Single-Wedge Lift-Out for Atom Probe Tomography Al/Ni Multilayers Specimen Preparation Based on Dual-Beam-FIB

Atomic probe tomography (APT) samples with Al/Ni multilayer structure were successfully prepared by using a focused ion beam (FIB), combining with a field emission scanning electron microscope, with a new single-wedge lift-out method and a reduced amorphous damage layer of Ga ions implantation. The optimum vertex angle and preparation parameters of APT sample were discussed. The double interdiffusion relationship of the multilayer films was successfully observed by the local electrode APT, which laid a foundation for further study of the interface composition and crystal structure of the two-phase composites.

Stagnation Zone Near a Corner in Viscoplastic Fluid Flow

The shape, size and location of the stagnation zone between flat non-parallel walls that make up the corner of a tube with non-circular cross-section through which a phase change material of the Bingham plastic type flows is investigated. We show that the stagnant area is bounded by a convex meniscus whose size depends on the degree of plasticity and the vertex angle. The maximum and minimum energy dissipation occurs at the wall and at the bisectrix, respectively. The stagnant zone can be altogether avoided by modifying the shape of the wall in the corner area. A new design of the cross-section of the tube that allows reducing or eliminating this area to optimize the mass transport is developed. Two optimal solutions a vertex with a straight cut and a concavely curved vertex are proposed.

Specific features of mathematical modeling of ceramic plates destruction under the influence of high-speed impactors

The paper examines the issues of mathematical modeling of ceramic armor panels’ penetration by high-speed cylindrical impactors. By means of the LS-DYNA software package, a corresponding numerical simulation methodology was developed by combining a chosen method, adjusted computational mesh cells size, appropriate Courant number, and values of linear and quadratic pseudo-viscosity coefficients. The results compared with experimental data show that Lagrangian and Eulerian numerical methods, unlike the SPH method (Smoothed Particle Hydrodynamics), improperly reproduce the process of the shock wave disintegration into an elastic precursor and a plastic wave. In addition, the common size of conical fractions dislodging from the ceramic plates was determined and the influence of the scale effect on the ceramics damage patterns was shown: an increase in the absolute value of the plate thickness leads to the increase in the dislodging cone semi-vertex angle.

The Influence of Variable Shell Thickness On the Vibrational Behavior of Composite Sandwich Conical Shells with Geodesic Lattice Cores

This paper investigates the vibrational behavior of sandwich conical shells with geodesic lattice core and variable skin thicknesses using analytical and numerical approaches. The filament wound conical shell has been considered to have varying skin thickness along the longitudinal direction. The smeared stiffener approach has been used to obtain the equivalent stiffness parameters due to the geodesic lattice core via the force and moment analyses of a unit cell. Superimposing the stiffness contribution of the stiffeners with those due to the inner and outer skins, one can calculate the equivalent stiffness of the whole structure. The equations of motion have been formulated based on the first-order shear deformation theory. The power series method has been implemented for extracting the natural frequencies of vibration. To validate the analytical results, a 3-D finite element model has been provided which is then used to conduct an extensive parametric study. The comparisons indicate an acceptable agreement between the two approaches. Moreover, the effect of variable skin thickness on the natural frequency has been examined. Furthermore, the influences of skin lamination angle, semi-vertex angle of the cone and stiffeners orientation angle have been discussed. The obtained results can be used for future relevant researches.

Evaluation of the Ability to Accurately Produce Angular Details by 3D Printing of Plastic Parts

3D printing is a process that has become widely used in recent years, allowing the production of parts with relatively complicated shapes from metallic and non-metallic materials. In some cases, it is challenging to evaluate the ability of 3D printers to make fine details of parts. For such an assessment, the printing of samples showing intersections of surfaces with low angle values was considered. An experimental plan was designed and materialized to highlight the influence of different factors, such as the thickness of the deposited material layer, the printing speed, the cooling and filling conditions of the 3D-printed part, and the thickness of the sample. Samples using areas in the form of isosceles triangles with constant height or bases with the same length, respectively, were used. The mathematical processing of the experimental results allowed the determination of empirical mathematical models of the power-function type. It allowed the detection of both the direction of actions and the intensity of the influence exerted by the input factors. It is concluded that the strongest influence on the printer’s ability to produce fine detail, from the point of view addressed in the paper, is exerted by the vertex angle, whose reduction leads to a decrease in printing accuracy.

