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Author: search.filters.author.Islam, Md Rushdie IbneSubject: search.filters.subject.Civil engineering

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    A computational framework for modelling impact induced damage in ceramic and ceramic-metal composite structures
    (Elsevier, 2017-03) Islam, Md Rushdie Ibne
    When ceramic or ceramic-metal composite structures are subjected to impact loading, they undergo various deformation phases such as plastic yielding, pulverization, fragmentation, tensile spalling, interface debonding, penetration etc. In order to study these phenomenological characteristics and produce insightful observation, numerical simulation is inevitable. Apart from reasonably accurate constitutive model, a numerical scheme must also accommodate any possible loss (in the case of fragmentation and material separation) of the continuum nature of the problem domain. This is generally difficult to achieve through mesh-based methods. In this study a computational framework based on smoothed particle hydrodynamics (SPH), a particle-based method, is explored and revamped. Damage growth and localized cracks are modelled through a pseudo-spring analogy, wherein particle-interactions are modulated based on material strength reduction after damage initiation. Different material models are coupled in this analogy for investigating different paradigms of penetration mechanics in ceramic and ceramic-metal composites. The computational framework is first validated through experimentally obtained results of flyer plate tests on Silicon Carbide (SiC) disc. Subsequently the framework is explored in simulating more complex failure mechanisms involving multiaxial crack interaction and fragmentation in ceramic-metal composite target system.
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    A computational model for failure of ductile material under impact
    (Elsevier, 2017-10) Islam, Md Rushdie Ibne
    In addition to an accurate mathematical representation of the material, a computational modelling method for assessing impact problems involving large plastic deformation, damage localization, fracture etc. requires a suitable discretization scheme which can simulate the relevant physical processes without introducing any numerical artifact or being unstable. In this paper, a computational framework based on Smoothed Particle Hydrodynamics (SPH) is presented for studying the deformation and failure of ductile material, steel plate, under impact loading. This provides a useful design tool to simulate penetration of the plate. Crack propagation is modelled through a pseudo spring analogy wherein the interacting particles are assumed to be connected through pseudo-springs and the interaction is continuously modified through an order-parameter based on the accumulated damage in the spring. At the onset of crack formation i.e., when the accumulated damage reaches the critical value, the spring breaks which results in termination of interaction between particles on either sides of the spring. A key feature of the computational model is that it can capture arbitrary propagating cracks without introducing any special treatment such as discontinuous enrichment, particle-splitting etc. This computational framework is used herein to study adiabatic shear plugging in metal plates when modelling penetration under impact loading by a flat-ended, cylindrical projectile. The effects of different damage criteria are discussed. Computed results are compared with the experimental observation given in the literature and the efficacy of the framework is demonstrated.
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    Extending incompressible SPH framework for simulation of axisymmetric free-surface flows
    (Elsevier, 2017-11) Islam, Md Rushdie Ibne
    Dynamics of a Newtonian fluid in a cylindrical symmetric domain can be conceptualized as axisymmetric flow. Full-scale 3D simulation of such problems requires large computational overhead. A new divergence-free Axisymmetric Incompressible Smoothed Particle Hydrodynamics (AxISPH) framework is proposed for modeling of Newtonian fluid flow with free-surface. The formulation employs the concept of variable axisymmetric volume based on current particle position to incorporate symmetry around the central axis. The framework utilizes a semi-implicit two-step approach to obtain hydrodynamic variables and minimizes errors in particle position. Laplace and gradient operators are modified to incorporate axisymmetric nature. A radial dam-break flow has been simulated with the proposed model and compared with three-dimensional ISPH result.
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    On consistency and energy conservation in smoothed particle hydrodynamics
    (Wiley, 2018-08) Islam, Md Rushdie Ibne
    Energy conservation and consistency are not easy to achieve simultaneously in smoothed particle hydrodynamics (SPH). In this study, an efficient strategy is proposed to achieve energy conservation in an SPH framework with a consistent basis function. Herein, at every particle pair interaction, a correction term is introduced such that energy conservation is restored locally and, at the same time, the total variation of different variables due to the correction term is minimum. The final form of the proposed formulation is such that no additional computational effort is required and the simplicity of SPH is preserved. The theoretical error estimate of the proposed formulation is performed. The proposed scheme is also compared with benchmark SPH formulations in terms of the L2 error norm for representative functional derivatives both in regular and irregular particle distributions. Finally, the efficacy of the proposed formulation in conserving energy and maintaining accuracy is demonstrated via few elastic, elastic-plastic impact and fracture problems.
