Defesa de Tese - Bruno Felippe Silva (12/12/2025)

DEFESA DE TESE DE DOUTORADO

Título: 

NUMERICAL AND EXPERIMENTAL ANALYSIS OF STRESS AND STRAIN CONCENTRATION IN PSEUDOELASTIC SHAPE MEMORY ALLOYS THIN SHEETS

Discente: Bruno Felippe Silva

Abstract

Shape memory alloys (SMA – Shape Memory Alloys) are materials that have a strong thermomechanical coupling associated with phase transformation processes. These alloys have special characteristics in terms of their stress-strain-temperature behavior, making them attractive for use in several applications of interest in engineering, such as actuators, intelligent structures and mechanical vibration absorbers. SMAs, when subjected to thermomechanical loads, present a complex non-linear behavior and require the use of specific tools and methodologies to assess their performance and integrity. The traditional design of mechanical components with complex geometries, involving geometric discontinuities such as notches and holes, has been treated through simplified mechanical design approaches involving stress concentration factors, both for monotonic and cyclic mechanical and/or thermal loadings. The presence of plastic strains increases the complexity of the analysis due to stress redistribution and non-linearities present, and mechanical design approaches involving elastoplastic stress concentration factors have also been used. Similarly, strains associated with the phase transformation process in shape memory alloys promote a stress field redistribution effect. This thesis aims to investigate, both experimentally and numerically, the stress concentration effect in pseudoelastic thin NiTi sheets, considering phase transformation and plasticity. Initially, the study includes training and heat treatment procedures established to stabilize and improve pseudoelastic behavior. Subsequently, Differential Scanning Calorimetry (DSC) analysis and standard ASTM E8 tensile tests are developed to characterize the pseudoelastic response and the coupling between stress-induced phase transformation and plastic deformation. In the next stage, thin NiTi plates containing holes of different diameters are tested to study the stress concentration effect. The strain fields around the holes are evaluated through the Digital Image Correlation (DIC) method, while temperature evolution is simultaneously monitored using infrared thermography, providing insight into the thermomechanical coupling mechanisms. A finite element numerical study is then developed and calibrated using the experimental data obtained from both the standard tensile specimens  and the plates with holes. The results show good agreement between the simulations and experimental observations. Finally, a numerical study is performed to analyze stress and strain concentration under load levels considering different training and heat treatment conditions. The proposed methodology provides a promising framework for studying stress concentration effects in pseudoelastic SMAs, contributing to the design of SMA-based components and to the broader understanding of their coupled thermomechanical behavior.

Keywords: Shape memory alloys, pseudoelasticity; Stress concentration factor; Finite element method  

Banca Examinadora:

Prof. Pedro Manuel Calas Lopes Pacheco (CEFET/RJ PPEMM) - Orientador / Presidente

Prof. Ricardo Alexandre Amar de Aguiar (CEFET/RJ - PPEMM) - Orientador

Profa. Luciana Loureiro da Silva Monteiro  (CEFET/RJ - PPEMM)

Prof. Marcelo Amorim Savi  (UFRJ - PPEMM)

Profa. Aline Souza de Paula (UnB)

Prof. Carlos José de Araújo (UFCG)

Prof. Arthur Adeodato (UERJ-IPRJ - suplente) 

Data: 12 de dezembro de 2025

Horário: 09:30h

Defesa na modalidade Híbrida

• Local: Auditório 5 (5o andar do Bloco E - campus Maracanã)
• Online (MS Teams): Banca de Doutorado (Bruno Felippe - PPEMM) | Ingresso na Reunião | Microsoft Teams