International Journal of Mechanics and Materials in Design最新文献

Laminated composite skew plates (LCSP), owing to their high strength- and stiffness-to-weight ratios, find application in diverse fields ranging from aerospace and space exploration to the marine industry. Skew plates resting on elastic foundations are widely used in applications with non-orthogonal edges, such as in aircraft fuselage or ship hulls, where rectangular plates fail to fulfil the constant curvature requirements of non-orthogonal edges. Elastic foundations alter the stress concentrations and load-carrying capacities, while cut-out and attached mass introduce additional localized stress while the mass of the plate is altered. Collectively elastic foundations, attached mass and cutouts affect the dynamic characteristics of LCSP. However, research on skew plates resting on elastic foundations, particularly considering the combined effects of cut-outs and attached masses, remains limited. This study attempts to bridge the significant gap by investigating the combined influence of cutouts, elastic foundation and attached mass, along with thickness ratios and skew angles, on the free vibration characteristics of LCSP. An efficient fast converging nine-noded isoparametric finite element skew plate model and incorporating the effects of rotatory inertia is developed, using the first-order shear deformation theory. The impact of plate geometric and material properties, as well as external factors such as elastic foundations and attached mass or cutouts, on the dynamic characteristics of the plate, is investigated. Additionally, a sensitivity analysis of the input parameters on the frequency response of plates is performed, and the most influential parameters are reported. This study aids in understanding the influence of elastic foundations, cutouts, attached mass, and skewed geometries on the dynamic behaviour of plates.

Polymer-based magnetoelectric materials, a type of three-phase polymer matrix smart composites, have emerged as a promising solution for enabling smart structural systems with advanced functionalities and demonstrating great potential for practical engineering applications. These smart composites come into contact with different rigid engineering components with the time-dependent multiphysics response. This study reports a novel hybrid element model for addressing the three-dimensional frictional sliding contact problem between a rigid spherical punch and such materials, in which the electro-magneto-viscoelastic behavior induced by the polymer matrix, piezoelectric phases, magnetostrictive phases are taken into account. Frequency response functions for unit electric, magnetic, and mechanical loads are derived based on the elastic–viscoelastic correspondence principle. During the transient regime analysis, the contact pressure, in-plane stress, and electric/magnetic potentials are numerically computed using the conjugate gradient method and discrete convolution-fast Fourier transform. The study delves into the combined effect of the surface electric/magnetic charge density and friction coefficient on the time-dependent contact behavior.

In this study, the problem of determining the length scale parameter and the transverse piezoelectric coefficient is addressed using an inverse identification method. This method is proposed as an alternative to traditional experimental techniques. Unlike conventional experimental methods, where the length scale parameter and the piezoelectric coefficient are calculated separately, both parameters are simultaneously estimated in the present work. The inverse approach provides an efficient and cost-effective approach for determining these key parameters, significantly reducing the high costs associated with traditional experimental techniques. First, a size-dependent mathematical model is proposed based on the modified couple stress theory, in which the microplate is modeled using the Kirchhoff plate theory. Additionally, Von Kármán nonlinear strains are incorporated into the mathematical model to account for geometric nonlinearities. Due to the substantial impact of the length scale parameter on mechanical behavior and the critical role of the transverse piezoelectric coefficient, accurate and affordable determination of these parameters is essential. Consequently, an inverse problem is defined, and a robust solution technique is developed. Finally, a thorough investigation is conducted to examine the influence of initial guesses and measurement errors on the accuracy and robustness of the proposed identification method.

