Abstract in English:Abstract An experimental programme to investigate the notched strength of open-hole woven fabric kenaf fiber-reinforced polymer (WKRP) composite plates under quasi-static tensile loading. It was found that all testing coupons were failed in net-section, fracture initiated at the hole edge due to stress concentrations and propagated to the plate edge. A two-dimensional numerical modelling framework was developed following previously experimental series. A constitutive model of the traction-separation relationship was incorporated by using extended finite element model (XFEM) and cohesive zone model (CZM). Moreover, the effects of elevated temperatures and thermal expansion coefficient was incorporated within the modelling framework. Both modelling techniques were evaluated and compared, albeit to insignificant differences of maximum load output in both techniques, XFEM does not require apriori failure path compared to CZM. Good agreements between the predicted modelling work and measured notched strength were obtained, with discrepancies in the range of 0.4 - 25%, both displayed consistency in the net-section failures.
Abstract in English:Abstract The brittle failure of rock is closely related to the rock crack initiation, propagation, coalescences and nucleation. Although many brittleness indexes have been proposed to describe the brittle behavior of rocks, the relationship between the brittleness index and crack initiation stress under triaxial compressive states has not been fully understood. This paper introduced the current main brittleness indexes and discussed their applicabilities for triaxial compressive tests. Granite specimens from a gold mine are prepared for experimental tests. The triaxial compressive tests are carried out on stiff testing machine and the confining pressures are 5 to 110 MPa. Experimental results on the stress-strain curves show that the post-peak behaviors of the granite under confining pressures are in Class I and Class II types. The brittleness indexes, crack initiation stress, compressive strength, elastic moduls and Poisson’s ratio of the granite are obtained and discussed. It has been found that, the crack initiation stress linearly increases with the increasing of confining pressure. Moreover, a power function can describe the relationship between the brittleness index and crack initiation stress for Class I rock behavior while an exponential function can describe the relationship between the brittleness index and crack initiation stress for Class II rock behavior.
Abstract in English:Abstract The diffraction of the waves from the two ends of floating breakwaters (FBWs) that have limited length, are practically a three-dimensional (3D). In order to perform a two-dimensional vertical (2DV) analysis to solve the wave diffraction problem, some “correcting factors” are required to modify the 2DV results and make them comparable and verifiable against 3D solutions. The main objective of the current study is to propose a method to obtain these correcting factors and demonstrate its usefulness through some example cases. An Artificial Neural Network (ANN) is trained by three main non-dimensional independent variables to predict the mentioned factors. In order to set up the ANN, a database including both 2DV and 3D results is required. The 2DV results are obtained by employing a semi-analytical method, namely the Scaled Boundary Finite Element Method (SBFEM). A basic change in the location of the scaling center is implemented. The 3D results are obtained via ANSYS AQWA software. Eighty-one cases are simulated on a floating object with rectangular cross-sections. The correlation factor R=0.9607 for a group of new samples shows that the predicted results are closely matched to the target values. The correcting factor applies the 3D effects of diffracted waves around the structures on 2DV results and produces a more accurate prediction.
Abstract in English:Abstract In recent years, the Meshless Local Petrov-Galerkin (MLPG) Method has attracted the attention of many researchers in solving several types of boundary value problems. This method is based on a local weak form, evaluated in local subdomains and does not require any mesh, either in the construction of the test and shape functions or in the integration process. However, the shape functions used in MLPG have complicated forms, which makes their computation and their derivative's computation costly. In this work, using the Moving Least Square (MLS) Method, we dissociate the point where the approximating polynomial's coefficients are optimized, from the points where its derivatives are computed. We argue that this approach not only is consistent with the underlying approximation hypothesis, but also makes computation of derivatives simpler. We apply our approach to a two-point boundary value problem and perform several tests to support our claim. The results show that the proposed model is efficient, achieves good precision, and is attractive to be applied to other higher-dimension problems.
Abstract in English:Abstract The current paper implementates a simple fully non-linear Kirchhoff-lovel shell penalty based finite element. The 6 nodes and 21 DoF triangular element developed in this work has a quadratic displacement field associated to it and the C1 continuity required by Kirchhoff-Love Hyphotesis is approximated by an internal penalty. The biggest novelty in this article is the simultaneous use of penalty and a Rodrigues incremental Rotation parameter (scalar DOF) between neighboring elements further explained in the text. The nonlinear finite element model developed in this article is compared to analytical results, commercial finite element code and another FEM model developed in bibliography. Simulations have demonstrated consistency when comparing results to other models and it is deemed that reliable mesh generation together with a powerfull triangular finite element is a good option for trustworthy thin shell simulations.
