Multi-field modelling and simulation of large deformation ductile fracture

In the present contribution we focus on a phase-field approach to ductile fracture applied to large deformation contact problems. Phase-field approaches to fracture allow for an efficient numerical investigation of complex three-dimensional fracture problems, as they arise in contact and impact situations. To account for large deformations the underlying formulation is based on a multiplicative decomposition of the deformation gradient into an elastic and plastic part. Moreover, we make use of a fourth-order crack regularization combined with gradient plasticity. Eventually, a demonstrative example shows the capability of the proposed framework

Mixed variational formulations for multi-field problems

General thermoelastic material models have been investigated over the past decades, see e.g. Reese and Govindjee [1], Holzapfel and Simo [2] and Miehe [3] among many oth- ers. In this paper we present a novel computational framework for large strain thermo- elasticity. The ideas of a new formulation for polyconvex large strain elasticity originally introduced by Ball [4] and recently resumed by Bonet et al. [5] are extended to non-linear coupled thermoelasticity, see also Dittmann [6]. In particular, the deformation gradient (line map), its co-factor (area map) and its determinant (volume map) along with the absolute temperature are formulated as independent variables to obtain a polyconvex free energy function. Moreover, we introduce work conjugate stresses to the extended kine- matic set to define a complementary energy principle of Hellinger-Reissner type, where the introduced conjugate stresses along with the deformed geometry and the absolute tem- perature constitute the set of primal variables, see also Hesch condensed.Eventually,quasi-staticaswellastransientnumericalexamplesareinvesti-gatedtodemonstratethecapabilityoftheproposedframework. et al. [7] for the application of a mixed Hu-Washizu type variational principle in the context of coupled phase-field fracture problems. The finite element discretization relies on a quadratic approximation of the deformed geometry and the absolute temperature, whereas discontinuous linear interpolations are used for the conjugate stresses such that the stress unknowns can b

RIDI: Robust IMU Double Integration

This paper proposes a novel data-driven approach for inertial navigation, which learns to estimate trajectories of natural human motions just from an inertial measurement unit (IMU) in every smartphone. The key observation is that human motions are repetitive and consist of a few major modes (e.g., standing, walking, or turning). Our algorithm regresses a velocity vector from the history of linear accelerations and angular velocities, then corrects low-frequency bias in the linear accelerations, which are integrated twice to estimate positions. We have acquired training data with ground-truth motions across multiple human subjects and multiple phone placements (e.g., in a bag or a hand). The qualitatively and quantitatively evaluations have demonstrated that our algorithm has surprisingly shown comparable results to full Visual Inertial navigation. To our knowledge, this paper is the first to integrate sophisticated machine learning techniques with inertial navigation, potentially opening up a new line of research in the domain of data-driven inertial navigation. We will publicly share our code and data to facilitate further research

Isogeometric Analysis and thermomechanical Mortar contact problems

Cataloged from PDF version of article.Thermomechanical Mortar contact algorithms and their application to NURBS based Isogeometric Analysis are investigated in the context of nonlinear elasticity. Mortar methods are applied to both the mechanical field and the thermal field in order to model frictional contact, the energy transfer between the surfaces as well as the frictional heating. A series of simplifications are considered so that a wide range of established numerical techniques for Mortar methods such as segmentation can be transferred to IGA without modification. The performance of the proposed framework is illustrated with representative numerical examples. (C) 2014 Elsevier B.V. All rights reserved

Hierarchical NURBS and a higher-order phase-field approach to fracture for finite-deformation contact problems

In this paper we investigate variationally consistent Mortar contact algorithms applied to a phase-field approach to brittle fracture. Phase-field approaches allow for an efficient simulation of complex fracture problems, as they arise in contact and impact situations. To improve accuracy and convergence, a fourth-order phase-field model is considered, requiring C1 continuity throughout the domain. An isogeometrical framework is used for the spatial discretisation subject to hierarchical refinements to resolve local features. This reduces the computational effort tremendously, as will be shown in a series of representative examples. © 2015 Elsevier B.V

The Influence of Quadrature Errors on Isogeometric Mortar Methods

Mortar methods have recently been shown to be well suited for isogeometric analysis. We review the recent mathematical analysis and then investigate the variational crime introduced by quadrature formulas for the coupling integrals. Motivated by finite element observations, we consider a quadrature rule purely based on the slave mesh as well as a method using quadrature rules based on the slave mesh and on the master mesh, resulting in a non-symmetric saddle point problem. While in the first case reduced convergence rates can be observed, in the second case the influence of the variational crime is less significant

Reduced basis isogeometric mortar approximations for eigenvalue problems in vibroacoustics

We simulate the vibration of a violin bridge in a multi-query context using reduced basis techniques. The mathematical model is based on an eigenvalue problem for the orthotropic linear elasticity equation. In addition to the nine material parameters, a geometrical thickness parameter is considered. This parameter enters as a 10th material parameter into the system by a mapping onto a parameter independent reference domain. The detailed simulation is carried out by isogeometric mortar methods. Weakly coupled patch-wise tensorial structured isogeometric elements are of special interest for complex geometries with piecewise smooth but curvilinear boundaries. To obtain locality in the detailed system, we use the saddle point approach and do not apply static condensation techniques. However within the reduced basis context, it is natural to eliminate the Lagrange multiplier and formulate a reduced eigenvalue problem for a symmetric positive definite matrix. The selection of the snapshots is controlled by a multi-query greedy strategy taking into account an error indicator allowing for multiple eigenvalues

A framework for polyconvex large strain phase-field methods to fracture

Variationally consistent phase-field methods have been shown to be able to predict complex three-dimensional crack patterns. However, current computational methodologies in the context of large deformations lack the necessary numerical stability to ensure robustness in different loading scenarios. In this work, we present a novel formulation for finite strain polyconvex elasticity by introducing a new anisotropic split based on the principal invariants of the right Cauchy-Green tensor, which always ensures polyconvexity of the resulting strain energy function. The presented phase-field approach is embedded in a sophisticated isogeometrical framework with hierarchical refinement for three-dimensional problems using a fourth order Cahn-Hilliard crack density functional with higher-order convergence rates for fracture problems. Additionally, we introduce for the first time a Hu-Washizu mixed variational formulation in the context of phase-field problems, which permits the novel introduction of a variationally consistent stress-driven split. The new polyconvex phase-field fracture formulation guarantees numerical stability for the full range of deformations and for arbitrary hyperelastic materials

S6K-STING interaction regulates cytosolic DNA-mediated activation of the transcription factor IRF3

Cytosolic DNA-mediated activation of the transcription factor IRF3 is a key event in host antiviral responses. Here we found that infection with DNA viruses induced interaction of the metabolic checkpoint kinase mTOR downstream effector and kinase S6K1 and the signaling adaptor STING in a manner dependent on the DNA sensor cGAS. We further demonstrated that the kinase domain, but not the kinase function, of S6K1 was required for the S6K1-STING interaction and that the TBK1 critically promoted this process. The formation of a tripartite S6K1-STING-TBK1 complex was necessary for the activation of IRF3, and disruption of this signaling axis impaired the early-phase expression of IRF3 target genes and the induction of T cell responses and mucosal antiviral immunity. Thus, our results have uncovered a fundamental regulatory mechanism for the activation of IRF3 in the cytosolic DNA pathway