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Laura De Lorenzis

Laura De Lorenzis
ETH Zurich | ETH Zürich · Department of Mechanical and Process Engineering

Prof. Dr.

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216
Publications
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Publications

Publications (216)
Chapter
Within the realm of isogeometric analysis, isogeometric collocation has been driven by the attempt to minimize the cost of quadrature associated with higher-order discretizations, with the goal of achieving higher-order accuracy at low computational cost. While the first applications of isogeometric collocation have mainly concerned linear problems...
Article
We propose Floating Isogeometric Analysis (FLIGA), which extends IGA to extreme deformation analysis. The method is based on a novel tensor-product construction of B-Splines for the update of the basis functions in one direction of the parametric space. With basis functions “floating” deformation-dependently in this direction, mesh distortion is ov...
Article
Full-text available
Contact mechanics models based on linearity assumptions, often using the viscoelastic half space theory and numerically implemented with the boundary element method, are known to provide accurate results for small mean square slope of the surface roughness. For large mean square slope, models accounting for finite deformations, often implemented wi...
Preprint
Full-text available
We propose a new approach for data-driven automated discovery of material laws, which we call EUCLID (Efficient Unsupervised Constitutive Law Identification and Discovery), and we apply it here to the discovery of plasticity models, including arbitrarily shaped yield surfaces and isotropic and/or kinematic hardening laws. The approach is unsupervis...
Article
Full-text available
We address brittle fracture in anisotropic materials featuring two-fold and four-fold symmetric fracture toughness. For these two classes, we develop two variational phase-field models based on the family of regularizations proposed by Focardi (2001), for which Γ-convergence results hold. Since both models are of second order, as opposed to the pre...
Preprint
Full-text available
We investigate phase-field modeling of brittle fracture in a one-dimensional bar featuring a continuous variation of elastic and/or fracture properties along its axis. Our main goal is to quantitatively assess how the heterogeneity in elastic and fracture material properties influences the observed behavior of the bar, as obtained from the phase-fi...
Article
Full-text available
In this paper, a computational framework for simulating ductile fracture in multipatch shell structures is presented. A ductile fracture phase-field model at finite strains is combined with an isogeometric Kirchhoff-Love shell formulation. For the application to complex structures, we employ a penalty approach for imposing, at patch interfaces, dis...
Preprint
Full-text available
We address brittle fracture in anisotropic materials featuring two-fold and four-fold symmetric fracture toughness. For these two classes, we develop two variational phase-field models based on the family of regularizations proposed by Focardi (Focardi, M. On the variational approximation of free-discontinuity problems in the vectorial case. Math....
Article
Full-text available
We extend the model-free data-driven paradigm for rate-independent fracture mechanics proposed in Carrara et al. (2020), to rate-dependent fracture and sub-critical fatigue. The problem is formulated by combining the balance governing equations stemming from variational principles with a set of data points that encodes the fracture constitutive beh...
Article
Full-text available
Phase-field models of brittle fracture can be regarded as gradient damage models including an intrinsic internal length. This length determines the stability threshold of solutions with homogeneous damage and thus the strength of the material, and is often tuned to retrieve the experimental strength in uniaxial tensile tests. In this paper, we focu...
Article
Full-text available
We address anisotropic elasticity and fracture in small intestine walls (SIWs) with both experimental and computational methods. Uniaxial tension experiments are performed on porcine SIW samples with varying alignments and quantify their nonlinear elastic anisotropic behavior. Fracture experiments on notched SIW strips reveal a high sensitivity of...
Article
Full-text available
We propose a new approach for data-driven automated discovery of isotropic hyperelastic constitutive laws. The approach is unsupervised, i.e., it requires no stress data but only displacement and global force data, which are realistically available through mechanical testing and digital image correlation techniques; it delivers interpretable models...
Article
Full-text available
Cracks developing within a masonry structure induce anomalies in its strain field under dead loads that can be exploited for damage identification purposes through the adoption of strain-based structural health monitoring techniques. "Smart bricks" are strain-sensing piezoresistive clay bricks that can be used for this purpose. Along these lines, t...
