scholarly journals A statistical DEM approach for modelling heterogeneous brittle materials

2021 ◽  
Author(s):  
Albin Wessling ◽  
Simon Larsson ◽  
Pär Jonsén ◽  
Jörgen Kajberg
Keyword(s):  
Crack Initiation ◽  
Numerical Models ◽  
Brittle Materials ◽  
Heterogeneous Materials ◽  
Numerical Approach ◽  
Discrete Elements ◽  
Proposed Model ◽  
Large Spread ◽  
Shaped Crack ◽  
Cement Strength

AbstractBy utilizing numerical models and simulation, insights about the fracture process of brittle heterogeneous materials can be gained without the need for expensive, difficult, or even impossible, experiments. Brittle and heterogeneous materials like rocks usually exhibit a large spread of experimental data and there is a need for a stochastic model that can mimic this behaviour. In this work, a new numerical approach, based on the Bonded Discrete Element Method, for modelling of heterogeneous brittle materials is proposed and evaluated. The material properties are introduced into the model via two main inputs. Firstly, the grains are constructed as ellipsoidal subsets of spherical discrete elements. The sizes and shapes of these ellipsoidal subsets are randomized, which introduces a grain shape heterogeneity Secondly, the micromechanical parameters of the constituent particles of the grains are given by the Weibull distribution. The model was applied to the Brazilian Disc Test, where the crack initiation, propagation, coalescence and branching could be investigated for different sets of grain cement strengths and sample heterogeneities. The crack initiation and propagation was found to be highly dependent on the level of heterogeneity and cement strength. Specifically, the amount of cracks initiating from the loading contact was found to be more prevalent for cases with higher cement strength and lower heterogeneity, while a more severe zigzag shaped crack pattern was found for the cases with lower cement strength and higher heterogeneity. Generally, the proposed model was found to be able to capture typical phenomena associated with brittle heterogeneous materials, e.g. the unpredictability of the strength in tension and crack properties.

scholarly journals Fracture Property of Y-Shaped Cracks of Brittle Materials under Compression

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
Xiaoyan Zhang ◽  
Zheming Zhu ◽  
Hongjie Liu
Keyword(s):  
Numerical Models ◽  
Brittle Materials ◽  
Test Results ◽  
Compression Tests ◽  
True Triaxial ◽  
Absolute Value ◽  
Branch Angle ◽  
Shaped Crack ◽  
Abaqus Code ◽  
Branch Crack

In order to investigate the properties of Y-shaped cracks of brittle materials under compression, compression tests by using square cement mortar specimens with Y-shaped crack were conducted. A true triaxial loading device was applied in the tests, and the major principle stresses or the critical stresses were measured. The results show that as the branch angleθbetween the branch crack and the stem crack is 75°, the cracked specimen has the lowest strength. In order to explain the test results, numerical models of Y-shaped cracks by using ABAQUS code were established, and the J-integral method was applied in calculating crack tip stress intensity factor (SIF). The results show that when the branch angleθincreases, the SIFKIof the branch crack increases from negative to positive and the absolute valueKIIof the branch crack first increases, and asθis 50°, it is the maximum, and then it decreases. Finally, in order to further investigate the stress distribution around Y-shaped cracks, photoelastic tests were conducted, and the test results generally agree with the compressive test results.

Localized Discrete Modelling of Contact Interfaces to Predict the Dynamic Behaviour of Assembled Structures under Random Excitation

2015 ◽  
Vol 807 ◽  
pp. 13-22
Author(s):  
Anuj Sharma ◽  
Wolfgang Mueller-Hirsch ◽  
Sven Herold ◽  
Tobias Melz
Keyword(s):  
Dynamic Behaviour ◽  
Numerical Models ◽  
Contact Stiffness ◽  
Computational Cost ◽  
Frequency Domain Analysis ◽  
Random Excitation ◽  
Discrete Elements ◽  
Time Dynamic ◽  
Proposed Model ◽  
Stiffness And Damping

