Thermoelastic properties on Cu-Zn-Al shape memory springs

Abstract

This paper present a thermomechanical study of actuators in form of helical springs made from shape memory alloy wires that can work as actuator and/or as sensor. These abilities are due to the martensitic transformation. This transformation is a diffusionless phase transition that occurs by a cooperative atomic rearrange mechanism. In this work, helical spring actuators were manufactured from Cu-Zn-Al shape memory alloy wires. The springs were submitted to constant tensile loads and thermal cycles. This procedure allows to determine thermoelastic properties of the shape memory springs. Thermomechanical properties were analyzed during 50 thermal cycles in the temperature range from 20 to 130 °C. Results of variations in critical transformation temperatures, thermoelastic strain and thermal hysteresis are discussed based on defects rearrangement and martensitic transformation theory.

Effects of Composition and Thermal Treatment of Cu-Al-Zn Alloys with Low Content of Al on their Shape-memory Properties

“…These results imply that martensitic transformation occurs in two steps during cooling. the Cu-25%Zn-4%Al alloy determined in this work are somewhat lower than the results of Oliveira et al 15 , obtained for the commercial SMA wire with the nominal composition Cu-25.3%Zn-4%Al and 0.9 mm diameter, and Prakash and Harchekar 16 , who reported a recovery temperature (As) of about 65 ºC for the Cu-26%Zn-4%Al alloy wire. Average enthalpy values of austenitic transformations based on the three heating runs were 0.50 J/g for directly quenched alloy, 0.49 J/g for the up-quenched alloy and 0.47 J/g for the step-quenched alloy.…”

Thermomechanical Analysis on Ti-Ni Shape Memory Helical Springs Under Cyclic Tensile Loads

“…During this process are introduced a large concentration of linear crystalline defects (dislocations). This large concentration of defects acts as an obstacle the occurrence of phase transformation through blocking of all variants of martensite 4,5,8,9 . The calorimetric curves for the samples treated at 400 °C (HT1-24h) and 500 °C (HT2-24) for 24 hours are shown in Figure 2b, c. Table 1 shows the results of the calorimetric analysis of the samples treated at 400 °C and 500 °C for times of 1, 2, 4, 8, 12 and 24 hours.…”

“…The presence of these stress fields promotes the Two Way Shape Memory Effect (TWSME) 4,5 . Study of thermoelasticity in shape memory springs will allow understanding the behaviors of austenitic and martensitic phases with external loadings.…”

Analysis of the transformations temperatures of helicoidal Ti-Ni actuators using computational numerical methods

“…The evaluation of the mechanical behavior and the shape memory effect of the actuator was performed by repeating 40 times the heating and cooling cycle for each applied load (stress) of 35, 70, 105, 135, 170 and 200 MPa 15,16 . Figure 2 shows the main parameters from a generic thermo-elastic deformation curve.…”

“…Figure 2 shows the main parameters from a generic thermo-elastic deformation curve. The tangent rule identifies the critical transformation temperatures (A s , A f , M s and M f ), thermo-elastic deformations in millimeters (ε t ) and the linear dislocation between cycles (X) 15 .…”