1,721,057 research outputs found
On quantifying the effect of noise in radial basis function based stochastic free vibration analysis of laminated composite beam
No full textThis paper presents the effect of noise on Radial basis function (RBF) based stochastic natural frequency analysis of thin-walled laminated composite beams. The RBF based method is built up on the basis of information acquired regarding the behaviour of the response quantity throughout the entire design space utilizing few algorithmically chosen design points The crucial issue of expensive computation involved in uncertainty quantification of composite structures and the development of radial basis function based uncertainty quantification algorithm to mitigate this lacuna. On the other hand, noise is an inevitable factor in every real life design methods and structural response monitoring for any practical systems. In this paper, a novel algorithm is developed to explore the effect of noise in surrogate based uncertainty quantification methods. The probability distributions for higher modes of natural frequencies (first eight) corresponding to the bending modes has been calculated. The study reveals that stochasticity/ system irregularity in structural and material attributes influences the system performance remarkably. To ensure robustness, safety and sustainability of the structure, it is very crucial to consider such forms of uncertainties during the analysis. The proposed method for quantifying the effect of noise for the proposed computationally efficient RBF based framework in this paper is general in nature and therefore, it can be further extended to explore other surrogate based approach of uncertainty quantification under the influence of noise
Multi-scale stochastic dynamic analysis of a damaged pretwisted composite strip
No full textThis paper proposes a stochastic approach for estimating the natural frequencies of reducible composite strips. The framework accounts for multi-scale uncertainty at micro, meso, and component levels; additionally, it accounts for damages due to matrix cracking and delamination in a pretwisted composite strip. An asymptotically accurate Variational Asymptotic Method (VAM) based model for cross-sectional stiffness is coupled with a one-dimensional Finite Element Method (FEM) approach for the determination of natural frequencies of the pretwisted strips. The proposed model is validated by comparing the deterministic natural frequencies of composite strips with experimental and numerical results reported in the literature. The quantification of uncertainty is carried out by determining the probabilistic variations in the first three natural frequencies of the strips and analyzing the local and global sensitivity measures. The study identifies the uncertainties in material attributes, addressed at micro and macro levels, influencing the free vibration response of the strips
Stochastic flexural buckling response of thin-walled composite strips
No full textThin-walled composite structures are susceptible to undergo buckling leading to undesirable structural integrity problems. This paper proposes an efficient modeling approach for determining the axial critical buckling load-carrying capacities of thin-walled composite strips. Taking advantage of the inherent geometrical features of a strip, it is modeled as a one-dimensional structure. The reduced one-dimensional (1D) strip model is developed by using the Variational Asymptotic Method (VAM). In this mathematical framework, the original 3D problem is separated into a 2D cross-section and a 1D problem along the span of the strip. Although the methodology readily provides 2D nonlinear cross-sectional stiffness, in this work we have restricted the analysis to only a linear problem. While the cross-sectional stiffness is determined analytically, the 1D prob lem is solved numerically to determine the critical buckling load using the finite element method. The buckling load results obtained from this model are validated with analytical and experimental results reported in the literature. The proposed model in this paper takes into account the non-classical parameters of the composite strip due to its inherent structural coupling properties, anisotropy, and complex geometrical attributes. Detailed parametric studies have been carried out to investigate the influence of the boundary conditions, ply angle variations, and different aspect ratios of the composite strips. The methodology is then extended to take into consideration the stochastic effects due to uncertain material proper ties at the constituent levels. The influence of these uncertainties is presented in the form of stochastic distribution of buckling load by adopting a probabilistic modeling approach. The stochastic response of delaminated composite strips is also analyzed. The stochastic distribution shows a wider response bound of critical buckling load. The presented study on the buckling behavior of healthy and delaminated thin-walled rectangular cross-section composite strips facilitates an exploration of structural stability in the presence of intricate geometric characteristics and variable material properties inherent to these composite strips
Stimuli-responsive programmable mechanics of bi-level architected nonlinear mechanical metamaterials
