Petr Frantík

Parallelization of lattice modelling for estimation of fracture process zone extent in cementitious composites

This paper is focused on the verification and validation of the developing technique for estimation of the extent (the size and shape) of the fracture process zone (FPZ) in quasi-brittle silicate-based specimens/structures during failure process (termed the ReFraPro -Reconstruction of Fracture Process - technique). Most experimental data published in the literature are incomplete for its sound validation; therefore, numerical simulations by means of physical discretization of continuum are used for supplementing the verification of the technique. A discrete spring network/lattice particle-type model formulated as a nonlinear dynamical system is utilized. Parallelized implementation within the CUDA environment helps to decrease the computational cost of the simulations to an admissible level. The conducted analysis demonstrates satisfactory agreement of the size and shape of the FPZ reconstructed by the ReFraPro technique with both the data of the performed simulations and selected experimental data from literature.

An application for the fracture characterisation of quasi-brittle materials taking into account fracture process zone influence

Abstract The paper introduces a Java application programmed for the advanced determination of the fracture characteristics of silicate-based materials failing in a quasi-brittle manner. The tool reconstructs the progress of a quasi-brittle fracture from the measured load–displacement curve and the knowledge of basic mechanical properties of the material. The main contribution of the proposed approach is that it takes the characteristics of the Fracture Process Zone (FPZ, particularly its extent, i.e. its size and shape) evolving at the tip of the propagating crack during the failure process into account and incorporates them into the fracture-mechanical parameter evaluation procedure(s). This approach is expected to substantially diminish the influence of the test specimen’s size/shape and the test geometry on the values of the parameters of nonlinear fracture models determined from the records of fracture tests on laboratory specimens. The application implements a developed technique for estimation of the size and shape of the FPZ. The technique is based on an amalgamation of several modelling concepts dealing with the failure of structural materials, i.e. multi-parameter linear elastic fracture mechanics, classical nonlinear fracture models for concrete (equivalent elastic crack and cohesive crack models), and the plasticity approach. The knowledge of the FPZ’s extent is employed for the relation of a part of the entire work of fracture to its characteristics within the presented approach. The verification and validation of the developed technique is performed via numerical simulations using the authors’ own computational code based on physical discretization of continuum and selected sets of experimental evidence published in the literature. Reasonable agreement is observed between the outputs of the presented semi-analytical technique and both the simulation results and the experimental data.

A Harmonized Perspective on Transportation Management in Smart Cities: the Novel IoT-Driven Environment for Road Traffic Modeling

The unprecedented growth of today’s cities together with increased population mobility are fueling the avalanche in the numbers of vehicles on the roads. This development led to the new challenges for the traffic management, including the mitigation of road congestion, accidents, and air pollution. Over the last decade, researchers have been focusing their efforts on leveraging the recent advances in sensing, communications, and dynamic adaptive technologies to prepare the deployed road traffic management systems (TMS) for resolving these important challenges in future smart cities. However, the existing solutions may still be insufficient to construct a reliable and secure TMS that is capable of handling the anticipated influx of the population and vehicles in urban areas. Along these lines, this work systematically outlines a perspective on a novel modular environment for traffic modeling, which allows to recreate the examined road networks in their full resemblance. Our developed solution is targeted to incorporate the progress in the Internet of Things (IoT) technologies, where low-power, embedded devices integrate as part of a next-generation TMS. To mimic the real traffic conditions, we recreated and evaluated a practical traffic scenario built after a complex road intersection within a large European city.

Multi-parameter crack tip stress state description for estimation of fracture process zone extent in silicate composite WST specimens

For wedge splitting test specimens, the stress and displacement fields both in the vicinity and also in larger distance from the crack tip are investigated by means of numerical methods. Several variants of boundary conditions were modeled. The stress intensity factor K, T-stress and even higher-order terms of William series were determined and subsequently utilized for analytical approximation of the stress field. A good fit between the analytical and numerical solution in dependence on the distance from the crack tip was shown, compared and discussed. Presented approach is considered as suitable for estimation of the fracture process zone extent in silicate composite materials.

Balanced Energy Dissipation at Propagating Crack Tip in Quasi-Brittle Materials? - Analysis via Soft-Computing Methods

Analysis on the aspects of the energy dissipation in the case of quasi-brittle fracture is presented. Dissipation both via cohesive forces at the crack faces and the one taking place within the volume of the fracture process zone is considered. Tools from the field of soft computing techniques are employed. The analysis is conducted on results from extensive experimental campaign.

