Imperial College London

DrArashSoleiman Fallah

Faculty of EngineeringDepartment of Aeronautics

Visiting Researcher
 
 
 
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Contact

 

+44 (0)20 7594 5140arash.soleiman-fallah Website

 
 
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Location

 

E358aACE ExtensionSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

53 results found

Navadeh N, Sareh P, Basovsky VG, Gorban IM, Fallah ASet al., 2021, Nonlinear vibrations in homogeneous non-prismatic timoshenko cantilevers, Journal of Computational and Nonlinear Dynamics, Vol: 16, Pages: 1-9, ISSN: 1555-1415

Deep cantilever beams, modelled using Timoshenko beam kinematics, have numerous applications in engineering. This study deals with the nonlinear dynamic response in a non-prismatic Timoshenko beam characterized by considering the deformed configuration of the axis. The mathematical model is derived using the extended Hamilton's principle under the condition of finite deflections and angles of rotation. The discrete model of the beam motion is constructed based on the finite difference method (FDM), whose validity is examined by comparing the results for a special case with the corresponding data obtained by commercial finite element (FE) software ABAQUS 2019. The natural frequencies and vibration modes of the beam are computed. These results demonstrate decreasing eigenfrequency in the beam with increasing amplitudes of nonlinear oscillations. The numerical analyses of forced vibrations of the beam show that its points oscillate in different manners depending on their relative position along the beam. Points close to the free end of the beam are subject to almost harmonic oscillations, and the free end vibrates with a frequency equal to that of the external force. When a point approaches the clamped end of the beam, it oscillates in two-frequency mode and lags in phase from the oscillations of the free end. The analytical model allows for the study of the influence of each parameter on the eigenfrequency and the dynamic response. In all cases, a strong correlation exists between the results obtained by the analytical model and ABAQUS, nonetheless, the analytical model is computationally less expensive.

Journal article

Soleiman Fallah A, Mehreganian N, 2021, Blast loading effects on aircraft fuselage, Multiphysics Simulations in Automotive and Aerospace Applications, Publisher: Elsevier, ISBN: 9780128178997

Given the book's comprehensive coverage, automotive and aerospace engineers, designers, graduate students and researchers involved in the simulation of practical coupling problems will find the book useful in its approach.

Book chapter

Mehreganian N, Fallah AS, Sareh P, 2021, Structural mechanics of negative stiffness honeycomb metamaterials, Journal of Applied Mechanics, Vol: 88, Pages: 051006-1-051006-10, ISSN: 0021-8936

The development of multi-stable structural forms has attracted considerable attention in the design of architected multi-materials, metamaterials, and morphing structures, as a result of some unusual properties such as negative stiffness and, possibly, negative Poisson's ratio. Multi-stability is achieved through a morphological change of shape upon loading, and in doing so multi-stable structures undergo transitions from one equilibrium state to another. This paper investigates the structural performance of the negative stiffness honeycomb (NSH) metamaterials made of double curved beams which are emerging in various applications such as sensors, actuators, and lightweight impact protective structures with structural tunability and recoverability. An analytical treatment is pursued using the Euler–Lagrange theorem and the stability of the honeycomb has been studied. Based on a static analysis of the nonlinear elastic system, the developed tangent stiffness matrix and ensuing deformation curve were assessed through multiple phases of deformation. The closed-form solution was in good agreement with the numerical finite element (FE) model at different bistability ratios. It was shown that the bistability ratio had a pronounced effect on the overall response of the honeycomb and the desired negativity in the stiffness matrix could be achieved with high bistability ratios.