Abstract in English:Abstract The current paper presents a brief survey of literature relevant to buckling of cone-cylinder intersection under different loads such as (i) internal pressure, (ii) external pressure, and (iii) axial compression. The paper explores the up-to-date knowledge on the buckling of cone-cylinder intersection and highlights the areas of gap in knowledge. This is aimed at contributing to better understanding of the relevant issues such as the influence of different types of imperfections in updating the current design guideline that is found to be vital in industrial practice. The review is thematically divided into: (i) the methods adopted in the past work (i.e., how the data were obtained, type of material used, type of design with/without reinforcement), (ii) the highlight and importance of past findings, (iii) the sensitivity to imperfection and its design implications and (iv) the current design recommendation and guidelines. Finally, the current paper provides a brief state-of-the-art and presents an update of related works for the future establishment of shells design guidelines.
Abstract in English:ABSTRACT The objective of this paper is to present a finite element solution for the wave propagation problems with a reduction of the velocity dispersion and spurious reflection. To this end, a high-order two-step direct integration algorithm for the wave equation is adopted. The suggested algorithm is formulated in terms of two Hermitian finite difference operators with a sixth-order local truncation error in time. The two-node linear finite element presenting the fourth-order of local truncation error is considered. The numerical results reveal that although the algorithm competes with higher-order algorithms presented in the literature, the computational effort required is similar to the effort required by the average acceleration Newmark method. More than that, the integration with the lumped mass model shows similar results to the integration using the average acceleration Newmark for the consistent mass model, which involves a higher number of computational operations.
Abstract in English:Abstract The solution for the buckling problem of composite laminates is usually based on the assumption that the panels are subjected to uniform edge loads without any discontinuity or damage. Nevertheless, in practice, the panels are provided with various sized opening subjected to non-uniform edge loads. Hence in this work, a finite element analysis is carried out to study the buckling behaviour of composite laminates with various sized elliptical openings under non-uniform edge loads. In the FE formulation, the panels are discretised by adopting 9-noded heterosis element and incorporating the effect of shear deformation and rotary inertia. The correctness of the formulation is validated by correlating the results with available literature. The influence of different sized elliptical cutouts on the buckling behaviour is investigated under the compressive and tensile type of non-uniform in-plane edge loads. The effect of various parameters such as cutout size, ply-orientation, ellipse-orientation, boundary condition and panel thickness is included in this work. It is observed from this work that the elliptical vertical cutout has higher buckling resistance as compared to that of the elliptical horizontal cutout.
Abstract in English:Abstract PELE (the Penetrator with Enhanced Lateral Effect) produces a large number of fragments after penetrating metal target plate, which can damage the high-value targets behind the shield plate in a large area. However, when facing the multi-layer spaced metal shield plates, it is difficult to penetrate them and damage the targets behind them due to the limited penetration ability of the fragments. Radial layered PELE was designed for damaging multi-layer spaced metal plates. The experiment and numerical simulation were carried out to study the deformation and fragmentation of the penetrator after penetrating 2A12 aluminum alloy or Q235 steel target plate at different velocities, as well as the damage to the witness plates after penetrating the main target plates. The results show that the fragmentation of PELE increases with the increase of impact velocity. At the same impact velocity and the same thickness of metal target plate, compared with penetrating the 2A12 aluminum alloy target plate, radial layered PELE is deformed and broken to a greater extent, resulting in heavier damage to the witness plates when penetrating the Q235 steel target plate. In the process of penetrating multi-layer metal target plates, the outer jacket of radial layered PELE is gradually broken to form a large number of flying fragments, but the inner jacket is difficult to deform and break, resulting in the strong penetration ability of the penetrator. Therefore, radial layered PELE has better penetration and damage capacity than non layered PELE.