Fractality of Simulated Fracture

The paper is focussed on numerical simulations of the fracture of a quasi-brittle specimen due to its impact onto a fixed rigid elastic plate. The failure of the specimen after the impact is modelled in two ways based on the physical discretization of continuum: via physical discrete elements and pseudo-particles. Advantages and drawbacks of both used methods are discussed. The size distribution of the fragments of the broken specimen resulting from physical discrete element model simulation follows a power law, which indicates the ability of the numerical model to identify the fractal nature of the fracture. The pseudo-particle model, on the other side, can successfully predict the kinematics of the fragments of the specimen under impact failure.

Analytical Approximation of Crack-Tip Stress Field: Study on Efficient Determination of Coefficients of Higher Order Terms of Williams Power Expansion

The paper presents a study on accuracy of the multi-parameter approximation of the stress field in a cracked body using Williams power series calibrated according to results of FEM computation. Main attention is paid to a detailed analysis of suitable selection of FE nodes, whose results serve as inputs to the over-deterministic method (ODM) employed for determination of the coefficients of terms of the Williams expansion describing the crack-tip field. Two different ways of FE nodal selection are compared – nodes selected from the crack tip vicinity versus nodes selected from a specific part of the test specimen body in a specific way. Comparison is made with the usage of the authors’ own developed procedures enabling both the determination of the coefficients of the analytical approximation of stress field based on the FE results and the backward reconstruction of the field from those determined terms’ coefficients/functions. The wedge-splitting test (WST) specimen with a crack is taken as example for the study.

Estimation of the Zone of Failure Extent in Quasi-Brittle Specimens with Different Crack-Tip Constraint Conditions from Stress Field

A multi-parameter fracture mechanics concept based on the Williams power series is applied on novel cracked specimen geometries utilizing combined boundary conditions of the wedge splitting and the three-point bending test. Crack tip stress fields for various configurations (causing different constraint conditions at the crack tip and thus also different fracture process zone extents) are numerically investigated and subsequently analytically reconstructed using developed procedure. An importance of using higher order terms of the Williams series is demonstrated.

Localization of Propagation of Failure in Concrete Specimens Assessed by Means of Acoustic and Electromagnetic Emission and Numerical Simulations

Localization of Propagation of Failure in Concrete Specimens Assessed by Means of Acoustic and Electromagnetic Emission and Numerical Simulations This paper presents a numerical analysis aimed at verification of the monitoring of failure - its propagation and the locations of the individual failure events - in quasi-brittle cement-based materials. The failure monitoring methodology in question is performed using a technique based on utilization of (a combination of) acoustic emission (AE) and electromagnetic emission (EME) phenomena. The analysis is conducted on concrete laboratory specimens and aims to reveal the type and intensity of failure which can be captured by this experimental technique. The computational tools ATENA and FyDiK are employed in the numerical analysis, the first being based on continuum mechanics with an implemented cohesive crack model while the second utilizes the physical discretization of continuum, again with a material model that takes account of the cohesive nature of quasi-brittle fracture. Lokalizace Průběhu Porušování V Betonových Vzorcích Stanovená Pomocí Akustické a Elektromagnetické Emise a Numerických Simulací V článku jsou prezentovány výsledky numerické analýzy zaměřené na verifikaci záznamu průběhu porušování - jeho postup a lokalizaci jednotlivých událostí - odehrávajícího se ve kvazikřehkých materiálech na bázi cementu. Experimentální metodika pro sledování porušení, která je zde zkoumána a verifikována, vychází z (kombinace) akustické a elektromagnetické emise (AE, resp. EME). Analýza je prováděna na zkušebních tělesech z betonu s cílem odhalit typ a intenzitu porušení, jež je schopna použitá technika zachytit. Pro zde prezentovanou numerickou analýzu jsou použity výpočetní nástroje ATENA, resp. FyDiK, založené na mechanice kontinua se zahrnutím modelu kohezivní trhliny, resp. na metodě fyzikální diskretizace kontinua, rovněž využívající materiálový model zohledňující kohezivní povahu kvazikřehkého lomu.

Parallelized implementation of dynamical particle system

The paper presents approaches to implementation of solution of discrete dynamical system of mutually repelling particles. Two platforms: a single-thread JAVA process and parallelized CUDA C solution, are employed for the dynamical simulation. Qualities of both platforms are discussed and explained as their performance when solving two proposed interaction laws is compared.