João de Aguiar | UFABC - Federal University of ABC (original) (raw)
Papers by João de Aguiar
La ecuacion de energia fue resuelta para computar el campo de temperatura resultante de la deform... more La ecuacion de energia fue resuelta para computar el campo de temperatura resultante de la deformacion plastica y la interaccion entre la herramienta y la pieza. Esta ecuacion incluye las condiciones de dispersion asociadas con el trabajo mecanico. Se presenta un modelo de elementos finitos del proceso de corte ortogonal con un acoplamiento termo-elastico-plastico del comportamiento material sometido a grandes deformaciones y basado en una formulacion actualizada de Lagrangian. Es asumida una condicion de estado plano de deformacion y que la tension de fluencia del material es una funcion de la deformacion, de la razon de deformacion, del endurecimiento por deformacion y de la temperatura. El problema es formulado y discretizado, y las ecuaciones resultantes resueltas con el metodo de los elementos finitos. Como una aplicacion el campo de temperatura es calculado para el caso del maquinado de un acero AISI 1020. In this paper the energy equation was solved to compute the temperature...
THE BENDING MOMENT DISTRIBUTION OF BEAMS OF VARIABLE WIDTH, WITH INITIAL CURVATURE, WHILE RESTING... more THE BENDING MOMENT DISTRIBUTION OF BEAMS OF VARIABLE WIDTH, WITH INITIAL CURVATURE, WHILE RESTING ON A LINEAR ELASTIC FOUNDATION, LOADED BY IN-PLANE AS WELL AS OUT-OF-PLANE RESULTANTS IS FORMULATED. A NUMERICAL PROCEDURE IS DEVELOPED TO GENERATE THE SOLUTION OF THE TWO POINT BOUNDARY VALUE PROBLEM. AS INTERFACE LOADING IS DEFORMATION DEPENDENT, AN ITERATIVE PROCEDURE IS DEVISED TO OBTAIN THE CORRECT LOADS. A SPECIFIC CASE IS ANALYZED AND ITS BENDING FIELD PRESENTED. DEPENDENCE WITH RESPECT TO THE INTERFACE VARIABLES, WEDGE ANGLE AND IMPERFECTION PROFILE IS CONSIDERED. COMPARISON TO THE UNIFORM BEAM CASE IS ALSO PERFORMED. WHILE INITIAL CURVATURE HAS LIMITED EFFECTS ON BENDING MOMENTS, WEDGING HAS DRAMATIC EFFECTS, DECREASING OVERALL VALUES DRAMATICALLY.
IN SOME CIRCUMSTANCES ICE FLOES MAY BE MODELED AS BEAMS. IN GENERAL THIS MODELING SUPPOSES CONSTA... more IN SOME CIRCUMSTANCES ICE FLOES MAY BE MODELED AS BEAMS. IN GENERAL THIS MODELING SUPPOSES CONSTANT THICKNESS, WHICH CONTRADICTS FIELD OBSERVATIONS. ACTION OF CURRENTS, WIND AND THE SEQUENCE OF CONTACTS, CAUSES THICKNESS TO VARY. HERE THIS EFFECT IS TAKEN INTO CONSIDERATION ON THE MODELING OF THE BEHAVIOR OF ICE HITTING INCLINED WALLS OF OFFSHORE PLATFORMS. FOR THIS PURPOSE, THE BOUNDARY VALUE PROBLEM IS FIRST EQUATED. THE SET OF EQUATIONS SO OBTAINED IS THEN TRANSFORMED INTO A SYSTEM OF EQUATIONS, THAT IS THEN SOLVED NUMERICALLY. FOR THIS SAKE AN IMPLICIT SOLUTION IS DEVELOPED, USING A SHOOTING METHOD, WITH THE ACCOMPANYING JACOBIAN. IN-PLANE COUPLING AND THE DEPENDENCY OF THE BOUNDARY TERMS ON DEFORMATION, MAKE THE PROBLEM NON-LINEAR AND THE DEVELOPMENT PARTICULAR. DEFORMATION AND INTERNAL RESULTANTS ARE THEN COMPUTED FOR HARMONIC FORMS OF BEAM PROFILE. FORMS OF GIVING SOME ADDITIONAL GENERALITY TO THE PROBLEM ARE DISCUSSED.