Abstract in English:Abstract This paper presents a procedure for the displacement-based seismic design of in-plan asymmetric buildings with earthquake-induced damage control. Damage is defined on the structural elements in the in-plan and elevation layout of the structure. The proposed method is based on the concepts of the performance-based seismic design philosophy and the application of basic equations of structural dynamics that are regularly used for the current design of buildings. In its application, the simultaneous bidirectional seismic demand is characterized by smooth design spectrum as proposed by most current regulations. To illustrate the steps required in the application of the design method proposed, the paper presents the design process of a 15- and 12-story buildings with in-plan asymmetric distribution of stiffnesses and subjected to a design demand given by the spectrum a real seismic event representative of soft soil sites such as those of the bed-lake of Mexico City. The results obtained are compared with the corresponding results of the nonlinear dynamic step-by-step analyses under the same seismic demand. Based on the results obtained, the relevance of this procedure in the displacement-based seismic design of asymmetric buildings and the implications for its consideration in future regulations are discussed. Graphical Abstract
Abstract in English:Abstract This article describes an analysis of the dynamic response of coupled soil-pile-foundation systems. The soil and the pile models were developed in previous research works. This article describes the influence of three issues on the vertical dynamic foundation response. First, the influence of the foundation bearing mechanism is investigated. The foundation may be supported by the soil, by the pile or by a combination of both supporting mechanisms. A parameter is introduced to allow for a continuous change in the foundation supporting mechanism. Second, the influence of the excitation mechanism is investigated. The considered excitation mechanism are external forces applied directly at the foundation and an incoming wave field impinging the soil-pile-foundation system. Third, the article investigates if, for both excitation mechanism, the response at the pile head only is able to describe properly the soil-pile response. The analysis presented in the article contributes to an in-depth understanding of the dynamic response of coupled soil-pile-foundation systems.
Abstract in English:Abstract Small strains are consistently incorporated into a large rotation piezoelectric beam theory, where the displacement is assumed to vary in accordance with the Timoshenko assumption and the electric potential has linear variation through each piezoelectric layer thickness. A finite element for planar frames, based on the total Lagrangian description, is then developed. The displacements and rotation are linearly approximated over the element and the voltage in a piezoelectric sensor layer is taken to be constant. In addition to the well-known membrane and shear lockings, it is disclosed the presence of locking in the application of Gauss law to the piezoelectric sensor layers. All the mechanical and electrical contributions to the internal load vectors are evaluated using a reduced one-point Gaussian quadrature to make this simple element efficient. No spurious modes are introduced in this process. An incremental-iterative approach, based on the Newton-Raphson algorithm, is employed in the solutions of the numerical examples to illustrate the large rotation capability of the developed model.
Abstract in English:Abstract This work presents an extension of the displacement fitting technique for the assessment of stress intensity factors (SIFs) of three-dimensional linear elastic fracture problems using the dual Boundary Element Method. The developed framework accounts for higher-order terms of the asymptotic displacement solution near crack front. The number and location of points surrounding the crack front are properly defined in order to accurately evaluate the SIFs. Three-dimensional benchmarks demonstrate the efficiency of the proposed framework. Moreover, two different fracture criteria illustrate the influence of SIFs values with respect to the crack propagation angle and equivalent factors calculations. The proposed higher-order technique has demonstrated superior performance in comparison with the conventional displacement fitting technique.
Abstract in English:Abstract Topology optimization is a well-suited method to establish the best material distribution inside an analysis domain. It is common to observe some numerical instabilities in its gradient-based version, such as the checkerboard pattern, mesh dependence, and local minima. This research demonstrates the generalized finite-volume theory's checkerboard-free property by performing topology optimization algorithms without filtering techniques. The formation of checkerboard regions is associated with the finite element method's displacement field assumptions, where the equilibrium and continuity conditions are satisfied through the element nodes. On the other hand, the generalized finite-volume theory satisfies the continuity conditions between common faces of adjacent subvolumes, which is more likely from the continuum mechanics point of view. Also, the topology optimization algorithms based on the generalized finite-volume theory are performed using a mesh independent filter that regularizes the subvolume sensitivities, providing optimum topologies that avoid the mesh dependence and length scale issues.