The operation of magnetic soft continuum robots depends on external magnetic fields to realize deformation and motion in their flexible magnetic tips, thereby achieving desired functionalities. These magnetic tips essentially behave as flexible cantilever beams. Precise prediction of the deformation behavior in such magnetic soft cantilevers is of critical importance for the design, control, and real-world applications of these robotic systems. The current approach to designing magnetic soft cantilevers predominantly depends on experienced designers refining the design through iterative processes involving extensive simulation and experimentation. Furthermore, studying their mechanical properties and responses typically requires labor-intensive testing or costly computational simulations. Compared to traditional methods, machine learning has revolutionized magnetic soft cantilever design, enabling deformation prediction and geometric generation without prior knowledge. It also shifts the design process from a forward to an inverse approach, eliminating repetitive simulations and offering a faster, more efficient solution. In this study, we introduced a machine learning-based method for forward prediction and inverse design, specifically tailored to magnetic soft cantilever under defined boundary conditions. The forward deformation prediction was carried out using a weighted ensemble method-based multi-layer perceptron (WEM-MLP) machine learning model, followed by simulation and experimental validations. For the inverse design problem, a cascade ensemble method-based MLP (CEM-MLP) model was proposed and validated through simulation. The results confirmed the effectiveness of the proposed methods. The coefficient of determination R² for forward prediction model reached 0.9962, while R² for inverse design model was 0.9490. The well-trained machine learning model offers an alternative approach, enabling faster high-precision calculations under resource-limited conditions. This facilitates the prediction of deformation results and inverse design of magnetic soft continuum robots, offering valuable guidance for the practical application of these systems.

Recent years have witnessed an increasing demand for hybrid composites due to their unique and enhanced properties in various structural applications, particularly in the field of ballistic impact, which finds its application in body armour, aerospace and automotive industries. This study concentrates on the response of hybrid composite armour, made up of woven fiber fabricated with ultra-high molecular weight polyethylene (UHMWPE) and Aluminium (Al6063), and subjected to a sub-ordinance range of ballistic impact. The fabrication of the Kevlar-29/UHMWPE/Al6063 hybrid composite laminates was done by the hand layup method, followed by a vacuum-assisted technique. In the experimental part, two staking sequences of hybrid laminate were taken into consideration, with five samples of each sequence impacted at five different velocities. In the first case, Kevlar-29 (K-29) was considered as a front plate and in the second case, K-29 was considered as a back plate. Both sequences were impacted by a hemispherical nose-type projectile, using a pneumatic gun setup, having a maximum pressure of 30 bars. The average energy absorbed is 29.51% in the first case and 28.38% for the second case, depicting good strength and a lightweight of 152 g along with 51,070.52 mm² surface area of the plate. The results reveal that the energy absorption in the first case is 1.13% more than in the second case. It was further observed that the kind of damage involved is delamination, fiber breakage, matrix cracking and fiber splitting. The results of this study contribute to enhancing the protection, designing a lightweight structure, and developing a new material for industrial purposes in the manufacturing of body armour.

In this paper, within the framework of the consistent couple stress elasticity theory, Green's functions are derived for the half-plane using Mindlin’s potential function method and Fourier transform technology. Using the general solution for a micro-structured elastic half-plane under concentrated load, we investigate the two-dimensional indentation problem beneath a rigid cylindrical indenter. Due to the complexity of the integral kernel, deriving an analytical solution is difficult. Therefore, we decompose it into a singular part and a regular part and numerically solve it using the Gauss–Chebyshev quadrature formula. Furthermore, we present a generalized expression for the pressure distribution incorporating scale effects and establish functional relationships among the contact half-width, applied load, and scale parameter, and compared with the numerical results. The results indicate that the elastic displacement response under the consistent couple-stress theory differs significantly from that in classical elasticity. The asymptotic behavior of the displacement components is influenced by the material length scale parameter, and the rotation becomes bounded. These findings contribute to the understanding of mechanical characteristics in micro-indentation tests and can be applied to simulate macroscopic responses in polymers or other composite materials affected by microscale influences.

Defects occur during the manufacturing of samples using additive technologies. These defects include interlayer adhesion failure, inter-track pores, deviations from the original geometry and which can adversely affect the physical and mechanical properties of the entire product. This work is devoted to conduct an experimental 4D X-ray computed tomography investigation of the morphology of multiscale pores, their origin, and their influence on the mechanical properties of unit cell. The study evaluates the changes in the internal structure of the specimen under load using computed tomography scanning. In the research cubic porous cells produced by additive technologies were investigated. The initial pores were ellipsoidal with different angles of orientation and inter-track pores that were formed during the 3D printing process. Specimens were tested using X-ray computed tomography combined with in-situ special tooling, tensile machine and numerical experiments. The study investigated the elastic modulus, lower and upper yield limits, and structural changes during specimen loading, while simultaneously assessing variations in the geometry and volume of inter-track pores and macropores under loading. Thus, the chaotic distribution of inter-track pores was observed, which significantly affected the values of physical and mechanical characteristics, however, their contribution decreases during plastic deformation. The study presents an approximating model to describe the mechanical properties within the plastic deformation zone and reveals the dependence of pore morphology on their orientation relative to the applied load. Additionally, it was determined that taking into account the chaotic distribution of inter-track pores using the rule of mixtures provides a close correspondence between numerical and experimental data. The largest changes in the pore volume were observed in the elastic zone, whereas a significant transformation of the pore shape occurs predominantly in the plastic deformation zone.

