Hilbeth Parente Azikri de Deus

A Vibro Acoustic Method for Non Destructive Test of Composite Sandwich Structures

The present work describes an investigation into a vibro-acoustic method to check the existence of superficial flaws in composite sandwich structures, based in a technique inspired in the well known Tap Test. In this case, however, a non-impulsive excitation is provided by an especial transducer and the acoustic response is captured with a microphone. A deconvolution technique is used in order to assess the systems impulse response and generate a “failure” map after post-processing the results. Post-processed parameters evaluated are: Loudness, Sharpness and a discrepancy indicator for the transfer function (named TFDI). Results suggest that Loudness and TFDI potentially indicate the existence of a damaged core and the lack of adhesive tape.

Some Aspects over Thixotropic Fluid Behavior

In this work some theoretical aspects of constitutive equations for thixotropic fluids and restrictions on their functional forms are formally discussed. In the current study a formal emphasis has been given to the structural nature of this substances. The behavior of thixotropic fluids is analyzed in terms of simple isothermal laminar shear flow.

A Numerical Approach on New Constitutive Model for Thixotropic Substances

The thixotropic substances can be found in different industrial sectors, such as chemical, biomedical, manufacturing and oil. These substances show a rheological time-dependent behavior, dependent of their structural level. Generally, a constitutive model for the thixotropic substances is composed by a pair of coupled equations: the constitutive equation (based on viscoelastic models) and the rate equation (that describes the structural evolution). In many works presented in the specialized literature, the shear modulus and viscosity dependencies with the structural nature are not formally considered in the dynamical principles from that the constitutive equation is originated. In the present work, a new, thermodynamically consistent, constitutive model for thixotropic substances, where such dependences are considered, is presented and some rheological tests are analyzed in a numerical simulation point of view (code developed in MATLAB). The constitutive model is based on Jeffreys’ model and the coagulation theory of Smoluchowsky.

Elastoplasticity 2D Problems: Numerical Applications of the Tikhonov Regularization Method

The numerical simulation is widely used, in now days, to verify the viability and to optimize structural mechanic designs. The numerical approach of elastoplastic materials can found some problems related to ill-conditioning of matrices (from FEM systems), associated to the critical points from the snap through or snap back shape of the equilibrium curve. Aiming to overcome this misfortune it is proposed a strategy via Tikhonov regularization method in association with L-curve technique to determine the regularization parameter. This strategy can be used in many numerical applications for structural analysis. The theoretical development about these Some numerical examples are presented to attest the efficiency of this proposed approach.

The Effect of Elastic Modulus Rate in Stress Controlled Tests on the Modified Jeffrey’s Model for Structured Fluids

Structured fluids are known to be dependable of their structural level. Examples of such fluids may be found in different industries as chemical, biomedical, manufacturing, food and oil. The mathematical models to describe structured fluids are normally composed by a coupled system: one constitutive equation (based on viscoelastic models) and one kinetics equation (an equation which describes the structural level evolution in time of the material). The works found in the literature use linear viscoelastic constitutive equations which do not account the dependence of the elastic modulus with the microstructural level in their fundamental hypothesis. In this sense, the present work aims to evaluate, through numerical simulation, the effect of a new constitutive equation in rheological tests and compare its results to those of the model developed by Souza Mendes and Thompson (2013), in which those considerations are not made.

A Finite Displacement Visco-Hypoelasticity Model

The objective of the work is to propose a dual visco-hypoelasticity model and a numerical procedure for the analysis of Polymeric materials subjected to large displacements and rotations. In the proposed dual approach, the Hencky’s logarithm strain measure is a function of the rotated Kirchhoff stress history in terms of a convolution equation. The material is assumed to be isotropic and the kernel functions, associated with the shear and bulk compliance moduli, are represented in Prony series. The problem is formulated within a Total Lagrangian framework and employs the Galerkin finite element method in the discretization process. Finally some numerical examples are presented in order to attest the proposed model and to verify the robustness and performance of the proposed numerical scheme.