No full textMechanical metamaterials which are often conceptualized as a periodic network of beams have been receiving significant attention over the last decade, wherein the major focus remains confined to the design of micro-structural configurations to achieve application-specific multi-functional characteristics in a passive framework. It is often not possible to actively modulate the metamaterial properties post-manufacturing, critically limiting the applications for a range of advanced intelligent structural systems. To achieve physical properties beyond conventional saturation limits attainable only through unit cell architectures, we propose to shift the design paradigm towards more innovative bi-level modulation concepts involving the coupled design space of unit cell geometries, architected beam-like members and their stimuli–responsive deformation physics. On the premise of revolutionary advancements in additive manufacturing technologies, we introduce hard magnetic soft (HMS) material architectures in the beam networks following physics-informed insights of the stress resultants. Through this framework, it is possible to achieve real-time on-demand control and modulation of fundamental mechanical properties like elastic moduli and Poisson’s ratios based on a contactless far-field stimuli source. A generic semi-analytical computational framework involving the large-deformation geometric non-linearity and material non-linearity under magneto-mechanical coupling is developed for the effective elastic properties of HMS material based bi-level architected lattices under normal or shear modes of mechanical far-field stresses, wherein we demonstrate that the constitutive behaviour can be programmed actively in an extreme-wide band based on applied magnetic field. Under certain combinations of the externally applied mechanical stress and magnetic field depending on the residual magnetic flux density, it is possible to achieve negative stiffness and negative Poisson’s ratio with different degrees of auxecity, even for the non-auxetic unit cell configurations. The results further reveal that a single metamaterial could behave like extremely stiff metals to very soft polymers through contactless on-demand modulation, leading to a wide range of applicability in statics, stability, dynamics and control of advanced mechanical, aerospace, robotics and biomedical systems at different length scales
Elementary-level intrusive coupling of machine learning for efficient mechanical analysis of variable stiffness composite laminates: a spatially-adaptive fidelity-sensitive computational framework
No full textOn exploiting the architecture of annual ring growth for developing a new class of bio-inspired composites
No full textInspired by several biological structures available in nature, bio-inspired composite structures are evidenced to exhibit a noteworthy enhancement in various mechanical and multi-physical performances as compared to conventional structures. This article proposes to exploit the architecture of annual ring growth of the stems of trees for developing a new class of bio-inspired composites with enhanced static and dynamic performances, including deflections, stresses, strain energy, and vibration. Concentric circular annual-ring geometries are considered where each layer of concentric circular fibers is analogous to the growth per annum of trees. The annual rings are modeled in a finite element-based computational framework by idealizing each layer as a composite of graphite fibers and epoxy matrix under different boundary conditions. The ratio of deflection to weight and frequency to weight of bio-inspired and traditional composites are compared by considering different parameters such as the number of annual rings, layers, and supporting stiffeners. The numerical results reveal that the proposed bio-inspired composites can enhance and modulate the static and dynamic properties to a significant extent, opening new design pathways for developing high-performance fiber network composites
Programmable constitutive mode-coupling in tubular origami metamaterials
No full textMetamaterials and metastructures developed based on tubular origami-inspired structural forms can leverage the convolution of crease architecture and the mechanics of deformation therein to provide unique multi-functional properties. In the existing literature, the intriguing aspect of deformation mode coupling between the axial and twisting modes in different classes of origami tubes has not been explored adequately. Based on computational and experimental investigations, here we present novel exploitable insights on tunable axial-twist coupling behaviour in tubular origami metamaterials, including the aspect of programming Poynting effects as a function of triangulated crease architecture. We focus on exploring whether there can be twisting or axial deformation under the application of either axial or twisting far-field actuation in a compulsory or discretionary way, and the functional relationship to modulate such constitutive coupling through triangulated crease architecturing. The corresponding energy landscapes are investigated, revealing their stability behaviour and the prospect of crease-dependent tailoring of multi-stability
Nonlinear functionally graded metamaterials for hydrogen storage and enhanced sustainability under extreme environments
