Influence of Grain Interaction on the Mechanical Behavior in Shape Memory Material in Flexion Test
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Mater. Res. Soc. Symp. Proc. Vol. 1243 © 2010 Materials Research Society
Influence of Grain Interaction on the Mechanical Behavior in Shape Memory Material in Flexion Test Jacinto Cortés1, Fernando N. García1, José G. González 2, Horacio Flores3 and Alberto Reyes4 1 Centro Tecnológico Aragón, FES Argón, UNAM. Edo. de México, México, C. P. 57130. 2 Instituto de Investigaciones en Materiales, UNAM. México D.F. México. 3 Maestría en Procesos y Materiales, Universidad Autónoma de Zacatecas, Zacatecas, México. 4 IME, FES Aragón, UNAM. Edo. de México, México, C. P. 57130. ABSTRACT An experimental study of the mechanical properties of a Cu-Al-Be shape memory alloy is presented. The samples are tested in a cantilever arrangement. They consist of polycrystalline thin plates of shape memory material with a MS near 0 oC and a monocrystalline sample with MS near -90 oC. The measurements are made with strain gauges attached to the top side of the samples. In these conditions, strain Vs load curves are obtained. A polycrystalline sample is instrumented and tested and then it is cut into three samples for further testing. The results show a relationship between the transformation stress and the sample grain size which differs from the typical Hall-Petch relationship. The analysis of transformation plane stress diagrams shows the development of a stress component perpendicular to those induced by the applied load. INTRODUCTION The study of mechanical behavior of shape memory material (SMM) polycrystals is very important for developing low cost applications taking advantage of their properties efficiently. This is rather complicated because their mechanical behavior is non linear, anisotropic and depends on temperature. Additionally, microstructural factors must be considered such as grain size and shape as well as crystalline texture. Studies performed by Sakamoto and Shimizu [1] in Cu-Al-Ni polycrystalline shape memory materials subjected to simple tension tests at several temperatures have shown that the transformation stress increases with respect to the theoretical value. This expected value had been calculated on basis of the transformation temperature (MS) obtained by a differential scanning calorimetry test. These phenomena induce an effect of decreasing of transformation temperature (MS) and lead to an apparent transformation temperature (MSap). On other hand, other investigations performed in polycrystalline Cu-Al-Ni [3, 4] and CuZn-Al [2, 4] shape memory materials have shown a effects on the transformation stress subjected to simple tension tests at constant temperature. The transformation stress increases when the relative grain size decreases, this involves mainly the relationship between the grain size and the sample thickness. The present investigation deals with polycrystalline samples and a monocrystal made of a Cu-Al-Be shape memory alloy type. Strain gages are attached to the samples for bending tests in a cantilever arrangement in order to investigate the effect of the ratio grains size/sample width on the tran
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