Alfredo Edmundo Huespe

Thermomechanical model of a continuous casting process

A model for the analysis of thermal stresses arising at the early stage of a continuous casting process is proposed. The model is used to simulate the casting of round billets assuming axial symmetry. Thermal analysis takes into account phase-change in the material and heat transfer through the mould. The heat balance equation is solved using an Eulerian formulation for the billet domain, while the mould is analyzed using a Lagrangian one. Heat transfer from billet to mould is simulated assuming non-linear heat conduction through the air gap formed between them. Air conductivity is taken as a function of temperature. Two mechanical models are built assuming elastoplastic and viscoplastic hardening materials. Both Lagrangian and Arbitrary Lagrangian Eulerian (ALE) techniques have been implemented and compared. In the latter, advection of the history-dependent material parameters is taken into account using an appropriate finite volume integration scheme. Stresses and strains obtained with both models are compared, showing a good agreement.

Phasewise numerical integration of finite element method applied to solidification processes

Abstract Phase change is a very complex physical phenomenon that governs a lot of industrial situations. Due to the inherent difficulties that arise in manufacturing activities they need a numerical treatment using models to predict the behavior of the different phases involved in the process. Historically, solidification problems were solved considering only the solution of an energy balance with isothermal phase change including conduction and or convection in the material. Nowadays computational fluid dynamics is becoming a well-suited numerical technique to investigate all kind of transport phenomena, especially when coupled fields are involved. This trend has addressed the research in solidification problems towards the solution of models combining incompressible Navier–Stokes equations coupled with heat and mass transfer including phase change. In this paper we present a phasewise discontinuous numerical integration method to solve thermal phase change problems in a fast and accurate way. Moreover, this methodology was extended to coupled fluid flow and energy balance equations with success and in a future work we will apply to binary alloy solidification with macrosegregation.

Visco-plastic constitutive models of steel at high temperature

Abstract Two constitutive elasto-visco-plastic models are adopted to simulate the behavior of plain carbon steel at high temperature, specifically at the austenitic range (950–1300°C), being particularly appropriate for the numerical simulation of casting and hot-working processes. The response in hardening, creep and non-uniform loading conditions is analyzed and compared with experimental data. An efficient numerical integration scheme is proposed and its accuracy is evaluated using iso-error maps. The consistent isothermal tangent matrix is computed and the final models are implemented into an FEM code. Several tests are performed to evaluate the accuracy and robustness of the integration scheme. Finally an application concerning the analysis of the thermal stresses produced at the early stage of a steel continuous casting process is shown.

Continuation methods for tracing the equilibrium path in flexible mechanism analysis

Presents an implementation of continuation methods in the context of a code for flexible multibody systems analysis. These systems are characterized by the simultaneous presence of elastic deformation terms and rigid constraints. In our formulation, the latter terms are introduced by an augmented Lagrangian technique, resulting in the presence of Lagrange multipliers in the set of unknowns, together with displacement and rotation associated terms. Essential aspects for a successful implementation are discussed: e.g. the selection of an appropriate metric for computing the path following constraint, a flexible description of control parameters which accounts for conservative and nonconservative loads, imposed displacements and imposed temperatures (dilatation effects), and the inclusion of second order derivatives of rigid constraints in the Jacobian. A large set of examples is presented, with the objective of evaluating the numerical effectiveness of the implemented schemes.

Crack Models with Embedded Discontinuities

This chapter presents a methodological approach for modeling concrete crack problems based on continuum constitutive relations and strong discontinuity kinematics. Fundamental aspects of this approach are presented in the initial Sections 1–2. The topics and ideas discussed in those points follow closely the work of Oliver (2002). A Finite Element technique with embedded strong discontinuities, particularly adapted for this methodology, is shown in Section 3. In the final Sections 4–6, some algorithmic aspects and several applications of the approach are addressed.

Stabilized Mixed Finite Elements With Embedded Strong Discontinuities for Shear Band Modeling

A stabilized mixed finite element with elemental embedded strong discontinuities for shear band modeling is presented. The discrete constitutive model, representing the cohesive forces acting across the shear band, is derived from a rate-independent J 2 plastic continuum material model with strain softening, by using a projection-type procedure determined by the Continuum-Strong Discontinuity Approach. The numerical examples emphasize the increase of the numerical solution accuracy obtained with the present strategy as compared with alternative procedures using linear triangles.

Continuum Approach to Computational Multi-Scale Modeling of Fracture

This paper presents a FE2 multi-scale framework for numerical modeling of the structural failure of heterogeneous quasi-brittle materials. The model is assessed by application to cementitious materials. Using the Continuum Strong Discontinuity Approach (CSD), innovative numerical tools, such as strain injection and crack path field techniques, provide a robust, and mesh-size, mesh-bias and RVE-size objective, procedure to model crack onset and propagation at the macro-scale.

Evolving Material Discontinuities: Numerical Modeling by the Continuum Strong Discontinuity Approach (CSDA)

The CSDA, as a numerical tool for modeling evolving displacement discontinuities in material failure problems, is addressed. Its specific features are: a) the explicit use of a (regularized) strong discontinuity kinematics, b) the introduction of the material failure constitutive model in a continuum (stress-strain) format, and c) the determination of the onset and propagation of the discontinuity by means of constitutive model material bifurcation analysis. Numerical applications to concrete failure and soil collapse problems are presented.

Model Order Reduction in computational multiscale fracture mechanics

Nowadays, the model order reduction techniques have become an intensive research eld because of the increasing interest in the computational modeling of complex phenomena in multi-physic problems, and its conse- quent increment in high-computing demanding processes; it is well known that the availability of high-performance computing capacity is, in most of cases limited, therefore, the model order reduction becomes a novelty tool to overcome this paradigm, that represents an immediately challenge in our research community. In computational multiscale modeling for instance, in order to study the interaction between components, a di erent numerical model has to be solved in each scale, this feature increases radically the computational cost. We present a reduced model based on a multi-scale framework for numerical modeling of the structural failure of heterogeneous quasi-brittle materials using the Strong Discontinuity Approach (CSD). The model is assessed by application to cementitious materials. The Proper Orthogonal Decomposition (POD) and the Reduced Order Integration Cubature are the pro- posed techniques to develop the reduced model, these two techniques work together to reduce both, the complexity and computational time of the high-delity model, in our case the FE2 standard model

Crack path field and strain injection techniques in dynamic fracture simulations

Dynamic fracture phenomena are studied employing low cost computational tools based on Finite Elements with Embedded strong discontinuities (E-FEM). Fracture nucleation and propagation are accounted for through the injection of discontinuous strain and displacement modes inside the finite elements. The Crack Path Field technique is employed to compute the trace of the strong discontinuity during fracture propagation. Unstable crack propagation and crack branching are observed upon increasing loading rates. The variation in terms of crack pattern and energy dissipation is studied and a good correlation is found between the maximum experimental crack speed and maximum dissipation at the onset of branching. Comparable results are obtained against simulations employing supraelemental techniques, such as phase-field and gradient damage models, considering coarser discretizations which can differ by two orders of magnitude.