J. M. A. Cesar de Sa

University of Porto | UP · Departamento de Engenharia Mecânica

Directed Energy Deposition (DED) is crucial in additive manufacturing for various industries like aerospace, automotive, and biomedical. Precise temperature control is essential due to high-power lasers and dynamic environmental changes. Employing Reinforcement Learning (RL) can help with temperature control, but challenges arise from standardizati...

The continuous evolution of metallic alloys in the automotive industry has led to the development of more advanced and flexible constitutive models that attempt to accurately describe the various fundamental properties and behavior of these materials. These models have become increasingly complex, incorporating a larger number of parameters that re...

Despite extensive studies on material models for fracture applicable to homogenous materials, the demand for advanced numerical methods to predict the failure in multi-materials and functionally graded materials (FGMs) remains substantial. This study aims to address this gap by using a phase-field approach for analyzing crack development and ductil...

During the last decades, metal additive manufacturing (AM) technology has transitioned from rapid prototyping application to industrial adoption owing to its flexibility in product design, tooling, and process planning. Thus, understanding the behavior, interaction, and influence of the involved processing parameters on the overall AM production sy...

Duplex Stainless Steels (DSS) and Super Duplex Stainless Steels (SDSS) processed by casting are still poorly characterized when compared with wrought routes, nevertheless, they are largely used in industry, especially in the fabrication of complex components for highly corrosive environments. Therefore, there is an urge for improving data collectio...

Despite many advantages of metallic additive manufacturing technology (AM), the difficulties in fully observing and modeling the complex nature of the process prevent its wide implementation in different industry sectors. There have been significant efforts during the last decade to develop reliable models to predict temperature field, melting stag...

Aortic aneurysm is a cardiovascular disease related to the alteration of the aortic tissue. It is an important cause of death in developed countries, especially for older patients. The diagnosis and treatment of such pathology is performed according to guidelines, which suggest surgical or interventional (stenting) procedures for aneurysms with a m...

In this work, the utilization of a phase-field ductile fracture model in the failure analysis of advanced steels is investigated. The importance of advanced steels is potentially proven, for instance in automotive industry, due to its light weight, which entails the crucial role of fracture analysis in these structures. A third generation advanced...

The latest demands in reduction of emissions compel the automobile industry to lighten the structure of vehicles using third generation advanced high strength steels. Due to the novelty of these steels, there is a need to characterize its fracture behavior during the forming process. This paper presents a study of strain field, crack locus and inst...

This study presents a microstructural model applicable to additively manufactured (AM) austenitic SS 316L components fabricated via a direct energy deposition (DED) process. The model is primarily intended to give an understanding of the effect of microscale and mesoscale features, such as grains and melt pool sizes, on the mechanical properties of...

In an effort to simulate the involved thermal physical effects that occur in Directed Energy Deposition (DED) a thermodynamically consistent phase-field method is developed. Two state parameters, characterizing phase change and consolidation, are used to allocate the proper material properties to each phase. The numerical transient solution is obta...

Feature selection is an important step to reduce the complexity of a dataset and decrease the required computational time to classify a sample. There are plenty of methods used in Machine Learning (ML) serially falling into the categories of supervised and unsupervised. Some of the commonly known unsupervised methods are K-mean, the simplest one, a...

Portugal This study adopts a computational framework to predict temperature and phase changing histories of additive manufacturing (AM) direct energy deposition (DED) processes. Based on recent literature [1-2], the main goal of the study is to focus on the modelling of the heating, melting and solidification of laser track(s) during the building p...

In an effort to simulate the involved thermal physical effects that occur in direct energy deposition (DED) a thermodynamically-consistent of phase-field method is developed. Two state parameters, characterizing phase change and consolidation, are used to allocate the proper material properties to each phase. The numerical transient solution is obt...

Continuum Damage Mechanics is successfully employed to describe the behaviour of metallic materials up to the onset of fracture. Nevertheless, on its own, it is not able to accurately trace discrete crack paths. In this contribution, Continuous Damage Mechanics is combined with the XFEM and a Cohesive Law to allow the full simulation of a ductile f...

The numerical assessment of the crack development in structures subjected to plastic deformations using a phase-field approach is investigated in the present study. By relying on distinctive features of phase-field diffusive crack concept, a recently-developed iterative staggered algorithm is employed for implementation of the overall system of equ...

Experimental and numerical study regarding the uniaxial tensile test and the forming limit diagram are addressed in this paper for AL2024 with the face-centered cube structure. First, representation of a grain structure can be obtained directly by mapping metallographic observations via scanning electron microscopy approach. Artificial grain micro-...

