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The use of mechanic waves for assessing structural integrity is a well-known non-destructive technique (NDT). The ultrasound applied in the guided wave in particular requires significant effort in order to understand the complexities of the propagation so as to develop new methods in damage detection, in this case, knowing the interaction between the wave propagation and the geometry of the waveguides is mandatory. In the present work, the wave propagation in rectangular steel rod is presented. In this study, the section dimensions were fixed as 5 × 15 [mm], a typical element of the flexible riser structural amour commonly used in the offshore oil industry. The studies here presented were restricted to [0, 100 KHz] frequencies. This frequency interval is in the range of commercial waveguide equipment commonly applied in ducts in NDT applications. The computation of the dispersion curves is performed by using three different methodologies: (i) analytical solutions, (ii) a method that combines analytical approaches with finite element methods (SAFE), and (iii) experimental method that extracted information from the rod using laser vibrometers and piezoelectric actuators. Finally, two applications based on the dispersion curves determined in the rectangular waveguide are presented to illustrate the possibilities of the curve dispersion knowledge related to the specific geometry in the development and application linked to NDT. The first application consists on showing the possibilities of the techniques that use a fiber grating Bragg cell (FGB) to measure the wave displacement and the second application involves the simulation of pre-fissured prismatic waveguide aimed at searching to induce three characteristic acoustic events. The model was built combining the finite element method and a version of the discrete element method.

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A têmpera é um procedimento térmico que busca a obtenção da microestrutura martensítica, visando melhoria nas propriedades dos materiais metálicos. O tratamento ocorre pelo aquecimento da peça, até que austenita seja obtida na sua composição, seguido de resfriamento, que deve ser rápido, impedindo que o carbono seja difundido no material. Esse resfriamento ocorre geralmente pela imersão do corpo sob alta temperatura em fluidos refrigerantes. Nesse sentido, existe a necessidade de taxas de resfriamento elevadas do corpo, provocadas pelo contato com o fluido, minimizando rapidamente sua temperatura. Atualmente, os fluidos poliméricos diluídos em água vêm sendo utilizadas para esse tratamento, posto que apresentam avanços em relação às demais classes de fluidos. Esses fluidos variam de forma relevante os níveis de transferência de calor, conforme a concentração é alterada na solução. Neste trabalho, as variações de temperaturas e taxas de variação térmica entre corpo e fluido foram avaliadas, empregando quatro concentrações de solução polimérica de polivinilpirolidona (PVP), com percentuais entre 10 e 25%. Palavras-chave: Curvas de Resfriamento. Têmpera. Polivinilpirolidona.

This paper presents the study of failure surface obtained in the truss-like Discrete Element Method (DEM). The element constitutive law considers the fracture energy of the material and its spatial variation is used to take into account the heterogeneity of the simulated materials. It is studied the influence of spatial distribution of fracture energy and the spatial lattice perturbation on the DEM failure surface. A DEM failure criterion is compared with concrete and rock failure.

This paper presents a study on the variation of strain rate influence with the scale effect in quasi-brittle materials. Works in the literature report an increase of dynamic resistance with strain rate. To study this relation, a numerical model that combines the Finite Element Method and the Lattice Discrete Element Method is employed. This mixed model was implemented on the commercial software Abaqus/Explicit. The samples are prepared with FEM at the extremity and LDEM for the central part, which has a reduction in the cross-section, so the rupture occurs in the middle. In the simulations, four model specimens with dimensional variations were subjected to direct tensile testing with different strain rates. The results showed that with the increase of applied strain rate, the resistances also increase and the body dimension influences this behavior. The variation of the tensile strength is found without modifications on the elemental constitutive relationship or material parameters. At last, a method that could lead to an independent relationship between the dynamic intensification and the stain rate of scale effect is also proposed.