scholarly journals Comparison of Various Criteria Determining the Direction of Crack Propagation Using the UDMGINI User Procedure Implemented in Abaqus

Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3382
Author(s):  
Jakub Gontarz ◽  
Jerzy Podgórski
Keyword(s):  
Crack Propagation ◽  
Crack Path ◽  
Displacement Vector ◽  
Crack Problem ◽  
Crack Tip ◽  
Maximum Principal Stress ◽  
Bending Test ◽  
Unit Distance ◽  
Stress Criterion ◽  
Pull Out

This paper describes a method of predicting the direction of crack propagation implemented by user subroutines in the Simulia-Abaqus FEA system with the use of the extended finite element method (X-FEM). This method is based on displacements and stresses according to Westergaard’s solution of Griffith’s crack problem. During the calculations, in each crack increment, the algorithm reads the stresses and displacements in the model around the crack tip, calculates the criterion values at the read points, reduces them to a unit distance from the crack tip, fits a polynomial to these points, and finds the minimum of the function closest to the last propagation angle. The algorithm also decides when the crack grows, depending on a chosen criterion. Four criteria have been implemented to predict the direction of failure propagation: the maximum principal stress criterion, the Ottosen–Podgórski criterion, the new criterion described here based on the minimum component values of the displacement vector, and the maximum circumferential tensile stress (MTS). These criteria were verified in two tests: the three-point bending test of the notched beam and the anchor pull-out test. For these tests, the criterion built into Simulia Abaqus does not correctly define the crack path, which causes the crack propagation direction to “rotate” when simulating the fracture. The criteria developed here, in most cases, determine the crack path and the maximum force very well compared to real laboratory tests.

scholarly journals Analysis of crack propagation in a “pull-out” test

2019 ◽  
Vol 41 (3) ◽  
pp. 160-170
Author(s):  
Jakub Gontarz ◽  
Jerzy Podgórski
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Crack Propagation ◽  
Computer Analysis ◽  
Laboratory Tests ◽  
Crack Path ◽  
Rock Fragment ◽  
The Finite Element Method ◽  
Pull Out ◽  
Method Model

Abstract The article describes a computer analysis of the pull-out test used to calculate the force needed to pull out a rock fragment and determine the shape of this broken fragment. The analyzed material is sandstone and porphyry. The analysis included the first approach to using own subroutine in the Simulia Abaqus system, that is, which task is undertaken to accurately determine the crack path of the Finite Element Method model. The work also contains a description of laboratory tests and analytical considerations.

Cleavage Crack Path Prediction in a PWR Vessel Steel

2014 ◽  
Author(s):  
Xiaoyu Yang ◽  
Stéphane Marie ◽  
Clémentine Jacquemoud
Keyword(s):  
Crack Propagation ◽  
Crack Path ◽  
Cleavage Crack ◽  
Extended Finite Element ◽  
Vessel Steel ◽  
Stress Criterion ◽  
Statistical Effect ◽  
Path Prediction ◽  
Crack Paths ◽  
Crack Path Prediction

Cleavage crack propagation has been tested for three different geometries of Compact Tensile (CT) specimens: CT25, CT50 and extended CT25 (CT25 with CT50 width) (Figure 3). The experimental results show that the crack paths are straight for CT25 and CT50, but they are unstable and curved for extended CT specimens (Figure 5 to 7). Numerical computation had been performed by extended finite element method (XFEM) in CAST3M software. 2D modeling was used in order to predict the crack path. The analysis was based on a local non-linear dynamic approach with a RKR fracture stress criterion depending on temperature and strain rate. In order to simulate the curvature of the cracks path, a statistical effect was introduced in the model to take into account the spatial distribution of cleavage initiators, which is the characteristic of cleavage fracture. At each step of propagation during the modeling, the direction was randomly chosen, according to a uniform defects distribution. The numerical results show a good agreement with experience. The different crack paths were curved in extended CT25, but remained almost straight in CT25 and CT50 specimens, despite of the instability introduced in the modeling in the propagation direction. These results show that the statistics of micro-defects can induce, jointly with the geometry of specimen, a large scatter of crack propagation paths.

