Hung Nguyen Dang

• Editor in Chief of Asia Pacific Journal of Computational Engineering
• Professor Emeritus at University of Liège

An overview of plastic-hinge model for steel frames under static loads is carried out in this paper. Both rigid-plastic and elastic-plastic methods for framed structures are reviewed, including advantages and disadvantages of each method. It concerns both analysis and optimization methodologies. The modeling of 3D plastic hinges by using the normal...

In this paper, an application of the duality principle in Finite Element shell analysis is presented. It is based upon LURE and GOLDENVEIZER's theory of thin shells. For the finite element analysis of thin shells, using the stress function, the problem of finding a stress fields in equilibrium and expressing their continuity across the interfaces i...

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We present in this paper a hybrid element model, which is a type of Metis element (mongrel element) derived from a two-field variational functional. In this model, the assumed boundary displacement field is unisolvent, and the plausible equilibrated stress field within each element is derived using an Airy's stress function. Based on this theoretic...

Based on Lekhnitskiis elasticity theory [l], the formulae of generalized plane strain state for the torsion problem of a prismatic bar are established. By this way, this problem in 3 dimensions (3D) is transformed into the problem in 2.5D. Metis models [3] constitute a bridge between the classical models in one field and the hybrid models in two fi...

 This book constitutes two volumes. The first volume contains the papers published in the last century beginning with my first paper appeared in 1967, one year after I was graduated Aero-Space Engineer by university of Liège. The second volume concerns the papers appeared in present century, from 2000 to 2010. The classification is according to th...

This is the first volume of Prof. Nguyen Dang Hung selected publications about Computation and Modeling in Structural and Mechanical Engineering dated from 1967 to 1999

The purpose of this work is to present an application of the inverse technique to the problem of detection of discontinuous geometry using an acoustic field. The bounday element method is used in modeling the acoustic field inside a two dimensional sheet with cracks and holes. The location of a hole and crack is based on the estimation of the energ...

Prof. Nguyen Dang Hung had the chance to obtain a Belgian scholarship to go to Belgium in 1960 to undertake engineering studies at the University of Liège... In 1966, as an engineer-researcher, fully immersed in Prof. B. Fraeijs de Veubeke's variational and numerical techniques, he dedicated his first works to the duality between displacement and e...

This paper present a new algorithm of plastic optimization for 3D steel frames under fixed loading (limit optimization) or repeated loading (shakedown optimization). The weights of the frames are minimized under constraints of plastic collapse (instantaneous mechanics/alternating plasticity). A 3D plastic-hinge considering two bending moments and a...

This paper presents two novel numerical procedures to determine upper and lower bounds on the actual collapse load multiplier for plates in bending. The conforming Hsieh–Clough–Tocher (HCT) and enhanced Morley (EM) elements are used to discrete the problem fields. A Morley element with enhanced moment fields is used. The constant moment fields is a...

This paper presents a new link between displacement and equilibrium finite elements through a novel family of smooth-strain finite elements. We prove the equivalence of a smooth strain finite element with a quasi-equilibrium element thereby explaining the superconvergence in the $H_1$ norm reported previously. The family of elements is based on str...

The anisotropic elasticity theory and solution of Lekhnitskii for generalized plane strain state are presented. Wang's singular solution is used to determine the stress singularity order and eigen coefficients. The stress intensity factors K i (i = I, II and III), which characterize the toughness of the structure, are calculated. A solution is also...

This paper describe a flat shell element composed of stretching effect represented by a quadratic displacement element and bending effect represented by an constant stress field equilibrium element. This kind of shell element is called also self dual element. The results from various examples of shells are illustrated and compared with the literatu...

This paper presents a procedure for computing the lower bound and the upper bound of limit load of bending Krichhoff plate. The lower bound is realized by using a new equilibrium element. The upper bound is determined by using the conforming HCT element. By applying the procedure of Richardson’s extrapolation for the load factors, we can obtain a r...

A new way is proposed to determine the material constants of fatigue based on Paris law and Circumferentially Cracked Round Bar specimens (CRB). And the accurate analytical formulas for stress intensity factor of CRB specimens are necessary to this determination. This is carried out by finite element calculations and literature review. Finally, a n...

The commercial finite element package SAMCEF including its post-processor SAMCEF Postfac is one of the most powerful tools to compute stress intensity factors (SIFs) of cracked problems. However, it is very complicated to generate a fine mesh of the structure with cracks. Moreover, the .FI3 command of the pre-processor SAMCEF Bacon can only generat...

