °C for PCD and CBN tools respectively. Furthermore, the technique has been used to study the integrity of the bulk tool material, and/or individual coatings on their substrates, when welded junctions formed between the tool and workpiece are separated. With regard to the latter it was observed that in all cases fracture was initiated in the bulk of the harder tool material rather than in the workpiece or at the welded junction interface. Secondly, a quick-stop technique was used to study chip formation and tool wear when cutting with carbides, CBN and PCD tools under nominally the same conditions. The predominant wear mechanisms for each of the tool materials was found to be based on a diffusion/dissolution process. The wear process is discussed in detail for each of the tool materials and reasons advanced for observed differences in performance when removing material from a titanium alloy workpiece. The wear resistance and quality of the machined surface was found to be superior when cutting with the ultra-hard materials than with the carbide grades and in particular the PCD tool was found to produce exceptionally good surface finish. In the case of coated carbide tool grades rapid removal of the coated layers occurred leaving the substrate vulnerable to reaction with the workpiece material and this is considered to explain the seeming absence of beneficial effects when cutting with these grades.

Orientador: Antonio Ludovico Beraldo / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agrícola / Made available in DSpace on 2018-08-18T21:29:11Z (GMT). No. of bitstreams: 1 Silva_RodolfoGomesda_M.pdf: 6103773 bytes, checksum: 67c3dbb9306dc2536b81c5cacff6876c (MD5) Previous issue date: 2011 / Resumo: A concentração da população mundial em grandes centros urbanos gera uma imensa demanda por madeira, o que tem levado à devastação das florestas tropicais, causando a extinção de várias espécies. O bambu é uma alternativa à madeira convencionalmente utilizada na movelaria, na construção, na produção de energia, na fabricação de papel e celulose e em outras atividades industriais. Apesar das numerosas vantagens econômicas e ambientais do bambu, seu uso esbarra na limitada durabilidade natural da maioria das espécies. A deterioração do bambu, causada por agentes físicos, químicos e biológicos, faz com que esse vegetal seja considerado um material de baixa qualidade, criando a falsa ideia de que o bambu somente deveria ser usado quando da falta de materiais mais apropriados para determinados fins. Os principais agentes deterioradores do bambu são os fungos e os insetos, dentre os quais se destaca a broca do bambu. A proteção do bambu pode ser feita por meio do uso de diversos produtos dentre os quais se destaca o ácido pirolenhoso, obtido a partir da pirólise de madeira e de outros materiais vegetais. No presente trabalho, buscou-se avaliar a eficácia do tratamento aplicado a taliscas de bambu por cozimento em ácido pirolenhoso em três diferentes diluições (10, 20 e 30%) durante cinco intervalos de tempo (15, 30, 60, 120 e 180 minutos), buscandose a sua proteção contra a deterioração pela broca do bambu, avaliando-se o dano nas taliscas de bambu através das variações na massa e na velocidade do pulso ultrassônico (VPU) através dessas taliscas. Os experimentos de deterioração foram realizados durante 20 semanas. Os dados foram sujeitos a testes de correlação e interações entre as variáveis. O teste T pareado indicou haver diferença significativa entre as medidas de VPU e massa no início e depois de 20 semanas de ensaio. Em média, a VPU diminuiu e a massa aumentou, resultado este influenciado pela variação de umidade no período. Buscou-se, ainda, determinar a porcentagem de fibras em relação aos outros tecidos por meio de análise de imagens de cortes transversais dos corpos de prova. Por fim, buscou-se estabelecer um método eficiente de criação de Dinoderus minutus para ensaios de deterioração do bambu / Abstract: The concentration of worldwide population in large urban centers creates huge demand for timber, which can lead to devastation of the rainforest, resulting in the extinction of several species. Bamboo is an alternative to wood commonly used on furniture, building, power generation, pulp and paper and other industrial purposes. Despite its many economic and environmental advantages, the bamboo utilization is hampered by the low natural durability of most species. The bamboo deterioration by physical, chemical and biological agents, makes it to be considered a low quality material, creating the misconception that it should only be used in the abscence of appropriate materials for certain purposes. The major spoilage agents on the bamboo are the fungi and insects, among which stands out the powder-post beetle. The bamboo protection can be done through the use of various protective agents such as the pyroligneous acid, obtained by pyrolysis of wood and other plant materials. This study aimed to evaluate the efficacy of the treatment applied to bamboo splits cooked in pyroligneous acid at three different solutions (10, 20 and 30%) over five time intervals (15, 30, 60, 120 and 180 minutes) searching for the protection against the deterioration of the powder-post beetle by measuring the variation of the mass and the ultrasonic pulse velocity (UPV) across the strips. The deterioration assays were performed during 20 weeks. The data were subjected to correlation and interaction between variables tests. The two-sample pooled t-test indicated significant differences between the measures of UPV and mass at starting and after 20 weeks testing. On average, the UPV decreased and increased mass, a result influenced by the increasing relative moisture. The study also aimed to determine the fiber content by image analysis of transverse sections of the bamboo splits. Finally, the study sought to establish an efficient method of creating Dinoderus minutus for bamboo deterioration tests / Mestrado / Construções Rurais e Ambiencia / Mestre em Engenharia Agrícola

This research focuses on carbon fiber treatment by nitric acid and 3- (trimethoxysilyl)propyl methacrylate silane, and how this affects carbon/vinyl ester composites. These composites offer great benefits, but it is difficult to bond the fiber and matrix together, and without a strong interfacial bond, composites fall short of their potential. Silanes work well with glass fiber, but do not bond directly to carbon fiber because its surface is not reactive to liquid silanes. Oxidizing surface treatments are often prescribed for improved wetting and bonding to carbon, but good results are not always achieved. Furthermore, there is the unanswered question of environmental durability. This research aimed to form a better understanding of oxidizing carbon fiber treatments, determine if silanes can be bonded to oxidized surfaces, and how these treatments affect composite strength and durability before and after seawater exposure. Nitric acid treatments on carbon fibers were found to improve their tensile strength to a constant level by smoothing surface defects and chemically modifying their surfaces by increasing carbonyl and carboxylic acid concentrations. Increasing these surface group concentrations raises fiber polar energy and causes them to cohere. This impedes wetting, resulting in poor quality, high void content composites, even though there appeared to be improved adhesion between the fibers and matrix. Silane was found to bond to the oxidized carbon fiber surfaces, as evidenced by changes in both fiber and composite properties. The fibers exhibited low polarity and cohesion, while the composites displayed excellent resin wetting, low void content, and low seawater weight gain and swelling. On the contrary, the oxidized fibers that were not treated with silane exhibited high polarity and fiber cohesion. / Their composites displayed poor wetting, high void content, high seawater weight gain, and low swelling. Both fiber treatment types resulted in great improvements in dry transverse tensile strength over the untreated fibers, but the oxidized fiber composites lost strength as the acid treatment time was extended, due to poor wetting. The acid/silane treated composites lost some transverse tensile strength after seawater exposure, but the nitric acid oxidized fiber composites appeared to be more seawater durable. / by Tye A. Langston. / Thesis (Ph.D.)--Florida Atlantic University, 2008. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2008. Mode of access: World Wide Web.