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Publications (294)
This paper presents the application of a stabilized mixed strain/displacement finite element formulation for the solution of nonlinear solid mechanics problems involving compressible and incompressible plasticity. The variational multiscale stabilization introduced allows the use of equal order interpolations in a consistent way. Such formulation p...
The development of slip lines, due to strain localization, is a common cause for failure of soil in many circumstances investigated in geotechnical engineering. Through the use of numerical methods – like finite elements – many practitioners are able to take into account complex geometrical and physical conditions in their analyses. However, when d...
In previous works, the authors have presented the stabilized mixed displacement/pressure formulation to deal with the incompressibility constraint. More recently, the authors have derived stable mixed stress/displ-acement formulations using linear/linear interpolations to enhance stress accuracy in both linear and non-linear problems. In both cases...
This paper presents an implicit orthotropic model based on the Continuum Damage Mechanics isotropic models. A mapping relationship is established between the behaviour of the anisotropic material and that of an isotropic one. The proposed model is used to simulate the failure loci of common orthotropic materials, such as masonry, fibre-reinforced c...
Friction stir welding (FSW) process is a solid-state joining process during which materials to be joined are not melted. As a consequence, the heat-affected zone is smaller and the quality of the weld is better with respect to more classical welding processes. Because of extremely high strains in the neighborhood of the tool, classical numerical si...
This work introduces a distributed memory machine and octree-based Finite Element (FE) framework for modeling metal Additive Manufacturing (AM) processes. In this sense, an Adaptive Mesh Refinement (AMR) is used to accurately capture the complex geometrical domain and the physical phenomena of AM processes for the part-scale analysis. AMR is used i...
Residual stresses, related distortions and cracks are detrimental in metallic Additive Manufacturing (AM). Previously developed stress-control strategies based on reducing thermal gradients hardly diminish the stress concentrations at the built basement and easily affect other physical phenomena involved in AM. To overcome this, a novel strategy, n...
Laser powder bed fusion (LPBF) additive manufacturing (AM) unavoidably generates residual stresses due to sharp thermal gradients and the strong mechanical constraints of the substrate. These stresses can lead to large warpages and cracking of AM builds, compromising their qualification. Annealing heat treatment (HT) after LPBF fabrication is an ef...
A novel Adaptive Formulation Refinement (AFR) strategy for Friction Stir Welding (FSW) problems is presented. In FSW, the accurate computation of strains is crucial to correctly predict the highly non-linear material behavior in the stir zone. Based on a posteriori error estimation, AFR switches between two mixed formulations depending on the requi...
Additively manufactured thin-walled structures through selective laser melting (SLM) are of great interest in achieving carbon-neutral industrial manufacturing. However, residual stresses and warpages as well as recoater crashes often occur in SLM, leading to the build failure of parts, especially for large-scale and lightweight geometries. The cha...
In this work an end-to-end optimization procedure to maximize the mechanical performance of Additive Manufacturing (AM) components is presented. Material Extrusion (ME) is the selected demonstrative AM technology, but the approach is applicable to other AM processes where the manufacturing toolpaths of the geometry of the printed component are desc...
In this work, the combined implementation of Adaptive Formulation Refinement (AFR) and Adaptive Mesh Refinement (AMR) strategies is proposed for the efficient and mesh objective evaluation of quasi-brittle fracture.
A critical issue when computing localized structural failure is the spurious mesh bias dependence of the crack trajectories and collap...
Additively manufactured components by laser powder bed fusion (LPBF) often suffer from stress-induced cracks (e.g. delamination), especially at the build-substrate interfaces where stiff mechanical constraints and large thermal gradients coexist. To reduce the probability of cracking, this work proposes an innovative strategy to optimize the geomet...
In this paper a new methodology developed for predicting the mechanical performance of the structures additively manufactured by Fused Filament Fabrication is presented.
The novelty of the approach consists in accounting for the anisotropy in the material properties induced by the printing patterns. To do so we partition the manufactured structure...
This work presents an h-adaptive finite-element (FE) strategy to address the numerical simulation of additive manufacturing (AM) of large-scale parts. The wire-arc additive manufacturing is chosen as the demonstrative technology for its manufacturing capabilities suitable for industrial purposes. The scanning path and processing parameters of the s...
In this work, the performance of the mixed 3-field displacement/deviatoric-strain/pressure (u/e/p) finite element is examined for nonlinear thermo-mechanical structural applications under incompressible behavior. The proposed FE model increases the solution accuracy in terms of strains and stresses, guaranteeing mesh-objective results in nonlinear...
As strain localization is usually prognostics of localized failure in solids and structures, prediction of its occurrence and quantification of its adverse effects are of both theoretical and practical significance. Regarding plastic solids, onset of strain localization was presumed to be coincident with strain bifurcation, and the discontinuous bi...