Journal article

Gorshkov V, Sareh P, Navadeh N, Tereshchuk V, Fallah ASet al., 2021, Multi-resonator metamaterials as multi-band metastructures, Materials & Design, Vol: 202, Pages: 1-13, ISSN: 0264-1275

Journal article

Fallah AS, Giannakeas IN, Mella R, Wenman MR, Safa Y, Bahai Het al., 2020, On the computational derivation of bond-based peridynamic stress tensor, Journal of Peridynamics and Nonlocal Modeling, Vol: 2, Pages: 352-378, ISSN: 2522-896X

The concept of ‘contact stress’, as introduced by Cauchy, is a special case of a nonlocal stress tensor. In this work, the nonlocal stress tensor is derived through implementation of the bond-based formulation of peridynamics that uses an idealised model of interaction between points as bonds. The method is sufficiently general and can be implemented to study stress states in problems containing stress concentration, singularity, or discontinuities. Two case studies are presented, to study stress concentration around a circular hole in a square plate and conventionally singular stress fields in the vicinity of a sharp crack tip. The peridynamic stress tensor is compared with finite element approximations and available analytical solutions. It is shown that peridynamics is capable of capturing both shear and direct stresses and the results obtained correlate well with those obtained using analytical solutions and finite element approximations. A built-in MATLAB code is developed and used to construct a 2D peridynamic grid and subsequently approximate the solution of the peridynamic equation of motion. The stress tensor is then obtained using the tensorial product of bond force projections for bonds that geometrically pass through the point. To evaluate the accuracy of the predicted stresses near a crack tip, the J-integral value is computed using both a direct contour approximation and the equivalent domain integral method. In the formulation of the contour approximation, bond forces are used directly while the proposed peridynamic stress tensor is used for the domain method. The J-integral values computed are compared with those obtained by the commercial finite element package Abaqus 2018. The comparison provides an indication on the accurate prediction of the state of stress near the crack tip.

Journal article

Giannakeas IN, Papathanasiou TK, Fallah AS, Bahai Het al., 2020, Coupling XFEM and Peridynamics for brittle fracture simulation: part II-adaptive relocation strategy, COMPUTATIONAL MECHANICS, Vol: 66, Pages: 683-705, ISSN: 0178-7675

Journal article

Giannakeas IN, Papathanasiou TK, Fallah AS, Bahai Het al., 2020, Coupling XFEM and peridynamics for brittle fracture simulation—part I: feasibility and effectiveness, Computational Mechanics, Vol: 66, Pages: 103-122, ISSN: 0178-7675

A peridynamics (PD)–extended finite element method (XFEM) coupling strategy for brittle fracture simulation is presented. The proposed methodology combines a small PD patch, restricted near the crack tip area, with the XFEM that captures the crack body geometry outside the domain of the localised PD grid. The feasibility and effectiveness of the proposed method on a Mode I crack opening problem is examined. The study focuses on comparisons of the J integral values between the new coupling strategy, full PD grids and the commercial software Abaqus. It is demonstrated that the proposed approach outperforms full PD grids in terms of computational resources required to obtain a certain degree of accuracy. This finding promises significant computational savings when crack propagation problems are considered, as the efficiency of FEM and XFEM is combined with the inherent ability of PD to simulate fracture.

Journal article

Soleiman Fallah A, Ghajari M, Safa Y, 2019, Computational modelling of dynamic delamination in morphing composite blades and wings, The International Journal of Multiphysics, Vol: 13, Pages: 393-430, ISSN: 1750-9548

Morphing blades have been promising in lifting restrictions on rated capacity of wind turbines and improving lift-to-drag ratio for aircraft wings at higher operational angles of attack. The present study focuses on one aspect of the response of morphing blades viz. dynamic delamination. A numerical study of delamination in morphing composite blades is conducted. Both components i.e. the composite part and the stiffener are studied. The eXtended Finite Element Method (XFEM) and nonlocal continuum mechanics (peridynamics) have both been used to study fracture in the isotropic stiffener used in conjunction with the blade. As for the composite morphing blade, cohesive elements are used to represent the interlaminar weak zone and delamination has been studied under dynamic pulse loads. Intraply damage is studied using the nonlocal model as the peridynamic model is capable of addressing the problem adequately for the necessary level of sophistication.The differences and similarities between delamination patterns for impulsive, dynamic, and quasi-static loadings are appreciated and in each case detailed analyses of delamination patterns are presented. The dependence of delamination pattern on loading regime is established, however; further parametric studies are not included as they lie beyond the scope of the study. Through the use of fracture energy alone the nonlocal model is capable of capturing intra- and interlaminar fractures. The proposed modelling scheme can thus have a major impact in design applications where dynamic pulse and impact loads of all natures (accidental, extreme, service, etc.) are to be considered and may therefore be utilised in design of lightweight morphing blades and wings where delamination failure mode is an issue.