In this paper, we have applied the element free Galerkin (EFG) method to solve problems in solid mechanics. The meshless equilibrium model is applied instead of the traditional displacement model. The stress field is expressed by the values of Airy stress function. Moving least square (MLS) approximation be employed for construction of the shape fu...

8-node quarter-point element was adjusted to satisfy: the coefficient of linear term in the distance to the tip must vanish. In this paper, we will compare this modified element with a broadly used element – collapsed 8-node quarter-point (CQ8) element. We employed the Displacement Correlation Technique to assess the stress intensity factors (SIFs)...

The "metis" finite element method is originally developed by Nguyen Dang Hung [1]. This method overcomes the lack of no-monotonic convergence provided by general hybrid displacement and stress models. The monotonic convergence of the "metis" element models is investigated in [2]. The unisolvent condition of the external displacement field permits t...

A computer program is proposed to calculate the limit states of the frameworks with the following problems: Elastic analysis, Limit analysis, First-order and second-order elastic-plastic analysis, Shakedown analysis, Optimization-Limit, Optimization-Shakedown have been realised by Nguyen-Dang Hung in 1980, namely CEPAO. All of these calculations ar...

This paper furthers the developments of a novel family of finite elements with smooth strains, offering remarkable properties. In the smooth strain finite element method,elements are divided into subcells. The strain at a point is written as a weighted average of the standard strain field over the element. This yields super convergent stresses, both i...

This paper mainly proposes an alternative way for numerical implementation of thin plates bending based on a new improvement of meshless method, which is combined between the standard element-free Galerkin method and one different shape functions building technique. The moving Kriging (MK) interpolation is applied instead of the traditional moving...

This paper promotes the development of a novel family of finite elements with smoothed strains, offering remarkable properties. In the smoothed finite element method (FEM), elements are divided into subcells. The strain at a point is defined as a weighted average of the standard strain field over a representative domain. This yields superconvergent...

This communication shows how the smoothed finite element method (SFEM) very recently proposed by G.R. Liu [14] can be extended to elasto-plasticity. The SFEM results are in excellent agreement with the finite element (FEM) and analytical results. For the examples treated, the method is quite insensitive to mesh distortion and volumetric locking. Mo...

A strain hardening rule for 3-D plastic-hinges is proposed in this paper. The linear strain hardening law is modelled as the expanse of the yield surface by two parameters: the effective strain and the plastic modulus. The definition of the effective strain and the method of fixing the value of plastic modulus are described. A conventional second-o...

This paper proposes a way to local buckling check according to Eurocode-3 for plastic-hinge analysis of 3-D steel frames with I-shaped sections. A useful technique for determination of stress distribution on cross-sections under axial force and bi-bending moments is proposed so that the concept of classification of cross-sections may be directly us...

This paper presents an efficient algorithm for both limit and shakedown analysis of 3-D steel frames by the kinematic method using linear programming technique. Several features in the application of linear programming for rigid-plastic analysis of three-dimensional steel frames are discussed, as: change of the variables, automatic choice of the in...

Meshless method is used for analysis of bending plates with success. Numerical results are shown.

A stabilized conforming nodal integration finite element method based on strain smoothing stabilization is presented. The integration of the stiffness matrix is performed on the boundaries of the finite elements. A rigorous variational framework based on the Hu–Washizu assumed strain variational form is developed. We prove that solutions yielded by...

The stabilized conforming nodal integration finite element method, based on strain smoothing stabilization, presented recently as the Smooth Finite Element Method (SFEM) is studied in detail. The integration of the stiffness matrix is performed on the boundaries of subcells in each finite element. A rigorous variational framework based on the Hu-Wa...

This paper presents and exercises a general structure for an object-oriented-enriched finite element code. The programming environment provides a robust tool for extended finite element (XFEM) computations and a modular and extensible system. The programme structure has been designed to meet all natural requirements for modularity, extensibility, a...

The metis element method (Hung 1978) has been applied to analyse free edge interlaminar stresses and delamination in composite laminates, which are subjected to extension and bending. The paper recalls Lekhnitskii's solution for generalized plane strain state of composite laminate and Wang's singular solution for determination of stress singularity...

We explore the tradeoffs of using an internal mesher in a XFEM code. We show that it allows an efficient enrichement detection scheme, while retaining the ability to have well- adapted meshes. We provide benchmarks highlighting the considerable gains which can be expected from a well designed architecture. The efficiency of the proposed algorithm i...

The "metis" finite element method is developed by Nguyen Dang Hung [1]. It is a special class of hybrid finite element. The unisolvent condition of the external displacement field permits to transform the integral of contour into integral of volume. This is a special class of the classic hybrid model. The present paper deals with the use the "metis...

