Search

This paper quantifies the influence of uncertainty in the low-velocity impact responses of sandwich plates with composite face sheets considering the effects of obliqueness in impact angle and twist in the plate geometry. The stochastic impact analysis is conducted by using finite element (FE) modelling based on an eight nodded isoparametric quadratic plate bending element coupled with multivariate adaptive regression spline (MARS) in order to achieve computational efficiency. The modified Hertzian contact law is employed to model contact force and other impact parameters. Newmark's time integration scheme is used to solve the time-dependent equations. Comprehensive deterministic as well as probabilistic results are presented by considering the effects of location of impact, ply orientation angle, impactor velocity, impact angle, face-sheet material property, twist angle, plate thickness and mass of impactor. The relative importance of various input parameters is determined by conducting a sensitivity analysis. The results presented in this paper reveal that the impact responses of sandwich plates are significantly affected by the effect of source-uncertainty that in turn establishes the importance of adopting an inclusive stochastic design approach for impact modelling in sandwich plates. • The compound effect of source-uncertainty on low-velocity impact of sandwich plates with face sheets made of composite laminates is quantified following an efficient hybrid simulation approach (MARS-FE). • Probabilistic results leading to the complete probabilistic characterization of the impact response quantities are presented considering the critical effects of oblique impact and twist in plate geometry. • The importance of adopting an inclusive design paradigm considering the effect of source-uncertainties in the impact analysis of sandwich structures is established through the presented numerical results. • An assessment of relative sensitivity of the critical parameters is presented for the impact responses to ensure adequate quality control in the optimum design and manufacturing of sandwich structures prone to impact loading. [ABSTRACT FROM AUTHOR]

The position of bound 1sns$$ 1 sns $$ (n=1−5$$ n=1-5 $$) states as well as doubly excited resonance 2sns$$ 2 sns $$, 2pnp$$ 2 pnp $$ (n=2−3$$ n=2-3 $$) states of  1Se$$ {}^1{\mathrm{S}}^e $$ symmetry has been determined for highly charged He‐like ions (C4+$$ {\mathrm{C}}^{4+} $$, Mg10+$$ {\mathrm{Mg}}^{10+} $$, Al11+$$ {\mathrm{Al}}^{11+} $$, Si12+$$ {\mathrm{Si}}^{12+} $$, S14+$$ {\mathrm{S}}^{14+} $$, and Ar16+) along with their respective one‐electron thresholds (1s$$ 1s $$, 2s$$ 2s $$, and 2p$$ 2p $$) under weakly coupled plasma environment. These particular ions and their respective charge states are selected due to their frequent occurrence in astrophysical and laboratory plasmas. Ritz variational method with multi‐exponent explicitly correlated Hylleraas type basis and pure‐exponential basis set are adopted for tackling He‐ and H‐like ions, respectively. The resonance width of a few low‐lying resonance states is determined using the stabilization method under different plasma conditions. Ionization potential depression is noted for both the bound and resonance states of the plasma‐embedded ions. It is evident that the width (or the lifetime) of the considered resonance states originating from different dominant configurations follows different patterns w.r.t. the plasma screening length. [ABSTRACT FROM AUTHOR]

The large compositional space of high entropy alloys (HEA) often presents significant challenges in comprehensively deducing the critical influence of atomic composition on their mechanical responses. We propose an efficient nonparametric kernel-based probabilistic computational mapping to obtain the optimal composition of HEAs under ballistic conditions by exploiting the emerging capabilities of machine learning (ML) coupled with molecular-level simulations. Compared to conventional ML models, the present Gaussian approach is a Bayesian paradigm that can have several advantages, including small training datasets concerning computationally intensive simulations and the ability to provide uncertainty measurements of molecular dynamics simulations therein. The data-driven analysis reveals that a lower concentration of Ni with a higher concentration of Al leads to higher dissipation of kinetic energy and lower residual velocity, but with higher penetration depth of the projectile. To deal with such conflicting computationally intensive functional objectives, the ML-based simulation framework is further extended in conjunction with multi-objective genetic algorithm for identifying the critical elemental compositions to enhance kinetic energy dissipation with minimal penetration depth and residual velocity of the projectile simultaneously. The computational framework proposed here is generic in nature, and it can be extended to other HEAs with a range of non-aligned multi-physical property demands. [ABSTRACT FROM AUTHOR]

