scholarly journals Mixed Mode Crack Propagation in Iliac Bone

2021 ◽  
Vol 29 (3) ◽  
pp. 67-74
Author(s):  
E. Baesu ◽  
DM. Iliescu ◽  
BV. Radoiu ◽  
S. Halichidis
Keyword(s):  
Crack Propagation ◽  
Critical Stress ◽  
Mixed Mode ◽  
Crack Path ◽  
Maximum Tensile Stress ◽  
Iliac Bone ◽  
Stress Criterion ◽  
Elastic Composite ◽  
Anisotropic Elastic ◽  
Maximum Tensile Stress Criterion

Abstract Bone is a complex material that can be regarded as an anisotropic elastic composite material. The problem of crack propagation in human bone is analyzed by using a generalization of the maximum tensile stress criterion (MTS). The results concern the critical stress for crack propagation and the direction of the crack path in Iliac bone.

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.

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.

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 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.

Failure Inception of a Spherical Contact Under Slip and Stick Conditions for Various Material Properties

2005 ◽  
Author(s):  
Victor Brizmer ◽  
Yuri Kligerman ◽  
Izhak Etsion
Keyword(s):  
Tensile Stress ◽  
Numerical Solution ◽  
Material Properties ◽  
Brittle Failure ◽  
Maximum Tensile Stress ◽  
Normal Loading ◽  
Stress Criterion ◽  
Plastic Yield ◽  
Von Mises ◽  
Maximum Tensile Stress Criterion

Failure inception of a deformable sphere loaded by a contacting rigid flat is analyzed separately for perfect slip and for full stick conditions and various material properties of the sphere. Ductile yielding and brittle failure inception of the sphere is identified by the critical interference and associated normal loading as well as the location of the first yield or failure occurrence. The analysis is based on the analytical Hertz solution for frictionless slip condition and on a numerical solution for stick condition. Failure inception is determined by using either the von Mises criterion of plastic yield or the maximum tensile stress criterion of brittle failure.

Tensile Fracture of Drawn Copper and Mild Steel

1982 ◽  
Vol 104 (1) ◽  
pp. 91-96 ◽  
Author(s):  
E. G. Thomsen
Keyword(s):  
Tensile Stress ◽  
Mild Steel ◽  
Maximum Tensile Stress ◽  
Complete Separation ◽  
Fair Agreement ◽  
Tensile Fracture ◽  
Ofhc Copper ◽  
Stress Criterion ◽  
Maximum Tensile Stress Criterion ◽  
Internal Fracture

Annealed OFHC copper and SAE 1018 steel were reduced by multipass drawing from diameters of 25.4 mm (and smaller) to 11.8 mm. A comparison was made of the experimental draw stresses and those calculated by Sachs’ and Avitzur’s equations and fair agreement exists. The drawn bars were subsequently reduced in diameter by 10 percent in order to provide gage sections and then were pulled in tension to fracture. It was found that in multipass draws some work softening occurs. The oxygen-free copper showed indications that fracture was initiated at the center of the specimen. The internal fracture grew to the near shape of a sphere and separation did not occur until the load had almost decreased to zero. The mild steel apparently also fractured in the center, but complete separation took place immediately after the tensile stress reached its maximum. The fracture theories of Latham and Cockcroft, as well as that of Chen and Kobayashi, were examined and it was found that fair agreement existed. It was also found that for these particular tests, the maximum tensile stress criterion gave more convincing results.

Modelling the Graphite Fracture Mechanisms

2012 ◽  
Author(s):  
C. Jacquemoud ◽  
S. Marie ◽  
M. Nédélec
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Fracture Mechanic ◽  
Critical Stress ◽  
Fracture Stress ◽  
Constitutive Law ◽  
Fracture Mechanisms ◽  
Stress Criterion ◽  
Notched Specimens ◽  
Experimental Fracture

In order to define a design criterion for graphite components, it is important to identify the physical phenomena responsible for the graphite fracture, to include them in a more effective modelling. In a first step, a large panel of experiments have been realised in order to build up an important database; results of tensile tests, 3 and 4 point bending tests on smooth and notched specimens have been analysed and have demonstrated an important geometry related effects on the behavior up to fracture. Then, first simulations with an elastic or an elastoplastic bilinear constitutive law have not made it possible to simulate the experimental fracture stress variations with the specimen geometry, the fracture mechanisms of the graphite being at the microstructural scale. That is the reason why a specific F.E. model of the graphite structure has been developed in which every graphite grain has been meshed independently, the crack initiation along the basal plane of the particles as well as the crack propagation and coalescence have been modelled too. This specific model has been used to test two different approaches for fracture initiation: a critical stress criterion and two criteria of fracture mechanic type. They are all based on crystallographic considerations as a global critical stress criterion gave unsatisfactory results. The criteria of fracture mechanic type being extremely unstable and unable to represent the graphite global behaviour up to the final collapse, the critical stress criterion has been preferred to predict the results of the large range of available experiments, on both smooth and notched specimens. In so doing, the experimental observations have been correctly simulated: the geometry related effects on the experimental fracture stress dispersion, the specimen volume effects on the macroscopic fracture stress and the crack propagation at a constant stress intensity factor. In addition, the parameters of the criterion have been related to experimental observations: the local crack initiation stress of 8MPa corresponds to the non-linearity apparition on the global behavior observed experimentally and the the maximal critical stress defined for the particle of 30MPa is equivalent to the fracture stress of notched specimens. This innovative combination of crack modelling and a local crystallographic critical stress criterion made it possible to understand that cleavage initiation and propagation in the graphite microstructure was driven by a mean critical stress criterion.

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