Magnetic Field Tunable Small-scale Mechanical Properties of Nickel Single Crystals Measured by Nanoindentation Technique

Nano- and micromagnetic materials have been extensively employed in micro-functional devices. However, measuring small-scale mechanical and magnetomechanical properties is challenging, which restricts the design of new products and the performance of smart devices. A new magnetomechanical nanoindentation technique is developed and tested on a nickel single crystal in the absence and presence of a saturated magnetic field. Small-scale parameters such as Young's modulus, indentation hardness, and plastic index are dependent on the applied magnetic field, which differ greatly from their macroscale counterparts. Possible mechanisms that induced 31% increase in modulus and 7% reduction in hardness (i.e., the flexomagnetic effect and the interaction between dislocations andmagnetic field, respectively) are analyzed and discussed. Results could be useful in the microminiaturization of applications, such as tunable mechanical resonators and magnetic field sensors.Comment: 6 pages, 4 figure

External uniform electric field removing flexoelectric effect in epitaxial ferroelectric thin films

Using the modified Landau-Ginsburg-Devonshire thermodynamic theory, it is found that the coupling between stress gradient and polarization, or flexoelectricity, has significant effect on ferroelectric properties of epitaxial thin films, such as polarization, free energy profile and hysteresis loop. However, this effect can be completely eliminated by applying an optimized external, uniform electric field. The role of such uniform electric field is shown to be the same as that of an ideal gradient electric field which can suppress the flexoelectricty effect completely based on the present theory. Since the uniform electric field is more convenient to apply and control than gradient electric field, it can be potentially used to remove the flexoelectric effect induced by stress gradient in epitaxial thin films and enhance the ferroelectric properties.Comment: 5 pages, 3 figure

Preliminary study on ductile fracture of imperfect lattice materials

AbstractThe ductile fracture behavior of two-dimensional imperfect lattice material under dynamic stretching is studied by finite element method using ABAQUS/Explicit code. The simulations are performed with three isotopic lattice materials: the regular hexagonal honeycomb, the Kagome lattice and the regular triangular lattice. All the three lattices are made of an elastic/visco-plastic metal material. Two typical imperfections: vacancy defect and rigid inclusion are introduced separately. The numerical results reveal novel deformation modes and crack growth patterns in the ductile fracture of lattice material. Various crack growth patterns as defined according to their profiles, “X”-type, “Butterfly”-type, “Petal”-type, are observed in different combinations of imperfection type and lattice topology. Crack propagation could induce severe material softening and deduce the plastic dissipation of the lattices. Subsequently, the effects of the strain rate, relative density, microstructure topology, and defect type on the crack growth pattern, the associated macroscopic material softening and the knock-down of total plastic dissipation are investigated

Electric-field-tunable mechanical properties of relaxor ferroelectric single crystal measured by nanoindentation

Electric field dependent mechanical properties of relaxor ferroelectric material Pb(Mn1/3Nb2/3)O3-PbTiO3 are investigated with the nanoindentation technique. Giant electric-field-tunable apparent elastic modulus (up to -39%), hardness (-9% to 20%) and energy dissipation (up to -13%) are reported. Based on experimental data, a characterization method of electromechanical coupled nanoindentation is proposed. In this method, an electric field tunable scaling relationship among elastic modulus, hardness and indentation work for ferroelectric materials can be determined. In addition, this method can be used to obtain the electric-field-dependent elastic modulus and hardness, and avoid the estimate of contact area in the Oliver-Pharr method. Finally, the different effects on elastic modulus between positive and negative electric fields can be explained by the flexoelectric effect.Comment: 14 pages, 4 figure

Multi-field nanoindentation apparatus for measuring local mechanical properties of materials in external magnetic and electric fields

Nano/micro-scale mechanical properties of multiferroic materials can be controlled by the external magnetic or electric field due to the coupling interaction. For the first time, a modularized multi-field nanoindentation apparatus for carrying out testing on materials in external magnetostatic/electrostatic field is constructed. Technical issues, such as the application of magnetic/electric field and the processes to diminish the interference between external fields and the other parts of the apparatus, are addressed. Tests on calibration specimen indicate the feasibility of the apparatus. The load-displacement curves of ferromagnetic, ferroelectric and magnetoelectric materials in the presence/absence of external fields reveal the small-scale magnetomechanical and electromechanical coupling, showing as the Delta-E and Delta-H effects, i.e. the magnetic/electric field induced changes in the apparent elastic modulus and indentation hardness.Comment: 17 pages, 7 figure

Implementing fractional order Fourier transformation and confocal imaging with microwave computational metamaterials

Computational metamaterials, artificially structured materials, have enabled the realization of mathematical operations, such as spatial integration, differentiation, and convolution when waves propagate through them. However, experimental verifications and relevant applications of microwave computational metamaterials have rarely been achieved so far. In this paper, we present the theoretical and experimental study on analog computing based on microwave computational metamaterials, to perform mathematical operations, such as fractional order Fourier transformation. To achieve such functionality, microwave metamaterials constructed with negative-refractive-index units are designed to implement the desired spatial operating function. We also explore the applications of the microwave metamaterial lens in the safety inspection of 3D printed objects and slice imaging by following the confocal imaging algorithm. We get good imagine results with high depth resolution at low frequencies. The technique allows us to demonstrate new approaches to real-time, multifunctional operating systems. We expect that microwave computational metamaterials will enable new capabilities in nondestructive testing (NDT) as well as signal acquisition and processing, improve microwave imaging, and drive new applications of microwaves

A magnetically controlled tunable acoustic super-resolution lens

Acoustic artificial structures have attracted much attention in recent decades due to their unique acoustic handling characteristics. The lightweight, easy-to-design feature and low cost of the thin-film acoustic artificial structure make it a great advantage in achieving super-resolution imaging and device miniaturization. However, since the film-type lens achieves super-resolution only at the resonance frequency, the frequency band in which it operates is greatly limited. In this work, considering the complexity of the vibration problem of the additional mass film, we propose a simple zero-mass method to design the operating frequency of the film-type prism. After that, a magnetic-field-controlled thin-film acoustic super-prism with a size of only six percent of the wavelength at working frequency is designed. Subsequently, based on the mechanism of magnetically induced stress, it achieves the super-resolution imaging within a frequency range from 350 Hz to 700 Hz. It provides a new idea for the design of an acoustic super-prism, and potential applications can be expected in acoustic imaging