Procedia IUTAM最新文献

The present paper provides a systematic treatment of modern differential-geometrical methods for modeling of incompatible finite deformations in solids and thin walled structures. The incompatibility of deformations may be caused by a variety of physical phenomena; among them are: growth, non-uniform thermal fields, shrinkage, etc. Incompatible deformations results in residual stresses and distortion of geometrical shape. These factors are associated with critical parameters in modern high-precision technologies, particularly, in additive manufacturing, and considered to be essential constituents in corresponding mathematical models. The methods in question are based on the representation of a body and physical space in terms of differentiable manifolds, namely material manifold and physical manifold. These manifolds are equipped with specific metrics and connections, non-Euclidian in general.

This study deals with the nonlinear dynamics of a uniformly heated and simply-supported rectangular thin plate in the presence of two adjacent in-plane stick-slip-stop boundaries in order to release the thermal stresses in the plate. The analysis of linear vibration of the plate shows that the natural frequency of mode (2, 1) decreases with an increase of temperature and may coincide with the natural frequency of mode (1, 1) if the assembly forces on the in-plane movable boundaries are not very strong. Hence, the study focuses on the one-to-one internal resonance of the plate subject to weak assembly forces and temperature rise. Both analysis and numerical examples show that the one-to-one internal resonance happens for different combination of excitation amplitude and assembly forces, and exhibits a great variety of periodic, quasi-periodic and chaotic vibrations.

For linear delay-differential equations, a question of ongoing interest is to determine conditions on the equation parameters that guarantee exponential stability of solutions. Recent results have shown an unexpected link between the stable manifold and the variety characterizing multiple characteristic spectral values allowing to the right-most root assignment. In this paper, such an idea is presented and exploited in the control of active vibrations.

The present paper aimed at experimental study for the distortion of geometrical shape of thin walled structures manufactured by stereolithography technologies. It is proposed that total distortion occurring due to layer-by-layer photopolymerisation can be estimate using experimental data about distortion caused by curing single intermediate or final layer. The experiments used a sample in the form of a hollow cube. The distortion of the cube is recorded using time-average holographic interferometry.

The role of a global dynamics analysis to assess a system robustness and actual safety in operating conditions is investigated by studying the effect of different local and global control techniques on the nonlinear behavior of a noncontact AFM via dynamical integrity concepts and tools.

This paper describes a model package that simulates wave transformation, overtopping and flooding in coastal reaches. The present model is extended from the non-linear shallow water equations by means of including the non-hydrostatic pressure terms in the momentum equations. The transformed vertical coordinate, i.e. the σcoordinate, is adopted to fit the free surface and the uneven bottom. When a wave is ready to break, the non-hydrostatic model is locally switched to hydrostatic model by suppressing the dispersive effects. The breaking wave front is handled as a shock, and the shock wave can be simulated by non-linear shallow water equations with conservative numerical strategy. The treatments of the wave breaking and the shoreline motion are validated by experiments. One extensive application of the model to predict flooding induced by large waves or storm surge is presented to verify the efficiency of the present model in modeling of wave transformation and flooding over complex geometry in coastal reaches.

This paper compares two numerical methods applied to compute the starting vortex flow past a flat plate. The plate is inclined relative to a constant background flow at angle α, with α = 90°, 60°, 30°. The numerical methods considered are (1) direct numerical simulation of the viscous flow (DNS), and (2) an inviscid vortex sheet model. The viscous DNS solves the Navier- Stokes equations by an operator splitting finite-difference method, for Reynolds numbers Re = 250, 500, 1000, 2000. The inviscid flow is computed by a regularized vortex sheet method, with the unsteady Kutta condition imposed at the edges of the plate, for regularization parameters δ = 0.2, 0.1, 0.05. We present viscous vorticity contours, and compare streaklines and shed circulation obtained with both methods. Good agreement is found in the large-scale features of the separated spiral streaklines and the shed circulation as Re increases and δ decreases. For small inclination angle α, secondary separation on the downwind side of the plate introduces small-scale features in the viscous flow that are absent in the inviscid model. The vortex sheet model is much less costly than the viscous DNS, but it is limited by the omission of the boundary layers present in the viscous flow.

This paper investigates regenerative and frictional grinding chatters affected by mass eccentricity in the workpiece. Time delays and velocity-soften friction coefficient are employed to represent regenerative and Stribeck effects in normal and tangential grinding forces. Eigenvalue calculation and continuation scheme are used to find stability boundaries for both regenerative and frictional instabilities, illustrating that a deep grinding enhances the regenerative stability but impairs the frictional one. Near each kind of boundaries, numerical simulations and bifurcation analyses are adopted to present various chatter motions in the grinding, either with or without mass eccentricity. It is found that the frictional chatter is prone to be quenched by the external excitation due to the mass eccentricity. On the contrary, the regenerative instability still persists, but is perturbed to be quasi-periodic.

The Ni₃Al intermetallics involve more attention because of inherent material properties especially interesting in high temperature application. In this study, the Selective Laser Melting (SLM) and Direct Laser Metal Deposition (DLMD) are used to manufacture the single-tracks and layers. The optical microscopy, SEM, XRD and EDX microelement analysis were involved for the comparison of the methods. The materials showed no significant differences but each SLM and DLMD have the target application.

Selective laser melting is a layer-by-layer technique to form a solid part from powder. The thermal cycle of this process can be as short as one millisecond and less. This is why it is favorable to obtain nanostructured materials with advanced properties. Metal matrix composite WC-Co is studied. Micron-sized Co powder was mixed with WC nanopowder in a planetary ball mill to prepare uniform composite powder. Single remelted beads and monolayers were obtained from the composite powder on the substrates of sintered WC-Co. No cracks and good adhesion to the substrate are observed. The high cooling rate up to 10⁶ K/s explains the fine microstructures. Increasing the scanning velocity is favourable because of refining the microstructure and decreasing the balling-effect. The attained values of surface roughness are as low as 1-2 μm.