Joints used to fasten different parts are the source of local non-linearity with predominance of contact damping in comparison to inherent material damping. The conventional numerical models can predict the dynamic behaviour to a good accuracy, but their implementation for the large system under real time dynamic excitations - like random vibration are encountered with problems of numerical convergence and high computational cost. This paper proposes an approach to model the contact interfaces using discrete elements, with a non-homogeneous definition for the equivalent contact stiffness and damping over the contact interface. The non-homogeneous definition captures the non-linear effects and the local linearisation provides the capability to perform the frequency domain analysis for non-deterministic excitations. The proposed model is validated with experimental results for a test structure excited with random white noise base excitation.

Probabilistic multiscale modeling of fracture in heterogeneous materials and structures

2020 ◽  
Vol 86 (7) ◽  
pp. 45-54
Author(s):  
A. M. Lepikhin ◽  
N. A. Makhutov ◽  
Yu. I. Shokin
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Method ◽  
Fracture Mechanics ◽  
Multiscale Modeling ◽  
Virtual Work ◽  
Numerical Models ◽  
Heterogeneous Materials ◽  
Heterogeneous Structure ◽  
Generalized Coordinates ◽  
Heterogeneous Structures

The probabilistic aspects of multiscale modeling of the fracture of heterogeneous structures are considered. An approach combining homogenization methods with phenomenological and numerical models of fracture mechanics is proposed to solve the problems of assessing the probabilities of destruction of structurally heterogeneous materials. A model of a generalized heterogeneous structure consisting of heterogeneous materials and regions of different scales containing cracks and crack-like defects is formulated. Linking of scales is carried out using kinematic conditions and multiscale principle of virtual forces. The probability of destruction is formulated as the conditional probability of successive nested fracture events of different scales. Cracks and crack-like defects are considered the main sources of fracture. The distribution of defects is represented in the form of Poisson ensembles. Critical stresses at the tops of cracks are described by the Weibull model. Analytical expressions for the fracture probabilities of multiscale heterogeneous structures with multilevel limit states are obtained. An approach based on a modified Monte Carlo method of statistical modeling is proposed to assess the fracture probabilities taking into account the real morphology of heterogeneous structures. A feature of the proposed method is the use of a three-level fracture scheme with numerical solution of the problems at the micro, meso and macro scales. The main variables are generalized forces of the crack propagation and crack growth resistance. Crack sizes are considered generalized coordinates. To reduce the dimensionality, the problem of fracture mechanics is reformulated into the problem of stability of a heterogeneous structure under load with variations of generalized coordinates and analysis of the virtual work of generalized forces. Expressions for estimating the fracture probabilities using a modified Monte Carlo method for multiscale heterogeneous structures are obtained. The prospects of using the developed approaches to assess the fracture probabilities and address the problems of risk analysis of heterogeneous structures are shown.

Analysis and Modeling of Defects in Unsupported Overhanging Features in Micro-Stereolithography

2016 ◽  
Author(s):  
Vito Basile ◽  
Francesco Modica ◽  
Irene Fassi
Keyword(s):  
Finite Element ◽  
Numerical Models ◽  
Numerical Approach ◽  
Fe Analysis ◽  
Test Cases ◽  
Layer By Layer ◽  
Failure Condition ◽  
Micro Scale ◽  
Part Geometry ◽  
Shape Component

In the present paper, a numerical approach to model the layer-by-layer construction of cured material during the Additive Manufacturing (AM) process is proposed. The method is developed by a recursive mechanical finite element (FE) analysis and takes into account forces and pressures acting on the cured material during the process, in order to simulate the behavior and investigate the failure condition sources, which lead to defects in the final part geometry. The study is focused on the evaluation of the process capability Stereolithography (SLA), to build parts with challenging features in meso-micro scale without supports. Two test cases, a cantilever part and a bridge shape component, have been considered in order to evaluate the potentiality of the approach. Numerical models have been tuned by experimental test. The simulations are validated considering two test cases and briefly compared to the printed samples. Results show the potential of the approach adopted but also the difficulties on simulation settings.

