Numerical modeling of tensile fracture initiation and propagation in snow slabs using nonlocal damage mechanics

Hydraulic fracturing process in fractured rockmass which with an existing single natural fracture at its various conditions: its different angles and different lengths was simulated by using RFPA2D(2.0)-Flow version which adopts the finite element method and considers the heterogeneous characteristics of rock in meso-scale, creates seepage-stress-failure coupling model. The effect tendency of natural fractures angle and length on the seepage characteristics of fractured rockmass was given through the description of tensile fracture initiation and propagation in the rock specimens. The simulation results show that the effect of these two factors on fractures initiation, propagation and rockmass stability under the hydraulic fracturing could be remarkable.

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Understanding Cohesive Law Parameters in Ductile Fracture Initiation and Propagation

European Journal of Computational Mechanics ◽

10.13052/ejcm1779-7179.3012 ◽

2021 ◽

Author(s):

Mariana R. R. Seabra ◽

José M. A. César de Sá

Keyword(s):

Ductile Fracture ◽

Damage Mechanics ◽

Damage Model ◽

Fracture Initiation ◽

Continuum Damage Mechanics ◽

Cohesive Law ◽

Fitting Method ◽

Initiation And Propagation ◽

Discrete Crack ◽

Crack Paths

Continuum Damage Mechanics is successfully employed to describe the behaviour of metallic materials up to the onset of fracture. Nevertheless, on its own, it is not able to accurately trace discrete crack paths. In this contribution, Continuous Damage Mechanics is combined with the XFEM and a Cohesive Law to allow the full simulation of a ductile fracture process. In particular, the Cohesive Law assures an energetically consistent transition from damage to crack for critical damage values lower than one. Moreover, a novel interpretation is given to the parameters of the cohesive law. A fitting method derived directly from the damage model is proposed for these parameters, avoiding additional experimental characterization.

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Nondestructive Estimation of Fracture Toughness Using Instrumented Indentation Technique

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.385-387.893 ◽

2008 ◽

Vol 385-387 ◽

pp. 893-896

Author(s):

Kyung Woo Lee ◽

Hyun Uk Kim ◽

Sang Wook Park ◽

Jung Suk Lee ◽

Kwang Ho Kim ◽

...

Keyword(s):

Fracture Toughness ◽

Damage Mechanics ◽

Volume Fraction ◽

Fracture Initiation ◽

Continuum Damage Mechanics ◽

Instrumented Indentation ◽

Initiation Point ◽

Indentation Technique ◽

Proposed Model ◽

Main Ideas

This study focused on the determination of fracture toughness by instrumented indentation technique. A theoretical model to estimate the fracture toughness of ductile materials is proposed and used to verify those results. Modeling of IIT to evaluate fracture toughness is based on two main ideas; the energy input up to characteristic fracture initiation point during indentation was correlated with material’s resistance to crack initiation and growth, and this characteristic fracture initiation point was determined by concepts of continuum damage mechanics. The estimated fracture toughness values obtained from the indentation technique showed good agreement with those from conventional fracture toughness tests based on CTOD. In addition, we confirmed that the proposed model can be also applied in the brittle material through modification of void volume fraction.

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Fracture Initiation and Propagation in a Deep Shale Gas Reservoir Subject to an Alternating-Fluid-Injection Hydraulic-Fracturing Treatment

SPE Journal ◽

10.2118/195571-pa ◽

2019 ◽

Vol 24 (04) ◽

pp. 1839-1855 ◽

Cited By ~ 12

Author(s):

Bing Hou ◽

Zhi Chang ◽

Weineng Fu ◽

Yeerfulati Muhadasi ◽

Mian Chen

Keyword(s):

Hydraulic Fracturing ◽

Shale Gas ◽

Fracture Initiation ◽

Fluid Injection ◽

Hydraulic Fractures ◽

Stress Difference ◽

Gas Reservoirs ◽

Complex Fracture ◽

Initiation And Propagation

Summary Deep shale gas reservoirs are characterized by high in-situ stresses, a high horizontal-stress difference (12 MPa), development of bedding seams and natural fractures, and stronger plasticity than shallow shale. All of these factors hinder the extension of hydraulic fractures and the formation of complex fracture networks. Conventional hydraulic-fracturing techniques (that use a single fluid, such as guar fluid or slickwater) do not account for the initiation and propagation of primary fractures and the formation of secondary fractures induced by the primary fractures. For this reason, we proposed an alternating-fluid-injection hydraulic-fracturing treatment. True triaxial hydraulic-fracturing tests were conducted on shale outcrop specimens excavated from the Shallow Silurian Longmaxi Formation to study the initiation and propagation of hydraulic fractures while the specimens were subjected to an alternating fluid injection with guar fluid and slickwater. The initiation and propagation of fractures in the specimens were monitored using an acoustic-emission (AE) system connected to a visual display. The results revealed that the guar fluid and slickwater each played a different role in hydraulic fracturing. At a high in-situ stress difference, the guar fluid tended to open the transverse fractures, whereas the slickwater tended to activate the bedding planes as a result of the temporary blocking effect of the guar fluid. On the basis of the development of fractures around the initiation point, the initiation patterns were classified into three categories: (1) transverse-fracture initiation, (2) bedding-seam initiation, and (3) natural-fracture initiation. Each of these fracture-initiation patterns had a different propagation mode. The alternating-fluid-injection treatment exploited the advantages of the two fracturing fluids to form a large complex fracture network in deep shale gas reservoirs; therefore, we concluded that this method is an efficient way to enhance the stimulated reservoir volume compared with conventional hydraulic-fracturing technologies.