The nonlinear stability characteristics of doubly curved panels made of three-phase composites with randomly dispersed carbon nanotubes [randomly dispersed carbon nanotube reinforced fiber composites (RD-CNTRFC)] subjected to practically relevant nonuniform in-plane loads are investigated in this study. Carbon nanotubes (CNTs), when mixed with resin polymer, may give rise to bundles, termed as agglomerations, which can have a profound impact on the effective material properties. There exists a strong rationale to investigate the influence of such agglomeration on the nonlinear equilibrium path of panels, which can subsequently be included in the structural stability design process to enhance operational safety. A multistage, bottom-up numerical framework is developed here to probe the nonlinear stability characteristics. The effective material properties of RD-CNTRFC panels are determined using the Eshelby–Mori–Tanaka approach and the Chamis method of homogenization. By considering von Kármán nonlinearity and Reddy's higher-order shear deformation theory, strain–displacement relations are established for the nonlinear stability analysis. The governing partial differential equations are simplified into nonlinear algebraic relations using Galerkin's method. Subsequently, by reducing the stiffness matrix neglecting the nonlinear terms and solving the Eigenvalue problem, we obtain critical load and nonlinear stability path of shell panels based on the arc-length approach. In the present study, various shell geometries such as cylindrical, elliptical, spherical, and hyperbolic shapes are modeled along with the flat plate-like geometry to investigate the nonlinear equilibrium paths, wherein a geometry-dependent programmable softening and hardening behavior emerges. [ABSTRACT FROM AUTHOR]

The application of smart materials and metastructures has been rapidly increasing in advanced multiphysical systems because of their ability to modify mechanical responses by adding circuits in a programmable way. This paper proposes to exploit functional gradation and programmed disorder for flexural wave manipulation to enhance broadband vibration control, leading to a new application of smart metamaterials. The graded metamaterial configuration involves arranging the shunted piezoelectric patches with algorithmically obtained spatially varying parameters, resulting in wideband wave attenuation and mode trapping. The considered locally grading parameter here is the shunt resonant frequency of the unit cells, designed following the rainbow trap idea and referred to as 'rainbow' metamaterials. Two metastructures are developed in this article by tuning the shunted piezoelectric electrical circuit in single and multiple configurations, each related to the unit cell. The computationally efficient spectral element method is employed to calculate the dynamic response, and the spectral transfer matrix method is integrated therein to obtain the dispersive diagram. Subsequently, effective vibration mitigation in a wider frequency band is realized through wave manipulation based on the concept of rainbow metamaterials. To this end, we have considered a unimorph beam hosting an array of piezoelectric unit cells with single and multiple resonant shunts for obtaining the numerical results, which demonstrate that the vibration attenuation zone of the multi-resonant rainbow arrangement becomes significantly wider than the single shunt configuration. The programmed disorder in the elastic waves imposes the veering effect, which generates an interaction between two dispersion curves showing a coupling phenomenon for the waves. It involves relevant energetic exchanges between the wave modes and strongly affect the undamped forced response of the system that can influence the wave trapping generated by the proposed metamaterial. Such outcomes lead to the realization of the benefit of rainbow smart metastructures compared to conventional locally resonant metamaterials on vibration and elastic bandwidth manipulation. • Design of smart rainbow metamaterials aiming to enhance single- and multi-broadband vibration and bandgap control. • Exploitation of functional gradation and programmed disorder for enhanced flexural wave manipulation. • Graded shunted piezoelectric patches to obtain spatially varying parameters for wideband wave attenuation and mode trapping. • Veering effect in the elastic waves involving energetic exchanges between the wave modes improving the vibration control. [ABSTRACT FROM AUTHOR]

Lightning strike damage can severely affect the thermo-mechanical performance of composite laminates. It is essential to quantify the effect of lightning strikes considering the inevitable influence of material and geometric uncertainties for ensuring the operational safety of aircraft. This paper presents an efficient support vector machine (SVM)-based surrogate approach coupled with computationally intensive transient thermal-electrical finite element simulations to quantify the uncertainty in lightning strike damage. The uncertainty in epoxy matrix thermal damage and electrical responses of unprotected carbon/epoxy composite laminates is probabilistically quantified considering the stochasticity in temperature-dependent multi-physical material properties and ply orientations. Further, the SVM models are exploited for variance-based global sensitivity analysis to investigate the input parameters' relative influence on the lightning strike-induced damage behavior. Due to the adoption of a coupled SVM-based simulation approach here, it has become possible to carry out a comprehensive uncertainty quantification leading to complete probabilistic descriptions of the electrical and lightning damage parameters despite the requirement of performing a large number of computationally intensive function evaluations. The results reveal that source-uncertainty of the unprotected laminates significantly influences the epoxy matrix decomposition, electrical current density and electric potential, wherein longitudinal electrical conductivity is most sensitive to stochastic variations followed by other electrical, thermal and geometric parameters. [ABSTRACT FROM AUTHOR]

