Abstract: Presents a fully coupled numerical model to simulate the slow transient phenomena involving heat and mass transfer in deforming partially saturated porous materials. Makes use of the modified effective stress concept together with the capillary pressure relationship. Examines phase changes (evaporation‐condensation(, heat transfer through conduction and convection, as well as latent heat transfer. The governing equations in terms of gas pressure, capillary pressure, temperature and displacements are coupled non‐linear differential equations and are discretized by the finite element method in space and by finite differences in the time domain. The model is further validated with respect to a documented experiment on partially saturated soil behaviour, and the effects of two‐phase flow, as compared to the one‐phase flow solution, are analysed. Two other examples involving drying of a concrete wall and thermoelastic consolidation of partially saturated clay demonstrate the importance of proper physical modelling and of appropriate choice of the boundary conditions.

Abstract: Considers the problem of stability of the enhanced strain elements in the presence of large deformations. The standard orthogonality condition between the enhanced strains and constant stresses ensures satisfaction of the patch test and convergence of the method in case of linear elasticity. However, this does not hold in the case of large deformations. By analytic derivation of the element eigenvalues in large strain states additional orthogonality conditions can be derived, leading to a stable formulation, regardless of the magnitude of deformations. Proposes a new element based on a consistent formulation of the enhanced gradient with respect to new orthogonality conditions which it retains with four enhanced modes volumetric and shear locking free behaviour of the original formulation and does not exhibit hour‐glassing for large deformations.

Abstract: Focuses on the inverse problems arising from the simulation of forming processes. Considers two sets of problems: parameter identification and shape optimization. Both are solved using an optimization method for the minimization of a suitable objective function. The convergence and convergence rate of the method depend on the accuracy of the derivatives of this function. The sensitivity analysis is based on a discrete approach, e.g. the differentiation of the discrete problem equations. Describes the method for non‐linear, non‐steady‐state‐forming problems involving contact evolution. First, it is applied to the parameter identification and to the torsion test. It shows good convergence properties and proves to be very efficient for the identification of the material behaviour. Then, it is applied to the tool shape optimization in forging for a two‐step process. A few iterations of the inverse method make it possible to suggest a suitable shape for the preforming tools.

Abstract: Investigates the efficiency of hybrid solution methods when incorporated into large‐scale topology and shape optimization problems and to demonstrate their influence on the overall performance of the optimization algorithms. Implements three innovative solution methods based on the preconditioned conjugate gradient (PCG) and Lanczos algorithms. The first method is a PCG algorithm with a preconditioner resulted from a complete or an incomplete Cholesky factorization, the second is a PCG algorithm in which a truncated Neumann series expansion is used as preconditioner, and the third is a preconditioned Lanczos algorithm properly modified to treat multiple right‐hand sides. The numerical tests presented demonstrate the computational advantages of the proposed methods which become more pronounced in large‐scale and/or computationally intensive optimization problems.

Abstract: Presents a modular method for obtaining either a quick or a precise calculation for three‐dimensional structure assemblies with local non‐linearities, such as unilateral contact with friction, or technological components, such as prestressed bolt joints. An iterative method, including a domain‐decomposition technique, is proposed to solve such quasi‐static problems in small perturbations. Two types of entities are introduced: sub‐structures and interfaces. A local and a global stage are successively carried out by an iterative algorithm until convergence. The linear problem in the global stage is solved by a FEM (3D case) or by another approach using Trefftz functions (2D axisymmetrical case). Applications developed with AEROSPATIALE‐Les Mureaux are presented and concern the study of structure joints with different types of flanges.

Abstract: Liquefaction phenomenon and its catastrophic nature can be analysed as a particular material behaviour of granular media under certain loading paths. Proposes a definition of liquefaction and its modelling by constitutive relations. Discusses this modelling in relation to the questions of stability and uniqueness. Considers the signs of three scalar quantities: the work of second order, the determinant of the symmetric part of the tangent constitutive tensor and the determinant of the tensor itself. Concludes that the liquefaction path is situated inside a potentially unstable domain and that in some cases this path reaches some states of loss of uniqueness, which are essentially bifurcation points.

Abstract: Presents a finite element formulation of hot isostatic pressing (HIP) based on a continuum approach using thermal‐elastoviscoplastic constitutive equations with compressibility. The formulation takes into consideration dependence of the viscoplastic part on the porosity. Also takes into account the thermomechanical response, including nonlinear effects in both the thermal and mechanical analyses. Implements the material model in an implicit finite element code. Presents experimental procedures for evaluating the inelastic behaviour of metal powders during densification and experimental data. Chooses the simulation of the dilatometer measurement of a cylindrical component during HIP and manufacturing simulation of a turbine component to near net shape (NNS) as a demonstrator example. Both components are made of a hot isostatically pressed hot‐working martensitic steel. Compares the result of the simulation in the form of the final geometry of the container with the geometry of a real component produced by HIP. Makes a comparison between the calculated and measured deformations during the HIP process for the cylindrical component. Measures the final geometry of the turbine component by means of a computer controlled measuring machine (CMM). Performs the complete process from design and simulation to geometry verification within a computer‐aided concurrent engineering (CACE) system.