Journal article

Mehreganian N, Fallah AS, Louca LA, 2019, Nonlinear dynamics of locally pulse loaded square Föppl-von Kármán thin plates, International Journal of Mechanical Sciences, Vol: 163, ISSN: 0020-7403

Modern armour graded thin steel plates benefit from significant elastic strength with high elastic energy storage capacity, which contributes to dissipation of total impulse from extensive blast loads within the bounds of the elastic region. Higher elastic energy storage capability mitigates the probability of catastrophic damage and ensuing large deformations compared to the conventional graded metallic panels. While blast assessment of such structures is important to design and application of protective systems, limited studies are available on their response to localised blasts.The present paper aims at deducing, from the minimization of Föppl-von Kármán (FVK) energy functional, the dynamic response of localised blast loaded thin elastic square plates undergoing large deformations. The presumed blast load function is a multiplicative decomposition of a prescribed continuous piecewise smooth spatial function and an arbitrary temporal function which may assume various shapes (e.g. rectangular, linear, sinusoidal, exponential).A kinematically admissible displacement field and the associated stress tensor were considered as a truncated cosine series with multiple Degrees-of-Freedom (DoF's). From the prescribed displacement field, having simply supported boundary conditions, useful expressions for stress tensor components were delineated corresponding to a unique mode and a series of differential equations were derived. The explicit solutions were sought using the Poincaré-Lindstedt perturbation method. The closed form solutions of each mode were corroborated with the numerical FE models and showed convergence when the first few modes were considered. The influence of higher modes, however, on the peak deformation was negligible and the solution with 3 DOF's conveniently estimated the blast response to a satisfactory precision.

Journal article

Soleiman Fallah A, Zhuk Y, Gorshko I, Navadeh Net al., 2019, Approximate Mode-based Simulation of Composite Wind Turbine Blade Vibrations using a Simplified Beam Model, European Journal of Computational Mechanics, ISSN: 1779-7179

Journal article

Gorshkov VN, Sareh P, Tereshchuk VV, SoleimanFallah Aet al., 2019, Dynamics of Anisotropic Break‐Up in Nanowires of FCC Lattice Structure, Advanced Theory and Simulations, Vol: 2, Pages: 1900118-1900118, ISSN: 2513-0390

Journal article

Soleiman Fallah A, Louca L, Mehreganian N, Thil N, Moatamedi Met al., 2019, Dynamic plastic response of beams subjected to localised pulse loads, International Journal of Protective Structures, Vol: 10, Pages: 198-228, ISSN: 2041-4196

Localised blast loads give rise to high gradients of overpressure detrimental to structural elements as beams and plates. This article presents an analytical study on the dynamic plastic response of beams made of a ductile metallic material due to close-in pulse pressure loading. The close-in pressure load is characterised by a spatially varying function constant over a central region and exponentially decaying beyond it. The temporal pulse shape is assumed to take different forms. The exact static plastic collapse load was obtained for the characteristic load using the framework of plastic limit analysis, whereby the analysis was then extended to the dynamic case by considering the appropriate yield surface and inclusion of inertia forces. The yield surfaces considered were representative of pure bending, the interactions between the bending moment and transverse shear, and bending moment and membrane force, each corresponding to a special case depending on the geometry of the beam. A time-dependent, kinematically admissible velocity profile was assumed to treat the dynamic formulations in interaction of each phenomenon. A study on the strain-rate sensitivity was also presented, and existence of a critical pressure triggering the apparition of travelling plastic hinges was hence highlighted. For blast loads of high magnitude, the expressions for normalised deflection were furnished in terms of the impulsive velocity. The analytical models were validated by performing a parametric study on the two-dimensional representative of the beam model in commercial finite element software ABAQUS 6.14. The numerical results show a good correlation with the analytical results in each case.