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    Physical reflective boundary conditions applied to smoothed particle hydrodynamics method for solving three-dimensional fluid dynamics problems
    (2019) Islam, Md Rushdie Ibne
    The mixing of continuum and microscopic laws is a contradiction often existing in the boundary conditions utilised in meshfree particle methods. Boundary techniques employing fictitious (or ghost) particles and artificial forces (defined in the molecular microscopic scale) are still used in SPH simulations and should be avoided. Currently, there is an effort in replacing boundary techniques that mix concepts of different scales by others that respect the continuum laws. This paper aims to present the implementation of the physical reflective boundary conditions (RBC) in Smoothed Particle Hydrodynamics (SPH) method for solving three dimensional (3-D) fluid dynamics problems. In this work, SPH was applied to solve the physical conservation equations for a Newtonian, incompressible, uniform and isothermal fluid. Applications in hydrostatics and hydrodynamics are presented as well as the validation of the results in 3-D domains. Two problems were studied: a still fluid inside an immobile reservoir and dam breaking flow. The results achieved presented a good agreement with the analytical solution and literature data.
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    High precise benchmarks by CSD (computational solid dynamics) with meshfree methods
    (SAE International, 2019) Islam, Md Rushdie Ibne
    The virtual optimisation of tooling equipment is nowadays one of the common challenges in mechanical serial production. Even some numerical Eulerian approaches (grid-based) exist for modelling solid materials under dynamic loading, most of them are not very successful. Especially the solids undergoing large deformation and the subsequent material separation and propagating cracks demonstrate the limitations: variables become discontinuous across the crack surface, and the computational domain loses its continuum nature. Grid-based methods are not naturally equipped to deal with such situations due to the mesh distortion, mesh entanglement and requirement of mesh refinement. Very promising alternatives to the Eulerian methods are meshfree Lagrangian methods. Among them, smoothed particle hydrodynamics (SPH) is entirely meshfree and naturally equipped to handle large material deformation. In SPH the computational domain is discretised by a set of particles. A given particle interacts only with its neighbouring particles through a kernel function whose support is defined by the smoothing length. The Bell-shape of the kernel function ensures that the interaction is at a maximum between immediate neighbours and gradually decreases with an increase in distance between interacting particles. During the deformation process, previously interacting particles may leave each other's influence domains and cease to interact further which makes SPH natural in handling large material deformation. Based on the SPH, a solver with multi-GPU acceleration for modelling solid materials has been developed, and is proven to be effective in several practical applications involving large deformation and material failure. In the present work, we discuss the current needs for virtual tool optimisation, the limitations of existing simulation software and the potential advantages and disadvantages of Lagrangian particle-based approaches especially SPH.
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    Numerical modelling of metal forming by SPH with multi-gpu acceleration
    (SAE International, 2019) Islam, Md Rushdie Ibne
    Large material distortion, plastic deformation and forging make the numerical modelling of metal forming a difficult task. Grid-based methods such as the Finite Element Method (FEM) are incapable of simulating this process as these schemes suffer from mesh distortion and mesh entanglement. The mesh-based numerical frameworks with discontinuous enrichment can model finite deformation problems with limited success. Moreover, the presence of flaws, multiple crack surfaces and their interaction make the simulation even more numerically and computationally intensive. In this regard, Lagrangian particle-based meshfree methods are more relevant. There exist several mesh-free methods and among these Smoothed Particle Hydrodynamics (SPH) is a truly meshfree method. In SPH the computational domain is discretised by a set of particles. A given particle interacts only with its neighbouring particles through a kernel function with a constant radius. The interaction between particles stops when the particles move out of each other’s influence domain. Due to the absence of mesh/grids, SPH is naturally equipped to handle large deformation problems. Based on SPH, a solver with multi GPU acceleration for modelling metal forming process is developed. SPH provides a detailed insight into the material deformation, accumulation of plastic strain, and material flow patterns. The effect of different parameters and their influence can also be investigated. The material hardening effects are considered. The presence of voids in the material, the asymmetry in the forging process, the material flaws and their interaction and evolution over time can be modelled accurately. In the present work, we discuss the current needs for a computational framework for metal forming, the limitations of existing simulation software and the potential advantages and disadvantages of SPH.