Abstract: Presents a range of numerical results obtained from the geometrically nonlinear analysis of a cantilevered cylindrical shell. Shows that, while the fine‐mesh solution involves no limit points, as the mesh is coarsened, an increasing series of “false limit points” is encountered.

Abstract: DYNROT is a code based on the finite element method which is intended to perform a complete study of the dynamic behaviour of rotors. Although initially designed to solve the basic linear rotordynamic problems (Campbell diagram for damped or undamped systems, unbalance response, critical speeds, static loading), it can be used for the study of non‐stationary motions of nonlinear rotating systems and for the torsional analysis of rotors and reciprocating machines. Explains that one of the distinctive features of the code is the use of complex co‐ordinates, both for isotropic and non‐symmetric systems. Makes extensive use of complex arithmetics in all parts of the analysis. Applies the modal approach in some of the solution routines to increase the efficiency of the computation or to compute an equivalent viscous damping in those cases where hysteretic damping cannot be introduced directly to the model. The dynamics of bladed discs is included in the code.

Abstract: Studies the effect of parameters controlling the biological growth method by applying it to the classical optimization problem of a plate with a central hole under biaxial stress state. It has been found that the optimization character of the method depends strongly on the so‐called reference stress. Depending on the magnitude of this parameter either a local or global optimum is approached. A global optimum corresponds to the minimum possible v. Mises stress along the hole boundary (and hence in the plate), whereas a local optimum presents the modified shape of the hole yielding an uniform stress distribution whose magnitude is larger than the minimum possible value and which is equal to the specified reference stress. The magnification factor applied to the iterative displacement results influences the optimization speed. Too large factors lead to divergence of the solution. Furthermore, it has been found that the dimension of the optimization domain has a critical effect on the optimization result.

Abstract: Describes the development of a dynamic‐explicit type finite‐element formulation based on elastic/crystalline‐viscoplastic theory to predict the dynamic forming limits of sheet metal. Formulates an evolution equation governing all the slip stages of a single crystal, by modifying Pierce and Bassani’s crystalline plasticity models. Interprets precisely the experimentally observed hardening evolution. Takes account of the importance of the strain rate and temperature sensitivity of the material in predicting dynamic plastic instability. Analyses the deformation and strain localization in a rectangular sheet under stretching, in relation to the plane strain assumption, using the numerical results to demonstrate the influences of tension force and temperature on strain localization, and to show the temperature dependence of shear band formation. Demonstrates that the deviation of tension direction from the axis of symmetry of a single crystal causes non‐simultaneous sliding between primary and conjugate slip systems, resulting in S‐shaped non‐symmetrical deformation.

Abstract: Argues that the dynamic‐explicit approach has in recent years been successfully applied to the solution of various quasi‐static, elastic‐plastic problems, especially in the metal forming area. A condition for the success has, however, been that the problems have been displacement‐driven. The solution of similar force‐driven problems, using this approach, has been shown to be much more complicated and computationally time consuming because of the difficulties in controlling the unphysical dynamic forces. Describes a project aiming to develop a methodology by which a force‐driven problem can be analysed with similar computational effort as a corresponding displacement‐driven one. To this end an adaptive loading procedure has been developed, in which the loading rate is controlled by a prescribed velocity norm. Presents several examples in order to exhibit the merits of the proposed procedure.

Abstract: Using examples of flexible mechanisms, demonstrates that while the Newmark method is unstable for nonlinear dynamics, time step refinement could in some cases lead to even earlier onset of instability in the form of a blown‐up response. As a remedy, develops a plane finite beam element based on the Simo‐Vu Quoc formulation for dynamics and integrates it with an energy‐conserving midpoint time‐stepping rule for solving problems in nonlinear dynamics. Shows that this combination produces a consistently stable and accurate dynamic analysis method even for large time steps.

Abstract: Using finite element (FE) method corrects the microstress field resulting from the theory of homogenization in the region of composite in vicinity of the boundary. Obtains the corrected microstress field via an unsmearing procedure based on the known global solution and local peturbation. Analyses two examples: near a free boundary and next to a constrained border. FE models are constructed using both commercial FE code and the authors’ program for homogenization with some interfacing procedures. Shows qualitative results of computations and estimates influence on the microstress description of the local perturbation near the boundary.