10º Congresso Brasileiro de Engenharia de Fabricação
10º Congresso Brasileiro de Engenharia de Fabricação
Anais do X Congresso Nacional de Engenharia Mecânica
Anais do IX Congresso Brasileiro de Engenharia de Fabricação
Boiling water reactors, BWR, commercially use fuel rods with a circular cross section. Set the op... more Boiling water reactors, BWR, commercially use fuel rods with a circular cross section. Set the operational conditions as well as the distribution of these rods, a specific power is established. Changing this form while conserving the cross sectional area may deliver a better performance. This fact is investigated here for a family of elliptic forms, in a thermal sense, using the finite element method. Two limiting values are considered: the melting temperature of the fuel and the critical flux rate. For 2d models, gains of the order of twenty percent in performance are estimated. It is also perceived the advantage of this alteration in other form of reactor, and discussed means of addressing other aspects of the problem.
Purpose: This paper aims to study the cutting parameters influence (cutting speed, feed rate, cut... more Purpose: This paper aims to study the cutting parameters influence (cutting speed, feed rate, cutting depth and tool radius nose) on the cutting forces (cutting force, feed rate cutting force and penetration cutting force) as well as on the residual stresses, in conical bearings made of steel DIN 100 CrMn6 hardened (62 HRc), searching correlations between the residual stresses and the cutting forces. Design/methodology/approach: A complete factorial planning was used to establish the correlations. At the same time, the cutting parameters influence in the microstructure of the material and it's correlation with the residual stress was studied. A turning center machine and CBN inserts was employed for the tests. To the cutting force measurements was carried out using a piezoelectric dynamometer. The residual stresses measurements were carried out by X-ray diffractometry. Findings: The penetration cutting force was the most important factor in the residual stress generation, and it was influenced by the feed rate and the cutting depth. A correlation between the cutting depth and the residual stresses was established. The results do not showed any changes in the microstructure of the material, even when the greater cutting parameters were used. Research limitations/implications: The residual stress is one of the major causes of failures in bearings by contact fatigue, keeping this on mind, this work helps the developer to select correct cutting parameters in order to increase the machined workpiece life in service. Originality/value: This work were based on the real components (conical bearings), real cutting conditions and with these results were possible to make greater improvements in the manufacturing and in the quality of the studied parts.
Internal bone remodeling models have been proposed in order to address behavior under everyday lo... more Internal bone remodeling models have been proposed in order to address behavior under everyday loading of hard tissues. Models, in general, are not general as to apply to all bones in human body. Also trauma cases are not covered by many of the models. Here, one such a model, Doblare's model of damage-repair is revisited, and modified in some aspects to address specific internal bone remodeling problems. In the model, elastic constitutive parameters are formulated in terms of the bone density and the fabric tensor, both dependent upon the amount of mechanical stimulus and the local present state of structure. Bone material is taken as inherently anisotropic. Density, instead of an intermediate tensor, configures the pseudo-damage variable, with a different undamaged state mapping. Strain energy equivalence is kept, however. Different elasto-damage surfaces are discussed in order to describe update of internal variables. Resorption and apposition are treated with similar, but dif...
El material óseo es radicalmente distinto a cualquier otro material tratado por la mecánica clási... more El material óseo es radicalmente distinto a cualquier otro material tratado por la mecánica clásica, su estructura es heterogénea y anisótropa, y sus propiedades mecánicas varían no solo entre distintos individuos, sino también, para un mismo hueso En los tratamientos e intervenciones quirúrgicas donde está presente la readaptación, el crecimiento inducido del hueso puede ser modelado mediante el empleo de los criterios de remodelación ósea interna propuesto por algunos autores (Cowin y R. Huiskes, R. Carter, Doblare y García, Jacob y Beaupré y otros).En este trabajo se toma el modelo de remodelación ósea propuesto por Jacob (1994) y se implementa con la utilización del programa Abaqus 6.4 utilizando una subrutina de usuario (UMAT), se aplico a un modelo 2D de hueso genérico con un sistema de cargas para comprobar los efectos de la remodelación y las variaciones de los valores de densidad. Como parte del trabajo fueron creados dos programas para el procesamiento de los datos, para u...