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    A total lagrangian sph method for modelling damage and failure in solids
    (Elsevier, 2019-07) Islam, Md Rushdie Ibne
    An algorithm is proposed to model crack initiation and propagation within the Total Lagrangian Smoothed Particle Hydrodynamics (TLSPH) framework. TLSPH avoids the tensile instability encountered in conventional Eulerian kernel-based Smoothed Particle Hydrodynamics (SPH) by making use of the Lagrangian kernel. In the present approach, the support domain of a particle is modified, where it only interacts with its immediately neighbouring particles. The gradient correction is employed to avoid the inconsistency of SPH approximation induced by insufficient neighbouring particles. A virtual link is used to define the level of interaction between each particle pair. The state of the virtual link is determined by damage law or cracking criterion. The virtual link approach allows easy and natural modelling of cracking surfaces without explicit cracking treatments such as particle splitting, field enrichment or visibility criterion. The performance of the proposed approach is demonstrated via a few numerical examples of both brittle and ductile failure under impact loading.
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    Implementation of three-dimensional physical reflective boundary conditions in mesh-free particle methods for continuum fluid dynamics: Validation tests and case studies
    (AIP, 2019-10) Islam, Md Rushdie Ibne
    Mesh-free particle methods applied to continuum fluid dynamics still use fictitious, ghost or virtual particles, and/or molecular dynamics concepts in the treatment of the boundaries. The aim of this paper is to present the implementation of the physical reflective boundary conditions (RBC), based on Newton’s restitution law and the foundations of analytical geometry, in the treatment of contours in a three-dimensional (3D) domain. In a previous paper [C. A. D. Fraga Filho, “An algorithmic implementation of physical reflective boundary conditions in particle methods: Collision detection and response,” Phys. Fluids 29, 113602 (2017)], RBC validation tests and simulation results were presented for a two-dimensional (2D) domain. The current work presents the validation of the collision detection and response algorithm employed for the RBC and its application in two cases (hydrostatics and hydrodynamics) in a 3D domain. Following an analysis of the simulation results, the applicability of the RBC to 3D continuum fluid dynamic problems is verified. In the hydrostatics case, a still liquid (Newtonian, incompressible, uniform, and isothermal) inside an immobile reservoir is studied. The fluid flow is modeled using an improved Smoothed Particle Hydrodynamics (SPH) formulation utilizing a modified concept of pressure. The simulation results are excellent, showing complete agreement with the analytical solution and the nonmotion of the particles throughout the simulation time. In the hydrodynamics case, 3D dam break flow modeling is carried out using the standard SPH formulation. Results provided by the RBC and standard SPH modeling are compared with the literature data demonstrating good agreement with the experimental findings.
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    Numerical modelling of crack initiation, propagation and branching under dynamic loading
    (Elsevier, 2020-02) Islam, Md Rushdie Ibne
    In this paper crack initiation, propagation and branching phenomena are simulated using the Pseudo-Spring Smoothed Particle Hydrodynamics (SPH) in two and three-dimensional domains. The pseudo-spring analogy is used to model material damage. Here, the interaction of particles is limited to its initial immediate neighbours. The particles are connected via springs. These springs do not provide any extra stiffness in the system but only define the level of interaction between the connecting pairs. It is assumed that a crack has passed through a spring connecting a particle pair if the damage indicator of that spring becomes more than a predefined value. The crack branching of a pre-notched plate under dynamic loading and the effect of loading amplitude are studied. The computed crack speeds, crack paths and surfaces are compared with experimental and numerical results available in the literature and are found to be in good agreement. Next, the effect of notch location for a plate with a circular hole is studied. The ability of the framework to model arbitrary crack paths and surfaces are also demonstrated via three-dimensional simulations of chalk under torsion, Kalthoff-Winkler experiment, Taylor bullet impact and crack branching.