Publications
119 results found
Soleiman Fallah A, Louca L, Mehreganian N, et 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.
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
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.
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.
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.
Mehreganian N, Louca LA, Langdon GS, et al., 2018, The response of mild steel and armour steel plates to localised air-blast loading-comparison of numerical modelling techniques, International Journal of Impact Engineering, Vol: 115, Pages: 81-93, ISSN: 0734-743X
This paper presents a comparative study of numerical, experimental and empirical techniques on the effect of localised air blast loads on mild steel and armour steel plates. The blast load effects on monolithic plates have been accounted for by using different approaches provided in the Finite Element hydrocode ABAQUS 6.13, namely an Eulerian Lagrangian and a Coupled Eulerian Lagrangian model. In the first model, the air and the explosive were modelled using multi-material Eulerian grids while the plate was modelled using a rigid Lagrangian mesh, while in the second model the rigid target was replaced with deformable plate.The transient deformation of the plate, strain localisation, pressure distribution on the plate have been investigated in the FE models, which have been validated against small scale experimental data for a limited range of charge sizes for both the mild steel and armoured steel. Despite the lower deflection of armour steel compared to mild steel plates, both plates were shown to undergo rupture upon similar charge mass and stand-off. For this purpose, a non-dimensional analysis was carried out with consideration of stand-off distance and slenderness ratio to predict the rupture impulse.
Soleiman Fallah A, Mehreganian N, Boiger GK, et 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.
Mouring SE, Louca LA, Brambleby RJ, 2017, Perforated steel-to-composite joints under static and dynamic loading, Pages: 262-267, ISSN: 1098-6189
Composite materials are being more widely used as primary structural members for advanced naval vessels due to increased damage tolerance, stealth, range, payload, stability, and corrosion resistance, and at the same time, a reduction in lifetime costs. However, composites materials are not typically used in isolation due to their insufficient stiffness and ductility compared to metallic materials. Thus, there has been growing interests in metal and composite combined structures. However, joints in composite structures are susceptible to failure when subjected to high rate loading from an impulsive load source. This paper presents results from tensile strength testing of steel-to-composite double lap joints, comparing pseudo-static strength with dynamic strength and comparing joints that exploit perforated steel plates with those manufactured with non-perforated steel plates. Finite Element Analysis (FEA) results are compared to experimental results for both perforated and non-perforated joints.
Mouring SE, Louca LA, Brambleby R, 2017, Experimental and Numerical Study of Hybrid Steel-to-Fiber Reinforced Polymer Joints Under Tensile Loading, SAMPE JOURNAL, Vol: 53, Pages: 7-14, ISSN: 0091-1062
Brambleby R, louca L, Mouring S, 2016, Influence of loading rate on the mode II fracture toughness of vinyl ester GRP, Composites Part A - Applied Science and Manufacturing, Vol: 93, Pages: 153-162, ISSN: 1359-835X
Four point bending end notched exure (4ENF) tests were used to evaluate the mode II fracture toughness(GIIC) of glass bre reinforced vinyl-ester (GFRP) specimens in order to expose the sensitivity of GIICtoloading rate. Tests were carried out at load displacement rates ranging from 1 to 6000 mm/minute. Finiteelement models were used to evaluate the correction factors that are required during data reduction in orderto compensate for geometrical non-linearity in the test. A high speed video camera was used in conjunctionwith the digital image correlation technique to measure crack propagation during the tests. It was foundthat, for short crack lengths, GIICtended to increase as loading rate was increased.
Nwankwo E, Soleiman Fallah A, Moatamedi M, et 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.
Chen A, Louca LA, Elghazouli AY, 2016, Behaviour of cylindrical steel drums under blast loading conditions, INTERNATIONAL JOURNAL OF IMPACT ENGINEERING, Vol: 88, Pages: 39-53, ISSN: 0734-743X
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Micallef K, Fallah AS, Curtis PT, et 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.
Pullen AD, Louca LA, Micallef K, et 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
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- Citations: 5
Soleiman Fallah A, Yang Y, Ward R, et 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.