Journal article

Mehreganian N, Fallah AS, Louca LA, 2019, Plastic dynamic response of simply supported thick square plates subject to localised blast loading, International Journal of Impact Engineering, Vol: 126, Pages: 85-100, ISSN: 0734-743X

Localised blast loads due to proximal charges are encountered in a variety of circumstances. This paper proposes an analytical solution for the dynamic plastic response of a rigid-perfectly plastic thick square plate subject to a localised explosion. The proposed model is an extension of the analytical model proposed by Micallef et al [1] to study circular plates which is adopted and modified in order to study impulsively loaded square plates where the effect of shear deformation is included. A piecewise continuous blast load function was assumed with axisymmetric spatial distribution of constant pressure in the central zone and exponentially decaying beyond it. Using the constitutive framework of limit analysis and incorporating the interactions between bending moment and transverse shear forces in the analyses, transverse displacement and response duration were examined on three classes of plates, classified according to the length to thickness ratio parameter ν. The results were furnished in terms of the impulsive velocity, which is a function of the localised blast load parameters. A theoretical solution for plates with ν > 2 was sought for the non-impulsive blast loads. Parametric studies were performed to elucidate the effect of loading parameters and plate thickness on the permanent deformation. The theoretical solutions have been found generic and can predict, by the correct choice of the load parameters, the dynamic response of most blast load scenarios brought about by proximal or distal charges. It was found that, for proximal impulsive blasts, the effect of transverse shear becomes irrelevant for even moderate values of ν which effect is inconsequential on both central and endpoint displacements at discontinuous interface in the range of ν > 5. Since the short duration pulse is of concern, localised pressure loads affect only a small area of the plated structures. Thus, whilst the theoretical treatments also examine the fully clamped pl

Journal article

Fallah AS, Navadeh N, Tereshchuk VV, Gorshkov VNet al., 2019, Phononic dispersion in anisotropic pseudo-fractal hyper-lattices, Materials & Design, Vol: 164, Pages: 107560-107560, ISSN: 0264-1275

Fractal and pseudo-fractal microstructures have proved promising in increasing the range of detectable frequencies for devices used in the realm of electromagnetism. Due to mechanical-electrical duality it is conjectured they may provide flexible solutions capable of closing/widening bandgaps and increasing tailorability in phononic lattices. Pseudo-fractal hyper-lattices have been considered in this work and different aspects of dispersion surface morphology and frequency band structure are studied. It has been observed that higher frequencies that can be excited in the simple square lattice are almost the same as those in the pseudo-fractal structures, however; through introduction of higher levels the pseudo-fractal hyper-lattice presents new features not observable in the ordinary lattice. By increasing the order of pseudo-fractal structure the number of degrees-of-freedom increases and dispersion surfaces morphologies change thus frequency gaps are eliminated. This phenomenon can be of advantage for acoustic/phononic visibility/detectability e.g. in designing sensors. In the classical analogy to quantum level repulsion surfaces flatten which sufficiently decreases the sound group velocity in the pseudo-fractal structure, and can be used for numerous practical applications.

Journal article

Chen Y, Sareh P, Yan J, Fallah AS, Feng Jet al., 2019, An integrated geometric-graph-theoretic approach to representing origami structures and their corresponding truss frameworks, Journal of Mechanical Design, ISSN: 1050-0472

Origami has provided various interesting applications in science and engineering. Appropriate representations and evaluation on crease patterns play an important role in developing an innovative origami structure with desired characteristics. However, this is generally a challenge encountered by scientists and engineers who introduce origami into various fields. As most practical origami structures contain repeated unit cells, graph products provide a suitable choice for the formation of crease patterns. Here, we will employ undirected and directed graph products as a tool for the representation of crease patterns and their corresponding truss frameworks of origami structures. Given that an origami crease pattern can be considered to be a set of directionless crease lines which satisfy the foldability condition, we demonstrate that the pattern can be exactly expressed by a specific graph product of independent graphs. It turns out that this integrated geometric-graph-theoretic method can be effectively implemented in the formation of different crease patterns, and provide suitable numbering of nodes and elements. Furthermore, the presented method is useful in constructing the involved matrices and models of origami structures, and thus enhances configuration processing for geometric, kinematic or mechanical analysis on origami structures.