Preprint
Full-text available
We propose a new approach for data-driven automated discovery of hyperelastic constitutive laws. The approach is unsupervised, i.e., it requires no stress data but only displacement and global force data, which are realistically available through mechanical testing and digital image correlation techniques; it delivers interpretable models, i.e., mo...
Preprint
Full-text available
We extend the model-free data-driven paradigm for rate-independent fracture mechanics proposed in Carrara et al. (2020), Data-driven Fracture Mechanics, Comp. Meth. App. Mech. Eng., 372 to rate-dependent fracture and sub-critical fatigue. The problem is formulated by combining the balance governing equations stemming from variational principles wit...
Article
Full-text available
Phase-field modeling of fracture has gained popularity within the last decade due to the flexibility of the related computational framework in simulating three-dimensional arbitrarily complicated fracture processes. However, the numerical predictions are greatly affected by the presence of uncertainties in the mechanical properties of the material...
Article
In this paper, a phase-field model is presented for the description of brittle fracture in a Reissner-Mindlin plate and shell formulation. The shell kinematics as well as the phase-field variable are described on the midsurface of the structure. Non-Uniform Rational B-Spline basis functions are used for the discretization of both the displacement/r...
Chapter
FEM simulations are widely recognized as essential tools in the analysis of the behaviour of dam systems. A detailed representation of the dam structure allows for a better understanding of the local response of important structural elements. The present paper intends to provide a FE modelling procedure of concrete arch-gravity dams. Case of study...
Article
Full-text available
We investigate primal and mixed u - p isogeometric collocation methods for application to nearly-incompressible isotropic elasticity. The primal method employs Navier’s equations in terms of the displacement unknowns, and the mixed method employs both displacement and pressure unknowns. As benchmarks for what might be considered acceptable accuracy...
Article
Full-text available
We present a computational framework for applying the phase-field approach to brittle fracture efficiently to complex shell structures. The momentum and phase-field equations are solved in a staggered scheme using isogeometric Kirchhoff–Love shell analysis for the structural part and isogeometric second- and fourth-order phase-field formulations fo...
Article
Full-text available
In variational phase-field modeling of brittle fracture, the functional to be minimized is not convex, so that the necessary stationarity conditions of the functional may admit multiple solutions. The solution obtained in an actual computation is typically one out of several local minimizers. Evidence of multiple solutions induced by small perturba...
Article
Full-text available
We present a new data-driven paradigm for variational brittle fracture mechanics. The fracture-related material modeling assumptions are removed and the governing equations stemming from variational principles are combined with a set of discrete data points, leading to a model-free data-driven method of solution. The solution at a given load step i...
Article
Full-text available
Ferroelectric phase field models based on the Ginzburg–Landau–Devonshire theory are characterized by a large number of material parameters with problematic physical interpretation. In this study, we systematically address the relationship between these parameters and the main properties of ferroelectric domain walls. A variational approach is used...
Article
We propose a mixed stress-displacement isogeometric collocation method for nearly incompressible elastic materials and for materials exhibiting von Mises plasticity. The discretization is based on isogeometric analysis (IGA) with non-uniform rational B-Splines (NURBS) as basis functions. As compared to conventional IGA Galerkin formulations, isogeo...
Preprint
Full-text available
We present a new data-driven paradigm for variational brittle fracture mechanics. The fracture-related material modeling assumptions are removed and the governing equations stemming from variational principles are combined with a set of discrete data points, leading to a model-free data-driven method of solution. The solution at a given load step i...
Article
Full-text available
In the numerical approximation of phase-field models of fracture in porous media with the finite element method, the problem of numerical locking may occur. The causes can be traced both to the hydraulic and to the mechanical properties of the material. In this work we present a mixed finite element formulation for phase-field modeling of brittle f...
Preprint
Full-text available
In variational phase-field modeling of brittle fracture, the functional to be minimized is not convex, so that the necessary stationarity conditions of the functional may admit multiple solutions. The solution obtained in an actual computation is typically one out of several local minimizers. Evidence of multiple solutions induced by small perturba...