This work develops a novel homogenization-based computational strategy for predicting the mechanical properties of Fused Filament Fabricated parts by characterizing the component according to the different printing patterns used. The anisotropic constitutive material models obtained for each printing pattern allows the accurate prediction of the be...
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In additive manufacturing (AM), residual stresses and microstructural inhomogeneity are detrimental to the mechanical properties of as-built AM components. In previous studies the reduction of the residual stresses and the optimization of the microstructur...
Residual stresses are one of the primary causes for the failure of parts or systems in metal additive manufacturing (AM) since they easily induce crack propagation and structural distortion. Although the formation of residual stresses has been extensively studied, the core factors steering their development in AM have not been completely uncovered....
In this work, a critical comparison between three different numerical approaches for the computational modelling of quasi-brittle structural failure is presented. Among the many finite element approaches devised to solve the problem, both using continuous and discontinuous methods, the present study examines the relative performance of the XFEM, th...
One of the advantages of Additive Manufacturing (AM) is the fabrication
exibility and the design freedom. The drawback when dealing with the numerical simulation of such a manufacturing process is the necessity of very �ne meshes at the Heat A�ected Zone (HAZ) able to represent the melt pool and the metal deposition sequence through the layer-by-l...
Structural size effect denotes the variation in the brittleness of a structure induced by a change in its size. In quasi-brittle materials failure takes place under the form of localized cracks and size effect is primarily caused by the release of stored elastic energy into the front of the fracture as it progresses.
Modelling of cracking and failu...
In this work an adaptive Finite Element strategy to deal with the numerical simulation of Additive Manufacturing (AM) processes is presented. The Selective Laser Melting (SLM) is chosen as the
reference technology because of its great diffusion in the industrial manufacturing chain, although the proposed methodology can be applied to the numerical...
Directed energy deposition of titanium alloy entails severe microstructural heterogeneity and layer bands due to diverse thermal histories. While the thermal-microstructure relationship in additive manufacturing has been reported, the details on how complex thermal histories influence the microstructural features and evolution have not been so addr...
Process parameters in Additive Manufacturing (AM) are key factors in the mechanical performance of 3D-printed parts. In order to study their effect, a three-zone model based on the printing pattern was developed. This modelization distinguished three different zones of the 3D printed part, namely cover, contour, and inner; each zone was treated as...
Thin-walled structures are of great interest because of their use as lightweight components in aeronautical and aerospace engineering. The fabrication of these components by additive manufacturing (AM) often produces undesired warpage because of the thermal stresses induced by the manufacturing process and the components’ reduced structural stiffne...
Strain localization analysis for orthotropic-associated plasticity in cohesive-frictional materials is addressed in this work. Specifically, the localization condition is derived from Maxwell's kinematics, the plastic flow rule and the boundedness of stress rates. The analysis is applicable to strong and regularized discontinuity settings. Expandin...
This work analyses the performance of parts built by Additive Manufacturing (AM) using Fused Filament Fabrication (FFF) demonstrating the correlation between the printing orientation and structural performance. FFF components present two regions showing different mechanical behaviour: the external contour and the inner structure (in-fills or lattic...
This paper investigates the capacity of solid finite elements with independent interpolations for displacements and strains to address shear, membrane and volumetric locking in the analysis of beam, plate and shell structures. The performance of the proposed strain/displacement formulation is compared to the standard one through a set of eleven ben...
The numerical modelling of fracture has been an active topic of research for over five decades. Most of the approaches employed rely on the use of the Finite Element Method, which has shown to be an effective and cost-efficient tool for solving many physical phenomena. However, the issue of the spurious dependency of the computed solution with the...
Substrate design optimization to reduce the residual stresses in DED. • Coupled thermomechanical analysis for AM by an in-house calibrated software. • Sensitivity of conformal and non-conformal substrates to the lower built surface. • Sensitivity of substrate stiffness and thermal resistance on residual stresses. This paper proposes a strategy to o...
This paper proposes a strategy to optimize the design of the substrate structures used in Additive Manufacturing (AM) by Directed Energy Deposition (DED) to minimize the residual stresses induced by this fabrication process. To this end, several numerical analyses were performed to analyse different substrate designs in order: (i) to reduce the sen...
This work exploits the high accuracy of the mixed 3−field u/e/p formulation to address materially non-linear inelastic problems including isochoric deformations.
Motivated by the strain-driven format of several constitutive equations used in FEA, the mixed u/s/p formulation is reinterpreted, selecting the deviatoric strains as primary variables, to...
This work exploits the high accuracy of the mixed u=e=p 3 …eld formulation to address strongly non-linear problems including isochoric deformations. Motivated by the strain-driven format of most of the constitutive equations used in FEA, the mixed u=s=p formulation is reinterpreted, selecting the deviatoric strains as primary variables, together wi...