A numerical analysis based on associated flow rule (AFR) and non-AFR is presented and applied to anisotropic sheet metals. The models are defined in the quadratic form of the Hill’48 anisotropic function under a general three-dimensional stress condition. The anisotropic parameters for the yield function are identified using the directional planar...

Chemical, physical, thermal, and mechanical behavior of complex alloys, such as super-duplex stainless steels (SDSS), is largely dependent on the characteristics of its multiphase microstructure which is controlled by chemical composition and cooling rate in the temperature range of 1000 to 300 ℃. During solidification, a microstructure composed of...

The plastic deformation included in the technological processes of sheet metal forming allows the production of different components with different geometries. Therefore, the formability of metallic materials is an essential feature in stamping processes. One of the inevitable scattering sources when considering these processes is the variability o...

The present contribution addresses the micromechanical and thermal analysis of directed energy deposition (DED)-manufactured, stainless steel 316L components by utilizing experimental and numerical analyses. It has been established that a combination of controlling process parameters, manufacturing environment and microstructural anisotropies could...

Additive manufacturing (AM) of metals proved to be beneficial in many industrial and non-industrial areas due to its low material waste and fast stacking speed to fabricate high performance products. The present contribution addresses several known challenges including mechanical behaviour and porosity analysis on directed energy deposition (DED) m...

A R T I C L E I N F O Keywords: Directed energy deposition Micro-cavities and porosities Phase-field diffusive model Micromechanical damage context Initiation and propagation of cracks A B S T R A C T Experimental and numerical study regarding fracture in laser-processed steel components is addressed in the present work. Samples of stainless steel...

Utilization of the phase-field diffusive crack approach in prediction of crack evolution in materials containing voids is investigated herein. It has been established that the ductile failure occurs predominantly due to nucleation, growth and coalescence of micro-voids and micro-cavities, which lead to initiation and propagation of cracks till fina...

A transient finite-element approach is proposed for numerical simulation of additive manufacturing technology of laser metal deposition (LMD) towards predicting temperature distribution, melt pool shape and dilution [1]. This computational model was implemented in ABAQUS suite (FE software) and validated throughout 1D line experiments of LMD. At ea...

This work addresses the evaluation of properties of a steel obtained by an additive manufacturing technology, with the goal of establishing a reliable material model that includes features as plasticity, anisotropy and fracture toughness. The material used is a 316L stainless steel obtained by direct energy deposition with a “zig-zag” strategy, usi...

Physical accuracy of discretization methods for frictional contact mechanics originates from precise representation of discontinuous frictional and normal interaction laws, appropriate time-integration for velocity and acceleration (which is unbounded at impacting points) and also contact discretization techniques. In terms of discontinuous behavio...

The diffusive concept of the phase field methodology, that has grounds in fracture mechanics, is used to model ductile failure by coupling it to the Rousselier damage model, which employs the void volume fraction to characterise material internal degradation, within a thermodynamically consistent framework. Defining a critical stage of cavity growt...

Numerical methods are an important requirement for the evaluation and analysis of sheet metal forming processes. In order that quality and development of the final component can be reproduced, it is important a higher accuracy of the obtained numerical results, which in turn needs the most correct material behavior characterization. This paper pres...

Relevance of finite strain shell piezoelectric analysis is significant due to the general use of polyvinylidene fluoride (PVDF). A finite-strain geometrically exact shell model for the analysis of piezoelectric laminated structures is introduced. An assumed-strain formulation is employed, with least-squares fitting of contravariant linear stress fi...

In this work, the analogous treatment between coupled temperature–displacement problems and material failure models is explored within the context of a commercial software (Abaqus®). The implicit gradient Lemaitre damage and phase field models are implemented utilizing the software underlying capabilities for coupled temperature–displacement proble...

The tough fuel economy and emissions standards facing automotive industry creates the need for lightweight construction and the use of new generation of materials. However, the use of non-conventional materials leads to difficulties in the prediction of material behaviour during sheet metal forming processes, including damage and formability limits...

Compatibility between element technology featuring assumed (finite)-strains based on least-squares and current constitutive formulations employed in elastic and inelastic contexts is a demanding task. Local frames are required for anisotropic and cohesive laws, some assumed-strain element technologies do not explicitly provide the deformation gradi...

In this work, the radial point interpolation technique (RPI) is extended to the analysis of material showing an elasto-plastic behavior. The RPI methodology permits to discretize the problem domain using only a set of scattered nodes, randomly distributed along the problem domain. Here, the RPI formulation is fully described: nodal connectivity; in...

