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Shrinkage and relaxation motions of flexible FePd nanohelices of FePd nanorobots are simulated by a molecular dynamics (MD) model where FePd is a paramagnetic shape memory alloy that can exhibit phase transformation accompanied by softening of the nanohelix under an applied magnetic field (H-field). Two designs of FePd nanorobots are used: (i) a FePd cylindrical head connected to a FePd nanohelix tail and (ii) a FePd nanohelix alone. The geometry and dimensions of the FePd robots are taken after the as-processed FePd nanorobots. In the MD simulation, the FePd head and nanohelix are divided into a number of segmented FePd spheres, each having its magnetic moment. The results of the MD model reveal that upon the applied constant magnetic field, the initial gaps (g=3 nm) between the adjacent turns of the FePd nanohelix are closed, resulting in the total shrinkage (Stot) of 47 nm of the FePd nanorobot. The effects of the applied H-field on Stot are examined by using the MD model and the M-H curve of FePd fitted with Langevin type, resulting in the smaller applied magnetic field leading to the smaller Stot. The results of the MD model provide us with an effective tool in the analysis and design of new nanorobots based on the paramagnetic shape memory alloy of FePd nanohelices that can exert dynamic vibrations on target cells under the oscillating magnetic field. [ABSTRACT FROM AUTHOR]

In this paper, the elastic field in an infinite elastic body containing a polyhedral inclusion with uniform eigenstrains is investigated. Exact solutions are obtained for the stress field in and around a fully general polyhedron, i.e., an arbitrary bounded region of three-dimensional space with a piecewise planner boundary. Numerical results are presented for the stress field and the strain energy for several major polyhedra and the effective stiffness of a composite with regular polyhedral inhomogeneities. It is found that the stresses at the center of a polyhedral inclusion with uniaxial eigenstrain do not coincide with those for a spherical inclusion (Eshelby's solution) except for dodecahedron and icosahedron which belong to icosidodeca family, i.e., highly symmetrical structure. [DOI: 10.1115/1.1362670]

Research was conducted to study the structure of segregated networks in SiC/Si3n4 particulate composites. The SiC powders that were utilized as starting powders were mixed with Si3n4 powders in an ethanol solution to form green composite solids while the average of SiC particles were measured by scanning electron microscopy. Results indicated that composites with segregated distribution of conductive particles in an insulator matrix becomes electrically conductive at much smaller amount of conducting particle to form percolating networks.

An arbitrary, convex polygon-shaped inclusion with uniform eingenstrains was analyzed to determine its elastic fields under a plane strain condition. The elastic fields are obtained with the use of an extension of Mura's (1987) procedure. The strain concentration matrix is then calculated to obtain the overall elastic constants of composite materials with polygon-shaped reinforcements. The resulting strain fields and strain energy inside the inclusion as well as the stiffness of the composites are presented.

Analytical examination of the relaxation of misfit strains between ceramic/metal interfaces by dislocation punching in planar and nonplanar interfaces helps determine conditions essential for dislocation punching for each interface. Metal coating/ceramic substrate system forms the planar type interface while ceramic filler/metal matrix composite system forms the nonplanar interface. Agreement between experimental and theoretical results proves the efficiency of the dislocation punching model.

Four different aligned W-1% ThO2 reinforced Fe-25Cr-8Al-0.5Y matrix fiber reinforced superalloys exhibit varying metallurgical and mechanical properties. Three materials with different fiber aspect ratios and one material with a small diameter, misoriented Al2O3 hybrid reinforcement are studied. Abrasive waterjet and turning procedures help convert composite billets to tensile forms before a FeCrAlY thermal spray coat is used to prevent oxidation. Thermal residual stresses induce considerable nonlinearity in the material.

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Ferromagnetic shape memory alloy (FSMA) particulate composites have been processed by spark plasma sintering with varying weight fractions of NiTi (51 at. % Ni) and Fe powders. An assortment of experimental processing conditions such as temperature, pressure, duration of sintering, and heating rate has been chosen to characterize the relative density and superelasticity behavior of the said FSMA composite. The effective magnetic properties of these processed composites have also been experimentally estimated using vibrating sample magnetometry. An attempt at predicting the effective magnetic properties of the FSMA composite based on Eshelby’s inhomogeneous inclusion method in conjunction with Mori-Tanaka’s mean-field theory for larger concentrations of the ferromagnetic phase has also been presented in this study. The analytical model results thus obtained are compared with experimental data resulting in reasonably good agreement. [ABSTRACT FROM AUTHOR]