Journal article

Mehreganian N, Fallah AS, Louca LA, 2019, Dynamic Performance of Simply Supported Rigid-Plastic Square Plates Subject to Localized Blast Loading, Journal of Engineering Mechanics, Vol: 145, ISSN: 0733-9399

This paper presents the theoretical solution to the response of a square plate undergoing plastic deformation due to a generic localized blast pulse. A localized blast load function was assumed multiplicative of its spatial distribution and temporal pulse shape. The spatial distribution was representative of constant pressure over the central zone, while exponentially decaying outside that zone. Considering an appropriate moment function and ignoring the membrane, transverse shear, and rotary inertia effects, the static plastic collapse was found, whereby the analysis was extended to the dynamic case by assuming a kinematically admissible, time-dependent velocity profile. The analytical model, which was validated against the numerical results obtained through ABAQUS hydrocode, showed close correlation in terms of the permanent transverse deflection profile. In order to consider the effect of temporal pulse shape, the results were formulated for rectangular as well as exponentially and linearly decaying pulses. For blast loads of high magnitude, the pressure load was replaced by an impulsive velocity. The calculations were simplified by utilizing the dimensionless form, and the results were corroborated with theoretical and experimental results from the literature. The model showed improvements in predicting the final deformation of square plates over previous models of simplified loading function.

Journal article

Rubiella C, Hessabi CA, Soleiman Fallah A, 2018, State of the art in fatigue modelling of composite wind turbine blades, International Journal of Fatigue, Vol: 117, Pages: 230-245, ISSN: 0142-1123

This paper provides a literature review of the most notable models relevant to the evaluation of the fatigue response of composite wind turbine blades. As wind turbines spread worldwide, ongoing research to maximize their lifetime – and particularly that of wind turbine blades – has increasingly popularized the use of composite materials, which boast attractive mechanical properties. The review first presents the wind turbine blade environment, before distributing fatigue models broadly between three categories: life-based failure criterion models, which are based on S-N curve formulations and constant-life diagrams to introduce failure criteria; residual property calculation models, which evaluate the gradual degradation of material properties; and progressive damage models, which model fatigue via the cycle-by-cycle growth of one or more damage parameters. These are then linked to current testing standards, databases, and experimental campaigns. Among the fatigue modelling approaches covered, progressive damage models appear to be the most promising tool, as they both quantify and qualify physical damage growth to a reasonable extent during fatigue. The lack of consensus and shortcomings of literature are also discussed, with abundant referencing.

Journal article

Mehreganian N, Soleiman Fallah A, Louca L, 2018, Inelastic dynamic response of square membranes subjected to localised blast loading, International Journal of Mechanical Sciences, Vol: 148, Pages: 578-595, ISSN: 0020-7403

Extensive shock and highly localised blast waves generated by detonation of near field explosives (such as improvised explosive devices (IEDs)) are catastrophic to structures and humans, resulting in injury or death, progressive damage, or perforation through the structure and collapse. Mitigating the effects of such waves is paramount in various aspects of design engineering. A theoretical model is presented here to predict the large inelastic deformation of ductile thin square membranes induced by a generic, short pulse pressure load, comprising a piecewise function of spatial and temporal parts. Using the constitutive framework of limit analysis and incorporating the influence of finite displacements, two patterns of kinematically admissible, time dependent velocity profiles were investigated. These patterns included stationery and moving plastic hinges. The results were investigated in two cases: once with the interaction between bending moment and membrane forces retained in the analyses, and then when the response was solely governed by membrane forces.For blast loads of high magnitude, the pressure was replaced by an impulsive velocity and the results were expressed in terms of dimensionless form of initial kinetic energy. The effects of boundary conditions and visco-plasticity have also been investigated. The theoretical results corroborated well with various experimental results in the literature, on ductile metallic plates such as high strength ARMOX steel and mild steel.

