Abstract
The following investigation has the purpose of describing, both experimentally and numerically, the fracture behavior of a giant magnetostrictive alloy commercially known as Terfenol-D. Single-edge precracked specimens have been analyzed via three-point bending tests, measuring fracture loads in the presence and absence of a magnetic field at various loading rates. The Strain Energy Density (SED), averaged in a finite control volume, has recently proved to be an excellent method of predicting brittle failures of cracked, U- and V-notched specimens made out of different materials. The effects of the magnetic field and of the loading rate on Terfenol-D failures have been studied, as well as discussing the ability of SED criterion to seize these effects, by performing coupled-field finite element analyses. Finally, a relationship between the size of the SED's control volume and the loading rate has been proposed and failures have then been estimated in terms of averaged SED.
Highlights
Magnetostriction is the variation of shape in a material when subjected to an external magnetic field
The following table contains the fracture loads, Pc, experimentally measured at each loading rate, in the presence and absence of the magnetic field: Bold numbers represent the average value at each condition, whereas numbers in brackets represent the relative standard deviations
Terfenol-D has shown a decrease in fracture load with a decrease in the loading rate, as other materials such as TiAl alloys (Cao et al, 2007) and piezoelectric ceramics (Shindo et al, 2009; Narita et al, 2012) have exhibited a similar behavior
Summary
Magnetostriction is the variation of shape in a material when subjected to an external magnetic field. According to Lazzarin and Zambardi (2001), the brittle failure of a component occurs when the total strain energy, W , averaged in a specific control volume located at a notch or crack tip, reaches the critical value Wc. In agreement with Beltrami (1885), named σt the ultimate tensile strength under elastic stress field conditions and E the Young's modulus of the material, the critical value of the total strain energy can be determined by the relation: Wc σ2 t. The trend of strain versus applied magnetic field is shown below (Fig. 4): The full dots stand for the experimental data, while the solid line represents the numerical trend, having considered the second order magnetoelastic constant
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