ANÁLISE DE SISTEMAS DE IMPLANTES DENTÁRIOS EM MANDÍBULAS EDÊNTULAS COM APLICAÇÃO DE CARREGAMENTO IMEDIATO.
LUIZ CARLOS GONÇALVES PENNAFORT JUNIOR
Orientador: Prof. Dr. Enio Pontes de Deus
Dissertação de mestrado apresentada como pré-requisito para a obtenção do grau de Mestre, pelo curso de Pós-Graduação em Engenharia e Ciência de Materiais, do Departamento de Engenharia Metalúrgica e de Materiais.
ABSTRACT
The present study aimed at obtaining comparative elements among the guided systems of fixed complete denture with 4 osseointegrated implants with immediate loading, considering the importance of understanding the implant project as a process where biomaterials and biomechanics are assessed. The three-dimensional finite element method was used to analyze the stress concentrations in the whole
implant-supported system, associated to the variation of the material of the prosthetic bar among the nickel-chromium, cobalt-chromium and Ti-6Al-4V alloys. Metallographic tests of the Ni-Cr and Co-Cr alloys, were made with the objective of identifying the micro-structure and consequently evaluate its influence in the mechanical behavior of the system. Two systems were analyzed, one with cantilever and another without it, but with tilted implants, submitted to a vertical load of 756N on the superior face of the prosthetic implant-supported bar. Parallel to this study the prosthetic groups (screw-abutment-implants) straight and tilted were also separately verified, submitted to a vertical load of 100N on the top of the abutment. The data found were compared and assessed according to values obtained in the literature.
The results demonstrated that the use of tilted implants avoiding the use of cantilever reduced considerably the stress levels in the prosthetic bar and in the abutments. However, in the implant-bone area an increase of approximately 1.5 times in stress levels was observed, compared to the straight implant under cantilever. The study of the alloys apponted the Co-Cr alloy as a material comparable to the other ones, regarding the mechanical behavior.
Keywords: Dental Prostheses Supported; Dental implantations; Biomechanics;
Finite Element Method. |
APLICAÇÃO DA MECÂNICA DA DANIFICAÇÃO EM MATERIAIS COMPÓSITOS POLIMÉRICOS REFORÇADOS POR FIBRAS DE VIDRO.
AUDELIS DE OLIVEIRA MARCELO JÚNIOR
Orientador: Prof. DSc. Enio Pontes de Deus
Dissertação apresentada ao Programa de Mestrado em Engenharia e Ciência de Materiais da universidade Federal do Ceará, como parte dos requisitos para obtenção do título de Mestre em Engenharia e Ciência de Materiais.
ABSTRACT
Among the materials used commonly in the world, there is a detached one that is special for polymeric composite materials, from the manufacture of toys to devices.
In this way, it is necessary an ample inquiry on all the referring aspects to these materials. Thus, this research intend to evaluate the damage processes of a polymeric composite (PMMA, reinforced by glass fibers) through a mathematical model for the normal stress.
Firstly, many tension tests were made and then, they were numerically simulated, where mathematical characteristic parameters of this material had been found. Relative aspects of the chemical and the metallographic characterization are also presented in this research. After that, numerical analysis were made by the Finite Element Method in a an internationally known software with the objective to verify the existing relation between the length of cracks and the value of the damage variable. With these data, the values for the Dc variable and the intervals of validity of the presented expression had been determined.
Finally, it is concluded the importance of studies as this to obtain descriptions of degradation of the material for a for posterior analysis of remaining life of it. In this research, the relation damage x length of the crack was determined, something original in our national literature, beyond the presentation of suggestions for new works, related with the damage mechanics in diverse materials. |
ESTUDO DA MECÂNICA DA DANIFICAÇÃO APLICADA AO CONCRETO COM EFEITOS DE CORROSÃO.
RODRIGO NOGUEIRA DE CODES
Orientador: Professor DSc. Enio Pontes de Deus
Dissertação apresentada ao Programa de Mestrado em Engenharia e Ciência de Materiais da Universidade Federal do Ceará como parte dos requisitos para obtenção do título de Mestre em Engenharia e Ciência de Materiais.
ABSTRACT
Damage and failure of concrete are widely investigated in the framework of continuum damage mechanics. Various models exist in the literature and describe quite well a variety of observed phenomena depending on their complexity. The main objective of the work is to investigate and model the effects of corrosion on damage and failure properties of concrete.