A Novel Robust Remeshing Finite Element Technique for Fracture Propagation

2020 ◽  
pp. 2050040
Author(s):  
L. D. C. Ramalho ◽  
J. Belinha ◽  
R. D. S. G. Campilho
Keyword(s):  
Finite Element ◽  
Crack Propagation ◽  
Crack Opening ◽  
Crack Tip ◽  
Weighted Average ◽  
Fixed Number ◽  
Stress Criterion ◽  
Maximum Tangential Stress Criterion ◽  
Maximum Crack ◽  
Element Technique

In this work, a novel and robust remeshing algorithm for crack opening problems is proposed, combined with triangular plane stress finite elements. In the proposed algorithm, the crack tip efficiently propagates until a pre-established maximum crack length is achieved and the crack propagation direction is defined considering the maximum tangential stress criterion. The stress state at the crack tip is obtained using a weighted average of the stresses of the integration points adjacent to the crack tip, to smoothen the stress field near the crack tip. In order to achieve accurate stress fields in the vicinity of the singularity, the proposed algorithm establishes that there is always a fixed number of nodes and elements surrounding the crack tip. To verify the accuracy of the algorithm, three benchmark tests were analyzed and the solutions were compared with results available in the literature. It was observed that the proposed technique allows to maintain the meshes regular during the propagation process, significantly reducing the number of distorted elements, which solves one of the main problems when simulating crack propagation with the finite element method (FEM). Additionally, the obtained results allowed to understand that this algorithm generally leads to accurate crack paths.

Mixed Mode Brittle Crack Propagation Modelling in a PWR Vessel Steel

2008 ◽  
Author(s):  
B. Prabel ◽  
S. Marie ◽  
A. Combescure
Keyword(s):  
Finite Element ◽  
Stress Field ◽  
Crack Propagation ◽  
Rapid Growth ◽  
Mixed Mode ◽  
Crack Path ◽  
Crack Tip ◽  
Crack Speed ◽  
Brittle Crack ◽  
Crack Propagation And Arrest

R&D activities and some development are performed at CEA on the brittle crack propagation and arrest. Phenomena occurring after the initiation of a brittle crack are not yet well understood. Absence of model able to predict the rapid growth of a brittle crack motivates this study. Due to the rapid growth of the crack, inertial effects and dynamic fracture should be considered. Assumption of a linear elastic solid are often preferred, but when plasticity of the material become non negligible (which is the case in the vicinity of the transition zone), these models become more limited. That’s why the paper presented here deals with dynamic crack propagation in elastic-viscoplastic material and aims at proposing a model able to predict the brittle crack propagation and arrest. To this end, experimental work is carried out for different geometries made of french RPV ferritic steel. Compact Tension specimens with different thickness, isothermal rings under compression with different positions of the initial defect to study also a mixed mode configuration. The test conditions and mains results (crack initiation, crack velocity measurements, ...) are collected and presented in a first part of the paper. To model efficiently the crack propagation in the Finite Element calculation, the eXtended Finite Element Method (X-FEM) implemented in the CEA F.E. software CAST3M is described in the second part of the paper. Thanks to this numerical technique, the crack path does not need to follow the element edges and the crack progress is directly incorporated in the degrees of freedom of the elements crossed by the crack. A two-steps methodology is presented in the third and fourth parts of this paper. The first step consider only the CT specimen, experimental crack speed evolution with time is imposed in numerical simulations. Energy terms and stress field at the crack tip are evaluated and discussed to build up a criterion. Then, the criterion identified on CT specimen is used in a second step as a predictive model to simulate crack propagation for each geometry studied (CT, ring in both mode I and mixed mode). In particular, crack propagation models based on the stress field evaluated at the crack tip and on a critical cleavage stress dependent on the strain rate, exhibit very good agreement with experimental data in term of crack speed, crack path and crack length at arrest. The mixed mode case is discussed in detail because to be pertinent, a model of brittle crack propagation should not only give the crack speed, but also its preferred direction of evolution.