Part warpage and residual stress are two of the main challenges for metal additive manufacturing (AM) as they result in lower geometric precision and poor mechanical properties of the products. This work investigates the effect of the building strategy on the heat transfer process and the evolution of the thermally induced mechanical variables in l...
In friction stir welding (FSW), the real contact conditions between the tool and the workpiece and the range of strain rates experienced remain quite unclear. In this work, a coupled 3D thermo-mechanical numerical model was used to simulate the FSW process. A Parametric finite element analysis of the evolution of the contact conditions, strain rate...
In this work an adaptive Finite Element strategy to deal with the numerical simulation of Additive Manufacturing (AM) processes is presented. The Selective Laser Melting (SLM) is chosen as the reference technology because of its great diffusion in the industrial manufacturing chain, although the proposed methodology can be applied to the numerical...
In this work an adaptive Finite Element strategy to deal with the numerical simulation of Additive Manufacturing processes is presented. The Selective Laser Melting (SLM) is chosen as the reference technology because of its great diffusion in the industrial manufacturing chain. An octree-based mesh adaptivity approach is adopted allowing for the us...
This paper discusses the finite element modeling of cracking of quasi-brittle materials under cyclic loading. A damage based crack model is proposed, which considers tensile and compressive damage, irreversible strains upon unloading in compression, as well as micro-crack closure-reopening effects (MCR) with special attention to the sliding of open...
In this paper, experimental evidence, theoretical predictions and the finite element modelling of the structural size effect in cracking problems of quasi-brittle materials are discussed and assessed against each other. The fracture process is modelled through the crack band approach, using an isotropic damage constitutive law. The correct dissipat...
An analysis of the evolution of the torque and of the temperature with welding conditions, in Friction Stir Welding (FSW) of aluminium alloys, was conducted. More precisely, torque and temperature results from a large number of publications, on FSW of AA2xxx, AA5xxx, AA6xxx and AA7xxx aluminium alloys series, were collected. The literature data was...
In this work the strain localization analysis of Hill's orthotropic plasticity is addressed. In particular, the localization condition derived from the boundedness of stress rates together with Maxwell's kinematics is employed. Similarly to isotropic plasticity considered in our previous work, the plastic flow components on the discontinuity surfac...
In contrast with other metal additive manufacturing technologies, powder-bed fusion features very thin layers and rapid solidification rates, leading to long build jobs and a highly localized process. Many efforts are being devoted to accelerate simulation times for practical industrial applications. The new approach suggested here, the virtual dom...
This work addresses the issue of the simulation and prediction of defect formation through the analysis of the material mixing during Friction Stir Welding (FSW). A coupled thermomechanical model is used for the FSW simulation. To follow the flow of the material, a tracing technique of the material particles is incorporated in the numerical model....
In industrial practice, additive manufacturing (AM) processes are often followed by post-processing operations such as heat treatment, subtractive machining, milling, etc., to achieve the desired surface quality and dimensional accuracy. Hence, a given part must be 3D-printed with extra material to enable this finishing phase. This combined additiv...
Numerical framework for high accuracy simulation of the FSW process
M. Chiumenti, M. Cervera and N. Dialami
Since its development, FSW has been pointed as an excellent alternative to fusion welding. Although this technology was initially settled for welding aluminum alloys, recent developments allowed extending its application to a more diversified range of base materials. Due to the complexity of the process, the use of numerical simulation become a com...
In the industrial practice, additive manufacturing processes are often followed by post-processing operations such as subtractive machining, milling, etc. to achieve the desired surface quality and dimensional accuracy. Hence, a given part must be 3D printed with extra material to enable such finishing phase. This combined additive/subtractive tech...
Residualstressesand distortion in Additive Manufactured (AM) parts are two key obstacles which seriously hinder the wide application of this technology. Nowadays, understandingthe thermomechanical behaviorinducedby the AM process is still a complex task which must take intoaccountthe effectsof both the process and the material parameters, themicros...
This work introduces an innovative parallel, fully‐distributed finite element framework for growing geometries and its application to metal additive manufacturing. It is well‐known that virtual part design and qualification in additive manufacturing requires highly‐accurate multiscale and multiphysics analyses. Only high performance computing tools...
Residual stresses and distortions are two technical obstacles for popularizing the Additive Manufacturing (AM) technology. The evolution of the stresses in AM components during the thermal cycles of the metal depositing process is not yet clear, and more accurate in-situ measurements are necessary to calibrate and validate the numerical tools devel...
Residualstressesand distortion in Additive Manufactured (AM) parts are two key obstacles which seriously hinder the wide application of this technology. Nowadays, understandingthe thermomechanical behaviorinducedby the AM process is still a complex task which must take intoaccountthe effectsof both the process and the material parameters, themicros...