scholarly journals Analysis of Crack Initiation and Propagation Thresholds of Inclined Cracks under High-Pressure Grouting in Ordovician Limestone

Energies ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 360
Author(s):  
Bin Xu ◽  
Shuning Dong ◽  
Shangxian Yin ◽  
Shuxia Li ◽  
Yanling Xu ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Mixed Mode ◽  
Crack Opening ◽  
Pressure Coefficient ◽  
Water Channel ◽  
Fracture Initiation ◽  
Simulation Software ◽  
Mode I ◽  
Ordovician Limestone ◽  
Grouting Pressure

Control of the grouting pressure within the critical grouting pressure for crack propagation in Ordovician limestone can not only ensure grout penetration length, but also prevent the risk of creating an artificial water channel. Based on the fracture mechanics theory, a formula was proposed to calculate the critical grouting pressure of mixed mode I-II cracks in Ordovician limestone. The necessary conditions for tilted crack opening, the rationality of the existing empirical value of the maximum allowable grouting pressure was investigated based on the mechanical model. The RFPA2D-Flow numerical simulation software was used to evaluate the deduced theory. The research results show that the deduced theoretical calculation formula of the critical grouting pressure agrees with the numerical simulation results; when the mixed mode I-II fracture initiation occurs, the grouting pressure exceeds the perpendicular stress of the overlying rock; the greater the density of the overlying rock mass, the greater the value of grouting pressure for fracture initiation; when the side pressure coefficient was ≥1, crack dip angle increased and the grouting pressure for fracture initiation tended to decrease; and the empirical grouting pressure at the maximum allowable grouting pressure is 2.0–2.5 pw, which will not cause propagation and failure of the existing crack.

Integrity Assessment of Mechanical Components Subjected to Mixed Mode Cracking

2016 ◽  
Author(s):  
Lingfu Zeng ◽  
Chouping Luo ◽  
Lennart G. Jansson
Keyword(s):  
Mixed Mode ◽  
Nuclear Power ◽  
Fracture Initiation ◽  
Mode I ◽  
Multiple Cracks ◽  
Straight Pipe ◽  
Element Analysis ◽  
Integrity Assessment ◽  
Failure Assessment ◽  
Metal Weld

This paper addresses a mixed mode driven cracking and its integrity assessment for applications in aging nuclear power piping. Following our earlier discussion on the use of mode-I based criteria in the current R6-method-based practice of integrity assessment, case studies conducted using finite element analysis are conducted and examined: (1) A plate with a single and multiple central crack(s) under tension; (2) A full-scale laboratory test of a straight pipe with an obliquely inserted crack in a dissimilar metal weld. Our results confirm the following earlier observations: For cases when mixed mode loading conditions are significant, (i) the fracture initiation predicted by using J-integral based mixed mode cracking criteria can approximately be achieved by an “effective stress intensity factor” based approach; (ii) it is not conservative to use a purely mode-I based criterion for the evaluation of the fracture failure assessment for typical problems of mixed mode driven cracking; (iii) The effect of multiple cracks can be significant and an assessment by only examining one crack, which is a common practice today, may not be fully conservative.

Numerical simulation of fatigue crack propagation in mixed-mode (I+II) using the program BemCracker2D

2019 ◽  
Vol 10 (4) ◽  
pp. 497-514
Author(s):  
Pedro G.P. Leite ◽  
Gilberto Gomes
Keyword(s):  
Numerical Simulation ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Propagation ◽  
Crack Growth ◽  
Mixed Mode ◽  
Mode I ◽  
Post Processing ◽  
Content Type

