Examinando por Autor "Cortazar Noguerol, Julen"

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  • Miniatura
    Ítem
    Influence of density of a polyurethane microcellular elastomer foam on its compressive energy absorption and time-dependent behavior
    (Elsevier Editora Ltda, 2025-01) Cortazar Noguerol, Julen; Cortés Martínez, Fernando; Elejabarrieta Olabarri, María Jesús
    This study comprehensively examines the influence of density on the energy absorption capacity and the time-dependent behavior of polyurethane microcellular elastomers (PUMEs) under compression. On the one hand, to evaluate the energy absorption capacity, stress-strain curves, which can be modelled as a bilinear elastic behavior, are obtained for three different densities at two different loading rates. The data show that higher-density PUMEs exhibit greater stiffness, which is also dependent on the loading rate. Additionally, the lowest density material demonstrates the highest energy absorption efficiency at lower peak stresses and increasing the loading rate reduces efficiency across all tested densities. On the other hand, the time dependent properties are characterized through the relaxation modulus of each of the densities. To obtain it, creep experimental data is gathered and converted to relaxation through the convolution relationship between these two properties by means of Maxwell and Kelvin generalized models. The results indicate increased stiffness and longer relaxation times for higher-density PUMEs, suggesting slower responses and lower deformations under the same load. In conclusion, the increased stiffness and reduced creep compliance make higher-density PUMEs suitable for high load-bearing applications, while lower-density PUMEs are better suited for high energy absorption at lower stresses.
  • Miniatura
    Ítem
    Preload influence on the dynamic properties of a polyurethane elastomeric foam
    (Multidisciplinary Digital Publishing Institute (MDPI), 2024-07) Cortazar Noguerol, Julen; Cortés Martínez, Fernando; Sarría, Imanol; Elejabarrieta Olabarri, María Jesús
    Polymeric foams are widely used in engineering applications for vibration attenuation. The foams usually work preloaded and it is known that the dynamic properties and attenuation ability of these polymers depend on the preload. In this paper, experimental characterization of a polyurethane elastomeric foam is performed in a frequency range between 1 and 60 Hz, a temperature range between −60 and 30 °C and a preload range between 2 and 12 N, using a Dynamic Mechanical Analyzer. When going from the minimum to the maximum preload, results show the linear viscoelastic range increases 57%. In the frequency sweeps, the storage modulus increases 58% on average, while the loss factor remains unaffected by preload. Moreover, the glassy transition temperature of the material decreases for greater preloads. From the curve-fitting of a four-parameter fractional derivative model using the experimental data, a seven-parameter mathematical model is developed, reducing the number of parameters needed to describe the influence of frequency and preload on the dynamic properties of the material. Hence, it has been established that the relaxation time, relaxed modulus and unrelaxed modulus depend on the exponential of the squared prestress. In contrast, the fractional parameter does not depend on preload for the range under study.