In this paper, we propose a simple 2D and 3D crack evolution algorithm which avoids the variable/DOF mapping within mesh adaptation algorithms. To this end, a new area/volume minimization algorithm for damaged elements is introduced with the goal of improving the crack path representation. In addition, the new algorithm consists of: (i) mesh-creati...

Laminated composite materials are widely implemented in several engineering constructions. For its relative light weight, these materials are suitable for aerospace, military, marine, and automotive structural applications. To obtain safe and economical structures, the modelling analysis accuracy is highly relevant. Since meshless methods in the re...

The accurate prediction of fracture in sheet metal forming process has become an important subject, bringing new challenges to material characterization. During this process, the sheet metal can be subjected to large localized deformations with significant through-thickness necking in which 3D stress states develop and dictate the fracture event of...

Glass forming techniques are still mostly based on empirical knowledge because practical experiments are in general quite expensive and time consuming. Computer simulation models allow to understand, control and optimize the process, offering suitable alternatives to experimental testing in order to reduce time and cost. This paper presents a numer...

In this work, the radial point interpolation technique (RPI) is extended to the analysis of material showing an elasto-plastic behavior. The RPI methodology discretizes the problem domain using only a set of scattered nodes, randomly distributed along the problem domain. Here, the RPI formulation is fully described as nodal connectivity; influence-...

Advanced high strength steels (AHSS) are seeing an increased use, mostly due to lightweight design in automobile industry and strict regulations on safety and greenhouse gases emissions. However, the use of these materials, characterized by a high strength to weight ratio, stiffness and high work hardening at early stages of plastic deformation, ha...

Traditionally, combination of equivalent plastic strain and stress triaxiality parameters are taken into account when performing characterization of material ductility. Some well-established models like Lemaitre model, GTN based models and many others perform relatively well at high-triaxiality stress states but fail to give adequate answers to low...

In this work, experimental tests were carried out, under different loading conditions, in order to assess different ductile failure criteria, namely based on GTN, Johnson-Cook or Lemaitre models and to establish new proposals for improvement. Corresponding characterization for damage parameters is performed by an inverse analysis procedure, using r...

Ductile damage can be dealt with continuous descriptions of material, resorting, for example, to continuous damage mechanic descriptions or micromechanical constitutive models. When it comes to describe material behaviour near and beyond fracture these approaches are no longer sufficient or valid and continuous/discontinuous approaches can be adopt...

In this work an integrated model for all the process of glass forming of glass containers is presented. The model addresses press-and-blow and blow-and-blow procedures from the gob forming to the final product. Glass forming involves coupled thermal-mechanical physical phenomena, in which the material viscous flow is highly dependent on heat transf...

Purpose – The purpose of this paper is to use PAM-CRASH, a finite element analysis solver, to assess the performance of a mass production vehicle cross car beam (CCB) under an overlap frontal crash scenario (crashworthiness). Simulation results were reviewed according to what is plausible to register regarding some critical points displacements and...

This work extends the radial point interpolation method (RPIM) to the elasto-static analysis of circular plates. Instead using a plate bending theory, the 2D axisymmetric deformation theory is assumed. The RPIM enforces the nodal connectivity with the influence-domain concept and integrates numerically the integrodifferential equations governing th...

In this chapter, some recent developments and proposals for improvement of material models at the constitutive level to deal with ductile damage at large plastic strains are addressed. Numerical tests are carried out to test their performance on shear-dominated stress states where their main differences lie. Subsequently, aspects of the use of nonl...

This preliminary study combines an advanced discretization meshless technique with a damage model for concrete materials. In this work, the radial point interpolation method (RPIM) is used in order to obtain the variable fields required by the damage model. The RPIM permits to discretize the problem domain using a random nodal distribution. Being t...

This work presents a finite strain quadrilateral element with least-squares assumed in-plane shear strains (in covariant/contravariant coordinates) and classical transverse shear assumed strains. It is an alternative to enhanced-assumed-strain (EAS) formulation and, in contrast to this, produces an element satisfying ab initio the Patch-test. No ad...

Two porous plasticity models, Rousselier and Gurson–Tvergaard–Needleman (GTN), are integrated with a new semi-implicit integration algorithm for finite strain plasticity. It consists of using relative Green– Lagrange during the iteration process and incremental frame updating corresponding to a polar decomposition. Lowdin's method of orthogonalizat...