scholarly journals Experimental and Numerical Crack Initiation Analysis of the Compressor Blades Working in Resonance Conditions

2011 ◽  
Vol 2011 (3) ◽  
pp. 134-153
Author(s):  
Lucjan Witek
Keyword(s):  
Finite Element ◽  
Crack Initiation ◽  
Transverse Vibration ◽  
Numerical Models ◽  
Fatigue Behavior ◽  
Time History ◽  
Fatigue Properties ◽  
Compressor Blades ◽  
Blade Vibration ◽  
Number Of Cycles

Experimental and Numerical Crack Initiation Analysis of the Compressor Blades Working in Resonance ConditionsThis paper presents the results of a complex experimental and numerical crack initiation analysis of the helicopter turbo-engine compressor blades subjected to vibrations. A nonlinear finite element method was utilized to determine the stress state of the blade during the first mode of transverse vibration. In this analysis, the numerical models without defects as well as those with V-notches were defined. The quality of the numerical solution was checked by the convergence analysis. The obtained results were next used as an input data into crack initiation (ε-N) analyses performed for the load time history equivalent to one cycle of the transverse vibration. In the fatigue analysis, the different methods such as: Neuber elastic-plastic strain correction, linear damage summation and Palmgreen-Miner rule were utilized. As a result of ε-N analysis, the number of load cycles to the first fatigue crack appearing in the compressor blades was obtained. Moreover, the influence of the blade vibration amplitude on the number of cycles to the crack initiation was analyzed. Values of the fatigue properties of the blade material were calculated using the Baumel-Seeger and Muralidharan methods. The influence of both the notch radius and values of the UTS of the blade material on the fatigue behavior of the structure was also considered. In the last part of the work, the finite element results were compared with the results of experimental vibration HCF tests performed for the compressor blades.

scholarly journals An efficient numerical approach for simulating contact in origami assemblages

2019 ◽  
Vol 475 (2230) ◽  
pp. 20190366 ◽  
Author(s):  
Yi Zhu ◽  
Evgueni T. Filipov
Keyword(s):  
Numerical Approach ◽  
Internal Force ◽  
Contact Forces ◽  
Model Parameters ◽  
Full Potential ◽  
Stationary Potential ◽  
Contact Potential ◽  
Proposed Model ◽  
Approach Infinity ◽  
Internal Force Vector

Origami-inspired structures provide novel solutions to many engineering applications. The presence of self-contact within origami patterns has been difficult to simulate, yet it has significant implications for the foldability, kinematics and resulting mechanical properties of the final origami system. To open up the full potential of origami engineering, this paper presents an efficient numerical approach that simulates the panel contact in a generalized origami framework. The proposed panel contact model is based on the principle of stationary potential energy and assumes that the contact forces are conserved. The contact potential is formulated such that both the internal force vector and the stiffness matrix approach infinity as the distance between the contacting panel and node approaches zero. We use benchmark simulations to show that the model can correctly capture the kinematics and mechanics induced by contact. By tuning the model parameters accordingly, this methodology can simulate the thickness in origami. Practical examples are used to demonstrate the validity, efficiency and the broad applicability of the proposed model.

scholarly journals Modeling Wear for Heterogeneous Bi-Phasic Materials Using Discrete Elements Approach

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
Matthieu Champagne ◽  
Mathieu Renouf ◽  
Yves Berthier
Keyword(s):  
Friction And Wear ◽  
Numerical Models ◽  
Real Life ◽  
Limited Range ◽  
Friction Material ◽  
Contact Interface ◽  
Discrete Elements ◽  
Proper Understanding ◽  
Scale Models ◽  
Automotive Brake

A proper understanding of the processes of friction and wear can only be reached through a detailed study of the contact interface. Empirical laws, such as Archard's, are often used in numerical models. They give good results over a limited range of conditions when their coefficients are correctly set, but they cannot be predicted: any significant change of conditions requires a new set of experimental coefficients. In this paper, a new method, the use of discrete element models (DEMs), is proposed in order to tend to predictable models. As an example, a generic biphasic friction material is modeled, of the type used in aeronautical or automotive brake systems. Micro-scale models are built in order to study material damage and wear under tribological stress. The models show what could be achieved by these numerical methods in tribological studies and how they can reproduce the behavior and mechanisms seen with real-life friction materials without any empirical law or parameter.