No full textFunctionally graded materials can exhibit remarkable tolerance towards extreme hot or cold environments and chemical surface degradation. This article exploits such properties of functionally graded materials to propose a new class of transversely curved metamaterial architectures with high specific stiffness for operations under extreme surrounding conditions. We envisage the next-generation concept design of hydrogen storage tanks with functionally graded metamaterial core for aerospace and automotive applications. Based on such innovative lattice metamaterial based design of hydrogen storage tanks it is possible to enhance the storage capability in terms of internal pressure and resistance to external loads and impacts. Most importantly the proposed concept would lead to a breakthrough in developing load-bearing energy storage devices. For the metamaterial core, hexagonal bending-dominated unit cell architecture with transversely curved connecting beam-like geometries would ensure the dual functionality of high specific stiffness and energy absorption capability which are mutually exclusive in traditional lattice metamaterials. The functionally graded beams, a periodic network of which constitutes the lattice, are modeled here using 3D degenerated shell elements in a finite element framework. Geometric nonlinearity using Green–Lagrange strain tensor is considered for an accurate analysis. The beam-level nonlinear deformation physics is integrated with the unit cell mechanics following a semi-analytical framework to obtain the effective in-plane and out-of-plane elastic moduli of the metamaterials. The numerical results show that the curved beam lattice metamaterials have significantly enhanced in-plane elastic properties than straight lattices along with a reduced disparity among the in-plane and out-of-plane elastic moduli.<br/
Probing the prediction of effective properties for composite materials
No full textThis article presents different micromechanical modelling techniques based on analytical and numerical approaches to determine the effective elastic and piezoelectric (piezoelastic) properties of graphene-based composite materials. Different types, orientations and shapes as well as different geometrical parameters of fiber reinforcement are considered for estimating the effective properties. The effective properties of composite are predicted with and without considering the strong covalent bond which provides interaction and in-plane stability of 2D crystalline graphene or strong van der Wall forces formed between graphene layers and the matrix. It is revealed that the axial, transverse and shear effective piezoelastic properties of graphene reinforced piezoelectric composite (GRPC) are significantly enriched due to the incorporation of graphene into the epoxy matrix. The importance of incorporating graphene as nanofillers/interphase into the conventional epoxy matrix to form an advanced composite and its effective properties are illustrated while these results show excellent agreement with previously reported experimental estimates. These results reveal that due to incorporation of graphene nanofillers, there is a significant enhancement in effective properties of composite. The results would also help to recognize the most important material properties with respect to different shapes and orientation of reinforcements which influences the performance of system significantly. To confirm safety, robustness and sustainability of the structure, it is the most prior requirement to determine the effective properties of composites considering different parameters for the different static and structural analyses.</p
A hybrid stochastic sensitivity analysis for low-frequency vibration and low-velocity impact of functionally graded plates
No full textThis paper deals with the stochastic sensitivity analysis of functionally graded material (FGM) plates subjected to free vibration and low-velocity impact to identify the most influential parameters in the respective analyses. A hybrid moment-independent sensitivity analysis is proposed coupled with the least angle regression based adaptive sparse polynomial chaos expansion. Here the surrogate model is integrated in the sensitivity analysis framework to achieve computational efficiency. The current paper is concentrated on the relative sensitivity of material properties in the free vibration (first three natural frequencies) and low-velocity impact responses of FGM plates. Typical functionally graded materials are made of two different components, where a continuous and inhomogeneous mixture of these materials is distributed across the thickness of the plate based on certain distribution laws. Thus, besides the overall sensitivity analysis of the material properties, a unique spatial sensitivity analysis is also presented here along the thickness of the plate to provide a comprehensive view. The results presented in this paper would help to identify the most important material properties along with their depth-wise spatial sensitivity for low-frequency vibration and low-velocity impact analysis of FGM plates. This is the first attempt to carry out an efficient adaptive sparse PCE based moment-independent sensitivity analysis (depth-wise and collectively) of FGM plates under the simultaneous susceptibility of vibration and impact. Such simultaneous multi-objective sensitivity analysis can identify the important system parameters and their relative degree of importance in advanced multi-functional structural systems
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