An Experimental Investigation on the Properties of Cu-Al-Be-X Shape Memory Alloys for Vibration Damping Applications

Abstract

Smart materials are a new class of materials that possess adaptive capabilities which include sensing, responding and regulatory in a precise manner to the change of its environment stimuli, and are of great interest in structural, robotics, biomedical, marine, aerospace, and spacecraft technologies. Fiber Optics, Piezoelectric (PE), Magnetorheological (MR), Magnetostrictive (MS), Chromogenic, Electrorheological (ER), Electrostrictive (ES), Shape Memory Polymers (SMPs), and Shape memory alloys (SMAs) are the most common smart materials. Among these, SMAs exhibit a peculiar property in that deformed material can restore its original/predefined shape either by increasing the temperature or removing the load, which is known as the shape memory effect (SME) and “pseudoelasticity (PE) or superelasticity (SE)”, respectively. In addition, certain SMAs can exhibit the magnetic shape memory effect (MSME) by undergoing magnetic-field-induced reverse martensitic transformations. The merits of these unique properties attract the use of SMAs as dampers and actuators in smart/adaptive structures to suppress unwanted vibrations and provide seismic protection with the adoption of passive, active, semi-active, or hybrid control strategies. The functional and mechanical properties of various groups of SMAs are still being progressive in the development and implementation of a novel, cost-effective, and long functional SMA for the vibration damping and isolation of mechanical and civil structures. Ni-Ti-based shape memory alloys (popularly known as Nitinol-based SMAs) are the most commonly used in many applications and already had a commercial presence due to their superior advantages, such as high strain recovery and long functional life, however, these are restricted its vast usage due to shortcomings like processing difficulties and high cost. Cu-Al-based SMAs are selected as a prime alternative to Ni-Ti-based SMAs owing to their ease of manufacture and economical, and this has motivated to develop the suitable Cu-Al- based shape memory alloys. The aim of this thesis is to design and develop Cu-Al-Be-based polycrystalline shape memory alloys with improved microstructure, enhanced mechanical properties, better pseudoelastic shape/strain recovery, and suitability for use as seismic protection material to isolate vibrations through a passive control strategy. The present investigation has been carried out on the influence of variations in the weight percentage of Copper (Cu), Aluminium (Al), Beryllium (Be) and the grain refiners, namely Boron (B), zirconium (Zr), on the alloy phases, microstructure, mechanical, and pseudoelastic hysteresis properties. Outcomes of the present investigation reveals that Al followed by Be plays a vital role in the alloy phase modifications i.e., parent austenite, martensite or mixed phase at room temperature. The minimal addition of quaternary boron and zirconium grain refiners leads to substantial grain refinement, enhanced mechanical properties, and better pseudoelastic shape recovery. Because of these improvements in properties, they are identified as suitable for the passive damper in mechanical and civil structure applications at ambient temperature.