La ecuacion de energia fue resuelta para computar el campo de temperatura resultante de la deform... more La ecuacion de energia fue resuelta para computar el campo de temperatura resultante de la deformacion plastica y la interaccion entre la herramienta y la pieza. Esta ecuacion incluye las condiciones de dispersion asociadas con el trabajo mecanico. Se presenta un modelo de elementos finitos del proceso de corte ortogonal con un acoplamiento termo-elastico-plastico del comportamiento material sometido a grandes deformaciones y basado en una formulacion actualizada de Lagrangian. Es asumida una condicion de estado plano de deformacion y que la tension de fluencia del material es una funcion de la deformacion, de la razon de deformacion, del endurecimiento por deformacion y de la temperatura. El problema es formulado y discretizado, y las ecuaciones resultantes resueltas con el metodo de los elementos finitos. Como una aplicacion el campo de temperatura es calculado para el caso del maquinado de un acero AISI 1020. In this paper the energy equation was solved to compute the temperature...
THE BENDING MOMENT DISTRIBUTION OF BEAMS OF VARIABLE WIDTH, WITH INITIAL CURVATURE, WHILE RESTING... more THE BENDING MOMENT DISTRIBUTION OF BEAMS OF VARIABLE WIDTH, WITH INITIAL CURVATURE, WHILE RESTING ON A LINEAR ELASTIC FOUNDATION, LOADED BY IN-PLANE AS WELL AS OUT-OF-PLANE RESULTANTS IS FORMULATED. A NUMERICAL PROCEDURE IS DEVELOPED TO GENERATE THE SOLUTION OF THE TWO POINT BOUNDARY VALUE PROBLEM. AS INTERFACE LOADING IS DEFORMATION DEPENDENT, AN ITERATIVE PROCEDURE IS DEVISED TO OBTAIN THE CORRECT LOADS. A SPECIFIC CASE IS ANALYZED AND ITS BENDING FIELD PRESENTED. DEPENDENCE WITH RESPECT TO THE INTERFACE VARIABLES, WEDGE ANGLE AND IMPERFECTION PROFILE IS CONSIDERED. COMPARISON TO THE UNIFORM BEAM CASE IS ALSO PERFORMED. WHILE INITIAL CURVATURE HAS LIMITED EFFECTS ON BENDING MOMENTS, WEDGING HAS DRAMATIC EFFECTS, DECREASING OVERALL VALUES DRAMATICALLY.
IN SOME CIRCUMSTANCES ICE FLOES MAY BE MODELED AS BEAMS. IN GENERAL THIS MODELING SUPPOSES CONSTA... more IN SOME CIRCUMSTANCES ICE FLOES MAY BE MODELED AS BEAMS. IN GENERAL THIS MODELING SUPPOSES CONSTANT THICKNESS, WHICH CONTRADICTS FIELD OBSERVATIONS. ACTION OF CURRENTS, WIND AND THE SEQUENCE OF CONTACTS, CAUSES THICKNESS TO VARY. HERE THIS EFFECT IS TAKEN INTO CONSIDERATION ON THE MODELING OF THE BEHAVIOR OF ICE HITTING INCLINED WALLS OF OFFSHORE PLATFORMS. FOR THIS PURPOSE, THE BOUNDARY VALUE PROBLEM IS FIRST EQUATED. THE SET OF EQUATIONS SO OBTAINED IS THEN TRANSFORMED INTO A SYSTEM OF EQUATIONS, THAT IS THEN SOLVED NUMERICALLY. FOR THIS SAKE AN IMPLICIT SOLUTION IS DEVELOPED, USING A SHOOTING METHOD, WITH THE ACCOMPANYING JACOBIAN. IN-PLANE COUPLING AND THE DEPENDENCY OF THE BOUNDARY TERMS ON DEFORMATION, MAKE THE PROBLEM NON-LINEAR AND THE DEVELOPMENT PARTICULAR. DEFORMATION AND INTERNAL RESULTANTS ARE THEN COMPUTED FOR HARMONIC FORMS OF BEAM PROFILE. FORMS OF GIVING SOME ADDITIONAL GENERALITY TO THE PROBLEM ARE DISCUSSED.