The dual analysis is extended to meshless mehod where good results are obtained and compared with literature.

The modeling and the experimental characterization of the delamination phenomenon become an important field of design and analysis of advanced composite materials and structures. It is one of the most frequently encountered types of fracture in composite laminates due to high stress concentration at the tip of delamination crack.The present paper u...

This contribution concerns the use a new metis finite element to compute free-edge stresses under extension, bending and twisting conditions. Some examples shown the efficiency of the teniques.

The paper describes a primal–dual algorithm for shakedown analysis of structures with the use of kinematically admissible finite elements. Starting from Koiter kinematic theorem, a primal–dual optimization condition is established by adopting static terms as complementary variables. Newton-like iterations are performed to give both upper and quasi-...

This contribution concerns a mew method of global error estimation with displacement and equilibrium meshless methods. Some numerical examples illustrate the results.

This contribution describes the use of a metis finite element to simulate directly or indirectly edge delamination in laminates. Numerous numerical examples illustrate the good results compared to the former ones

The aim of this paper is to analyze the fatigue growth of cracks under cyclic loading conditions. The propagation is modeled by successive linear extensions, which are determined by the stress intensity factors (SIFs) obtained after a linear elastic analysis. We use a meshless method to perform the successive analyses. A new contribution of this pa...

A special form finite element technique is presented for the calculation of displacement and stress field of cracked (or uncracked) plates and shells. The method based on a particular set of hybrid displacement finite element, namely “Metis elements”. Several numerical examples are considered to evaluate the performance of this model. For cracked p...

The meshless method is particularly appropriate to solve crack prop-agation problems. In this paper, the fatigue growth of cracks in two-dimensional bodies is considered. The analysis is based upon Paris' equa-tion. New enriched weight functions are introduced in the meshless method formulation to capture the singularity at the crack tip. Simple pr...

Shakedown analysis with the discretization in kinematically admissible finite elements and the use of von Mises yield criterion is considered in this paper. The shakedown load multiplier formulated by kinematic theorem under nonlinear form is proved to be the primal form of the shakedown load multiplier formulated by static theorem. Based on this d...

The paper describes the duality in limit and shakedown analysis of structures. Starting from Koiter's kinematic theorem, the primal-dual optimization condition is established by adopting static terms as complementary variables. A highly effective algorithm is developed with the use of displacement-based finite elements. Newton-like iterations are p...

The Commission of the European Communities has supported the LISA project on Limit and Shakedown Analysis for industrial use, which connects direct methods of plasticity with stochastic methods of structural reliability in a general purpose Finite Element package. There was no commercial Finite Element Code that could perform either of this kind of...

A conformable and convergent finite element technique is presented for calculation of stress intensity factors for cracked plate membrane problem, which is based on the formulation of the hybrid displacement finite element method, named "Metis elements". In order to achieve a high convergence, this element is combined with an isoparametric element...

This lecture concerns a numerical tool useful for the calculation of three-dimensional crack propagation by finite element method: the fissbox. The new tool renders the 3D meshing around a crack more direct and fast.

This contribution describes an analysis of uncracked and cracked plate bending problem using metis finite element model. It appears that this new metis finite element brings back very precise results in term of stresses and stress intensity factors

This contribution describes the investigating of three kind of plane contact problem by penalty method. Numerical examples are shouwn.

A meshless method to solve elastostatic problems based on an equilibrium model is presented. This means that the equilibrium and constitutive equations are satisfied a priori and that the approximation only concerns the compatibility equations. The application of this method together with the classical displacement meshless method leads to upper an...

This lecture describes the modeling of the interactions between interlocking blocks, soil and water of pitched dike revetment using SAMCEF software.

A new body integration technique is presented and applied to the evaluation of the stiffness matrix and the body load vector of elastostatic problems obtained by a meshless method. It does not rely on a partition of the integration domain into small cells, but rather on a partition of unity by a set of moving least squares shape functions each defi...

This contribution concerns the determination of the toughness of the quasi-3D structure by using the metis finite element mode. Various numerical examples illustrate the results

This contribution concerns the limit analysis of 2D curved beams by linear optimisation programming Numerical examples are shown and compared with literature.

A finite-element model is proposed for mixed-mode delamination of composites which takes into account R-curve effects like fibre bridging at cracked interfaces or plastic deformation at crack tips. An elastic/ideal-plastic damage model is used to describe the initiation and propagation of interfacial cracks. The laminate is modelled as a set of mon...

The lecture describes an incremental plasticity limit of structures subjected to variable loading. Numerical examples illustrate the results.