Initially, we made tests of traction and compression in some specimens of concrete, some of them submitted to the corrosion in a salt spray chamber (with different periods of time) and others without any corrosion, to determine the mechanical behaviour of the concrete taking itself in consideration the effect of the corrosion. For the traction test, we developed a device composed of steel parts, where, with this test, we can obtain the stress strain curve using the same specimens in traction and in compression. With these experimental results, using the Continuum Damage Mechanics, an elastic model coupled to damage was used to model the behaviour of the concrete. A first stage, isotropic elasticity and isotropic damage (with only one scalar variable D) was used, but including corrosion effects.
With the results, we can analyze the evolution of damage in the concrete with relation to the time of exposition of the specimens in the salt spray chamber and function of the mechanical loading.
Keywords: Continuum Damage Mechanics, concrete, corrosion, traction and compression. |
ESTUDO DA DANIFICACÃO EM BARRAS DE AÇO UTILIZADAS NA CONSTRUÇÃO CIVIL SUBMETIDAS À CORROSÃO ATRAVÉS DA MECÂNICA DO DANO.
JOSENALDO BASTOS DE SOUZA
Orientador: Professor DSc. Enio Pontes de Deus
Dissertação apresentada ao Programa de Mestrado em Engenharia e Ciência de Materiais da Universidade Federal do Ceará como parte dos requisitos para obtenção do título de Mestre em Engenharia e Ciência de Materiais.
ABSTRACT
Structures of reinforced concrete, as any another structure that uses metallic components, are subjected to corrosion, being this, one of the main factors for the degradation of these structures. Thus, a study of this phenomenon is very important to describe the mechanical behavior of them.
In this way, this research has as main objective to analyze the degradation of the mechanical properties of steel bars used in the civil construction, considering the effect of corrosion in these properties, and to develop a simplified model for the evolution of the damage, through the theory of the Continuum Damage Mechanics. A study was developed in steel bars CA-50A.
Steel bars specimens were confectioned and some of them were submitted to an accelerated corrosion test (Salt Spray) for different intervals of time. The others specimens were involved in cylinders of concrete and
submitted to a different accelerated corrosion test, "the electrolytic cell". After the corrosion test, the specimens were submitted to the mechanical test of traction with loading and unloading, getting the Elasticity Modulus for each unloading.
Then, the concept of measure of damage through the variation of the Elasticity Modulus, introduced by LEMAITRE, was applied. The damage in function of the deformation for each specimen was obtained. Finally, with the analysis of the damage in the different specimen, the variable Damage in function of the mechanical loading and the corrosion was written.
Keywords: Damage Mechanics, Corrosion, reinforced concrete and structural integrity. |
EFEITO DO HIDROGÊNIO NA PROPAGAÇÃO DE TRINCAS NO AÇO 2 1/4Cr-1Mo UTILIZADO EM REATORES DE HIDROPROCESSAMENTO.
ALEXANDRE CAMPOS BEZERRA
Orientador: Prof. DSc. Enio Pontes de Deus
Dissertação apresentada ao Departamento de Engenharia Mecânica e Produção da Universidade Federal do Ceará como parte dos requisitos para obtenção do título de Mestre em Engenharia e Ciência de Materiais.
ABSTRACT
Usualfy, hydrotreating reactors used in petroleum refineries are compound by a base metal with a double overlay cladding of aust enitic stainless steel. These materials have different thermal-elastic properties causing high overlay stresses during reactor shutdowm, leading to crack nucleation and propagation. Moreover, the reactor wall is submitted to a corrosive environment, rich in hydrogen, at high pressure and temperature. In such a case, there is a strong possibility of hydrogen embrittlement what would cause a reduction of:ductility; threshold stress intensity for crack propagation; and time to material failure. For a better study of these problems, the work was divied in two parts: computational simulation of reactor wall and experimental studies.
First, it was performed a computational simulation of a typical hydrotreating reactor wall, 2 1/4 Cr-1Mo base metal (ASTM A387 degree 22 class 2) and a double overlay cladding of 309 (buttering) and 347 type stainless steel. This simulation show through stress distribution along the reactor wall, with and without a crack and the potentiality of thermal overlay stresses to propagate cracks.
In the experimental part, the steel (2 1/4 Cr-1Mo) was characterized at hydrogen charged state and compared to the obtained results for non-hydrogen charged state. Besides, hydrogen embrittlement was quantified by fracture toughness determination of the material, at both states, through integral.
Computational results proved the high probability of a cladding crack get at metal base interface after some startup-shutdow cycles. However, the crack would plastify there. Experimental results confirmed the high hydroen embrittlement susceptibility of the studied material.
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