Extended Finite Element Method for Crack Propagation

Pommier, Sylvie; Gravouil, Anthony; Combescure, Alain; Moës, Nicolas

doi:10.1002/9781118622650

Cited by 19 publications

(21 citation statements)

References 17 publications

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“…It is also well known that fatigue-driven crack propagation is accompanied by localized plastic deformation around the crack tip. 77 Therefore, it is clarified that the reported 'material embrittlement' at bulk level 41 is purely a structural change and at the material-level, the membrane material continues to remain ductile and undergoes local plastic deformation even after prolonged mechanical degradation. Chemical stressors are necessary to induce any material-level embrittlement of the membrane via changes in its molecular structure in order to generate brittle fracture features such as the Y-shaped cracks seen in our previous work.…”

Section: Resultsmentioning

confidence: 99%

3D Failure Analysis of Pure Mechanical and Pure Chemical Degradation in Fuel Cell Membranes

Singh

Orfino

Dutta

et al. 2017

J. Electrochem. Soc.

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Lifetime-limiting failure of fuel cell membranes is generally attributed to their chemical and/or mechanical degradation. Although both of these degradation modes occur concurrently during operational duty cycles, their uncoupled investigations can provide useful insights into their individual characteristics and consequential impacts on the overall membrane failure. X-ray computed tomography is emerging as an advantageous tool for fuel cell failure analysis due to its non-destructive and non-invasive 3D imaging capabilities at ambient conditions. In the present work, post-mortem failure analysis of pure mechanical and pure chemical membrane degradation modes is performed three-dimensionally using this technique. A uniquely comprehensive analysis afforded by this technique reveals that membrane failure is almost exclusively characterized by crack formations during mechanical degradation and by severe thinning accompanied by electrode shorting and pinhole formation during chemical degradation, respectively. Catalyst layer cracks, particularly on the cathode side, are found to interact strongly with mechanically induced membrane cracks. The conjoint effect of chemical and mechanical stressors is established as a necessary requirement for: (i) exclusive membrane crack development independent of catalyst layer cracks; and (ii) crack branching during membrane crack propagation. Overall, the membrane failure analysis improves its reliability and quantitative character with the adoption of 3D imaging. The transportation sector is a significant contributor to global greenhouse gas emissions and with ever-growing concerns around the global warming effect, research and development of novel clean energy based automotive solutions is being pursued worldwide. Hydrogen fuel cells have thus far emerged as a promising alternative to fossil fuel based internal combustion engines due to their clean, noisefree, and efficient operation.1 Polymer electrolyte membrane (PEM) fuel cells 2 are widely used in fuel cell electric vehicles (FCEVs) and supply electrical energy from the electrochemical conversion of hydrogen and oxygen (usually supplied as air) into water. In automotive applications, the fluctuating operating conditions due to vehicle dynamics, variations in loads and environmental conditions, startups and shutdowns, fuel starvation, contamination, and freeze-thaw cycles pose significant durability challenges for the PEM fuel cells. 3Understanding the specific durability problems and developing suitable solutions remains a key research focus in automotive PEM fuel cell technology research and is critical to the long-term and large-scale commercial adoption of this technology. Given the complex interplay of multiple physical phenomena that are simultaneously active in an operating PEM fuel cell, various deleterious factors affecting PEM fuel cell components can collectively lead to a gradual performance loss and eventual failure.In PEM fuel cells, the electrodes are separated by a polymeric membrane which allows selective tran...

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Section: Resultsmentioning

confidence: 99%

3D Failure Analysis of Pure Mechanical and Pure Chemical Degradation in Fuel Cell Membranes

Singh

Orfino

Dutta

et al. 2017

J. Electrochem. Soc.

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“…This method is capable of simulating non-planar or 'out of plane' effects [56], however, the elements should be very small in order to precisely predict the path and shape of HF, and the one first order scalar damage index cannot represent the anisotropic damage for a single element, which can be solved by introducing more damage indices with higher orders [63]. Actually, the geometric choice of crack modelling depends on the its size compared to the micro-structure of rock, to the overall structure, the crack initiation, propagation, and local behaviour in crack zone [71]. Adaptive mesh strategy could be used to increase the accuracy and create reasonable mesh distribution [67].…”

Section: Numerical Methods For Hydraulic Fracturing Modelingmentioning

confidence: 99%

“…PL3D assumes that the shape of hydraulic fracture is arbitrary and can be represented by a Green's function [77]. But it requires a consistency condition between layers [5], and cannot simulate 'out of plane' fractures [15], and the use of Green's function makes it not easy for nonlinear or anisotropic rocks [71]. Thus, fully 3D model is in need to simulate hydraulic fracturing process.…”

Section: Numerical Methods For Hydraulic Fracturing Modelingmentioning

confidence: 99%

A review on hydraulic fracturing of unconventional reservoir

et al. 2015

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a b s t r a c tHydraulic fracturing is widely accepted and applied to improve the gas recovery in unconventional reservoirs. Unconventional reservoirs to be addressed here are with very low permeability, complicated geological settings and in-situ stress field etc. All of these make the hydraulic fracturing process a challenging task. In order to effectively and economically recover gas from such reservoirs, the initiation and propagation of hydraulic fracturing in the heterogeneous fractured/ porous media under such complicated conditions should be mastered. In this paper, some issues related to hydraulic fracturing have been reviewed, including the experimental study, field study and numerical simulation. Finally the existing problems that need to be solved on the subject of hydraulic fracturing have been proposed.Unconventional gas mainly includes shale gas, tight gas and coal seam gas. Shale gas is commonly in mudstone, shale and between them the interlayers of sandstone. Tight gas often has been stored in tight sandstone or sometimes limestone. Coal bed methane is contained within coal seams. Their common attribute is that the permeability of the matrix is very low, and the permeability often has been improved by artificial or natural fractures [55]. However, the differences between them are also significant. For example, the effective shale thickness for gas production should be more than 15 m while the height of coal is generally from 0.6 m to 5.0 m [68], as coal seams to be fractured may be multiple and thin, hydraulic fracturing in coal needs to be more accurately designed and controlled. Moreover, the Young's modulus of coal is smaller than shale and tight sandstone, the permeability of coal is more sensitive to stress due to the development of cleat system, and leakoff in coal may be more severe, which can significantly affect the fracturing result. Due to the complexity of unconventional reservoirs, it is challenging to predict the initiation and propagation of hydraulic fractures [39]. For example, the complex in situ stress state and distribution of rocks of varied attributes, which may change the profile of hydraulic fractures [38]; the existence of arbitrary pre-existing interfaces may diversify or arrest hydraulic fractures [93]; the temperature effect [75]; the fluid loss and transport of proppant; the competition between hydraulic fractures, and its recession and closure [4]. Thus, it is crucial to explore how hydraulic fracturing process will happen in complex geological settings.Firsthand materials of hydraulic fracturing come from in-door experiments, and field study. Laboratory study undergoes from small-scale rock samples with several cubic centimetres to large ones with one cubic metre or more. Since it is easy to control the stress conditions and make artificial structures within samples, hydraulic fracturing process with different stress field and rock structures can be conveniently studied. Especially in large scale experiments, it is possible to build a full size borehole, or to contr...

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“…This version of XFEM with an extrinsic enrichment is available in the commercial FE software Abaqus (6.12) [34]. More information about the details and development of XFEM can be found in [35][36][37][38].…”

Section: Xfem Simulationmentioning

confidence: 99%