Evaluation of nonlocal approaches for modelling fracture near nonconvex boundaries

Integral-type nonlocal damage models describe the fracture process zones by regular strain profiles insensitive to the size of finite elements, which is achieved by incorporating weighted spatial averages of certain state variables into the stress-strain equations. However, there is no consensus yet how the influence of boundaries should be taken into account by the averaging procedures. In the present study, nonlocal damage models with different averaging procedures are applied to the modelling of fracture in specimens with various boundary types. Firstly, the nonlocal models are calibrated by fitting load-displacement curves and dissipated energy profiles for direct tension to the results of mesoscale analyses performed using a discrete model. These analyses are set up so that the results are independent of boundaries. Then, the models are applied to two-dimensional simulations of three-point bending tests with a sharp notch, a V-type notch, and a smooth boundary without a notch. The performance of the nonlocal approaches in modelling of fracture near nonconvex boundaries is evaluated by comparison of load-displacement curves and dissipated energy profiles along the beam ligament with the results of meso-scale simulations. As an alternative approach, elastoplasticity combined with nonlocal or over-nonlocal damage is also included in the comparative study

A modular extension of a finite element contact implementation

The structural mechanics module of the OOFEM finite element software has been developed to include various algorithms for solving contact mechanics problems. After developing small strain contact algorithms in the 2D domain and their extension to large strain applications [1, 2], the present contribution extends the existing framework to the 3D domain. After reviewing the current code and comparing existing solutions found in the literature, we identify the common ground between 2D and 3D applications, then propose and implement the necessary changes and additions to smoothly integrate the 3D support into existing code. Tests and example problems are presented to confirm the functionality of the resulting implementation

Topology Reduction for Approximate Symbolic Analysis

The paper deals with a procedure for approximate symbolic analysis of linear circuits based on simplifying the circuit model. The procedure consists of two main steps. First, network elements whose influence on the circuit function is negligible are completely removed, i.e. their parameters are removed from the resulting symbolic formula. The second step consists in modifying the voltage and current graphs in order to decrease the number of common spanning trees. The influence of each modification of the circuit model is ranked numerically. A fast method based on the use of cofactors is presented. It allows evaluating all the prospective simplifications using at most two matrix inversions per one frequency point

Protection of personal data in security alert sharing platforms

In order to ensure confidentiality, integrity and availability (so called CIA triad) of data within network infrastructure, it is necessary to be able to detect and handle cyber security incidents. For this purpose, it is vital for Computer Security Incident Response Teams (CSIRT) to have enough data on relevant security events and threats. That is why CSIRTs share security alerts and incidents data using various sharing platforms. Even though they do so primarily to protect data and privacy of users, their use also lead to additional processing of personal data, which may cause new privacy risks. European data protection law, especially with the adoption of the new General data protection regulation, sets out very strict rules on processing of personal data which on one hand leads to greater protection of individual's rights, but on the other creates great obstacles for those who need to share any personal data. This paper analyses the General Data Protection Regulation (GDPR), relevant case-law and analyses by the Article 29 Working Party to propose optimal methods and level of personal data processing necessary for effective use of security alert sharing platforms, which would be legally compliant and lead to appropriate balance between risks

FINITE ELEMENT IMPLEMENTATION OF GEOMETRICALLY NONLINEAR CONTACT

The OOFEM finite element software has been recently updated to include contact algorithms for small strain applications. In this work, we attempt to extend the contact algorithms to large strain problems. Reviewing the current code and comparing it with approaches encountered in literature, we arrive at a specific algorithmic solution and integrate it into the current code base. The current code is explained, the necessary extensions are derived and documented, and the algorithmic changes are described. Tests confirm the functionality and quadratic rate of convergence of the proposed implementation

Gradient polyconvexity and modeling of shape memory alloys

We show existence of an energetic solution to a model of shape memory alloys in which the elastic energy is described by means of a gradient-polyconvex functional. This allows us to show existence of a solution based on weak continuity of nonlinear minors of deformation gradients in Sobolev spaces. Admissible deformations do not necessarily have integrable second derivatives. Under suitable assumptions, our model allows for solutions which are orientation-preserving and globally injective everywhere in the domain representing the specimen. Theoretical results are supported by three-dimensional computational examples. This work is an extended version of [36]

LOCALIZATION ANALYSIS OF AN ORTHOTROPIC MULTI-SURFACE PLASTICITY MODEL UNDER UNIAXIAL STRESS

Numerical simulations of masonry structures are often based on continuum macromodelling approaches that need constitutive laws able to phenomenologically reproduce the behavior of the material. To capture the deformation process up to failure, appropriate softening laws are needed to take into account the contraction of the yield stress domain caused by cracking and crushing. It is well known that softening may lead to localization of inelastic strain. This paper focuses on localization analysis of an orthotropic macro-scale model in the framework of multi-surface plasticity, which describes the in-plane behavior of masonry structures. Preliminary results reported in this short paper are limited to uniaxial stress states. Analytical localization conditions are first derived for uniaxial stress states with principal axes aligned with the material axes of orthotropy. Then, localization analysis is extended to an arbitrary angle between the principal stress axes and the axes of orthotropy

Current Issues of Malicious Domains Blocking

Cyberattackers often use the Domain Name System (DNS) in their activities. Botnet C&C servers and phishing websites both use DNS to facilitate connection to or from its victims, while the protocol does not contain any security countermeasures to thwart such behavior. In this paper, we examine capabilities of a DNS firewall that would be able to filter access from the protected network to known malicious domains on the outside network. Considering the needs of Computer Security Incident Response Teams (CSIRTs), we formulated functional requirements that a DNS firewall should fulfill to fit the role of a cybersecurity tool. Starting from these requirements, we developed a DNS firewall based on the DNS Response Policy Zones technology, the only suitable open source technology available yet. However, we encountered several essential limitations in the DNS RPZ technology during the testing period. Still, our testing results show that simple DNS firewall can prevent attacks not detected by other cybersecurity tools. We discuss the limitations and propose possible solutions so that the DNS firewall might be used as a more complex cybersecurity tool in the future. Lessons learned from the deployment show that while the DNS firewall can indeed be used to block access to malicious domains, it cannot yet satisfy all the requirements of cybersecurity teams