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Fracture Initiation and Propagation in Fatigue Contact Loading of AA6082 Aluminium Alloy

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.324-325.1091 ◽

2006 ◽

Vol 324-325 ◽

pp. 1091-1094

Author(s):

Angela Benedetti ◽

Pier Gabriele Molari ◽

Piero Morelli

Keyword(s):

Aluminium Alloy ◽

Contact Area ◽

Contact Fatigue ◽

Fracture Initiation ◽

Free Edge ◽

Element Analysis ◽

Contact Loading ◽

Linear Finite Element ◽

Initiation And Propagation ◽

Microscopy Analysis

This paper presents the results of an experimental investigation on surface contact fatigue of AA6082 aluminium alloy. After testing, microscopy analysis of the specimen contact area shows plastic deformation at the centre and circumferential cracks at the very edge of the print. Major cracks develop at a certain depth under the border of the contact area and propagate beneath the surface, in the direction of both the centre of contact and the lateral free edge of the specimens. No cracks have been observed at the centre of contact, neither on the surface, nor inside the material. Tensile properties of the alloy have been measured and a non linear finite element analysis has been performed in order to calculate the field of deformation and stress in the contact zone. Finally, stress intensities are correlated with the crack initiation points and an interpretation of the propagation paths, in regard to stress distribution, is given.

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A discrete nonlocal damage mechanics approach

Mechanics of Advanced Materials and Structures ◽

10.1080/15376494.2020.1839984 ◽

2020 ◽

pp. 1-8

Author(s):

Arun R. Srinivasa ◽

J. N. Reddy ◽

Nam Phan

Keyword(s):

Damage Mechanics ◽

Nonlocal Damage

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Further Development of the Nonlocal Damage Model of Rousselier for the Transition Regime of Fracture Toughness and Different Stress States

Volume 3: Design and Analysis ◽

10.1115/pvp2014-28714 ◽

2014 ◽

Cited By ~ 2

Author(s):

Sarah Gehrlicher ◽

Michael Seidenfuss ◽

Xaver Schuler

Keyword(s):

Fracture Toughness ◽

Damage Mechanics ◽

Damage Model ◽

Nonlocal Damage ◽

Brittle Transition ◽

Mechanics Model ◽

Element Size ◽

Transition Area ◽

Ductile To Brittle Transition ◽

Stress States

In nuclear power engineering failure has to be excluded for components with high safety relevance. Currently, safety assessments mainly use fracture mechanics concepts. Especially in the transition region of fracture toughness where limited stable crack extension may appear before cleavage fracture the currently applied methods are limited. This Paper deals with the development and verification of a closed concept for safety assessment of components over the whole range from the lower shelf to the upper shelf of fracture toughness. The results of classical used local damage mechanics models depend on the element size of the numerical model. This disadvantage can be avoided using an element size depending on microstructure. With high stress gradients and small crack growth rates usually smaller elements are required. This is in conflict with an element size depending on microstructure. By including the damage gradient as an additional degree of freedom in the damage mechanics model the results depend no longer at the element size. In the paper damage mechanics computations with a nonlocal formulation of the Rousselier model are carried out for the evaluation of the upper transition area. For the prediction of fracture toughness from the ductile to brittle transition area the nonlocal Rousselier model is coupled with the Beremin model. Thus ductile crack growth and failure by brittle fracture can be described in parallel. The numerical prediction of the behaviour of fracture toughness specimens (C(T)-specimens and SE(B)-specimens with and without side grooves) and the experimental results are highly concordant. The load displacement behavior of the specimens and the developed crack front from the ductile to brittle transition area can be well calculated with the nonlocal damage model. The instability in relation to temperature calculated with the coupled damage mechanics model predicts the variations of the experimental results very well. For further application of the nonlocal Rousselier model experiments and numerical calculations of specimens with different stress states and multi-axiality are carried out. Modified fracture toughness specimens like CTS-specimens (compact tension shear specimens) are taken to investigate the applicability of the nonlocal damage model of Rousselier to mixed mode fracture.

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