Journal article

Toolabi M, Fallah AS, Louca L, 2018, Enhanced mixed interpolation XFEM formulations for discontinuousTimoshenko beam and Mindlin-Reissner plate, International Journal for Numerical Methods in Engineering, Vol: 115, Pages: 714-737, ISSN: 0029-5981

Shear locking is a major issue emerging in the computational formulation of beam and plate finite elements of minimal number of degrees of freedom as it leads to artificial overstiffening. In this paper, discontinuous Timoshenko beam and Mindlin‐Reissner plate elements are developed by adopting the Hellinger‐Reissner functional with the displacements and through‐thickness shear strains as degrees of freedom. Heterogeneous beams and plates with weak discontinuity are considered, and the mixed formulation has been combined with the extended finite element method (FEM); thus, mixed enrichment functions are used. Both the displacement and the shear strain fields are enriched as opposed to the traditional extended FEM where only the displacement functions are enriched. The enrichment type is restricted to extrinsic mesh‐based topological local enrichment. The results from the proposed formulation correlate well with analytical solution in the case of the beam and in the case of the Mindlin‐Reissner plate with those of a finite element package (ABAQUS) and classical FEM and show higher rates of convergence. In all cases, the proposed method captures strain discontinuity accurately. Thus, the proposed method provides an accurate and a computationally more efficient way for the formulation of beam and plate finite elements of minimal number of degrees of freedom.

Journal article

Navadeh N, Hewson RW, Fallah AS, 2018, Dynamics of transversally vibrating non-prismatic Timoshenko cantilever beams, Engineering Structures, ISSN: 0141-0296

Journal article

Soleiman Fallah A, Mehreganian N, Boiger GK, Louca LAet al., 2017, Response of Armour Steel Plates to localised Air Blast Load – A Dimensional Analysis, International Journal of Multiphysics, Vol: 11, Pages: 387-412, ISSN: 1750-9548

We report on the results of dimensional analyses on the dynamic plasticresponse of square armour steel plates due to detonation of proximalcylindrical charges and ensued air blast loading. By assuming a genericfunction for the blast load, which is multiplicative comprising its spatial andtemporal parts, a set of 14 dimensionless parameters, representative of theload and plate deformation, were identified and recast in the form ofdimensionless functions of stand-off to charge diameter ratio. Parametricstudies were performed using commercial code ABAQUS’s module of FiniteElement hydrocode using MMALE and MMAE techniques, and combinedwith regression analyses to quantify the dimensional parameters and theexpressions for dimensionless functions. A few numerical studies withvarious FE mesh types were also performed to validate the transientdeflections against the small-scale experiments. For pulse loading due toproximal charges of small orders of stand-off/charge diameter ratio, themagnitude of the transverse deflection increased abruptly with incrementaldecrease in stand-off, in contradistinction to the plate deformations athigher stand-offs where variations in displacement are smooth. Thisconfirmed the existence of a stand-off at which a transition in behaviourtakes place. For stand-off values less than charge diameter, a dimensionlessenergy absorbing effectiveness factor was considered to investigate theprediction of rupture in the plate corresponding to different charge masses.This factor is measured as a baseline parameter to predict, using solelynumerical means, the blast loads which ensue rupture on full-scaleprototypes.

Journal article

Navadeh N, Gorshko IO, Zhuk YA, Soleiman Fallah Aet al., 2017, An FEM-based AI approach to model parameter identification for low vibration modes of wind turbine composite rotor blades, European Journal of Computational Mechanics, Vol: 26, Pages: 541-556, ISSN: 1779-7179

An approach to construction of a beam-type simplified model of a horizontal axis wind turbine composite blade based on the finite element method is proposed. The model allows effective and accurate description of low vibration bending modes taking into account the effects of coupling between flapwise and lead–lag modes of vibration transpiring due to the non-uniform distribution of twist angle in the blade geometry along its length. The identification of model parameters is carried out on the basis of modal data obtained by more detailed finite element simulations and subsequent adoption of the ‘DIRECT’ optimisation algorithm. Stable identification results were obtained using absolute deviations in frequencies and in modal displacements in the objective function and additional a priori information (boundedness and monotony) on the solution properties.

