Acta Mechanica最新文献

This article investigates the dynamic features of domain walls in a bilayer piezoelectric-magnetostrictive heterostructure under the influence of piezo-induced strains, inertial damping, and dry friction dissipation. We assume that the magnetostrictive material belongs to the transversely isotropic hexagonal crystal. The analysis is carried out within the framework of the inertial Landau-Lifshitz-Gilbert equation, which describes the ultrafast evolution of magnetization inside the magnetostrictive materials. By employing the classical traveling wave ansatz, the study explores how various factors such as magnetoelasticity, dry friction, inertial damping, crystal symmetry, and a tunable external magnetic field characterize the motion of the magnetic domain walls in both steady-state and precessional dynamic regimes. The results present valuable insights into how these key parameters can effectively modulate dynamic features such as domain wall width, threshold, Walker breakdown, and domain wall velocity. The obtained analytical results are further numerically illustrated, and a qualitative comparison with recent observations is also presented.

A new analytical model for thermoelastic responses of a multi-layered composite plate with imperfect interfaces is developed. The composite plate contains an arbitrary number of layers of dissimilar materials and is subjected to general mechanical loads (both distributed internally and applied on edges for each layer) and temperature changes, which can vary from layer to layer and along two in-plane directions. Each layer is regarded as a Kirchhoff plate, and each imperfect interface is described using a spring-layer interface model, which can capture discontinuities in the displacement and stress fields across the interface. Unlike existing models, the governing equations and boundary conditions are simultaneously derived for each layer by using a variational procedure based on the first and second laws of thermodynamics, which are then combined to obtain the global equilibrium equations and boundary conditions for the multi-layered composite plate. A general analytical solution is developed for a symmetrically loaded composite square plate with an arbitrary number of layers and imperfect interfaces by using a new approach that first determines the interfacial normal and shear stress components on one interface. Closed-form solutions for two- and three-layer composite square plates are obtained as examples by directly applying the general analytical solution. Numerical results for two-, three- and five-layer composite plates under different loading and boundary conditions predicted by the current model are provided, which compare well with those obtained from finite element simulations using COMSOL, thereby validating the newly developed analytical model.

This paper develops a size-dependent Kirchhoff plate model for bending and free vibration analyses using a semi-analytical higher-order finite strip method (H-FSM) based on the nonlocal strain gradient theory (NSGT). To satisfy the various longitudinal boundary conditions, the continuous trigonometric function series and the interpolation polynomial functions are employed in the transverse direction. In solving nanoplate problems using the H-FSM, the higher-order polynomial shape functions (higher-order Hermitian shape functions) are utilized to evaluate the second derivatives, in addition to the displacement and first derivative. The stiffness and mass matrices, and force vector of the nanoplates are derived using the weighted residual method. A numerical study is conducted to investigate the impact of different factors, such as boundary conditions, nonlocal and strain gradient parameters, aspect ratio, and types of transverse loading. The Navier solution is utilized to analyze the effects of material length scale parameters on bending and free vibration responses of nanoplates for preliminary comparisons. The numerical results show that, when the transverse load on the nanoplate is uniform or hydrostatic and the plate has a CCCC boundary condition, the nonlocal effect does not affect the deflection results and is the same as the obtained results in the local mode.

We present a model-based feedforward control strategy suitable for designing swift rest-to-rest maneuvers for liquids in arbitrarily shaped containers. We employ the commonly used equivalent pendulum model to represent the sloshing dynamics and suggest a novel parameter identification scheme suitable for arbitrary container shapes and any number of sloshing modes. By computing natural modes and fluid reaction forces and torques for imposed harmonic container motions via a finite element model, we obtain data for the identification scheme. A fitting procedure then yields highly accurate parameters for a physical pendulum model, where each pendulum represents one sloshing mode. We also provide a thorough analysis of parameter identifiability and guidelines for obtaining robust parameter estimates. The proposed feedforward control method uses a virtual tray pendulum on which we place the container (in the form of its equivalent pendulum model). Designing the virtual tray such that the fluid’s dominant sloshing mode cannot be excited by horizontally moving the tray pendulum pivot effectively zeros out any sloshing motion in this mode. We then exploit the flatness property of the resulting system to design rest-to-rest maneuvers where any residual sloshing motion (in higher modes) can be exactly stopped at the end of the maneuver. The effectiveness of the proposed method is demonstrated through extensive simulations and experimental results using a Martini cocktail glass, whose shape is challenging in terms of sloshing. The experimental results show the successful, accurate suppression of sloshing, validating the efficacy of the proposed concept.

This study delves into the complexity of optimizing multiple actuators on a cantilever beam, focusing on the flexoelectric effect caused by the non-uniform electric field generated by an atomic force microscope (AFM) probe. Multiple actuators control has significant research value in enhancing the flexoelectric effect, greatly alleviating stress concentration and achieving precise vibration control. The current challenge in multiple flexoelectric actuators research is multi-objective optimization, addressed here using the Newton–Raphson iterative method, known for its robustness in the convex function domain, as an optimization framework. By analyzing structural parameters and flexoelectric actuator parameters, significant influencing factors are selected to form the vector space, determining actuator positions and driving voltages. These variables constitute the optimization space and are incorporated into the Newton–Raphson general iterative equation to derive the iteration matrix, which is computed using MATLAB. Case studies confirm that the Newton–Raphson method effectively identifies optimal actuator positions and driving voltages at different modes without external force, significantly improving flexoelectric control efficiency. Additionally, it quickly stabilizes vibrations at different modes under external force. However, the study has limitations, as the Newton–Raphson method cannot effectively solve non-convex function optimization in linear space. This research advances the understanding of multiple actuators optimization control structure dynamics and promotes the development of more effective engineering solutions, particularly in achieving more precise actuation and control in the field of micro- and nano-structure engineering.

In this paper, a variable-order fractional model is proposed to characterize the complex nonlinear temperature-dependent mechanical behaviors of amorphous glassy polymers, which play a crucial role in the wide applications. At a specific temperature, the variable order is defined to follow the microbial growth curve, which is consisted of a logarithmic growth stage and decay stage. The two stages are naturally connected on the conception that the growth rate is approaching to 0. The variable order is further physically interpreted based on microscopic mechanism. Furthermore, the relationships between elastic modulus, relaxation time and temperature are incorporated into the established model to demonstrate the temperature dependence. Various experimental results are observed to be well characterized by the proposed model, which validates the rationality and reliability. The predictive ability of the proposed model is also explored to verify its effectiveness.

This paper presents a multi-dimensional variable-kinematics finite element model for nonlinear static analyses of structures with complex geometries. The approach incorporates higher-order beam models and classical solid finite elements in a unified framework, enabling refined modeling of complex geometries. The finite element procedure proposed follows the Carrera Unified Formulation (CUF) and uses a pure displacement-based methodology. The governing equations are derived within the classical continuum mechanics framework, and weak-form equilibrium equations are established using the Principle of Virtual Displacements (PVD). Within the CUF framework, higher-order beam and hexahedral solid models are defined in a unified manner, and the governing equations are written in terms of invariants of mathematical models used and the theory of structures approximation. A coupling technique is used between the beam and solid elements at the nodal level using superposition. The capabilities of fully nonlinear variable-kinematics models are investigated for the static analysis of various rectangular and curved structures. The numerical results are compared with solutions obtained using commercial software. Finally, the proposed methodology is applied to analyze more complex geometries in engineering applications. The results show the capabilities of variable-kinematics models in terms of both accuracy and computational efficiency for the computation of highly nonlinear deformed states and localized phenomena, such as stress concentrations and buckling.