The use of a semi-implicit algorithm at the constitutive level allows a robust and concise implementation of low-order effective shell elements. We perform a semi-implicit integration in the stress update algorithm for finite strain plasticity: rotation terms (highly nonlinear trigonometric functions) are integrated explicitly and correspond to a c...

We propose, in this paper, a distinct perspective on the solution of the Coulomb frictional contact problem. By combining the prediction/correction method for the contact force vector with the correction step being a cone projection and writing the friction cone surface in the quadratic form, we directly calculate the contact force. The distance al...

This work recovers an established technique for improving quadrilateral shell element performance in both out-of-plane and in-plane bending cases using a mixed formulation. A four-field variational principle is established and we relate, at the discrete level, the Lagrange multipliers and secondary right Cauchy–Green field with the displacement and...

This work is concerned with the consistent linearisation of non-local models of the integral type whenever the non-local variable is an implicit function of the other constitutive variables. The general framework for the derivation of consistent non-local tangent operators is initially presented for elasto-plastic materials. Then, closed-form analy...

Sensitivity analysis of an XFEM crack propagation model is developed for shape and material parameters, where the direct differentiation method is applied to large strain problems with hyperelastic neo-Hookean materials. The presence of level set functions to describe the crack position requires the development of a proper differentiation technique...

A multibody frictional mortar contact formulation (Gitterle et al., 2010) is extended for the simulation of solids undergoing finite strains with inelastic material behavior. The framework includes the modeling of finite strain inelastic deformation, the numerical treatment of frictional contact conditions and specific finite element technology. Se...

Over the past years, the non-local method has established itself as an effective remedy to the well-known pathological mesh dependency that inherently affects softening media. The non-local method incorporates an intrinsic length into the traditional continuum theory and therefore the size of the localising zone is resolved, attenuating the unwante...

IsoGeometric Analysis (IGA) is increasing its popularity as a new numerical tool for the analysis of structures. IGA provides: (i) the possibility of using higher order polynomials for the basis functions; (ii) the smoothness for contact analysis; (iii) the possibility to operate directly on CAD geometry. The major drawback of IGA is the non-interp...

The introduction of new effects, both in the plastic flow rule of the material and in the evolution laws for internal variables like damage, namely the importance of taking into account triaxiality and the influence of the third invariant of the deviatoric stress tensor in the modeling of mechanical behavior of metallic materials is here assessed....

Isogeometric Analysis (IGA) has become very popular for the analysis of structures, fluids and fluid-structure interaction problems. IGA suffers from the same problems depicted by other numerical methods when dealing with constrained problems as those associated with handling of incompressibility or transverse shear effects on thin structures, givi...

Originally Continuum Damage Mechanics and Fracture Mechanics evolved separately. However, when it comes to ductile fracture, an unified approach is quite beneficial for an accurate modelling of this phenomenon. Ductile materials may undergo moderate to large plastic deformations and internal degradation phenomena which are well described by continu...

From the theoretical point of view, an energetically transition from damage to fracture should occur for totally damaged material. Nevertheless, in terms of numerical simulation, this condition leads to a singularity in the constitutive equations, when the Lemaitre model for ductile damage is used to describe material behavior. In this work, a cohe...

In this chapter, some recent developments and proposals for improvement of material models at the constitutive level to deal with ductile damage at large plastic strains are addressed. Numerical tests are carried out to test their performance on shear-dominated stress states where their main differences lie. Subsequently, aspects of the use of nonl...

The XFEM is a powerful method to handle strong discontinuities in a finite element environment, especially in the study of the final stages of material failure, modelling the propagation of cracks, suppressing the need of remeshing. Nevertheless, for some materials undergoing large strain processes without noticeable volume changes, the discretizat...

Isogeometric analysis has recently become very popular for the numerical modeling of structures and fluids. Among other potential features, advantages of using a non-uniform rational B-splines (NURBS)-based isogeometric analysis over the traditional finite element method include the possibility of using higher-order polynomials for the basis functi...

Significant progress has been made on computational contact mechanics over the past decade. Many of the drawbacks that were inherent to the standard node-to-segment element strategy, such as locking/over-constraint and non-physical jumps in the contact forces due to the discontinuity of the contact surface, have been systematically overcome. In par...

In this contribution, a continuum-discontinuum model for ductile failure is presented. The degradation of material properties through deformation is described by a Continuum Damage Mechanics model, which uses a non-local integral formulation to avoid mesh dependence. In the final stage of failure, the damaged zone is replaced by a macro crack for a...