This study concentrates on developing an analytical mode-matching method, combined with the Galerkin approach, to investigate the scattering of radiation through a flexible shell within a finite, coaxial lined chamber connected by membrane discs at the interfaces. The modeled problem involves dynamical boundary and interface conditions, as well as various ring conditions. Eigenfunction expansions are derived in different regions with homogeneous media and boundary conditions, incorporating unknown coefficients. The associated eigenfunctions are non-orthogonal, forming non-Sturm-Liouville systems. The dynamical behavior of the membrane discs is formulated using the Galerkin approach. By applying field matching at the interfaces and utilizing generalized orthogonal properties, the differential systems are transformed into linear algebraic systems. Numerical solutions of these systems, after truncation, yield the unknown amplitudes. The validation of the matching conditions at the interfaces and the convergence of the computed powers strongly support the accuracy of the truncated solution and the algebraic procedures. The interaction between the flexible shell and the compressible fluid within it significantly influences the system’s vibration characteristics. Results on scattering powers and transmission loss across various parametric settings provide insights for optimizing the attenuation of fluid–structure coupled modes within the guiding channel.

In this paper, the nonlinear free vibration and static bending of functionally graded porous graphene platelets-reinforced (FGP-GPLs) composite plates with discretized piezoelectric patches integrated on the upper and lower surfaces are numerically studied. For the first time, this research examines how the flexoelectric effect affects the stiffness of functionally graded graphene plates with piezoelectric laminates, and it explores the influence of porosity coefficient and graphene weight fraction on the strength of the flexoelectric effect. The material model of the composite layer comprises various porosity and GPLs distributions. Both porosity types and graphene patterns in the thickness direction are categorized into three distinct groups: uniform, symmetric, and asymmetric. The Halpin–Tsai micromechanical model, the rule of mixture, and the closed-cell Gaussian random field (GRF) scheme are used to determine the effective material properties of the composite layer. The computational model for piezoelectric smart structures is developed by considering the material characteristics, piezoelectric effect, flexoelectric effect, and von Kármán nonlinearity assumption. The nonlinear governing equations for the structures are derived by Hamilton principle combined with the first-order shear deformation theory (FSDT). The numerical model is discretized via the isogeometric analysis (IGA) technique and solved using a direct iterative method. The solution approach is validated against existing literature to confirm its accuracy and effectiveness. Finally, this paper thoroughly examines the effects of various parameters on the nonlinear static bending and free vibration of piezoelectric smart structures. These parameters include porosity and GPLs distribution patterns, porosity coefficients, GPLs weight fractions, load parameters, and the flexoelectric effect. Results indicate that the numerical model exhibits a stiffness-hardening mechanism under the flexoelectric effect.

Within active vibration control (AVC) Lead Zirconate Titanate (PZT) elements are a very popular choice as both sensors and actuators. Notably they have a smaller influence on the stiffness and mass of the host structure and have a high force output to weight/size ratio compared to alternatives. This research envisions their use with a flexible robot manipulator link within an AVC application. For systems using PZT sensors it has been previously found that their characteristics provide unconventional responses when part of a control system. Thus, this research aims to investigate this further through the employment of a proportional-integral-derivative (PID) control scheme in addition to combinations of the constituent gains. Additionally, the dynamics of a system including PZT sensors and/or actuators subsequently lead to issues with employing popular PID tuning methods. Thus, two alternative methods are employed to obtain the gains for the system, parametric sweeps of the gains, and an optimisation of them based on the minimisation of the integral of the time-weighted absolute error (ITAE).