Journal article

Soleiman Fallah A, Gorshkov VN, Navadeh N, 2017, A study of frequency band structure in two-dimensional homogeneous anisotropic phononic K3-metamaterials, Smart Materials and Structures, Vol: 26, ISSN: 0964-1726

Phononic metamaterials are synthesised materials in which locally resonant units are arranged in a particular geometry of a substratum lattice and connected in a predefined topology. This study investigates dispersion surfaces in two-dimensional anisotropic acoustic metamaterials involving mass-in-mass units connected by massless springs in K3 topology. The reasons behind the particular choice of this topology are explained. Two sets of solutions for the eigenvalue problem $| {\boldsymbol{D}}({\omega }^{2},{\boldsymbol{k}})| =0$ are obtained and the existence of absolutely different mechanisms of gap formation between acoustic and optical surface frequencies is shown as a bright display of quantum effects like strong coupling, energy splitting, and level crossings in classical mechanical systems. It has been concluded that a single dimensionless parameter i.e. relative mass controls the order of formation of gaps between different frequency surfaces. If the internal mass of the locally resonant mass-in-mass unit, $m,$ increases relative to its external mass, $M,$ then the coupling between the internal and external vibrations in the whole system rises sharply, and a threshold ${\mu }^{* }$ is reached so that for $m/M\gt {\mu }^{* }$ the optical vibrations break the continuous spectrum of 'acoustic phonons' creating the gap between them for any value of other system parameters. The methods to control gap parameters and polarisation properties of the optical vibrations created over these gaps were investigated. Dependencies of morphology and width of gaps for several anisotropic cases have been expounded and the physical meaning of singularity at the point of tangential contact between two adjacent frequency surfaces has been provided. Repulsion between different frequency band curves, as planar projections of surfaces, has been explained. The limiting case of isotropy has been discussed and it has been shown that, in the isotropic case, the lower gap always forms, irr

Journal article

Soleiman Fallah A, Gorshkov VN, Navadeh N, Tereshchuk VV, Sareh Pet al., 2017, Sonic metamaterials: Reflection on the role of topology on dispersion surface morphology, Materials and Design, Vol: 132, Pages: 44-56, ISSN: 1873-4197

Investigating dispersion surface morphology of sonic metamaterials is crucial in providing information on related phenomena as inertial coupling, acoustic transparency, polarisation, and absorption. In the present study, we look into frequency surface morphology of two-dimensional (2D) metamaterials of K3,3 and K6 topologies. The elastic structures under consideration consist of the same substratum lattice points and form a pair of sublattices with hexagonal symmetry. We show that, through introducing universal localised mass-in-mass phononic microstructures at lattice points, six single optical frequency-surfaces can be formed with required properties including negative group velocity. Splitting the frequency-surfaces is based on the classical analog of the quantum phenomenon of ‘energy-level repulsion’, which can be achieved only through internal anisotropy of the nodes and allows us to obtain different frequency band gaps.

Journal article

Nwankwo E, Soleiman Fallah A, Moatamedi M, Louca LAet al., 2016, Numerical simulation of the dynamic response in pulse-loaded fibre-metal-laminated plates, International Journal of Protective Structures, Vol: 7, Pages: 469-494, ISSN: 2041-4196

This article presents a three-dimensional constitutive model to replicate the dynamic response of blastloadedfibre–metal laminates made of 2024-0 aluminium alloy and woven composite (glass fibre–reinforcedpolypropylene). Simulation of the dynamic response is challenging when extreme localised loads are ofconcern and requires reliable material constitutive models as well as accurate modelling techniques. It is wellknown that back layers in a fibre–metal laminate provide structural support for front layers; thus, propermodelling of constituent failure and degradation is essential to understanding structural damage and failure.The improved developed model to analyse damage initiation, progression and failure of the composite isimplemented in finite element code ABAQUS, and a good correlation is observed with experimental resultsfor displacements of the back and front faces as presented by other researchers. The model was also able topredict accurately the tearing impulses. Finally, the concepts of the ‘efficiency of the charge’ and ‘effectivenessof the target’ are proposed in the context of localised blast loading on a structure. Dimensionless parametersare introduced to quantify these parameters.