scholarly journals Numerical Study on Crack Propagation by Using Softening Model under Blasting

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Rong Hu ◽  
Zheming Zhu ◽  
Jun Xie ◽  
Dingjun Xiao
Keyword(s):  
Numerical Simulation ◽  
Crack Propagation ◽  
Numerical Study ◽  
Numerical Models ◽  
Incident Angle ◽  
Damage Model ◽  
Maximum Principal Stress ◽  
Stress Criterion ◽  
Proposed Model ◽  
Simulation Results

A mixed failure criterion, which combined the modified maximum principal stress criterion with the damage model of tensile crack softening, was developed to simulate crack propagation of rock under blasting loads. In order to validate the proposed model, a set of blasting models with a crack and a borehole with different incident angles with the crack were established. By using this model, the property of crack propagation was investigated. The linear equation of state (EOS) was used for rock, and the JWL EOS was applied to the explosive. In order to validate the numerical simulation results, experiments by using PMMA (polymethyl methacrylate) with a crack and a borehole were carried out. The charge structure and incident angle of the blasting experimental model were the same as those in the numerical models. The experiment results agree with the numerical simulation results.

Crack Path Investigation Using the Generalized Maximum Tangential Stress Criterion: Antisymmetrical Four-Point Bending Specimen

2013 ◽  
Vol 436 ◽  
pp. 108-113 ◽  
Author(s):  
Lucie Šestáková Malíková
Keyword(s):  
Fracture Mechanics ◽  
Crack Propagation ◽  
Tangential Stress ◽  
Series Expansion ◽  
Mixed Mode ◽  
Crack Path ◽  
Stress Criterion ◽  
Four Point Bending ◽  
Special Cases ◽  
Maximum Tangential Stress Criterion

A mixed-mode geometry has been chosen in order to investigate crack propagation through the specimen. There exist several criteria for estimation of the crack path, and this work enriches the concept by application of multi-parameter fracture mechanics. Particularly, the classical MTS criterion is presented in its generalized form when several initial terms of the so-called Williams series expansion are used for the tangential stress approximation. The results obtained show that the generalized approach can be important in some special cases, when the criterion shall be applied in a larger distance from the crack tip.

Simulation Implementation on the Direction Prediction of Crack Propagation Based on the First Principal Stress

2019 ◽  
Vol 795 ◽  
pp. 361-366 ◽  
Author(s):  
Cai Ming Liu ◽  
Dun Ji Yu ◽  
Xu Chen
Keyword(s):  
Crack Propagation ◽  
Principal Stress ◽  
Crack Extension ◽  
Crack Tip ◽  
Maximum Tensile Stress ◽  
Maximum Principal Stress ◽  
Linear Elastic ◽  
Complex Crack ◽  
3D Crack Propagation ◽  
2D And 3D

The study attempts to present a new finite element method to implement the direction prediction of crack extension for 2D and 3D cracks based on the maximum tensile stress (MTS) criterion by identifying the first principal stress direction. Especially in the 3D crack propagation, this paper gave a detailed and innovative research method to overcome the challenge of direction prediction on crack extension. The maximum principal stress of the node of crack tip and its neighboring nodes were calculated to determine the increment and the direction of crack tip respectively. Some examples of complex crack propagation were performed under a variety of mixed fracture modes based on linear elastic analysis by ANSYS software. A reasonable evaluation was executed and the advantages of this method were analyzed in detail.

scholarly journals Experimental Investigation of Crack Propagation and Strain Fields Evolution around a Crack Tip in 5A05 Aluminum Alloy