10º Congresso Brasileiro de Engenharia de Fabricação
10º Congresso Brasileiro de Engenharia de Fabricação
Anais do X Congresso Nacional de Engenharia Mecânica
Anais do IX Congresso Brasileiro de Engenharia de Fabricação
Boiling water reactors, BWR, commercially use fuel rods with a circular cross section. Set the op... more Boiling water reactors, BWR, commercially use fuel rods with a circular cross section. Set the operational conditions as well as the distribution of these rods, a specific power is established. Changing this form while conserving the cross sectional area may deliver a better performance. This fact is investigated here for a family of elliptic forms, in a thermal sense, using the finite element method. Two limiting values are considered: the melting temperature of the fuel and the critical flux rate. For 2d models, gains of the order of twenty percent in performance are estimated. It is also perceived the advantage of this alteration in other form of reactor, and discussed means of addressing other aspects of the problem.
Purpose: This paper aims to study the cutting parameters influence (cutting speed, feed rate, cut... more Purpose: This paper aims to study the cutting parameters influence (cutting speed, feed rate, cutting depth and tool radius nose) on the cutting forces (cutting force, feed rate cutting force and penetration cutting force) as well as on the residual stresses, in conical bearings made of steel DIN 100 CrMn6 hardened (62 HRc), searching correlations between the residual stresses and the cutting forces. Design/methodology/approach: A complete factorial planning was used to establish the correlations. At the same time, the cutting parameters influence in the microstructure of the material and it's correlation with the residual stress was studied. A turning center machine and CBN inserts was employed for the tests. To the cutting force measurements was carried out using a piezoelectric dynamometer. The residual stresses measurements were carried out by X-ray diffractometry. Findings: The penetration cutting force was the most important factor in the residual stress generation, and it was influenced by the feed rate and the cutting depth. A correlation between the cutting depth and the residual stresses was established. The results do not showed any changes in the microstructure of the material, even when the greater cutting parameters were used. Research limitations/implications: The residual stress is one of the major causes of failures in bearings by contact fatigue, keeping this on mind, this work helps the developer to select correct cutting parameters in order to increase the machined workpiece life in service. Originality/value: This work were based on the real components (conical bearings), real cutting conditions and with these results were possible to make greater improvements in the manufacturing and in the quality of the studied parts.
Internal bone remodeling models have been proposed in order to address behavior under everyday lo... more Internal bone remodeling models have been proposed in order to address behavior under everyday loading of hard tissues. Models, in general, are not general as to apply to all bones in human body. Also trauma cases are not covered by many of the models. Here, one such a model, Doblare's model of damage-repair is revisited, and modified in some aspects to address specific internal bone remodeling problems. In the model, elastic constitutive parameters are formulated in terms of the bone density and the fabric tensor, both dependent upon the amount of mechanical stimulus and the local present state of structure. Bone material is taken as inherently anisotropic. Density, instead of an intermediate tensor, configures the pseudo-damage variable, with a different undamaged state mapping. Strain energy equivalence is kept, however. Different elasto-damage surfaces are discussed in order to describe update of internal variables. Resorption and apposition are treated with similar, but dif...
El material óseo es radicalmente distinto a cualquier otro material tratado por la mecánica clási... more El material óseo es radicalmente distinto a cualquier otro material tratado por la mecánica clásica, su estructura es heterogénea y anisótropa, y sus propiedades mecánicas varían no solo entre distintos individuos, sino también, para un mismo hueso En los tratamientos e intervenciones quirúrgicas donde está presente la readaptación, el crecimiento inducido del hueso puede ser modelado mediante el empleo de los criterios de remodelación ósea interna propuesto por algunos autores (Cowin y R. Huiskes, R. Carter, Doblare y García, Jacob y Beaupré y otros).En este trabajo se toma el modelo de remodelación ósea propuesto por Jacob (1994) y se implementa con la utilización del programa Abaqus 6.4 utilizando una subrutina de usuario (UMAT), se aplico a un modelo 2D de hueso genérico con un sistema de cargas para comprobar los efectos de la remodelación y las variaciones de los valores de densidad. Como parte del trabajo fueron creados dos programas para el procesamiento de los datos, para u...