Pedro M C L Pacheco (original) (raw)

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Papers by Pedro M C L Pacheco

Research paper thumbnail of NON-LINEAR DYNAMICS OF AN ELASTO–PLASTIC OSCILLATOR WITH KINEMATIC AND ISOTROPIC HARDENING

Journal of Sound and Vibration, 1997

This contribution reports on a dynamic analysis of an elasto-plastic oscillator. Kinematic and is... more This contribution reports on a dynamic analysis of an elasto-plastic oscillator. Kinematic and isotropic hardening are considered. The equations of motion have five state variables associated with complementary conditions. System dynamics is treated by performing a split in phase space in two parts. This split is suggested by an analysis of the equations of motion near equilibrium points and permits conclusions about high dimensional dynamical system by analyzing subspaces with lower dimension. This physical consideration is in close agreement with the operator split technique used for the numerical solution. Some numerical results are shown for free and forced vibrations of the oscillator with kinematic, isotropic and kinematic/isotropic hardening.

Research paper thumbnail of Tensile-compressive asymmetry influence on shape memory alloy system dynamics

Chaos, Solitons & Fractals, 2008

The remarkable properties of shape memory alloys (SMAs) are attracting much technological interes... more The remarkable properties of shape memory alloys (SMAs) are attracting much technological interest in several science and engineering fields, varying from medical to aerospace applications. Hysteretic response of these systems is one of their essential ...

Research paper thumbnail of Phenomenological Modeling of Shape Memory Alloys

AIP Conference Proceedings, 2008

Shape memory alloys exhibit two characteristic effects, viz., shape memory and superelasticity or... more Shape memory alloys exhibit two characteristic effects, viz., shape memory and superelasticity or pseudoelasticity, due to a reversible solid‐solid transformation brought about by either temperature or stress or both. The two important aspects involved in modeling the macroscopic SMA ...

Research paper thumbnail of Shape memory alloy helical springs: modeling, simulation and experimental analysis

Shape memory alloys (SMAs) are metallic materials that have the capability to recover its origina... more Shape memory alloys (SMAs) are metallic materials that have the capability to recover its original shape eliminating residual deformations when subjected to adequate thermal process. This behavior is related to phase transformation induced by stress or temperature and several alloys present this behavior. During the phase transformation process of a SMA component, large loads and/or displacements can be generated in a relatively short period of time making this component an interesting mechanical actuator. Because of such remarkable properties, SMAs have found a number of applications in different areas. The present contribution deals with the modeling, simulation and experimental analysis of SMA helical springs. Basically, it is assumed a one-dimensional constitutive model to describe its thermomechanical shear behavior and, afterwards, helical springs are modeled by considering classical approach. A numerical method based on the operator split technique is developed. SMA helical spring thermomechanical behavior is investigated through experimental tests performed at different loads. Numerical results show that the model is in close agreement with those obtained by experimental tests.

Research paper thumbnail of Transient chaos in an elasto-plastic beam with hardening

ABSTRACT This contribution discusses the transient chaos on a pin-ended elasto-plastic beam with ... more ABSTRACT This contribution discusses the transient chaos on a pin-ended elasto-plastic beam with both kinematic and isotropic hardening. An iterative numerical procedure, based on the operator split technique, is developed. Numerical simulations show that transient chaos causes sensitivity on initial conditions, which imply that the system response may become unpredictable.

Research paper thumbnail of Modeling of quenching process in steel cylinders

This article deals with the modeling and simulation of quenching in steel cylinders using a multi... more This article deals with the modeling and simulation of quenching in steel cylinders using a multi-phase constitutive model with internal variables formulated within the framework of continuum mechanics and the thermodynamics of irreversible processes. Phenomenological aspects of quenching involve couplings among different physical processes and its description is unusually complex. Basically, three couplings are essential: thermal, phase transformation and mechanical phenomena. A numerical procedure is developed based on the operator split technique associated with an iterative numerical scheme in order to deal with non-linearities in the formulation. The proposed general formulation is applied to the quenching of steel cylinders. Three examples considering progressive induction hardening and through hardening are presented. Numerical results present a good agreement with those of experimental data obtained by the authors in previous works.

