Fracture Events Localization by Numerical Simulations of Cementitious Composites

2015 ◽  
Vol 665 ◽  
pp. 253-256
Author(s):  
Jakub Sobek ◽  
Michal Štafa ◽  
Václav Veselý
Keyword(s):  
Numerical Simulations ◽  
Building Materials ◽  
Numerical Study ◽  
Aggregate Size ◽  
Cohesive Crack ◽  
Type Model ◽  
Failure Behavior ◽  
Crack Model ◽  
Simulation Tools ◽  
Splitting Test

This paper presents a numerical study of failure behavior of cementitious composite materials differing in their composition (aggregate size). A set of four different materials was tested in atypical splitting test geometry. During these tests, apart from the typical outputs such as the load–displacement curves, signals from failure events causing acoustic emission (AE) were recorded. However, reliability of the procedures of the failure events localization might seem questionable in some cases – therefore, the test evaluation procedures were accompanied by analyses using 3D numerical simulation tools based on nonlinear fracture-mechanics approach and propagation of fracture events in the specimens are performed using two computational codes. One is a commercial non-linear FEM code with implementation of cohesive crack model (in the smeared cracks formulation). The second one is an own developed discrete lattice-type model. The comparison of AE records from the tests with the results of the performed numerical simulations can answer questions on the distribution and magnitude (and possibly the energy dissipation amount) of the recorded failure events and generally help in the interpretation and exploitation of AE in the research of failure of non-electric building materials.

Application of a multisurface discrete crack model for clear wood taking into account the inherent microstructural characteristics of wood cells

Holzforschung ◽  
2016 ◽  
Vol 70 (9) ◽  
pp. 845-853 ◽  
Author(s):  
Markus Lukacevic ◽  
Josef Füssl
Keyword(s):  
Building Materials ◽  
Load Capacity ◽  
Failure Mechanisms ◽  
Failure Criteria ◽  
Failure Behavior ◽  
Crack Model ◽  
Clear Wood ◽  
Discrete Crack ◽  
Splitting Test ◽  
Definition Of

Abstract A more accurate prediction of the mechanical behavior of wood is needed to increase its ability to compete with other building materials. Especially, when it comes to estimate failure loads, the lack of appropriate prediction tools becomes obvious. The present work contributes to this goal in two different ways: First, a damage concept for wood is revisited, which allows for transferring information about failure processes through different scales of observation. In this concept, the failure behavior of clear wood is linked to the different characteristic of earlywood and latewood layers in softwoods. This reduces the number of empirically determined strength parameters, while the definition of multisurface failure criteria is still possible. Secondly, it will be demonstrated that the combination of these models with discrete crack modeling based on the extended finite element method provides a numerical simulation tool capable to describe failure mechanisms more realistically than existing approaches. The results obtained by numerical calculations and experiments by means of a micro wedge splitting test show very good agreement, especially, if the load capacity and failure mechanisms are in focus. The presented approach shows a much better performance compared to linear elastic or elastoplastic simulations.

Wedge-Splitting Test – Determination of Minimal Starting Notch Length for Various Cement Based Composites Part I: Cohesive Crack Modelling

2010 ◽  
Vol 452-453 ◽  
pp. 77-80 ◽  
Author(s):  
Václav Veselý ◽  
Ladislav Řoutil ◽  
Stanislav Seitl
Keyword(s):  
Fracture Mechanics ◽  
Cohesive Crack ◽  
Crack Model ◽  
Singular Stress ◽  
Initiation Point ◽  
Linear Elastic ◽  
Wedge Splitting Test ◽  
Splitting Test ◽  
Notch Length ◽  
Wedge Splitting

The geometric proportions of cube-shaped specimens subjected to wedge-splitting tests are numerically studied in the paper. The minimal notch length for specimens made of cement based composites varying in characteristic length of the material (a measure of material brittle-ness/heterogeneity) is verified using finite element method code with an implemented cohesive crack model (ATENA). The problem of assigning the crack initiation point (the notch tip vs. the groove corner in the load-imposing area of the specimen) is solved numerically also using both the theory of linear elastic fracture mechanics and the theory of the fracture mechanics of generalized singular stress concentrators in the second part of the two-part paper. Results ob-tained by the different approaches are compared. The minimal notch length is recommended.

Wedge-Splitting Test – Determination of Minimal Starting Notch Length for Various Cement Based Composites Part II: Crack and Notch Fracture Mechanics Approaches

2010 ◽  
Vol 452-453 ◽  
pp. 81-84 ◽  
Author(s):  
Stanislav Seitl ◽  
Jan Klusák ◽  
Václav Veselý ◽  
Ladislav Řoutil
Keyword(s):  
Fracture Mechanics ◽  
Initial Crack ◽  
Cohesive Crack ◽  
Crack Model ◽  
Singular Stress ◽  
Initiation Point ◽  
Wedge Splitting Test ◽  
Splitting Test ◽  
Notch Length ◽  
Wedge Splitting

The paper focuses on the geometrical proportions of cube-shaped quasi-brittle specimens subjected to a wedge-splitting test (WST). The minimal/optimal initial crack/notch length for successful performance of WST on these specimens is studied numerically (ANSYS). This second part of the paper treats the problem asymptotically, i.e. from the point of view of a very fine grained silicate composite material with negligible characteristic length which describes the level of the material brittleness (i.e. brittle). The problem of competition of the crack initiation point between the notch tip and the groove corner in the load-imposing area of the specimen is solved using theories of both linear elastic fracture mechanics and fracture mechanics of generalized singular stress concentrators. The numerically obtained crack/notch length is compared to results of numerical simulations using cohesive crack model reported in the first part of the paper. The minimal notch length is recommended.