Metals ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 685
Author(s):  
Jijun Li ◽  
Wencai Li ◽  
Chunwang Zhao ◽  
Yongming Xing ◽  
Fengchao Lang ◽  
...  
Keyword(s):  
Aluminum Alloy ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Shear Strain ◽  
Crack Tip ◽  
Bending Test ◽  
Propagation Path ◽  
Normal Strain ◽  
Load Direction ◽  
Strain Fields

In situ scanning electron microscopy three-point bending test was employed in this study to investigate the crack initiation and propagation in 5A05 aluminum alloy. The microscale strain fields around the crack tip were measured by using the geometric phase analysis method. Results show that prior to the crack initiation, the normal strain εyy (y direction is perpendicular to the load direction) was tensile around the notch, whereas the normal strain εxx (x direction is parallel to the load direction) was compressive around the notch. The shear strain εxy was nearly zero. With the increase in load, the normal strains εyy and εxx gradually increased, but the change in shear strain εxy was not evident. When the stresses at several sharp points at the notch root reached the breaking strengths, a few microcracks initiated at these points. At this moment, the normal strains εyy and εxx were much greater than the shear εxy, and dominated the strain fields around the crack tip. In the crack propagation process, the normal strains εyy and εxx, and the shear strain εxy dominated the strain fields around the crack tip, thereby leading to a Z-form of crack propagation path in the specimen.

Image Based Displacement Vector Estimation Method around the Fatigue Crack Tip

2010 ◽  
Vol 452-453 ◽  
pp. 341-344
Author(s):  
Masao Moriyama ◽  
Daisuke Ushijima ◽  
Junichi Katsuta
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Strain Field ◽  
High Speed ◽  
Displacement Vector ◽  
Estimation Method ◽  
Crack Tip ◽  
Instantaneous Strain ◽  
Fatigue Crack Propagation Test

To clarify the instantaneous strain field during the fatigue crack propagation test, an attempt is made to estimate the displacement vector of the small area of the crack tip from the high speed movie. The key theory of the estimation is Particle Image Velocimetry (PIV) which is frequently use in the fluid dynamical data analysis. PIV means the area based correlation matching between the sequential image pair. At first the earlier image divided into the small subareas, and on the later image most correspondent position to the subarea is searched. The each displacement of the subarea position between earlier and later image means the local deformation of the crack tip. Through the numerical simulation, the subarea size and search area size are defined to get the realistic result. To make the instantaneous deformation within a cycle of the fatigue crack propagation test, high-speed camera with high-power camera is used. The frame rate is beyond 1000Hz and shutter speed is 1/8000 second. By using the such camera and optimized PIV algorithm, the instantaneous strain field can be estimated and this will analyze the phenomenon of fatigue crack propagation.

Effect of Microscopic Inhomogeneity on Creep-Fatigue Crack Propagation of Transversally Loaded Directionally Solidified Superalloy

2007 ◽  
Author(s):  
Masato Yamamoto ◽  
Takayuki Kitamura ◽  
Takashi Ogata
Keyword(s):  
Crack Propagation ◽  
Crack Path ◽  
Crack Tip ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Local Deformation ◽  
Transverse Load ◽  
Directionally Solidified ◽  
Propagation Behavior ◽  
Creep Fatigue

Directionally solidified superalloy, which has elongated large grains, is used for a gas-turbine blade because of its high creep strength. Since the grain size is not small enough in comparison with the size of component and crack, the inhomogeneous microstructure strongly affects the crack propagation behavior. The aim of this research is to clarify the microstructural effect in the creep-fatigue under a transverse load. The experiment reveals characteristic crack path and fluctuation of crack propagation rate in detail. Several intergranular sub-cracks initiated ahead of the tip of main crack occasionally connect with each other and form a complicated crack path. The deformation near the crack tip during a loading cycle is highly dependent on the local grain boundary network, grain shape, and crack shape. The magnitude of da/dN is correlated fairly well with that of local deformation in the vicinity of crack tip. This suggests that the stress field near the crack tip governs the crack propagation.

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