Department of Applied Mechanics

The paper presents an application of a phenomenological material model for the viscoelastic stress response at large strains. The model is used for the simulation of carbon-black filled rubber in monotonic and cyclic deformation processes under isothermal conditions. The material stress response is decomposed into two constitutive parts which act in parallel : an elastic equilibrium stress response and a rate-dependent viscoelastic overstress response. The response of a particular filled rubber in the cyclic and relaxation tests was measured experimentally. The parameters of the constitutive functions are determined from the experimental data by an identification process employing nonlinear optimization methods. The paper concludes with a simulation by FEM of the cyclic loading of a simple rubber specimen.

h i g h l i g h t s Fiber sliding mechanism is observed in E-glass composite. Fiber pull out in carbon composite delays the impact propagation. E-glass composites show smaller damaged area than carbon composites. Basalt composites have poor impact resistance. Residual strength of carbon and Eglass composites reduced according damaged area.

Thermal characterization of geopolymer powder was investigated at room and elevated temperatures. The physical, chemical and mass change with respect to various temperatures have been studied. The physical properties such as density, porosity, and particle size were analyzed in geopolymer powder. The chemical and phase compositions were determined by x-ray fluorescence. The surface images of solid blocks of geopolymer were examined at room and elevated temperatures using scanning electron microscopy. Thermal expansion, shrinkage, and mass loss behavior towards the elevated temperatures were investigated by differential scanning calorimetry (DSC). The endothermic peak arising in the DSC curve is due to evaporation of water, chemical, gases and weight loss.

Ao longo da história as migrações sempre foram uma necessidade para o homem, pois eles a todo momento precisavam se deslocar na perspectiva de garantir a sobrevivência. Todavia, em cada época são diversas as causas que motivam nas mobilidades, nas implicações, no significado e nas emoções que promovem tanto entre aqueles de onde saem os imigrantes quanto entre aqueles que os acolhem. Ademais, uma das características relevantes da história do capitalismo tem sido a mobilidade espacial da população. Dentro de cada país, as cidades se transformaram em lócus hegemônico da acumulação de capital, intensificando o processo de urbanização, fruto não só do crescimento vegetativo da população, mas principalmente das migrações internas oriundas do campo, visto que, como afirma Brito (1995, p. 53), "[...] não houve economia e sociedade que se desenvolvessem sem que houvesse uma intensa mobilidade espacial da população". Destarte, presencia-se no território brasileiro ao longo do século XXI, metamorfoses socioeconômicas advindas de políticas públicas elaboradas pelos agentes que têm atuação na esfera pública (federal, estadual e municipal), como também privada. Tais políticas, entre outros, tiveram como foco, a dinamização de regiões e Estados, até então, não entrelaçados pela atuação de capitais hegemônicos nacionais e globais. A materialização de tais políticas, permitiu com que houvesse uma dispersão das atividades econômicas pelo território nacional, porém de maneira seletiva. A região Nordeste do Brasil, em especial o Estado do Ceará, foi um dos espaços em que a instalação de investimentos internos e externos proporcionou com que novas dinâmicas territoriais e consequentemente populacionais fossem notadas. Assim, inúmeros movimentos migratórios passaram fazer parte do cotidiano cearense, entre eles, a migração internacional de africanospara trabalho e estudo Nesse contexto, o presente trabalho busca compreender as características da migração dos africanos para o Brasil, sobretudo, para o Ceará no início do século XXI. O foco de análise é a população de estudantes africanos/as que realizam mobilidade para o Ceará, com vistas a atingir a qualificação profissional, todavia, não nos limitamos a este grupo focal, já que migrantes africanos com outros perfis se inserem no Ceará e portanto merecem atenção na nossa investigação. No Brasil, a estruturação do território, traduz muito sobre a história dos movimentos migratórios, já que o Brasil é um país formado também por migrantes europeus, africanos, latinos, asiáticos, dentre outros. Para tanto, é necessário antes de mais nada discorrer sobre o conceito de território que foi construído pela sociedade ao longo do tempo em diferentes escalas, e que não podemos analisar apenas sob a ótica do território nacional mais também enquanto Estado-nação 1 , como é o caso da migração internacional. 1 Conforme Goettert (2010, p.22-23) "[…] a primeira condição das migrações internacionais é a existência de Estados-nações, que, ao se constituírem como fundamento temporal-espacial de modo

In this paper we present an attempt to identify experimentally the coefficients of strain energy function of the hyperelastic orthotropic material of the thin cylindrical air-spring. The components of the deformation gradient are determined from measured displacements of the grid points drawn on the cylindrical surface of the spring. The true Cauchy stress tensor is calculated from the membrane theory. The deformed shape of the spring surface is determined from the photographic records. The strain energy function is expressed in terms of tensorial invariants with regard to the assumed material symmetry. The coefficients are determined by means of the nonlinear least squares method. The deformation field is then calculated by solving the system of five first-order ordinary differential equations with the material constitutive law and proper boundary conditions.

