PSI - Issue 64

Ali Jafarabadi et al. / Procedia Structural Integrity 64 (2024) 2059–2066 A. Jafarabadi et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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4

(a)

Initial state

Pre-straining

Assembly

Activation

Heating

FID>OD s Clearance

IID

Contact

Steel Tube

Fe-SMA Tube

Evolution of strains

(b)

Experiment setup

Cooling

Axial

Heating

Circumferential

Figure 1. (a) Schematic illustration of the clamping workflow. (b) Experimental test setup utilized for quantification of the interface contact

namely the FID — with a nominal tolerance of ++ 00 . . 01 5 . It should be noted that, the FID for the Fe-SMA tubes matches the outer diameter of the steel tube. Therefore, after pre-straining it is possible to place the Fe-SMA tube around the steel tube, as shown in the assembly section of the figure 1a. Table 1 describes the Fe-SMA tubes with various geometrical, expansion and post-processing conditions investigated in this study.

2.1. Experiment setup

Fig. 1b illustrates the geometry of the steel tube utilized for measurement of principal strains as a result of the contact pressure between Fe-SMA and steel tubes. A tool steel with the commercial name of Böhler V155 was machined to produce the elastic tube. Thermo-mechanical properties of V155 tubes are adopted following the manufacturer’s data sheet , and reported as 210 GPa and 12.1 ppm m/m.K for the modulus of elasticity and the coefficient of thermal expansion, respectively. Four Fe-SMA tubes were machined to investigate the effect of heat treatment on the gripping performance of the Fe-SMA joints. Table 1 contains the details of the studied parameters. The heat-treated and as-received conditions of the Fe-SMA tubes are studied focusing on the free and restrained (by the steel tube) recovery behavior. In order to quantify the contact pressure between the steel tube and Fe-SMA, a T rosette high-temperature strain-gauge was applied at the inner surface of the steel tube to measure the axial ( ) and circumferential ( ) principal strains. The strains are measured throughout the course of activation utilizing a quarter bridge self-compensated strain-gauges with a commercial name of HBM TM11. The strain-gauges are suitable for measurements in the temperature range of -200 to 300°C. However, the thermal self-compensation temperature range — which is tailored for ferritic steels ( α =10.8 ppm m/m.K) — is limited to -200 – 250°C. Self-compensated strain gauges are designed to offset temperature-induced strain by matching their temperature response to the material being measured, ensuring accurate readings despite temperature changes. The bending radius, maximum tensile and compressive elongations for this strain-gauge is limited to 5 mm, 1% and 1.5%, respectively. EP 310 N, a warm cured