40 results found
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.
Wong LLC, Villafranca PMB, Menner A, et al., 2013, Hierarchical Polymerized High Internal Phase Emulsions Synthesized from Surfactant-Stabilized Emulsion Templates, LANGMUIR, Vol: 29, Pages: 5952-5961, ISSN: 0743-7463
Chen BY, Tay TE, Baiz PM, et al., 2013, Numerical analysis of size effects on open-hole tensile composite laminates, Composites Part A: Applied Science and Manufacturing, Vol: 47, Pages: 52-62
The tensile strength of open-hole fibre reinforced composite laminates depends on in-plane, thickness and ply lay-up scaling. Translaminar (fibre direction) mode I fracture toughness has recently been experimentally determined to be thickness dependent. This paper presents a computational study of the tensile strength prediction of open-hole laminates using a cohesive zone model. To the authors’ knowledge, it is for the first time in the literature that the thickness-dependence of translaminar fracture toughness is accounted for in the numerical modelling of composites. The thickness size effect in the strength of open-hole composite laminates failed by pull-out is accurately predicted for the first time by a deterministic model. It is found that neglecting delamination in the numerical models will lead to mesh-dependency and over-estimation on the predicted strength. Smeared crack model with cohesive elements to model delamination is able to predict the correct failure mode; but it is found not suitable for accurate strength predictions for laminates failed by delamination.
Baiz PM, Chen BY, Pinho ST, et al., 2013, Modelling Multiple Discontinuities within an Element for Applications in Composite Fracture, UK National Conference on Computational Mechanics in Engineering
Leung H, Baiz PM, 2012, Partition of Unity and Drilling Rotations in the Boundary Element Method (BEM), International Journal of Solids and Structures
Hale JS, Baiz PM, 2012, A locking-free meshfree method for the simulation of shear-deformable plates based on a mixed variational formulation, Computer Methods in Applied Mechanics and Engineering
The problem of shear-locking in the thin-plate limit is a well known issue that must be overcome when discretising the Reissner-Mindlin plate equations. In this paper we present ashear-locking-freemethod utilising meshfree maximum-entropy basis functions and rotated Raviart-Thomas-Nédélec elements within amixedvariationalformulation. The formulation draws upon well known techniques in the finite element literature. Due to the inherent properties of the maximum-entropy basis functions our method allows for the direct imposition of Dirichlet (essential) boundary conditions, in contrast to methodsbased on moving least squares basis functions. We present benchmark problems that demonstrate the accuracy and performance of the proposed method.
Baiz PM, Hale J, 2012, A Meshless Method for the Reissner-Mindlin Plate Model based on a Stabilised Mixed Weak Form, 13th International Conference on Boundary Elements Techniques
Chen B, Baiz PM, Pinho ST, et al., 2012, An Extended Phantom Node Method for Crack Interactions in Composites, ECCOMAS 2012
Natarajan S, Baiz PM, Bordas S, et al., 2011, Natural frequencies of cracked functionally graded material plates by the extended finite element method, COMPOSITE STRUCTURES, Vol: 93, Pages: 3082-3092, ISSN: 0263-8223
Natarajan S, Baiz PM, Ganapathi M, et al., 2011, Linear free flexural vibration of cracked functionally graded plates in thermal environment, COMPUTERS & STRUCTURES, Vol: 89, Pages: 1535-1546, ISSN: 0045-7949
Baiz PM, 2011, Application of Partition of Unity concepts in the Boundary Element Method (Keynote), XFEM 2011 (The eXtended Finite Element Method, Partition of Unity Enrichment: Recent Developments and Applications)
Baiz PM, Albuquerque EL, Sollero P, 2011, Drilling Rotations and Partition of Unity in Composite Plates by the Boundary Element Method, 12th International Conference on Boundary Elements Techniques
Baiz PM, Natarajan S, Bordas SPA, et al., 2011, Linear buckling analysis of cracked plates by SFEM and XFEM, Journal of Mechanics of Materials and Structures, Vol: 6, Pages: 1213-1238
In this paper, the linear buckling problem for isotropic plates is studied using a quadrilateral element with smoothed curvatures and the extended finite element method. First, the curvature at each point is obtained by a nonlocal approximation via a smoothing function. This element is later coupled with partition of unity enrichment to simplify the simulation of cracks. The proposed formulation suppresses locking and yields elements which behave very well, even in the thin plate limit. The buckling coefficient and mode shapes of square and rectangular plates are computed as functions of crack length, crack location, and plate thickness. The effects of different boundary conditions are also studied.
