PSI - Issue 36

Volodymyr Iasnii et al. / Procedia Structural Integrity 36 (2022) 284–289 Volodymyr Iasnii, Lukasz Sobaszek, Petro Yasniy / Structural Integrity Procedia 00 (2021) 000 – 000

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Structural damping devices based on shape memory alloys (SMA) have been already studied by some researchers (Ozbulut et al. (2011), Torra et al. (2012), Dolce et al. (2005), Qiang and Cho (2007), Abdulridha and Palermo (2017), Morais et al. (2017)). There are known some passive damping devices in which SMA bunched wires were used as functional elements in the systems to protect structural elements under dynamic loading. These devices have both self-centering and damping capabilities. Taking into account the loss of the SMA functional properties under cyclic loading conditions, namely, residual strain increase under displacement or stress amplitude control and decrease of pseudoelastic hysteresis of stress – strain (Iasnii et al. (2018), Predki et al. (2006), Iasnii and Junga (2018), Iasnii et al. (2019)), different methods are used to stabilize their properties (Soul and Yawny (2015)). In particular, this is so called «stabilization training» due to the pre -tension strain or previous cyclic loading. Damping devices based on pre-tensioned SMA wires (Ozbulut et al. (2011), Torra et al. (2012), Morais et al. (2017), Yasniy and Iasnii (2019)), have a high equivalent damping coefficient, which even reaches a value of 0.11, as well as the re-centring ability (Soul and Yawny (2015)). At the same time, different loading schemes of SMA wires are realized. In all cases, this is the pre-tension that ensures that even at low displacement values the device will operate effectively on the martensitic transformation plateau. A group of bunched wires are used in some devices that elongates under tensile loading and shortened when a compressive force is applied (Ozbulut et al. (2011), Dolce et al. (2005)). Also, some devices are based on two groups of bunched wires, one of which elongates and the other shortens when a tensile force is applied, and their behaviour changes to the opposite under the compressive force (Morais et al. (2017)). Pre-tension to the middle part of the martensitic transformation plateau ensures the most effective operation of pseudoelastic SMA wires in the wide range of strain. Self-centring springs which are pre-compressed and are balanced in the absence of external loading, have been proposed in some studies. In other devices, self-centring is implemented by pre-stretched SMA wires, which at the same time are a damping element (Dolce et al. (2005)). The aim of the experiment was to verified in a prototype a functional properties and damping capacity of the device under cyclic loading in the wide range of frequencies and displacement amplitude. 2. Experiment The parameters of device are given in Table 1 (Iasnii (2020)).

Table 1. Structural parameters of damping device.

Parameters of spring (self-centering group)

Parameters of SMA wire

Wire diameter, mm

Length, mm

Number of active coils

Stiffness, N/mm

Maximal loading, N

Length L w ,

Diameter d w , mm

6.30

70

5.8

217.68

3513.40

343

1.5

The functional properties of damping device (Fig. 1) were studied on servohydraulic STM-100 testing machine (Yasniy et al. (2005)). Tests were performed in displacement control mode at frequency range of 0.001 − 2 Hz and displacement range of 3 − 9 mm under symmetric cyclic loading. Structural parameters of damping device and testing technique were presented on Fig. 1 (Iasnii (2020)). The offered damping device includes an axis 1 with two side fixing systems 2 on it. Springs 3 and 4 are placed between these systems. The springs are separated by a central locking device 5, the side mounting systems are equipped with fastening sleeves 6 with apertures on which the cone 7 is placed with a conical sleeve 8, between which the 9 SMA wires are fixed. Each side fixing system is equipped with a cylindrical cage 10 with an inner ring stop 11 on one side and an inner thread 12 on the opposite side, in which the threaded collar 13 is threaded pressing the conical sleeve through the intermediate washer. The threaded collar 13 of the left side fixing system is connected with the connecting rod 14. To stabilize the functional properties of the SMA wires, the damping device had been loaded during 50 cycles with frequency of 0.5 Hz and displacement amplitude = 5 mm. Due to the one-side strain accumulation, the decrease of pre-strain has taken place under cyclic loading.