Effective elastic moduli of lattice-based materials are one of the most crucial parameters for the adoption of such artificial microstructures in advanced mechanical and structural systems as per various application-specific demands. In conventional naturally occurring materials, these elastic moduli remain invariant under tensile and compressive normal modes or clock-wise and anti-clock-wise shear modes. Here we introduce programmed domain discontinuities in the cell walls of the unit-cells of lattice metamaterials involving a bi-level microstructural design to achieve non-invariant elastic moduli under tensile and compressive normal modes or clock-wise and anti-clock-wise shear modes. More interestingly, such non-invariance can be realized in the linear small deformation regime and the elastic moduli can be tailored to have higher or lower value in any mode compared to the other depending on the placement and intensity of the discontinuities in a programmable paradigm. We have derived an efficient analytical framework for the effective elastic moduli of lattice materials taking into account the influence of domain discontinuity. The axial and shear deformations at the beam level are considered along with bending deformation in the proposed analytical expressions. The numerical results ascertain that the domain discontinuities, in conjunction with unit cell level geometric parameters, can impact the effective elastic constants significantly under different modes of far-field stresses. It is further revealed that the degree of auxeticity of such lattices can be programmed to have target values (including non-invariance under different modes of deformation) as a function of the intensity and location of domain discontinuity when axial and shear deformations are included at the beam level. Realization of the unusual non-invariant elastic moduli of bi-level architected lattice materials would lead to a range of technologically demanding niche applications where one mode of deformation requires more or less force to deform compared to the opposite mode. Besides being able to perform as a load-bearing component, the proposed metamaterial can be used as an integrated sensor for measuring the level of stress or strain in structures. • In conventional naturally occurring materials, elastic moduli remain invariant under tensile and compressive normal modes or clock-wise and anti-clock-wise shear modes. • We introduce programmed domain discontinuities in the cell walls of lattice metamaterials involving a bi-level microstructural design. • Non-invariant elastic moduli under tensile and compressive normal modes or clock-wise and anti-clock-wise shear modes are realized. • The non-invariance can be realized in the linear small deformation regime and the elastic moduli can be tailored to have higher or lower value in any mode compared to the other. • Degree of auxeticity can be programmed to have target values (including non-invariance under different modes) as a function of the intensity and location of domain discontinuity. [ABSTRACT FROM AUTHOR]

This paper presents the quantification of uncertain natural frequency for laminated composite plates by using a novel surrogate model. A group method of data handling in conjunction to polynomial neural network (PNN) is employed as surrogate for numerical model and is trained by using Latin hypercube sampling. Subsequently the effect of noise on a PNN based uncertainty quantification algorithm is explored in this study. The convergence of the proposed algorithm for stochastic natural frequency analysis of composite plates is verified and validated with original finite element method (FEM). Both individual and combined variation of stochastic input parameters are considered to address the influence on the output of interest. The sample size and computational cost are reduced by employing the present approach compared to direct Monte Carlo simulation (MCS). [ABSTRACT FROM AUTHOR]

Bi-level tailoring of cellular metamaterials involving a dual design space of unit cell and elementary beam level architectures has recently gained traction for the ability to achieve extreme elastic constitutive properties along with modulating multi-functional mechanical behavior in an unprecedented way. This article proposes an efficient analytical approach for the accurate evaluation of all constitutive elastic constants of asymmetric multi-material variably-thickened hexagonal lattices by considering the combined effect of bending, stretching, and shearing deformations of cell walls along with their rigid rotation. A tri-member unit cell is conceptualized, wherein all nine constitutive constants are obtained through the mechanics under one cell wall direction and subsequent repetitive coordinate transformations. We enhance the design space of lattice metamaterials substantially here by introducing multiple exploitable dimensions such as asymmetric geometry, multi-material unit cells and variably-thickened cell walls, wherein the conventional monomaterial auxetic and non-auxetic hexagonal configurations can be analyzed as special cases along with other symmetric and asymmetric lattices such as a range of rectangular and rhombic geometries. The generic analytical approach along with extensive numerical results presented in this paper opens up new avenues for efficient optimized design of the next-generation multi-functional lattices and cellular metamaterials with highly tailored effective elastic properties. • Bi-level tailoring of cellular metamaterials involving a dual design space of unit cell and elementary beam-level architectures. • Accurate evaluation of all constitutive elastic constants of asymmetric multi-material variably-thickened hexagonal honeycomb lattices. • Expanded design space by introducing multiple exploitable dimensions such as: asymmetric geometry, composite multi-material unit cells, variably-thickened cell walls (derived through physics-based rationale) and their coupled effect. • New avenues for efficient optimized design of the next-generation multi-functional lattices and cellular metamaterials with highly tailored effective elastic properties. [ABSTRACT FROM AUTHOR]