Influence of Coarse Aggregate Size on Softening Curve of Concrete

2012 ◽  
Vol 446-449 ◽  
pp. 636-641
Author(s):  
Zhi Fang Zhao ◽  
Xiao Jie Feng ◽  
Zhi Gang Zhao ◽  
Li Jian Yang
Keyword(s):  
Inverse Analysis ◽  
Coarse Aggregate ◽  
Aggregate Size ◽  
Crack Model ◽  
Element Mesh ◽  
Softening Curve ◽  
Increase With Increase ◽  
Splitting Test ◽  
Linear Softening ◽  
Wedge Splitting

The program by Fortran to determine softening curve of concrete by inverse analysis was developed based on the wedge splitting test and Fictitious Crack Model (FCM). The four-linear softening curves were obtained by the inverse analysis program for the wedge splitting (WS) specimens which size are all 200mm×300mm×300mm with different coarse aggregate size. The approach of refining element mesh was presented for the inverse analysis calculation. It is shown that the three control parameters of softening curve, which are the tensile strength ft, maximum crack width wc and fracture energy GF, increase with increase of the maximum coarse aggregate size dmax.

scholarly journals Numerical Study on Strength and Failure Behavior of Rock with Composite Defects under Uniaxial Compression

Energies ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4418
Author(s):  
Xiaofei Wang ◽  
Zhiguo Xia ◽  
Peng Li ◽  
Hongning Liu
Keyword(s):  
Numerical Simulations ◽  
Uniaxial Compression ◽  
Failure Modes ◽  
Numerical Study ◽  
Numerical Models ◽  
Displacement Vector ◽  
Surrounding Rock ◽  
Failure Behavior ◽  
Underground Engineering ◽  
Combined Defects

The cracks and holes in underground engineering are the critical factors that cause the instability of the surrounding rock. It is helpful to control the stability of surrounding rock to study the samples with combined defects of cracks and holes. In this study, PFC 2D is used to analyze the numerical models. Seven combined models of single circular hole and double cracks with different angles are established, and the fracture angle varies from 0° to 90° with an interval of 15°. First, uniaxial compression experiments and numerical simulations are carried out in the 0° defect combination model, and the microscopic parameters of PFC 2D are determined. Then, the numerical simulations of seven defect models under uniaxial compression are carried out, and the crack development law and acoustic emission characteristics of different defect combination models are studied. The failure modes, mechanical behavior, and stress states are studied. The displacement vector distributions of different defect combination models are analyzed; it is found that there are three main types of macro cracks in the defect combination samples. The results show that the combined defects reduce the strength of the model. Meanwhile, the distributions of the stress and displacement are changed by the cracks with different angles in the defective models.

Using Ansys for Design and Numerical Study of a Specific Fixed Wing UAV

2018 ◽  
Vol 55 (4) ◽  
pp. 652-657 ◽  
Author(s):  
Gabriel Murariu ◽  
Razvan Adrian Mahu ◽  
Adrian Gabriel Murariu ◽  
Mihai Daniel Dragu ◽  
Lucian P. Georgescu ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Unmanned Aerial Vehicle ◽  
Numerical Study ◽  
Flight Time ◽  
Cluster System ◽  
Numerical Results ◽  
Operational Performance ◽  
Gliding Flight ◽  
Aerial Vehicle ◽  
Constant Altitude

This article presents the design of a specific unmanned aerial vehicle UAV prototype own building. Our UAV is a flying wing type and is able to take off with a little boost. This system happily combines some major advantages taken from planes namely the ability to fly horizontal, at a constant altitude and of course, the great advantage of a long flight-time. The aerodynamic models presented in this paper are optimized to improve the operational performance of this aerial vehicle, especially in terms of stability and the possibility of a long gliding flight-time. Both aspects are very important for the increasing of the goals� efficiency and for the getting work jobs. The presented simulations were obtained using ANSYS 13 installed on our university� cluster system. In a next step the numerical results will be compared with those during experimental flights. This paper presents the main results obtained from numerical simulations and the obtained magnitudes of the main flight coefficients.

scholarly journals On Hydromechanical Interaction during Propagation of Localized Damage in Rocks

Minerals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 162
Author(s):  
A.A. Jameei ◽  
S. Pietruszczak
Keyword(s):  
Numerical Study ◽  
Fluid Pressure ◽  
Implicit Time ◽  
Integration Scheme ◽  
Internal Length ◽  
Element Analysis ◽  
Equivalent Permeability ◽  
Mechanical Coupling ◽  
Splitting Test ◽  
Localized Damage

This paper provides a mathematical description of hydromechanical coupling associated with propagation of localized damage. The framework incorporates an embedded discontinuity approach and addresses the assessment of both hydraulic and mechanical properties in the region intercepted by a fracture. Within this approach, an internal length scale parameter is explicitly employed in the definition of equivalent permeability as well as the tangential stiffness operators. The effect of the progressive evolution of damage on the hydro-mechanical coupling is examined and an evolution law is derived governing the variation of equivalent permeability with the continuing deformation. The framework is verified by a numerical study involving 3D simulation of an axial splitting test carried out on a saturated sample under displacement and fluid pressure-controlled conditions. The finite element analysis incorporates the Polynomial-Pressure-Projection (PPP) stabilization technique and a fully implicit time integration scheme.

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