Presentation
Full-text available
We have recently devised a phase-field fracture formulation for the (strongly) anisotropic surface energy when Gc is given by the four-fold symmetric (butterfly-shaped) function of polar angle. Attached is a couple of slides from our presentation intended for the SIAM MS 20 Congress to be held in Bilbao in May 2020, as well as for the EMI 2020 / P...
Chapter
In this paper the isogeometric collocation (IGA-C) method is used to solve the dynamic problem of geometrically exact beams. The kinematics of a spatial Timoshenko beam undergoing finite displacements and rotations involves the Lie group \({\mathrm{SO(3)}}\). Most of the computational complexities originate from the presence of such a non-additive...
Chapter
Full-text available
In this work we employ isogeometric analysis (IGA) in the field of computational homogenization. We present the nonlinear governing equations for the elasticity problem with finite deformations discretized with both IGA Galerkin and collocation methods in a nested multiscale problem and then explore the accuracy and computational performance of the...
Article
Accurate and reliable predictions of the dynamic behaviour of dams is essential to ensure their correct management and the safety of the downstream population. In this context, structural monitoring and testing procedures for their dynamic characterization are essential tools for the calibration of numerical models of dams. This paper presents some...
Chapter
Full-text available
These lecture notes address the main challenging computational aspects of phase-field modeling of brittle fracture. We focus, in particular, on the irreversibility constraint and the iterative solution strategy for non-convex minimization problems. In the former case, we present multiple options of incorporating the constraint and discuss the equiv...
Book
The book examines innovative numerical methods for computational solid and fluid mechanics that can be used to model complex problems in engineering. It also presents innovative and promising simulation methods, including the fundamentals of these methods, as well as advanced topics and complex applications. Further, the book explores how numerical...
Article
Full-text available
We propose a novel approach to the implicit dynamics of shear-deformable geometrically exact beams, based on the isogeometric collocation method combined with the Newmark time integration scheme extended to the rotation group SO(3). The proposed formulation is fully consistent with the underlying geometric structure of the configuration manifold. T...
Article
A novel variational framework to model the fatigue behavior of brittle materials based on a phase-field approach to fracture is presented. The standard regularized free energy functional is modified introducing a fatigue degradation function that effectively reduces the fracture toughness as a proper history variable accumulates. This macroscopic a...
Article
Full-text available
In this paper, the impact problem and the subsequent wave propagation are considered. For the contact discretization an intermediate NURBS layer is added between the contacting finite element bodies, which allows a smooth contact formulation and efficient element‐based integration. The impact event is ill‐posed and requires a regularization to avoi...
Article
Full-text available
One of the biggest challenges in fracture modeling is the correct physical description of the fracture processes. Over the past decade, the well‐established phase‐field modeling framework has gained a lot of attention, due to its ability to predict the fracture phenomena adequately. It has shown very promising results for a three dimensional solid...
Article
Full-text available
The difficulties in dealing with discontinuities related to a sharp crack are overcome in the phase-field approach for fracture by modeling the crack as a diffusive object being described by a continuous field having high gradients. The discrete crack limit case is approached for a small length-scale parameter that controls the width of the transit...
Article
Full-text available
In this paper, a contact problem between two bodies, discretized by finite elements, is solved by adding an auxiliary NURBS layer between the bodies. The advantages of a smooth contact formulation in a NURBS approach are combined with simple mesh generation procedures for the bodies discretized with finite elements. Mesh tying conditions are used t...
Article
Irreversible evolution is one of the central concepts as well as implementation challenges of both the variational approach to fracture by Francfort and Marigo (1998) and its regularized counterpart by Bourdin, Francfort and Marigo (2000, 2007 and 2008), which is commonly referred to as a phase-field model of brittle fracture. Irreversibility of th...
Article
Full-text available
This paper presents a new isogeometric mortar contact formulation based on an extended finite element interpolation to capture physical pressure discontinuities at the contact boundary. The so called two-half-pass algorithm is employed, which leads to an unbiased formulation and, when applied to the mortar setting, has the additional advantage that...
Article
A new finite element procedure for thin plates and shells is presented. It combines a geometrically non-linear, rotation-free Kirchhoff–Love formulation with triangular and quadrilateral Bernstein–Bézier elements and C ¹ and G ¹ inter-element continuity conditions, as well as boundary conditions for clamping and for symmetry. The formulation is fre...