Abstract: Describes the development of a dynamic‐explicit finite‐element simulation code based on anisotropic elastic‐plastic theory and non‐linear contact friction theory. Points out that whereas in industrial production the dynamic‐explicit finite‐element code has proved to be an efficient and robust tool for sheet metal forming, in the automobile industry sheet metal forming is usually a quasi‐static process; therefore seeks to make clear the dynamics of deformation and strain and to evaluate mass scaling, damping scaling and material viscosity scaling parameters. Introduces the penalty method and the kinematic description method as means to derive a rate‐type contact force formulation employing the four‐node degenerated shell finite element. Also introduces the jewely patch scheme to describe the tool geometry. Analyses the hemispherical punch deep‐drawing of a square plate and compares this with the experimental results. Confirms the applicability of the newly developed finite‐element code to the quasi‐static forming process.

Abstract: Two‐noded curved beam elements, CMLC and IMLC, are developed on the basis of Timoshenko’s beam theory and curvilinear co‐ordinates. These elements are developed by the separation of the radial displacement into the bending and the shear deflection and the projection of the shear deflection into bending deflection. In the CMLC element, field‐consistent membrane strain interpolation is adapted for removing the membrane locking. The CMLC element shows the rapid and stable convergence on the wide range of radius, thickness and length of the curved beam. The field‐consistent membrane strain and the separation of radial displacement produce the most efficient linear element possible.

Abstract: Uses a rigid viscoplastic formulation to simulate hot and cold forging processes. The finite element solution uses mixed methods in which the independent variables can be velocities, pressures and deviatoric stresses. Uses interface elements both in the mechanical and the thermal analysis, to take into account the effects of contact and friction, thermal conductivity of lubricants and heat generated by friction. The code developed includes an adaptive mesh refinement, triggered by an error estimator based on energy norms evaluated from nodal stress values, recovered from a local continuous polynomial expansion, and those given by the numerical solution. Assesses the code developed, using experimental results.

Abstract: Presents a computational algorithm for the numerical integration of triaxial concrete plasticity formulations. The specific material formulation at hand is the so‐called extended leon model for concrete. It is based on the flow theory of plasticity which entails isotropic hardening as well as fracture energy‐based softening in addition to non‐associated plastic flow. The numerical algorithm resorts to implicit integration according to the backward Euler strategy that enforces plastic consistency according to the closes‐point‐projection method (generalized radial‐return strategy). Numerical simulations illustrate the overall performance of the proposed algorithm and the significant increase of the convergence rate when the algorithmic tangent is used in place of the continuum operator.

Abstract: The non‐isothermal filling of a powder/binder mixture in metal injection moulding is simulated by the viscoplastic and the heat conduction finite element methods. Proposes a simplified three‐dimensional scheme for the moulding of products with a non‐uniform thickness distribution. The computing time for the simplified three‐dimensional scheme is of the same order as that for two‐dimensional problems. Deals with complex overlapping between the surfaces of the mixture, resulting from the occurrence of jetting during the moulding, by the use of a remeshing scheme. The material flow in metal injection moulding into a rectangular die with a linear thickness distribution is simulated. The jetting behaviour is remarkably influenced by the thickness distribution of the die.

Abstract: Presents an approach for optimal design of geometrically non‐linear structures, using adaptive mesh refinement (AMR). The optimization technique adopted is based on the multi‐point approximation method. The finite element method is used for the structural analysis. Reformulation of the optimal design problem is applied to circumvent complications caused by the non‐linear behaviour of the structure. The latter may lead to bifurcations, limit points and/or significant reduction of the structural stiffness for individual intermediate designs generated by an optimization algorithm. Discretization errors are controlled using AMR. To reduce computational costs, the requested global and local discretization errors are not taken as fixed values but are specified on the basis of the current status of the optimization process. In the beginning relatively large errors are accepted, while as the process progresses discretization errors are reduced. The method is applied to thin‐walled structures with geometrically non‐linear behaviour.

Abstract: Addresses the computational aspects involved in the numerical simulation of sheet stamping processes. Focuses on some numerical aspects of the intrinsic complexity of these problems, the first of which is the necessity to take into account properly membrane and bending effects. Presents a well‐adapted shell element. The second aspect concerns the description and the implementation of the initial orthotropic plastic behaviour for sheet metal parts, based on a formulation in a rotating frame using the initial microstructure rotation. The stress calculation algorithm is based on a particular implementation of the elastic predictor‐plastic corrector method. The last aspect concerns the solution procedures with a particular development concerning the treatment of the blankholder load as a constraint. A set of computational results validated with experiments prove the accuracy of the proposed approach in solving stamping problems.

