Thermomechanical Characterization and Modeling of NiTi Shape Memory Alloy Coil Spring

Area of Science:

• Materials Science
• Mechanical Engineering
• Physics

Background:

• Shape memory alloys (SMAs), particularly NiTi, are crucial in various scientific and engineering applications.
• Understanding the thermomechanical behavior of NiTi SMA coil springs is essential for optimizing their performance.
• Existing models may not fully capture the complex viscoelastic response and atomic mobility of SMAs.

Purpose of the Study:

• To characterize the thermomechanical behavior of NiTi SMA coil springs under varying electric current intensities.
• To evaluate the viscoelastic properties and damping capacity of NiTi SMAs.
• To interpret the observed behavior using fractional calculus and compare it with a phenomenological model.

Main Methods:

• Mechanical loading-unloading tests were conducted on NiTi SMA coil springs with electric currents from 0 to 2.5 A.
• Dynamic Mechanical Analysis (DMA) was employed to determine the complex elastic modulus (E*) and damping capacity (tan δ).
• The Fractional Zener Model (FZM) and a proposed phenomenological model were used for data interpretation.

Main Results:

• The study identified a maximum damping capacity (tan δ) around 70 °C for NiTi SMA.
• Fractional orders derived from the FZM correlate with the atomic mobility in the martensite and austenite phases.
• The FZM provides a framework for understanding the temperature-dependent storage modulus (E') of NiTi SMAs.

Conclusions:

• Fractional calculus, specifically the FZM, offers a robust method for analyzing the thermomechanical behavior and atomic mobility of NiTi SMAs.
• The study successfully characterized the viscoelastic response and damping properties of NiTi SMA coil springs.
• Comparison with a phenomenological model highlights the effectiveness of fractional calculus in describing SMA behavior.