Investigation on the free vibration behavior of sandwich conical shells with reinforced cores

The free vibration behavior of sandwich conical shells with reinforced cores is investigated in the present study using experimental, analytical, and numerical methods. A new effective smeared method is employed to superimpose the stiffness contribution of skins with those of the stiffener in order to achieve equivalent stiffness of the whole structure. The stiffeners are also considered as a beam to support shear forces and bending moments in addition to the axial forces. Using Donnell’s shell theory and Galerkin method, the natural frequencies of the sandwich shell are subsequently derived. To validate analytical results, experimental modal analysis (EMA) is further conducted on the conical sandwich shell. For this purpose, a method is designed for manufacturing specimens through the filament winding process. For more validation, a finite element model (FEM) is built. The results revealed that all the validations were in good agreement with each other. Based on these analyses, the influence of the cross-sectional area of the stiffeners, the semi-vertex angle of the cone, stiffener orientation angle, and the number of stiffeners are investigated as well. The results achieved are novel and can be thus employed as a benchmark for further studies.

Analysis of the Particles’ Movement Over the Flat and Profiled Rotating Discs surface in the Velocity Layer of the Viscous Gas

Experiments on the rotating in the air cones with vertex angle β = 120º and flat disc shown that on frequencies Ω ≥ 2.5 hertz exists a qualitative difference in movement for the particles with diameters d ≈ 1 mm and d ≈ 0.1 mm. The particles with d ≈ 0.1 mm move in the near-surface region, the particles with d ≈ 1 mm jump up to 3 cm. Comparison of the spherical and aspheric (ellipsoid with axles d, d and 4 /3 d) particles' kinematics moving shown the inevitability of the large particles jump occurrence. Large particles come to self-oscillation regime by reason of periodically appearance of the Magnus force. Small particles are localized in the velocity layer

Optimization of dynamic properties for laminated multiphase nanocomposite sandwich conical shell in thermal and magnetic conditions

This paper extends an optimization procedure to obtain the optimal dynamic properties of laminated sandwich multiphase nanocomposite truncated conical shell under magneto-hygro-thermal conditions. Based on principle of Hamilton, the equations of motion are obtained and solved by differential quadrature method and Bolotin's methods for obtaining the dynamic stability region. Based on particle swarm optimization and harmony search algorithms, a novel hybrid optimization method basis HS and PSO is proposed to enhance the performance and convergence of optimum dynamic conditions in this problem. By applying the hybrid optimization algorithm namely as HS-PSO, the volume percent of CNT and carbon fiber, number of laminas, cone semi vertex angle and moisture changes are optimized and the effects of magnetic field and temperature are shown on the dynamic stability of system. The result illustrates that proposed PSO-HS method with same conditions by other optimization methods as harmony memory size (number of particles) of 5 and total iterations of 100 shows the superior convergence performance compare to HS and PSO algorithms.

The study of the nonlinear vibration of S-S and C-C laminated composite conical shells on elastic foundations through an approximate method

This paper investigates the nonlinear vibration responses of laminated composite conical shells surrounded by elastic foundations under S-S and C-C boundary conditions via an approximate approach. The laminated composite conical shells are modeled based on classical shell theory of Love employing von Karman nonlinear theory. Nonlinear vibration equation of the conical shells is extracted by handling Lagrange method. The linear and nonlinear vibration responses are obtained via an approximate method which combines Lindstedt-Poincare method with modal analysis. The validation of this study is carried out through the comparison of the results of this study with results of published literature. The effects of several parameters including the constants of elastic foundations, boundary conditions, total thickness, length, large edge radius and semi-vertex angle on the values of fundamental linear frequency and curves of amplitude parameter versus nonlinear frequency ratio for laminated composite conical shells with both S-S and C-C boundary conditions are investigated.

A Double-Layered Elbow Exoskeleton Interface With 3-PRR Planar Parallel Mechanism for Axis Self-Alignment

Designing a mechanism for elbow self-axis alignment requires the elimination of undesirable joint motion and tissue elasticity. The novelty of this work lies in proposing a double-layered interface using a 3-PRR planar parallel mechanism as a solution to the axis alignment problem. 3-PRR planar parallel mechanisms are suitable candidates to solve this as they can span the desired workspace in a relatively compact size. In this paper, we present the modeling, design, prototyping, and validation of the double-layered elbow exoskeleton interface for axis self-alignment. The desired workspace for the self-axis alignment mechanism is specified based on the estimated maximum possible misalignment between the exoskeleton joint and the human anatomical elbow joint. Kinematic parameters of the 3-PRR planar mechanism are identified by formulating an optimization problem. The goal is to find the smallest mechanism that can span the specified workspace. The orientation angle of the mechanism’s plane addresses the frontal frustum vertex angle of the elbow’s joint, while the translational motion allows the translational offsets between the user’s elbow and the exoskeleton joint. The designed exoskeleton axis can passively rotate around the frontal plane ±15 deg and translate along the workspace 30 mm in the frontal plane. Experimental results (quantitative and qualitative) confirmed the capability of the proposed exoskeleton in addressing the complex elbow motion, user’s satisfaction, and ergonomics.