Journal article

Micallef K, Fallah AS, Curtis PT, Louca LAet al., 2015, On the dynamic plastic response of steel membranes subjected to localised blast loading, International Journal of Impact Engineering, Vol: 89, Pages: 25-37, ISSN: 1879-3509

Permanent plastic deformation is expected when close-in blasts due to e.g. detonation of Improvised Explosive Devices (IED's) hit thin metallic targets. A circular thin steel plate i.e. a membrane is studied in the present work subject to a general form of a localised blast loading. The spatial shape of the pulse is fixed and different temporal shapes are investigated. Dynamic analyses are conducted and the permanent transverse displacements are found for each case.For high amplitude pulse loads of short duration, it was found that the permanent transverse displacement can be found by replacing the load by an impulse without the loss of accuracy. Excellent correlation with numerical simulations obtained from ABAQUS/Explicit is achieved. The predicted final displacements for different pulse shapes are also found to be similar, thus where membrane action is dominant, the response is insensitive to pulse shape.

Journal article

Pullen AD, Louca LA, Micallef K, Fallah AS, Curtis PTet al., 2015, Characterization of the Mechanical Behavior of a Polymer-Based Laminate and Constituent Fibers at Various Quasi-Static Strain Rates, JOURNAL OF AEROSPACE ENGINEERING, Vol: 28, ISSN: 0893-1321

Journal article

Soleiman Fallah A, Yang Y, Ward R, Brambleby R, Tootkaboni M, Louhghalam A, Louca Let al., 2015, Wave propagation in two-dimensional anisotropic acoustic metamaterials of K4 topology, Wave Motion, Vol: 58, Pages: 101-116, ISSN: 0165-2125

An acoustic metamaterial is envisaged as a synthesised phononic material the mechanical behaviour of which is determined by its unit cell. The present study investigates one aspect of mechanical behaviour, namely the band structure, in two-dimensional (2D) anisotropic acoustic metamaterials encompassing locally resonant mass-in-mass units connected by massless springs in a K4 topology. The 2D lattice problem is formulated in the direct space (r-space) and the equations of motion are derived using the principle of least action (Hamilton’s principle). Only proportional anisotropy and attenuation-free shock wave propagation have been considered. Floquet-Bloch’s principle is applied, therefore a generic unit cell is studied. The unit cell can represent the entire lattice regardless of its position. It is transformed from the direct lattice in r-space onto its reciprocal lattice conjugate in Fourier space (k-space) and point symmetry operations are applied to Wigner-Seitz primitive cell to derive the first irreducible Brillouin Zone (BZ). The edges of the first irreducible Brillouin Zone in the k-space have then been traversed to generate the full band structure. It was found that the phenomenon of frequency filtering exists and the pass and stop bands are extracted. A follow-up parametric study appreciated the degree and direction of influence of each parameter on the band structure.

Journal article

Soleiman Fallah A, Micallef K, Pope DJ, Louca LA, Moatamedi Met al., 2015, On dimensionless loading parameters for close-in blasts, International Journal of Multiphysics, ISSN: 1750-9548

Journal article

Fallah AS, Micallef K, Langdon GS, Lee WC, Curtis PT, Louca LAet al., 2014, Dynamic response of Dyneema® HB26 plates to localised blast loading, International Journal of Impact Engineering, Vol: 73, Pages: 91-100, ISSN: 0734-743X

This paper reports on the dynamic response of a potential blast-resistant lightweight alternative to steel for military applications, namely ultra-high molecular weight polyethylene (UHMwPE) fibre composites known as Dyneema®. The results of localised air-blast loading tests on Dyneema HB26 panels are reported and analysed. Various failure modes were observed, including permanent deformation, delamination, in-plane shear, buckling around the boundary, localised melting and matrix damage. Total penetration (rupture) at the highest charge masses was also exhibited by the Dyneema panels. The experimental results are compared to the numerically simulated responses of mild steel and armour steel plates of equal areal density and reasonable correlation was observed in most cases. Dimensional analysis was used to compare the responses and showed that there is a possibility of unifying all the results i.e. the responses for all materials once a newly proposed slenderness ratio was incorporated into the formulation. Simple dimensionless expressions are proposed to predict permanent midpoint transverse displacements, irrespective of the particular material type. It was also observed that armour steel and Dyneema HB26 offer potential displacement reductions of almost 50% and 30%, respectively for the range of impulses tested.

Journal article

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