Preprint
Irreversible evolution is one of the central concepts as well as implementation challenges of both the variational approach to fracture by Francfort and Marigo (1998) and its regularized counterpart by Bourdin, Francfort and Marigo (2000, 2007 and 2008), which is commonly referred to as a phase-field model of brittle fracture. Irreversibility of th...
Preprint
Full-text available
Irreversible evolution is one of the central concepts as well as implementation challenges of both the variational approach to fracture by Francfort and Marigo (1998) and its regularized counterpart by Bourdin, Francfort and Marigo (2000, 2007 and 2008), which is commonly referred to as a phase-field model of brittle fracture. Irreversibility of th...
Preprint
Full-text available
A novel variational framework to model the fatigue behavior of brittle materials based on a phase-field approach to fracture is presented. The standard regularized free energy functional is modified introducing a fatigue degradation function that effectively reduces the fracture toughness as a proper history variable accumulates. This macroscopic a...
Article
Full-text available
This paper presents an isogeometric formulation for frictionless contact between deformable bodies, based on the recently proposed concept of the third medium. This concept relies on continuum formulations not only for the contacting bodies but also for a fictitious intermediate medium in which the bodies can move and interact. Key to the formulati...
Article
Full-text available
We initiate the study of three-dimensional shear-deformable geometrically exact beam dynamics through explicit isogeometric collocation methods. The formulation we propose is based on a natural combination of the chosen finite rotations representation with an explicit, geometrically consistent Lie group time integrator. We focus on extending the in...
Conference Paper
Full-text available
Tapered beams are widely used in both civil and industrial engineering for a more efficient exploitation of material in comparison to prismatic beams. In the wind energy sector, tapered box girders are commonly used as the main structural elements of composite wind turbine blades. In the scientific literature, it is long known that the internal dis...
Book
Full-text available
Safety and proactive vision are key aspects in the management of large structures such as dams. Nowadays, finite element (FE) simulations are essential tools to analyse the behaviour of dam systems. A detailed representation of the dam structure allows to better understand the local and the global system response. In arch and arch-gravity dams a cr...
Article
An isogeometric thin shell formulation allowing for large-strain plastic deformation is presented. A stress-based approach is adopted, which means that the constitutive equations are evaluated at different integration points through the thickness, allowing the use of general 3D material models. The plane stress constraint is satisfied by iterativel...
Article
Full-text available
Obtaining the mesostructure of concrete from X-ray computed tomography (CT) requires segmentation of the data into distinct phases, a process complicated by the limited contrast between aggregates and mortar matrix. This paper explores the possibility to add baryte or hematite into the concrete mixture to enhance the contrast between cement paste a...
Article
An isogeometric analysis formulation for simulating red blood cell (RBC) electro-deformationis presented. Electrically-induced cell deformation experiments are receiving increasing attention as an attractive strategy for single-cell mechanical phenotyping. As the RBC structure consists in a very thin biological membrane enclosing a nearly-incompres...
Article
Full-text available
This paper aims at investigating the adoption of non-intrusive global/local approaches while modeling fracture by means of the phase-field framework. A successful extension of the non-intrusive global/local approach to this setting would pave the way for a wide adoption of phase-field modeling of fracture, already well established in the research c...
Article
Full-text available
We propose a mechanical and computational model to describe the coupled problem of poromechanics and cracking in variably saturated porous media. A classical poromechanical formulation is adopted and coupled with a phase-field formulation for the fracture problem. The latter has the advantage of being able to reproduce arbitrarily complex crack pat...
Article
Full-text available
We present projection methods and transfer operations required for adap-tive mesh refinement/coarsening in problems with internal variables. We extend the results of Hennig et al. 2016 on Bézier extraction of truncated hierarchical B-splines and its application to adaptive isogeometric analysis. It is shown that isogeometric analysis improves the p...
Chapter
Full-text available
In the last few years, several authors have proposed different phase-field models aimed at describing ductile fracture phenomena. Most of these models fall within the class of variational approaches to fracture proposed by Francfort and Marigo [13]. For the case of brittle materials, the key concept due to Griffith consists in viewing crack growth...