Soleiman Fallah A, Micallef K, Pope DJ, et al., 2015, On dimensionless loading parameters for close-in blasts, International Journal of Multiphysics, ISSN: 1750-9548
Chen A, Elghazouli AY, Louca LA, 2015, Blast assessment of industrial steel structures, CONFAB 2015 - Int Conference on Structural Safety under fire and Blast, Pages: 500-509
Chen A, Louca LA, Elghazouli AY, 2015, Blast assessment of steel switch boxes under detonation loading scenarios, INTERNATIONAL JOURNAL OF IMPACT ENGINEERING, Vol: 78, Pages: 51-63, ISSN: 0734-743X
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Langdon GS, Lee WC, Louca LA, 2015, The influence of material type on the response of plates to air-blast loading, INTERNATIONAL JOURNAL OF IMPACT ENGINEERING, Vol: 78, Pages: 150-160, ISSN: 0734-743X
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- Citations: 46
Mouring SE, Louca LA, Brambleby R, 2015, Investigation into hybrid perforated steel-to-composite joints
There are many advantages of advanced composite materials compared to traditional metallic materials including high stiffness- and strength-to-weight ratios, corrosion resistance, damage tolerance, and improved stealth characteristics. Thus, they are being used more often as primary structural members in both civil and military applications. However due to insufficient stiffness and ductility of composites compared to metallic materials, these materials are not typically applied in isolation. This has led to a rapid expansion of interests in metal and composite combined structures. One of the major structural challenges in this area is the design of hybrid metal-to-composite joints. Hybrid joints usually entail both material and geometry discontinuities leading to stiffness mismatch and local stress concentrations. Current research at Imperial College London (ICL) and the U.S. Naval Academy (USNA) shows that among the various types of novel metal-to-composite joints, perforated hybrid steel-to-composite joints demonstrate significant potential in naval structural applications. In these joints, perforations are cut into the steel increasing the cohesion between steel and composite parts, and thus improving the transfer of load between two parts. Apart from the benefit of mechanical interlocking, the perforated steel plate also is believed to decrease the elastic mismatch between the stiff steel part and the relatively compliant composite part. This paper reviews an Office of Naval Research (ONR) - sponsored research project focusing on the perforated hybrid steel-to-composite joint design.
Fallah AS, Micallef K, Langdon GS, et 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.
Brambleby RJ, Louca LA, Mouring SE, 2014, Dynamic strength testing of perforated steel - GRP double lap joints
Joints between metals and composites are being employed in a range of applications, but the performance of such joints under dynamic loading is not well documented. This paper presents some initial results investigating the tensile strength of steel to GRP double lap joints comparing pseudo static strength with dynamic strength and comparing joints that have non-perforated steel plates with joints that have perforated steel plates. The effect of an intentional manufacturing flaw is also considered. It has been observed that the strength enhancement provided by the perforations is significant, but marginally lower under dynamic loading than under static loading.
Nwankwo E, Soleiman-Fallah A, Louca LA, 2013, Semi-analytical study of interfacial stresses in adhesively bonded single lap joints subject to transverse shock loading., J Acoust Soc Am, Vol: 134
Debonding in adhesively bonded lap joints is a detrimental failure mode contingent upon the level of stresses developed in the adhesive. A semi-analytical model is developed to estimate the peel and shear stresses in an isotropic elastic adhesive in a single lap joint subjected to transverse shock loads. The proposed semi-analytical model is an extension of existing mathematical models to study the coupled transverse and longitudinal vibrations of a bonded lap joint system. The adhesive is modeled as an isotropic material in Abaqus. The interfacial stresses obtained by finite element simulations were used to validate the analytical model. The maximum peel and shear stresses predicted by the analytical model in the adhesive were found to correlate well with the maximum stresses predicted by the corresponding numerical models. The peel stresses in the adhesive were found to be higher than shear stresses, a result which is consistent with intuition for transversally pulse loaded joints. The semi-analytical model is able to predict the maxim stresses in the edges where debonding initiates due to the highly asymmetrical stress distribution as observed in the finite element simulations and experiment. The stress distribution under uniformly distributed transverse pulse loading was observed to be similarly asymmetric.
Soleiman-Fallah A, Nwankwo E, Langdon GS, et al., 2013, Inelastic deformation and failure of partially strengthened profiled blast walls., J Acoust Soc Am, Vol: 134
Blast walls that separate the potentially hazardous regions of the topside on an offshore platform were designed to resist lower loads than those envisaged today thus it is desirable to upgrade their blast resistance in a cost-effective and non-intrusive manner. One proposal is to retrofit the existing blast walls partially with centrally located composite patches. This study presents an assessment tool, which provides understanding of the effect of a composite patch on the blast resistance of blast walls. Numerical simulations of a proposed retrofitted wall are performed to gain insight into the failure progression of the wall ab initio. Damage in the composite patch was considered, and the numerical simulations showed that fiber fracture did not occur thus there was no significant loss of in-plane stiffness and strength. Based on these observations, the rapid assessment tool, analytically formulated to incorporate the effect of the composite patch which strengthens the wall and moves the plastic hinge locations away from the wall centre to the composite-steel edge, is deemed a suitable tool. The assessment tool and the numerical simulations are partially validated by the experimental results. The tool runs quickly and provides reasonable accurate predictions for the deformation response of the walls.