Abstract in English:Abstract This paper proposes a methodology to obtain the transient response of structural system interacting with soil-foundation schemes supported by viscoelastic soils. The structure and soil are divided into sub-systems. The time domain solution for each subsystem is formulated by an appropriated methodology. The equations of motion of structure are solved by Newmark integration algorithm. The transient response of the soil is obtained by a convolution integral. The convolution integral uses transient impulse response of viscoelastic soils. Newmark and convolution algorithms are formulated as input and output schemes, which, in turn, are plugged to the time stepping iterative algorithm. The scheme is applied to vertical response of a dynamical system interacting with a massless foundation laying on a soil modelled as a three-dimensional homogeneous viscoelastic half-space. For two distinct external forces, the resulting coupled displacements, interface forces, errors and number of iterations within each time step are provided.
Abstract in English:Abstract Tapered steel beams and columns have been increasingly used as primary load carrying members. The determination of their accurate ultimate capacity can only be achieved employing advanced numerical methods such as the finite element method (FEM). This paper presents a systematic study on the influence of FE model parameters on the ultimate load of I-section tapered beam-columns typically used in medium-span steel frames. It aims the determination of optimal FE mesh size and sub-step number to be used during the arc-length scheme for the performance of an accurate, robust and efficient inelastic post-buckling parametric analysis (PA) as well as the evaluation of the parameters influence. Once validated the FE model, using hexahedral 8-node finite elements, FE edge sizes of 20, 25 and 30 mm and 10 sub-steps have been selected for use in the future PA. Several FE analyses were also carried out to evaluate how it is and quantify the influence of each of the parameters, leading to empirical equations with errors in the range of -35% to 35% for equations without crossed terms and -23% to 23% with first-order crossed terms.
Abstract in English:Abstract This paper presents an exact solution for the boundary-value problem which describes the linear buckling of axially-compressed cylindrical panels with frames attached to the circular edges. The boundary conditions differ from the classical simply supported ones, often assumed for design purposes, in the sense that the torsion resisted by the frames are also taken into account. The quality of the results reported herein may be valuable benchmark data.
Abstract in English:Abstract The evaluation of the effective properties of nonhomogeneous solids using analytical methods is, in general, based on the assumption that these solids have infinite dimensions. Here, we investigate the influence of both the number of holes and the boundary layer of a solid with finite dimensions on the determination of these properties. We use the Asymptotic Homogenization Method (AHM) to determine the effective shear modulus of an elastic solid with infinite dimensions containing a uniform and periodic distribution of circular cylindrical holes arranged on a hexagonal lattice. We also use the Finite Element Method (FEM) to determine this modulus in the case of a solid with finite dimensions containing the same uniform distribution of cylindrical holes away from its boundary. Near the boundary, we consider a layer of material with no holes, which is usually left in the fabrication process of samples. Both solids have the same elastic properties and are subjected to similar anti-plane shear loadings. For the finite medium, we study two sequences of domains discretized by the FEM, which are called the Fixed Layer Sequence (FLS) and the Fixed Domain Sequence (FDS). For the FLS, the layer thickness is kept fixed and both the dimensions of the domain and the number of holes vary. For the FDS, the dimensions of the domain are kept fixed and both the number of holes and the layer thickness vary. Results obtained from numerical simulations are then used to generate graphs of the effective shear modulus versus void volume fraction. It is observed that, in the FLS case, the shear modulus obtained from the numerical simulations converges to the analytical solution obtained via AHM. It is also observed that, in the FDS case, the shear modulus obtained from the numerical simulations converges to a limit function, which is close to the analytical solution obtained via AHM. For comparison purposes, we have also calculated the effective shear modulus of porous elastic solids containing a square array of circular cylindrical holes. We then show graphs of this modulus versus void volume fraction for both hexagonal and square arrangements that are very close to each other up to void volume fraction of 0.5.
Abstract in English:ABSTRACT Strength degradation of structural materials is an inevitable process, due to deleterious actions such as corrosion and fatigue. These phenomena are also typically random, with degradation rates and starting time of degradation process largely uncertain. In reinforced concrete structures, corrosion of reinforcing bars caused by chloride ions is one of the main pathological manifestations. Past studies on the time-variant reliability of reinforced concrete structures subject to corrosion have relied on simplified analytical models for estimating the depassivation time. This study contributes with an accurate modelling of chloride diffusion through concrete using the boundary element method, which is employed for the first time within a time-variant reliability framework. Cumulative failure probabilities are evaluated in time by considering random depassivation times, random corrosion evolution, and random load processes. The time-variant reliability problem is solved using Monte Carlo simulation. An application example is presented, demonstrating the capabilities of the proposed framework.