Tavares SMO, Häusler SM, Baiz PM, et al., 2011, Crack Growth Simulation in Integrally Stiffened Structures Including Residual Stress Effects from Manufacturing. Part II: Modelling and Experiments Comparison, SDHM: Structural Durability & Health Monitoring, Vol: 7, Pages: 191-210
This article is the second part of a two parts paper which presents, compares and discusses the different crack growth simulation models which were introduced for fatigue crack growth assessment during the DaToN project. In the first part, different simulation approaches were applied to determine a calibration of the stress intensity factors as a function of the crack length for a two stiffeners panel with a central crack. Due to the residual stress field promoted by the different manufacturing processes, its influence was included in the numerical models to determine the stress intensity factors. In this second part, the stress intensity factors calibrations are applied in different crack growth models in order to determine the fatigue life under cyclic loads. Paris, Walker, Forman and NASGRO were used for this purpose. The incorporation of the load ratio variation and of the effect of the residual stresses is in general possible in all of them allowing to determine the influence of the residual stress field in the fatigue crack growth. The results were tested and compared with experimental results with the purpose of validation of the models. These numerical models demonstrate that (i) it is possible to predict the fatigue life in stiffened welded panels and (ii) the residual stress field originated by welding processes can be detrimental or beneficial depending on the location where the crack starts.
Häusler SM, Baiz PM, Tavares SMO, et al., 2011, Crack Growth Simulation in Integrally Stiffened Structures Including Residual Stress Effects from Manufacturing. Part I: Model Overview, SDHM: Structural Durability & Health Monitoring, Vol: 7, Pages: 163-190
This article represents the first part of a two-part article which presents, compares and discusses the different crack growth simulation models which were introduced for fatigue crack growth assessment during the DaToN project. The project was funded by the EC within the 6th framework program and was specifically devoted to investigate innovative manufacturing techniques for metallic structures with special focus on the effects of residual stresses on the fatigue crack growth and residual strength behaviour. Within this first part the different simulation approaches, including the residual stress modelling approaches will be introduced and stress intensity factor results will be presented and compared. Within this context it could be observed that residual stress effects do have a significant influence on the resulting stress intensity factor solution whose magnitude strongly depends on the input parameters (residual stress field input) but also, to certain extent, on the simulation approaches for stress intensity factor determination as well as residual stress modelling. The residual stress effect also plays an important role for the fatigue crack growth simulations which will be presented in detail in the second part including a comparison with fatigue crack growth results from experiments.
Wen PH, Dirgantara T, Aliabadi MH, et al., 2010, The Boundary Element Method for Geometrically Nonlinear Analyses of Plates and Shells, Boundary Element Methods in Engineering and Sciences, Editors: Aliabadi, Wen, Publisher: Imperial College Pr, ISBN: 9781848165793
Baiz PM, 2010, Drilling Rotations in BEM, 11th International Conference on Boundary Elements Techniques.
Baiz PM, Natarajan S, Kerfriden P, et al., 2010, Linear Buckling Analysis of Cracked Isotropic Plates using XFEM, UK National Conference on Computational Mechanics in Engineering.