Abstract: Presents a new B‐spline finite element for the dynamic analysis of unsymmetrical sandwich shells of revolution. The formulation takes account of the membrane and bending effects in isotropic or orthotropic elastic facings, and membrane, bending and transverse shearing effects in an isotropic or othotropic elastic core. Both geometry and local displacements are interpolated by a set of B‐spline functions. The main aspects added by the sandwich structure of the element are the transverse shearing and membrane‐bending coupling effects in the core. These are well represented by a set of new variables which are the mean end relative in‐plane displacements of the facing middle surfaces. Together with the transverse displacement, these variables constitute the degrees of freedom (dofs) of this new B‐spline sandwich element. The finite elements are grouped into super‐elements with C1 continuity to obtain the whole finite element model. For each super‐element a total of five dofs per node is then obtained except f...

Abstract: Describes the thermo‐mechanical consolidation coupling analysis and its discretization method for the simulations of nuclear waste storage on jointed rock mass using the finite element method. An anisotropic stress‐strain and permeable constitutive laws are employed for combining arbitrary oriented joint sets using compliance matrices. Evaluates the influence of non‐linear permeability of joint by cubic‐law assuming parallel plate flow caused by excavation and the local change of permeability around the excavated cavern in different joint angles. The results of the two‐dimensional rock mass models with combining arbitrary oriented joint sets show that the fluid flow direction followed along the direction of the joint sets, and this seemed to be clearly explained from the influence of joint orientations.

Abstract: Presents a pseudo‐elastic approach to topological optimization. In comparison with the well‐known homogenization method for topological optimization it is not based on a micro‐cellular structure, but approximates the elastic properties directly. A characteristic difficulty of these methods is the birth of new inner boundaries: thinning out the material can be interpreted as reducing the density of a composite micro‐structure, but eventually this process can result in a bubble with zero‐density. Therefore, the bubble‐method is a valuable asset to topological optimization, which helps to overcome this difficulty.

Abstract: In an arbitrary assembly of triangles or tetrahedra there is often a requirement to recover or construct edges or triangles which are formed by the connections between nodes. Such is the case in computational methods where grids of triangles or tetrahedra must conform to prespecified boundaries. Discusses general techniques which can be applied to recover edges and triangles within unstructured assemblies of triangles and tetrahedra. The methods described involve the intersection of the required edges and triangles with other nodes, edges, triangles and tetrahedra and then locally performing transformations of the element connectivities. The method is applied to the recovery of fixed boundary triangles for finite element meshes and to the construction of multidomains within unstructured grids. Several applications of the method are given to real practical problems.

Abstract: Based on the asymptotic solution for predicted natural frequencies of a two‐dimensional elastodynamic problem from the finite element analysis, presents the concept of the asymptotic error, which is an approximate error but tends to the exact error when the characteristic length of elements approaches zero, and a practical error estimator. The present practical error estimator contains two criteria: one is the error estimator criterion, the other the finite element mesh design criterion. Using this practical error estimator, not only can the accuracy of a finite element solution for natural frequencies of a two‐dimensional elastodynamic problem be directly evaluated without any further finite element calculation, but also a new target finite element mesh for the desired accuracy of solution can be immediately designed from the relevant information of an original finite element solution. Generally, for the purpose of designing a new target finite element mesh, this original finite element solution is obtainable from a very coarse mesh of a few elements and usually does not satisfy the accuracy requirement. Since the new target finite element mesh could result in a finite element solution with a desire accuracy, the finite element solution so obtained can be used for a structural design in engineering practice. The related numerical results from vibration problems of three representative plates of different shapes under plane stress conditions have demonstrated the correctness and applicability of the present practical error estimator.

Abstract: Presents the natural frequencies and vibration mode shapes of curved panels with variable thickness by using the transfer matrix method. The transfer matrix is derived from the non‐linear differential equations for the curved panels with variable thickness, by using the Fourier series expansions in the longitudinal direction and then applying a numerical integration in the circumferential direction. Investigates the accuracy and convergence characteristics of this method and examines the influences of cross‐section thickness variation on the natural frequencies and mode shapes of curved panels with variable thickness.

Abstract: Describes the development of a static‐explicit type finite‐element formulation based on non‐linear elastic plastic shells, non‐linear contact friction and Barlat anisotropic plasticity with modified corner theory. Newly introduces the spin of the anisotropic axes as a means of deriving the objective stress rate. Demonstrates that a C0 continuous shell is an efficient finite element for large‐scale computation. Uses membrane shell theory to derive a kinematic description of the external contact force. Offers an explanation of the ways in which the material, press load and lubrication affect the deformation and strain localization in the automotive sheet metal forming process. Demonstrates a trial of virtual manufacturing incorporating finite‐element simulation, a visualized inspection system and a heuristic process optimization scheme.

Abstract: Draws a comparison between the use of a genetic algorithm and the sequential function specification method for the solution of a one‐dimensional linear inverse thermal field problem, based on the use of noisy measurements. In solving this problem aims to estimate the value of a single constant convective heat transfer coefficient. Documents the findings that both approaches can provide estimates within 1 per cent of the target solution and that the sensitivity and robustness of each approach to measurement location, time step size and measurement errors are markedly different.