This contribution concerns the finite element modelling of delamination of laminated composites. Various numerical results illustrate the efficiency of the method.

A new dual shakedown analysis of structures is presented. Finite elelment method and non linear techniques are used. Various numerical examples are shown.

This contribution concerns the Initiation and propagation of mixed-mode interlaminar cracks in composite samples. Numerical results are illustrated.

This paper describes a direct shakedown analysis of structures subjected to variable thermal and mechanical loading. The classical kinematical shakedown theorem is modified to be implemented with any displacement-based finite elements. The plastic incompressibility condition is imposed by the penalty function method. The shakedown limit is found vi...

Damage models based on imperfect interface and steady-state R-curve concepts are proposed to describe the development of delamination mechanisms in laminated composites. Different energy absorbing sources are taken into account: (i) an intrinsic fracture toughness resulting from actual adhesion bonding at interfaces, and (ii) additional energy diss...

This contribution concerns the description of a software using boundary element method for general solutions od 3D elastic solids. This software is written in such a way that useful memory is restricted and it may run easily on personal computer.

A new truly meshless Galerkin method is implemented to get numerical results for elastic plane structures

This contribution presents a very general isoparametric metis displacement element which gives very good performance in term of convergence and the stability of the numerical solutions.

This contribution concerns the 3D slope stability analysis by direct boundary element method. Some numerical examples illustrate the results.

This contribution presents a method for the prevision of ceramic pieces after drying and firing. Finite element technique is used. Some numerical examples are shown

This contribution describes the simulation,computation of mattress of placed blocks for pitched slope protection by SAMCEF-MECANO software. This structure of concrete blocks freely connected together to form a carpet is very efficient in protection of beach and shore.

The R-curve effects in delamination damage mechanism is simulated via special finite elements

The present report introduces the use of numerical limit analysis in ductile fracture mechanics. Limit analysis is a structural mechanics method, which finds increasing application in engineering fracture mechanics. Emphasis is put on possible improvements in the integrity assessment of crack containing components which may be achieved by combining...

A numerical procedure with interface finite elements has been carried out in order to investigate the influence of imperfect interlaminar interfaces on the local mechanical behaviour of composite laminates. By modelling laminates at a mesoscopic scale, interlaminar interfaces are clearly represented and the effects of interfacial imperfections are...

Theoretical and numerical methods of limit and shakedown analysis are presented for the applications of shell and pipe structures under mechanical and thermal loading. Kinematical upper bound method and its numerical implementation are developed. Simplified shakedown analysis is proposed in absence of thermal loading. The numerical results of shell...

Theoretical and numerical methods of limit and shakedown analysis are presented for the applications to shell and pipe structures under mechanical and thermal loading. The kinematical theorem and its numerical implementation are developed. A method of simplified shakedown analysis is proposed. The numerical results for shell and pipe structures are...

A numerical analysis with interface finite elements has been carrried out to investigate the effects of imperfect interlaminar interfaces on the overall mechanical behaviour of composite laminates. The laminate is modelled as a set of monolayers separated by zero thickness adhesive interfaces. Across each interface, interlaminar tractions remain co...

Limit analysis of cracked structures using mathematical programming and finite element method is presented. This direct algorithm is based on a proposition of the modified Markov variational principle. The obtained upper bound formula is applicable with any kinematic admissible finite elements. The regularization of plastic dissipation function is...

In this paper a practical limit load estimating procedure is proposed for general pipe-elbow structures subjected to complex loading (in-plane and out-of-plane bending, internal pressure and axial force). The explicit calculating formulae are presented on the basis of theoretical analysis combined with numerical simulation. Von Mises' yield criteri...

In this paper, we present a new pipe elbow element based on a previous simplified model proposed by Bathe and Almeida [1, 2] and modified by Militello and Huespe [3]. It is really a beam-type element but it describes the ovalization, warping, radial expansion and non-symmetric deformation of cross-section of curved pipe with Fourier series. Therefo...

Interface finite element are introduced for the computation of Delamination of multi-layered composites by interface finite elements. Various examples illustrate the good results.

Computation of shakedown loads under variable thermal and mechanical laodings

Kinematic formulation of shakedown analysis is implemented to obtaine the upper bounds of shakedown limit loads. Various numerical examples are shown and compared with the literature.

Limit analysis of cracked structures are examined using finite element method and mathematical programming

This contribution indicates the influence of the internal effect particularly the internal pressure on the limit load of elbows. Numerical simulation are obtained by an sophisticate elbow finite element

This contribution concerns the collapse load computation of pipe and shells by finite element method and mathematical programming technique. Some examples illustrates the good results of the method.