The Evolving Basis for the Design of Light Gauge Steel Systems

2020 ◽  
Vol 20 (13) ◽  
pp. 2041008
Author(s):  
Pinelopi Kyvelou ◽  
David A. Nethercot ◽  
Nicolas Hadjipantelis ◽  
Constantinos Kyprianou ◽  
Leroy Gardner
Keyword(s):  
Numerical Models ◽  
Numerical Approach ◽  
Superior Performance ◽  
Exact Nature ◽  
Beneficial Effects ◽  
Plate Elements ◽  
Different Types ◽  
Test Behavior ◽  
General Basis ◽  
The Many

The importance of allowing for the many different types of structural interaction that have an effect on the performance of light gauge members when used in practical situations is emphasized. A distinction is drawn between internal interactions involving the various plate elements of the steel profiles and external interactions involving the other components in the system. Although full-scale testing of representative systems can capture this behavior, the costs involved make this an impractical general basis for design; codified methods generally consider only isolated plates within members and isolated members within systems, thereby neglecting the potentially beneficial effects of both forms of interaction. Properly used, modern methods of numerical analysis offer the potential to systematically allow for both forms of interaction — provided the numerical models used have been adequately validated against suitable tests. The use of such an approach is explained and illustrated for three commonly used structural systems: roof purlins, floor beams, and columns in stud walls. In each case, it is shown that, provided sufficient care is taken, the numerical approach can yield accurate predictions of the observed test behavior. The subsequently generated large portfolio of numerical results can then provide clear insights into the exact nature of the various interactions and, thus, form the basis for more realistic design approaches that are both more accurate in their predictions and which lead to more economic designs. Building on this, modifying existing arrangements so as to yield superior performance through specific modifications is now possible. Two such examples, one in which improved interconnection between the components in a system is investigated and a second in which prestressing is shown to provide substantial enhancement for relatively small and simple changes, are presented.

scholarly journals Bidirectional Response of Weak-Axis End-plate Moment Connections: Numerical Approach

Metals ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 964
Author(s):  
Eduardo Nuñez ◽  
Guillermo Parraguez ◽  
Ricardo Herrera
Keyword(s):  
Brittle Failure ◽  
Numerical Models ◽  
Failure Mechanisms ◽  
Numerical Approach ◽  
Axial Loads ◽  
Moment Connections ◽  
Design Procedures ◽  
Moment Resisting ◽  
Ductile Behavior ◽  
Partially Restrained

Brittle failure mechanisms can affect the seismic performance of structures composed of intersecting moment resisting frames, if the biaxial effects are not considered. In this research, the bidirectional cyclic response of H-columns with weak-axis moment connections was studied using numerical models. Several configurations of joints with bidirectional effects and variable axial loads were studied using the finite element method (FEM) in ANSYS v17.2 software. The results obtained showed a ductile behavior when cyclic loads are applied. No evidence of brittle failure mechanisms in the studied joint configurations was observed, in line with the design philosophy established in current seismic provisions. However, beams connected to the column minor axis reached a partially restrained behavior. Joints with four beams connected to the column exhibited a partially restrained behavior for all axial load levels. An equivalent force displacement method was used to compare the hysteretic response of 2D and 3D joints, obtaining higher deformations in 3D joints with respect to 2D joints with a similar number of connected beams. Consequently, design procedures are not capable of capturing the 3D deformation phenomenon.

Sign in / Sign up

Export Citation Format

Share Document