Investigating the Mullins Effect and Energy Dissipation in Magnetorheological Polyurethane Elastomers.

The aim of this article was to investigate the mechanical performance of magnetorheological polyurethane elastomers reinforced with different concentrations of carbonyl iron microparticles (CIPs) in which stress softening, energy dissipation, residual strains, microparticles orientation, and magnetic flux density effects will be considered. Other aspects, such as the determination of the dissipated energy during cyclic loading and unloading, were investigated by considering a pseudo-elastic network model that takes into account residual strains, magnetic field intensity, and the isotropic and anisotropic material behavior. Theoretical predictions confirmed that the material shear modulus becomes sensitive not only for higher concentrations of CIPs added into the elastomer material matrix, but also to the magnetic flux intensity that induces attractive forces between CIPs and to the strong bonds between these and the elastomer matrix. It was also found that the addition of CIPs when embedded into the polymer matrix with a predefined orientation enhances the material shear modulus as well as its capacity to dissipate energy when subjected to magnetic flux density in loading and unloading directions.

Modelagem computacional da biotransferência de calor no tratamento por hipertermia em tumores de duodeno através do método dos volumes finitos em malhas não estruturadas / Computational modeling of the bioheat transfer during the hypertermic treatment of duodenum tumors using an unstructured mesh finite volume method

Tumores de duodeno não-operáveis podem ser irradiados com fontes de laser por via endoscópica. Sua função é causar uma elevação de temperatura local a fim de destruir as células cancerígenas, sem, no entanto, causar dano térmico à região sadia circunvizinha. A exatidão do cálculo das temperaturas está ligada à utilização de métodos numéricos adequados. O presente trabalho apresenta a análise térmica de um procedimento terapêutico, onde um tumor de duodeno de 2 cm de diâmetro é aquecido por uma sonda de laser Nd:YAG, através da utilização do método dos volumes finitos (MVF) para solucionar a equação da biotransferência de calor em malhas bidimensionais triangulares não-estruturadas. É feita uma descrição detalhada do modelo físico-matemático pertinente e da função dano térmico. São apresentadas as propriedades termofísicas dos tecidos envolvidos, bem como a escolha dafonte de laser mais adequada à utilização no procedimento a ser simulado. Em seguida é descrita brevemente a formulação do método dos volumes finitos com estrutura de dados por arestas e apresentados os resultados obtidos da análise térmica dos tecidos.

Tumors that cannot be surgically removed could be irradiated using laser sources through endoscopic procedures. The idea is to increase the local temperature to kill the cancer cells without a thermal damage on the healthy tissues in the neighborhood. The accuracy of the estimated temperatures is directly related to the proper choice ofthe adopted numerical methods. In this work a computational tool using the finite volume method was developed, in order to obtain the approximate equations of the bioheat transfer equation using bidimensional unstructured triangular meshes. The analyzed problem consists of a duodenum tumor with 2 cm of diameter that is heated using a Nd:YAG laser probe. The following items will be described: the appropriate physical-mathematical model; the damage function; the thermo-physical properties of the tissues involved; as well as the choice of the best laser source to be used in the procedure to be simulated. Next, the edge based finite volume formulation is described and the results obtained from the tissue thermal analysis are presented.