The 3-D displacements of inflated cylindrical shell of air-spring made of cord-rubber composite are measured by the application of the stereo-correlation technique. The 3-D coordinates of points in the central part of air-spring shell are obtained at different stages of loading by the matching of a series of stereo images. By the use of the nonlinear optimization technique, the deformations of the air-spring shell are determined. The material parameters of strain energy function are identified. The deformations of inflated air-spring shell were determined by numerical solution the system of ordinary differential equations based on the membrane theory.

Friction of rubber depends on different parameters e.g. velocity, roughness, normal pressure and temperature. The coefficient of friction is measured by ball-on-disc method at ambient temperature. The dependence of the coefficient on different sliding velocities and on different normal forces is observed. The coefficient of friction is compared with the rubber damping properties determined by dynamic mechanical analysis.

Nonlinear hyperelastic constitutive equations for large deformations of orthotropic composite material are incorporated into the finite strain analysis by FEM. The parameters of material are determined from experiments. Results for the deformation of the inflated air-spring shell made of composite with rubber matrix reinforced by textile cords are given.

This paper contains the project overview of complex research of conveyor belts affected especially by impact (shock) loading. The main task is to increase working life of conveyor belt based on optimization of size and shape of transported parts, dropping height, design of the belt and impact area. Project contains theoretical, experimental and numerical analyses. The best types of modifications will be realized in the surface mining company. Project is oriented especially to optimization of drive and return stations using of detailed numerical models, new design concepts and materials. Project also proves possibilities for size and shape monitoring of transported parts and active modification of geometry based on type of transported materials. T&L 1 INTRODUCTION This paper contains the research and development project overview of conveyor belts affected by shocks in brown coal surface mine. The project started on 3/2012 and finish is planned on 12/2014. This project is solved in co...

An orthotropic hyperelastic constitutive model is proposed which can be applied to numerical simulation for the response of the nonlinear anisotropic hyperelastic material of the air-spring sheet used in inhibitive vibration of driver's seat and of the biological soft tissue. The parameters of strain energy function are fitted to the experimental results by the nonlinear least squares method. The deformation field of inflated cylindrical membrane of air-spring sheet is calculated by solving the system of five first-order ordinary differential and by the finite element method (FEM). Stability analysis is carried out in finite element analysis (FEA) to detect limit points by arc-length method.

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1-3 piezocomposites are often subjected to mechanical pre-stress under elevated temperatures in naval and offshore applications, actuators, and so on, where the presence of the ductile epoxy matrix causes considerable creep in the system. This deteriorates the system efficiency and its overall performance. To address this issue, experiments are performed to capture the electromechanical response for thermo-mechanical creep of 1-3 piezocomposites for different fiber volume fractions under various thermal loads, wherein mechanical depolarization is observed. The piezo-coupling coefficient is observed to degrade. Higher thermal loads resulted in an increase in creep strain coupled with a decrease in creep polarization. A Kelvin-Voigt fractal derivative viscoelastic model is used to capture the creep strain. The creep strain is decomposed into ferroelastic and anelastic parts. The evolution of creep polarization is obtained using the ferroelastic component of the creep strain. The model predictions are found to be in agreement with the experimental observations.

The clinical practice shows that the loosening of acetabular cups is more frequent than stem loosening. With standard cups, the incidence of dislocation failure is highest in the first year after arthroplasty implantation. The aim of the study was to quantitatively evaluate the implant-bone stability of a cementless acetabular cup prosthesis by using a device based on resonance frequency analysis. The evaluation of this device was done by finite element analysis and in vitro experiments. It was shown that not all the resonance frequencies can be measured by our device. The resonance frequencies vary within the range of 500–3000 Hz. The proposed power spectrum measurement gives the information about the absolute stiffness of the press-fit implant.

Digital models based on finite element (FE) analysis are widely used in orthopaedics to predict the stress or strain in the bone due to bone-implant interaction. The usability of the model depends strongly on the bone material description. The material model that is most commonly used is based on a constant Young's modulus or on the apparent density of bone obtained from computer tomography (CT) data. The Young's modulus of bone is described in many experimental works with large variations in the results. The concept of measuring and validating the material model of the pelvic bone based on modal analysis is introduced in this pilot study. The modal frequencies , damping, and shapes of the composite bone were measured precisely by an impact hammer at 239 points. An FE model was built using the data pertaining to the geometry and apparent density obtained from the CT of the composite bone. The isotropic homogeneous Young's modulus and Poisson's ratio of the cortical and trabecular bone were estimated from the optimization procedure including Gaussian statistical properties. The performance of the updated model was investigated through the sensitivity analysis of the natural frequencies with respect to the material parameters. The maximal error between the numerical and experimental natural frequencies of the bone reached 1.74% in the first modal shape. Finally, the optimized parameters were matched with the data sheets of the composite bone. The maximal difference between the calibrated material properties and that obtained from the data sheet was 34%. The optimization scheme of the FE model based on the modal analysis data provides extremely useful calibration of the FE models with the uncertainty bounds and without the influence of the boundary conditions.