Programa de Pós-graduação em Engenharia Elétrica e da Computação
URI Permanente desta comunidade
Navegar
Navegando Programa de Pós-graduação em Engenharia Elétrica e da Computação por Assunto "Acoustic birefringence"
Agora exibindo 1 - 1 de 1
Resultados por página
Opções de Ordenação
Item Avaliação de propriedades acustoelásticas do polímero termoplástico polimetilmetacrilato por ultrassom(Universidade Federal de Goiás, 2017-11-17) Rezende, Ana Cláudia Barbosa; Vieira, Sílvio Leão; http://lattes.cnpq.br/1254102050392862; Vieira, Sílvio Leão; Fagundes Neto, Marlipe Garcia; Silva, Jonas Oliveira daUltrasound is a powerful tool used in modern medical and industrial applications. The portability, applicability and ease of working with ultrasound, together with the fact that it is a non-destructive technique and of lower costs, contribute to its use. Modernly, thermoplastic polymer polymethylmethacrylate (acrylic) or PMMA has been used for a variety of applications, from transparent aerospace components to medical-hospital equipment. The study of PMMA’s acustoelasticity using ultrasonic methods allows the indirect inspection of certain physical characteristics of this material. It is known that acoustic waves are a ected by the characteristics of the medium, such as temperature, texture and tension. The research was divided into three stages, the first one to analyze the influence of temperature on the velocity of critically refracted longitudinal ultrasonic waves (Lcr) in PMMA. For this, the transmission method was used for three di erent frequencies. In the second, the structural anisotropy was evaluated using the acoustic birefringence using the pulse-echo method. At this stage a rectangular sample was fractured transversely and rejoined to simulate a symmetry break. The third and final step was devoted to characterizing the acoustoelastic constants L22, L21 and L23 of homogeneous samples by means of longitudinal and shear waves in the pulse-echo mode and the application of an uniaxial force. The results with the waves Lcr showed a significant influence of the temperature on the propagation velocity of the ultrasonic waves, another factor of influence was the frequency of the transducers. On the other hand, with acoustic birefringence it was possible to identify a great variation of this magnitude near the fractured zone, that is, of greater anisotropy. The acoustoelastic constants L22, L21 and L23 were characterized and an increase in the propagation time of the ultrasound wave as a function of the strain was observed for the constants L22 and L23. The constant L21 decreased the propagation time of the ultrasonic shear wave as a function of the deformation. The ultrasonic techniques employed were relevant and allowed to obtain new results not yet described in the literature. The characterization of the acoustoelastic constants also made it possible to estimate the third order elastic constants (l, m, n and A, B, C). The constants characterized in this research are important to obtain a complete understanding of the elastic properties of polymethylmethacrylate.