Purpose The purpose of this paper is to present the application of the boundary element method (BEM) in linear elastic fracture mechanics for analysis of fatigue crack propagation problems in mixed-mode (I+II) using a robust academic software named BemCracker2D and its graphical interface BemLab2D. Design/methodology/approach The methodology consists in calculating elastic stress by conventional BEM and to carry out an incremental analysis of the crack extension employing the dual BEM (DBEM). For each increment of the analysis, the stress intensity factors (SIFs) are computed by the J-Integral technique, the crack growth direction is evaluated by the maximum circumferential stress criterion and the crack growth rate is computed by a modified Paris equation, which takes into account an equivalent SIF to obtain the fracture Modes I and II. The numerical results are compared with the experimental and/or BEM values extracted from the open literature, aiming to demonstrate the accuracy and efficiency of the adopted methodology, as well as to validate the robustness of the programs. Findings The paper addresses the numerical simulation of fatigue crack growth. The main contribution of the paper is the introduction of a software for simulating two-dimensional fatigue crack growth problems in mixed-mode (I+II) via the DBEM. The software BemCracker2D coupled to the BemLab2D graphical user interface (GUI), for pre/post-processing, are very complete, efficient and versatile and its does make relevant contributions in the field of fracture mechanics. Originality/value The main contribution of the manuscript is the development of a GUI for pre/post-processing of 2D fracture mechanics problems, as well as the object oriented programming implementation. Finally, the main merit is of educational nature.

Towards a Process for the Assessment of Mixed Mode I+II Fracture Toughness

2018 ◽  
Author(s):  
Afaf Bouydo ◽  
Valéry Lacroix ◽  
Rachid Chaouadi ◽  
Vratislav Mares
Keyword(s):  
Fracture Toughness ◽  
Mixed Mode ◽  
Ferritic Steel ◽  
Crack Opening ◽  
Pressure Vessels ◽  
Mode I ◽  
J Integral ◽  
Mode I Crack ◽  
Standard Mode ◽  
Material Fracture

In fracture mechanics, a flaw behavior in pressure vessels is assessed with respect to the material fracture toughness. Fracture toughness which most Fitness-for-Service (FFS) codes relies on, only considers mode-I crack opening. However, in presence of tilted flaws, like quasi-laminar hydrogen flakes, this mode-I toughness may be too severe, and a mixed mode I+II fracture toughness seems to be more appropriate. In order to address the assessment of the fracture toughness curve, mixed mode I+II tests were performed by the authors on ferritic steel samples by adjusting the standard mode I CT specimen geometry to a geometry subjected to mixed mode I+II. Then, XFEM simulations of the mixed mode tests were performed in order to calculate the J-integral along the crack front. Based on tests and calculations results, the paper explains how the authors work towards proposing a method to measure the material fracture toughness in case of flaws subjected to mixed mode (I+II) loading.

scholarly journals Study on Compound Mode Crack Propagation Law of Semi Circular Arch Roadway Under Impact Load

2021 ◽  
Author(s):  
Chengxiao Li ◽  
Renshu Yang ◽  
Yuantong Zhang ◽  
Chen An
Keyword(s):  
Numerical Simulation ◽  
Crack Propagation ◽  
Mixed Mode ◽  
Impact Load ◽  
Central Axis ◽  
Mode I ◽  
Finite Element Software ◽  
Circular Arch ◽  
Propagation Law ◽  
The Impact

Abstract Various kinds of defects are usually contained in the underground roadway. When the roadway is impacted by external load, the location of defects will influence the roadway with different degrees. In order to study the effect of the location of defects on crack propagation in roadway, in this paper, the stress wave produced by the bullet impacting the incident rod was used as the impact load. Meanwhile, the variations of speed, displacement and dynamic stress intensity factor (DSIF) of cracks, during crack propagation, were obtained by using the experimental system of digital laser dynamic caustics (DLDC). And the extended finite element software ABAQUS is used for numerical simulation. Based on the method of experimental-numerical simulation, the crack propagation path is verified and the impact fracture behavior of semi-circular arch roadway with different defect positions is presented. It can be concluded that when the prefabricated crack is located at the central axis of sample, the crack propagation belongs to pure mode I; when the prefabricated crack is 5mm away from the central axis, the crack propagation appears between mode I and I-II mixed mode alternately; when the prefabricated crack is at the edge of semi-circular arch roadway, the crack propagation follows I-II mixed mode

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