Wang Z, Liang X, Fallah AS, et al., 2013, A novel efficient method to evaluate the dynamic response of laminated plates subjected to underwater shock, Journal of Sound and Vibration, Vol: 332, Pages: 5618-5634, ISSN: 0022-460X
Mouring SE, Janowski ME, Louca LA, et al., 2013, Behavior of hybrid protruded steel-to-fiber reinforced polymer joints, Pages: 153-157, ISSN: 1098-6189
Composite materials have advanced material properties such as high stiffness- and strength-to-weight ratios, corrosion resistance, damage tolerance, and stealth characteristics and are being widely used for primary structural members. However, these materials are not typically applied in isolation due to insufficient stiffness and ductility of the composite compared to traditional metallic materials. Thus there has been a growing interest in combined metal and composite structures. Design of metal-to-composite hybrid joints appears to be one of the major structural challenges. Hybrid joints often entail both geometry and material discontinuities which can lead to a stiffness mismatch and cause local stress concentrations. Research at Imperial College London (ICL) and the U.S. Naval Academy (USNA) shows that among the various novel steel-to-fiber reinforced polymer (FRP) joint design, hybrid protruded joints demonstrate significant potential in naval structural applications. These joints are fabricated using a surface treatment technique called Surfi-Sculpt which uses a power electron beam to create metal protrusions onto which the FRP is laid and cured. This paper reviews the ongoing Office of Naval Research (ONR) sponsored research project focusing on the hybrid protruded joint design. Both experimental and finite element analysis (FEA) results will be discussed and compared. Copyright © 2013 by the International Society of Offshore and Polar Engineers (ISOPE).
Toolabi M, Fallah AS, Baiz PM, et al., 2013, Dynamic analysis of a viscoelastic orthotropic cracked body using the extended finite element method, Engineering Fracture Mechanics, Vol: 109, Pages: 17-32, ISSN: 0013-7944
The extended finite element method (XFEM) is found promising in approximating solutions to locally non-smooth features such as jumps, kinks, high gradients, inclusions, voids, shocks, boundary layers or cracks in solid or fluid mechanics problems. The XFEM uses the properties of the partition of unity finite element method (PUFEM) to represent the discontinuities without the corresponding finite element mesh requirements. In the present study numerical simulations of a dynamically loaded orthotropic viscoelastic cracked body are performed using XFEM and the J-integral and stress intensity factors (SIF’s) are calculated. This is achieved by fully (reproducing elements) or partially (blending elements) enriching the elements in the vicinity of the crack tip or body. The enrichment type is restricted to extrinsic mesh-based topological local enrichment in the current work. Thus two types of enrichment functions are adopted viz. the Heaviside step function replicating a jump across the crack and the asymptotic crack tip function particular to the element containing the crack tip or its immediately adjacent ones. A constitutive model for strain-rate dependent moduli and Poisson ratios (viscoelasticity) is formulated. A symmetric double cantilever beam (DCB) of a generic orthotropic material (mixed mode fracture) is studied using the developed XFEM code. The same problem is studied using the viscoelastic constitutive material model implemented in ABAQUS through an implicit user defined material subroutine (UMAT). The results from XFEM correlate well with those of the finite element method (FEM). Three cases viz. static, dynamic and viscoelastic dynamic are studied. It is shown that there is an increase in the value of maximum J-integral when the material exhibits strain rate sensitivity.
Fallah AS, Nwankwo E, Louca LA, 2013, Pressure-Impulse Diagrams for Blast Loaded Continuous Beams Based on Dimensional Analysis, ASME Journal of Applied Mechanics, Vol: 80, Pages: 051015-051015, ISSN: 0021-8936
Pressure-impulse diagrams are commonly used in preliminary blast resistant design to assess the maxima of damage related parameter(s) in different types of structures as a function of pulse loading parameters. It is well established that plastic dynamic response of elastic-plastic structures is profoundly influenced by the temporal shape of applied pulse loading (Youngdahl, 1970, “Correlation Parameters for Eliminating the Effect of Pulse Shape on Dynamic Plastic Deformation,” ASME, J. Appl. Mech., 37, pp. 744–752; Jones, Structural Impact (Cambridge University Press, Cambridge, England, 1989); Li, and Meng, 2002, “Pulse Loading Shape Effects on Pressure–Impulse Diagram of an Elastic–Plastic, Single-Degree-of-Freedom Structural Model,” Int. J. Mech. Sci., 44(9), pp. 1985–1998). This paper studies pulse loading shape effects on the dynamic response of continuous beams. The beam is modeled as a single span with symmetrical semirigid support conditions. The rotational spring can assume different stiffness values ranging from 0 (simply supported) to ∞ (fully clamped). An analytical solution for evaluating displacement time histories of the semirigidly supported (continuous) beam subjected to pulse loads, which can be extendable to very high frequency pulses, is presented in this paper. With the maximum structural deflection, being generally the controlling criterion for damage, pressure-impulse diagrams for the continuous system are developed. This work presents a straightforward preliminary assessment tool for structures such as blast walls utilized on offshore platforms. For this type of structures with semirigid supports, simplifying the whole system as a single-degree-of-freedom (SDOF) discrete-parameter model and applying the procedure presented by Li and Meng (Li and Meng, 2002, “Pulse Loading Shape Effects on Pressure–Impulse Diagram of an Elastic–Plastic, Single-Degree-of-Freedom Structural
Micallef K, Fallah AS, Curtis PT, et al., 2013, A homogenised continuum constitutive model for visco-plastic deformation of uni-directional composites, Composite Structures, ISSN: 0263-8223
Nwankwo E, Soleiman Fallah A, Louca LA, 2013, An investigation of interfacial stresses in adhesively-bonded single lap joints subject to transverse pulse loading, Journal of Sound and Vibration, Vol: 332, Pages: 1843-1858, ISSN: 0022-460X
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