Research paper thumbnail of Modelos Constitutivos para o Pulmão: Caso Unidimensional

A simulação de fenômenos vitais pode contribuir tanto no sentido de definir as condições mais ade... more A simulação de fenômenos vitais pode contribuir tanto no sentido de definir as condições mais adequadas aos seres vivos quanto no sentido de determinar o tratamento de afecções. Essas simulações exigem a elaboração de modelos capazes de descrever o comportamento dos sistemas biológicos e o processo de elaboração desses modelos envolve estudos experimentais e analíticos. A simulação da mecânica do sistema respiratório pode contribuir para avaliar detalhes de sua fisiologia. O pulmão é um órgão fundamental nesse processo e, usualmente, a descrição de seu comportamento mecânico é feita através de modelos que descrevem o comportamento mecânico do tecido biológico associados a modelos que descrevem o efeito da tensão superficial nas paredes alveolares. Este trabalho apresenta uma revisão sobre os modelos constitutivos para o tecido biológico e sugere modelos viscoelásticos para descrever a resposta do pulmão de uma forma geral. Consideram-se os modelos elásticos não-lineares, polinomial e exponencial, utilizados para descrever o comportamento elástico do tecido biológico. Propõem-se alguns modelos viscoelásticos em um contexto unidimensional. Simulações numéricas apresentam respostas qualitativamente coerentes. Palavras-chave: Biomecânica, Equações constitutivas, Mecânica do pulmão.

Research paper thumbnail of Analysis of Magneto-Piezoelastic Anisotropic Materials

Metals, 2015

The paper is concerned with the analysis of magneto-piezoelastic anistropic materials. Analytical... more The paper is concerned with the analysis of magneto-piezoelastic anistropic materials. Analytical modeling of magneto-piezoelastic materials is essential for the design and applications in the smart composite structures incorporating them as actuating and sensing constituents. It is shown that Green's function method is applicable to time harmonic magneto-elastic-piezoelectricity problems using the boundary integral technique, and the exact analytical solutions are obtained. As an application, a two-dimensional static plane-strain problem is considered to investigate the effect of magnetic field on piezoelectric materials. The closed-form analytical solutions are obtained for a number of boundary conditions for all components of the magneto-piezoelectric field. As a special case, numerical results are presented for two-dimensional static magneto-electroelastic field of a piezoelectric solid subjected to a concentrated line load and an electric charge. The numerical solutions are obtained for three different piezoelectric materials and they demonstrate a substantial dependence of the stress and electric field distribution on the constitutive properties and magnetic flux.

Research paper thumbnail of NON-LINEAR DYNAMICS OF AN ELASTO–PLASTIC OSCILLATOR WITH KINEMATIC AND ISOTROPIC HARDENING

Journal of Sound and Vibration, 1997

This contribution reports on a dynamic analysis of an elasto-plastic oscillator. Kinematic and is... more This contribution reports on a dynamic analysis of an elasto-plastic oscillator. Kinematic and isotropic hardening are considered. The equations of motion have five state variables associated with complementary conditions. System dynamics is treated by performing a split in phase space in two parts. This split is suggested by an analysis of the equations of motion near equilibrium points and permits conclusions about high dimensional dynamical system by analyzing subspaces with lower dimension. This physical consideration is in close agreement with the operator split technique used for the numerical solution. Some numerical results are shown for free and forced vibrations of the oscillator with kinematic, isotropic and kinematic/isotropic hardening.

Research paper thumbnail of Tensile-compressive asymmetry influence on shape memory alloy system dynamics

Chaos, Solitons & Fractals, 2008

The remarkable properties of shape memory alloys (SMAs) are attracting much technological interes... more The remarkable properties of shape memory alloys (SMAs) are attracting much technological interest in several science and engineering fields, varying from medical to aerospace applications. Hysteretic response of these systems is one of their essential ...

Research paper thumbnail of Phenomenological Modeling of Shape Memory Alloys

AIP Conference Proceedings, 2008

Shape memory alloys exhibit two characteristic effects, viz., shape memory and superelasticity or... more Shape memory alloys exhibit two characteristic effects, viz., shape memory and superelasticity or pseudoelasticity, due to a reversible solid‐solid transformation brought about by either temperature or stress or both. The two important aspects involved in modeling the macroscopic SMA ...