Metal forming by large inelastic deformation gives rise to more or less inelastic flow localization inside narrow bands. This strong localization is often the prelude to ductile damage initiation and growth leading to the formation of macroscopic cracks inside the formed part. Accordingly, any numerical simulation of metal forming process should in...

This contribution is devoted to the formulation and numerical implementation of a ductile damage constitutive model enriched with a thermodynamically consistent nonlocal theory of integral type. In order to describe ductile deformation, the model takes finite strains into account. To model elasticity, a Hencky-like hyperelastic free energy potentia...

This contribution describes the numerical treatment and calibration strategy for a new micromechanical damage model, which employs two internal damage variables. The new micromechanical model is based on Gurson's theory incorporating the void volume fraction as one damage parameter and a shear mechanism, which was formulated considering geometrical...

In this contribution, a continuum-dicontinuum model for ductile failure is presented. The degradation of material properties trough deformation is described by Continuum Damage Mechanics in a non-local integral formulation to avoid mesh dependence. In the final stage of failure, the damaged zone is replaced by a cohesive macro crack and subsequent...

This paper presents a numerical approach for failure prediction in sheet metal forming operations. The approach is based on the coupling of anisotropic elasto-plasticity and ductile damage, described by Lemaitre´s damage evolution law, within the framework of Continuum Damage Mechanics. The constitutive relations were assessed and the developed mod...

In this contribution, the implementation of a nonlocal formulation is described aiming to improve the reliability of the numerical prediction of ductile failure. The nonlocal model, which is based on a simplified version of Lemaitre’s material model [1], is achieved by redefining the damage variable to be nonlocal using an integral formulation. The...

This paper describes an efficient numerical integration algorithm of a new model for metal plasticity and fracture [2]. The constitutive equations of the material model critically include both the effect of pressure through the triaxiality ratio and the effect of third deviatoric stress invariant through the lode angle in the description of materia...

In this work a computational model based on a meshless method, the Element Free Galerkin Method (EFG), is applied in the simulation of forging processes. Contact and friction are handled by blending finite elements with the EFG in order to overcome the difficulty of meshless methods in dealing with essential boundary conditions. Special interface f...

The optimisation of sheet metal processes by using numerical simulations has become a key factor to a continuously increasing requirement for time and cost efficiency, for quality improvement and materials saving, in many manufacturing areas such as automotive, aerospace, building, packaging and electronic industries. The introduction of new materi...

In the hollow glass industry, lubricants contribute to the control of heat transfer at the glass/mould interface and consequently to the success of the forming process. The LAMIH of the University of Valenciennes has developed a laboratory test method to determine the evolution of the heat transfer coefficient in different glass/mould contact condi...

Continuous Damage Mechanics (CDM) may constitute an alternative to the traditional use of Forming Limit Diagrams (FLDs) to predict the onset of formability in sheet metal forming [1], In CDM, at the constitutive level, a damage variable is introduced to model, at the macro scale, the internal material degradation due to microdefects that occur duri...

The introduction of new materials brought new challenges to sheet metal forming processes. The optimization of these processes by using numerical simulations has become a key factor to a continuously increasing requirement for time and cost efficiency, for quality improvement and materials saving, in many manufacturing areas such as automotive, aer...

Numerical modeling of the glass forming processes requires the accurate knowledge of the heat exchange between the glass and the forming tools. A laboratory testing is developed to determine the evolution of the heat transfer coefficient in different glass/mould contact conditions (contact pressure, temperature, lubrication...). In this paper, tria...

The formability in sheet metal forming processes is mainly conditioned by ductile fracture resulting from geometric instabilities due to necking and strain localization. The macroscopic collapse associated with ductile failure is a result of internal degradation described throughout metallographic observations by the nucleation, growth and coalesc...

A non-local model for material softening, in which the internal dissipative variable adopted is the damage, is implemented. The ductile damage model utilised is based on an enhanced Lemaitre model which includes a clear distinction between damage evolution for compressive and tensile stress states. The model adopted is an implicit gradient model in...

A non-local gradient damage formulation, based on an improved Lemaitre damage model, is adopted in order to address the modelling of internal damage of the material in metal forming processes, like forging, or to describe processes in which fracture is a part of the process itself, as in sheet blanking or metal cutting. The damage model takes into...

In this contribution, Lemaitre's ductile damage model is coupled with Hill's orthotropic plasticity criterion. The coupling between damaging and material behaviour is accounted for within the framework of Continuum Damage Mechanics (CDM). The resulting constitutive equations are implemented in the Abaqus/Explicit code, for the prediction of fractur...