Analysis of the Geometric Nonlinear Effect on the Mechanical Behavior of Pseudoelastic Shape Memory Alloy Helical Springs

Marcelo Amorim Savi¹; Mauricio S. Garcia¹; Pedro Manuel Calas Lopes Pacheco²; Ricardo Alexandre Amar de Aguiar²; Luís Felipe Guimarães de Souza²; Rodolpho Barbosa da Hora²

¹ COPPE/UFRJ - Department of Mechanical Engineering; ² CEFET/RJ - Department of Mechanical Engineering

doi:10.20906/CPS/COB-2015-0480

Resumo

Due to the special characteristics of Shape Memory Alloys (SMAs), several industrial applications are developed in areas such as aeronautics, medicine and robotics. SMA actuators are being employed as an alternative to electric, hydraulic and pneumatic actuators, and also, in response to a growing need to develop smaller and lighter systems. In this regard, the use of SMAs is increasing in different fields of human knowledge due to its good power-weight ratio. This paper deals with an investigation of nonlinear geometric effect on the mechanical behavior of pseudoelastic shape memory alloy (SMA) helical springs. Initially, SMA wires characterization is presented. Afterward, a discussion about the design and fabrication of SMA helical springs are performed. Experimental tensile tests are then carried out showing the nonlinear geometric influence. Results show a coupling between constitutive and geometric nonlinearities that defines the spring stiffness. Two springs with different geometries are built from SMA wires, defining springs with weak and strong nonlinear geometric influence. Numerical analysis is developed employing the finite element method confirming the general conclusions showed in experimental observations.

Palavras-chave: Shape memory alloys; pseudoelasticity; spring; geometric nonlinearities; finite element analysis