Research paper thumbnail of Shape memory alloy helical springs: modeling, simulation and experimental analysis

Shape memory alloys (SMAs) are metallic materials that have the capability to recover its origina... more Shape memory alloys (SMAs) are metallic materials that have the capability to recover its original shape eliminating residual deformations when subjected to adequate thermal process. This behavior is related to phase transformation induced by stress or temperature and several alloys present this behavior. During the phase transformation process of a SMA component, large loads and/or displacements can be generated in a relatively short period of time making this component an interesting mechanical actuator. Because of such remarkable properties, SMAs have found a number of applications in different areas. The present contribution deals with the modeling, simulation and experimental analysis of SMA helical springs. Basically, it is assumed a one-dimensional constitutive model to describe its thermomechanical shear behavior and, afterwards, helical springs are modeled by considering classical approach. A numerical method based on the operator split technique is developed. SMA helical spring thermomechanical behavior is investigated through experimental tests performed at different loads. Numerical results show that the model is in close agreement with those obtained by experimental tests.

Research paper thumbnail of Transient chaos in an elasto-plastic beam with hardening

ABSTRACT This contribution discusses the transient chaos on a pin-ended elasto-plastic beam with ... more ABSTRACT This contribution discusses the transient chaos on a pin-ended elasto-plastic beam with both kinematic and isotropic hardening. An iterative numerical procedure, based on the operator split technique, is developed. Numerical simulations show that transient chaos causes sensitivity on initial conditions, which imply that the system response may become unpredictable.

Research paper thumbnail of Modeling of quenching process in steel cylinders

This article deals with the modeling and simulation of quenching in steel cylinders using a multi... more This article deals with the modeling and simulation of quenching in steel cylinders using a multi-phase constitutive model with internal variables formulated within the framework of continuum mechanics and the thermodynamics of irreversible processes. Phenomenological aspects of quenching involve couplings among different physical processes and its description is unusually complex. Basically, three couplings are essential: thermal, phase transformation and mechanical phenomena. A numerical procedure is developed based on the operator split technique associated with an iterative numerical scheme in order to deal with non-linearities in the formulation. The proposed general formulation is applied to the quenching of steel cylinders. Three examples considering progressive induction hardening and through hardening are presented. Numerical results present a good agreement with those of experimental data obtained by the authors in previous works.

Research paper thumbnail of Modelos Constitutivos para o Pulmão: Caso Unidimensional

A simulação de fenômenos vitais pode contribuir tanto no sentido de definir as condições mais ade... more A simulação de fenômenos vitais pode contribuir tanto no sentido de definir as condições mais adequadas aos seres vivos quanto no sentido de determinar o tratamento de afecções. Essas simulações exigem a elaboração de modelos capazes de descrever o comportamento dos sistemas biológicos e o processo de elaboração desses modelos envolve estudos experimentais e analíticos. A simulação da mecânica do sistema respiratório pode contribuir para avaliar detalhes de sua fisiologia. O pulmão é um órgão fundamental nesse processo e, usualmente, a descrição de seu comportamento mecânico é feita através de modelos que descrevem o comportamento mecânico do tecido biológico associados a modelos que descrevem o efeito da tensão superficial nas paredes alveolares. Este trabalho apresenta uma revisão sobre os modelos constitutivos para o tecido biológico e sugere modelos viscoelásticos para descrever a resposta do pulmão de uma forma geral. Consideram-se os modelos elásticos não-lineares, polinomial e exponencial, utilizados para descrever o comportamento elástico do tecido biológico. Propõem-se alguns modelos viscoelásticos em um contexto unidimensional. Simulações numéricas apresentam respostas qualitativamente coerentes. Palavras-chave: Biomecânica, Equações constitutivas, Mecânica do pulmão.

Research paper thumbnail of Analysis of Magneto-Piezoelastic Anisotropic Materials

Metals, 2015

The paper is concerned with the analysis of magneto-piezoelastic anistropic materials. Analytical... more The paper is concerned with the analysis of magneto-piezoelastic anistropic materials. Analytical modeling of magneto-piezoelastic materials is essential for the design and applications in the smart composite structures incorporating them as actuating and sensing constituents. It is shown that Green's function method is applicable to time harmonic magneto-elastic-piezoelectricity problems using the boundary integral technique, and the exact analytical solutions are obtained. As an application, a two-dimensional static plane-strain problem is considered to investigate the effect of magnetic field on piezoelectric materials. The closed-form analytical solutions are obtained for a number of boundary conditions for all components of the magneto-piezoelectric field. As a special case, numerical results are presented for two-dimensional static magneto-electroelastic field of a piezoelectric solid subjected to a concentrated line load and an electric charge. The numerical solutions are obtained for three different piezoelectric materials and they demonstrate a substantial dependence of the stress and electric field distribution on the constitutive properties and magnetic flux.