Troyani NL, Gomes CJ, Baiz PM, 2010, Capability for Capturing Temperability as a Criterion for the Validity of Thermoviscoelastic Constitutive Equations, JOURNAL OF THERMAL STRESSES, Vol: 33, Pages: 37-54, ISSN: 0149-5739
Baiz PM, Aliabadi MH, 2010, Post buckling analysis of shear deformable shallow shells by the boundary element method, Int. J. Numer. Meth. Engng, Vol: 84, Pages: 379-433
This paper presents four boundary element formulations for post buckling analysis of shear deformable shallow shells. The main differences between the formulations rely on the way non-linear terms are treated and on the number of degrees of freedom in the domain. Boundary integral equations are obtained by coupling boundary element formulation of shear deformable plate and two-dimensional plane stress elasticity. Four different sets of non-linear integral equations are presented. Some domain integrals are treated directly with domain discretization whereas others are dealt indirectly with the dual reciprocitymethod. Each set of non-linear boundary integral equations are solved using an incremental approach, where loads and prescribed boundary conditions are applied in small but finite increments. The resulting systems of equations are solved using a purely incremental technique and the Newton–Raphson technique with the Arc length method. Finally, the effect of imperfections (obtained from a linear buckling analysis) on the post-buckling behaviour of axially compressed shallow shells is investigated. Results of severalbenchmark examples are compared with the published work and good agreement is obtained.
Sharif Khodaei Z, Baiz PM, Aliabadi MH, 2009, Fatigue Crack Initiation and Propagation in Thick Multilayer Metallic Laminates, 8th International Conference on Fracture and Damage Mechanics
Baiz PM, Sharif Khodaei Z, Aliabadi MH, 2009, Fracture Mechanics Analysis of Multilayer Metallic Laminates by BEM, 10th International Conference on Boundary Elements Techniques
Troyani N, Perez A, Gomes C, et al., 2009, Selective finite element refinement in torsional problems based on the membrane analogy, FINITE ELEMENTS IN ANALYSIS AND DESIGN, Vol: 45, Pages: 547-554, ISSN: 0168-874X
Baiz PM, Aliabadi MH, 2009, Buckling and Post-buckling Analysis of Thin Walled Structures by the Boundary Element Method, UK National Conference on Computational Mechanics in Engineering
Baiz PM, Aliabadi MH, 2009, Local buckling of thin-walled structures by the boundary element method, Engineering Analysis with Boundary Elements, Vol: 33, Pages: 302-313, ISSN: 0955-7997
In this work a multi-region boundary element formulation for linear local buckling analysis of assembled plate and shallow shell structures is presented. The assembly is divided into sub-regions. In each sub-region, the formulation is formed by coupling boundary element formulations of shear deformable plate bending and two-dimensional plane stress elasticity. Domain integrals appearing in the formulation (due to the curvature and due to the domain load) are transformed into equivalent boundary integrals. Membrane stresses at discrete domain points of each sub-region (plate or shallow shell) in the assembly are obtained from the prebuckling state, resulting in a set of linear buckling equations in terms of the buckling deflection and the buckling load factor. Buckling equation is presented as a standard eigenvalue problem. Results are compared with FEM solutions and it is shown that good accuracy can be achieved with the present multi-region BEM formulation.
Aliabadi MH, Baiz PM, Albuquerque EL, 2009, Stability Analysis of Plates, Recent Advances in Boundary Element Methods, Editors: Manolis, Polyzos, Publisher: Springer 2009, ISBN: 1402097093
Baiz PM, Aliabadi MH, 2008, DBEM for Fracture Analysis of Stiffened Curved Panels (Plates and Shallow Shells Assemblies), 9th International Conference on Boundary Elements Techniques
Albuquerque EL, Baiz PM, Aliabadi MH, 2008, Stability Analysis of Composite Plates by the Boundary Element Method, 9th International Conference on Boundary Elements Techniques
Baiz PM, Aliabadi MH, 2008, Geometrically Nonlinear Analysis of Cracked Stiffened Curved Panels by DBEM, 7th International Conference on Fracture and Damage Mechanics, Publisher: TRANS TECH PUBLICATIONS LTD, Pages: 13-16, ISSN: 1013-9826
Aliabadi MH, Baiz PM, 2008, The Boundary Element Method for Buckling and Post-buckling Analysis of Plates and Shells, Buckling and Postbuckling Structures, Editors: Falzon, Aliabadi, England, Publisher: Imperial College Press, ISBN: 978-1860947940
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