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Mechanical behaviour and phase transition mechanisms of a shape memory alloy by means of a novel analytical model

100%

Carpinteri A. , Di Cocco V. , Fortese G. , Ronchei C. , Scorza D. , Vantadori S. , Zanichelli A. , Iacoviello F. , Natali S.

Acta Mechanica et Automatica

2018

tom Vol. 12, no. 2

105--108

The aim of the present paper is to examine both the fatigue behaviour and the phase transition mechanisms of an equiatomic pseudo-elastic NiTi Shape Memory Alloy through cyclic tests (up to 100 loading cycles). More precisely, miniaturised dog-bone specimens are tested by using a customised testing machine and the contents of both austenite and martensite phase are experimentally measured by means of X-Ray diffraction (XRD) analyses. On the basis of such experimental results in terms of martensite content, an analytical model is here formulated to correlate the stress-strain relationship to the phase transition mechanisms. Finally, a validation of the present model by means of experimental data pertaining the stress-strain relationship is performed.

Effects of tool rotation and transverse speed on fatigue properties of friction stir welded AA 1050-H18 aluminium alloy

86%

Kemal Kulekci M. , Sik A.

tom Vol. 51, iss. 2

213-216

In this study fatigue behaviour of friction stir welded butt joints of Al-1050-H18 was investigated. Friction stir welds of Al 1050-H18 aluminium alloy material was performed on a semiautomatic milling machine. In the study the same material was welded with different parameters to identify the effect of parameters variation on fatigue behaviour of studied aluminium alloy. FSW tool rotation and transverse speed were accepted as variable parameters while others held fixed. The results of fatigue tests of welded joints showed that the temperature regimes in FSW over required level negatively affect the fatigue endurance limit of the studied joints. Comparison of test results obtained with different tool rotation and transverse speed show that an optimisation is needed to obtain reasonable fatigue endurance limit.

W pracy przedstawiono wyniki zmęczeniowych badań połączeń z Al-1050-H18, przeprowadzonych sposobem tarciowym. Spawy ze stopu Al-1050-H18 wykonano za pomocą półautomatycznego urządzenia. Zmieniano parametry spawania, aby zbadać ich wpływ na zmęczeniowe zachowanie badanego stopu Al. Zmiennymi parametrami były predkość obrotowa wrzeciona oraz przesuw poprzeczny, pozostałe parametry były ustalone. Wyniki prób zmęczeniowych pokazały, że spawanie tarciowe, w zakresie temperatur powyżej wymaganego poziomu, negatywnie wpływa na wytrzymałość zmęczeniowa złączy. Porównanie wyników testów, otrzymanych przy różnych prędkościach obrotowych i przesuwu wskazuje na potrzebę optymalizacji parametrów w celu uzyskania odpowiedniej wytrzymałości zmęczeniowej.

Effect of austempering temperature on microstructure and cyclic deformation behaviour of multiphase low-carbon steel

86%

Long X. Y. , Branco R. , Macek W. , Nejad R. M. , Lesiuk G. , Zhu S. P. , Amaro A. M.

tom Vol. 23, no. 3

art. no. e201, 2023

This paper examined the cyclic deformation behaviour of multiphase low-carbon steel that was subjected to austempering heat treatments at four temperatures (190 °C, 230 °C, 275 °C, and 315 °C) below the martensite start temperature (Ms = 353 °C). The tests were conducted at room temperature, under fully reversed strain-controlled conditions, with strain amplitudes in the range 0.5–1.0%. The microstructure was observed by transmission electron microscopy, and the fracture surfaces were examined by scanning electron microscopy. The steel had a bainite/martensite microstructure, with increasing bainite content for higher austempering temperatures. Irrespective of the tested conditions, it strain-hardened during the first two cycles and then, strain-softened until failure. The austempering temperature did not significantly affect the stress-based, strain-based and energy-based relationships. However, lower austempering temperatures slightly improved the fatigue performance.