Fracture Nucleation Research Articles

Brief destructions of basic nodes of excavators and critical size of cracks

The article studies brittle fractures of metal structures of mine and hydraulic excavators basic units. Based on the data analyzed and physics of the brittle fracture process, recommendations are given to improve the reliability of machines. For the analysis of brittle fractures, statistical data on machine failures under the conditions of the Korshunovsky GOK and ALROSA quarries were used. The approach to the control of nucleation and formation of brittle fractures by non-destructive methods, which substantially reduces the costs of repair works is described. The analysis of brittle fractures of mining excavators basic units revealed general patterns of destruction causes. Accurate identification of brittle fractures requires simplification of repair works. The method of nondestructive control of machines should be applied. The non-destructive control method is used to control the a brittle cracking in advance and eliminate during scheduled repairs. The scheduled identification and elimination of cracks reduces laboriousness of repair and recovery operations of large-sized units and aggregates of excavators.

Machine learning models for the prediction of energy, forces, and stresses for Platinum

Materials properties such as defect diffusion and/or dissociation, mechanical fracture and void nucleation, under extreme temperatures and pressures, are all governed by the interactions between individual and/or groups of atoms. Computational tools have been instrumental in understanding the atomistic properties of materials at these length scales. Over the past few decades, these tools have been dominated by two levels of theory: quantum mechanics (QM) based methods and semi-empirical/classical methods. The former are time-intensive, but accurate and versatile, while the latter methods are fast but are significantly limited in veracity, versatility and transferability. Machine learning (ML) algorithms, in tandem with quantum mechanical methods such as density functional theory, have the potential to bridge the gap between these two chasms due to their (i) low cost, (ii) accuracy, (iii) transferability, and (iv) ability to be iteratively improved. In this work, we prescribe a new paradigm in which potential energy, atomic forces, and stresses are rapidly predicted by independent machine learning models, all while retaining the accuracy of quantum mechanics. This platform has been used to study thermal, vibrational, and diffusive properties of bulk Platinum, highlighting the framework’s ability to reliably predict materials properties under dynamic conditions. We then compare our ML framework to both QM, where applicable, and several Embedded Atom Method (EAM) potentials. We conclude this work by reflecting upon the current state of ML in materials science for atomistic simulations.

Influence of fracture nucleation and propagation rates on fracture geometry: insights from geomechanical modelling

We combine a power-law microfracture size distribution function with an expression for fracture propagation rate derived from subcritical fracture propagation theory and linear elastic fracture mechanics, to derive a geomechanically based deterministic model for the growth of a network of layer-bound fractures. This model also simulates fracture termination due to intersection with perpendicular fractures or stress-shadow interaction. We use this model to examine key controls on the emergent geometry of the fracture network. First, we examine the effect of fracture propagation rates. We show that at subcritical fracture propagation rates, the fracture nucleation rate increases with time; this generates a very dense network of very small fractures, similar to the deformation bands generated by compaction in unconsolidated sediments. By contrast, at critical propagation rates, the fracture nucleation rate decreases with time; this generates fewer but much larger fractures, similar to the brittle open fractures generated by tectonic deformation in lithified sediments. We then examine the controls on the rate of growth of the fracture network. A fracture set will start to grow when the stress acting on it reaches a threshold value, and it will continue to grow until all the fractures have stopped propagating and no new fractures can nucleate. The relative timing and rate of growth of the different fracture sets will control the anisotropy of the resulting fracture network: if the sets start to grow at the same time and rate, the result is a fully isotropic fracture network; if the primary fracture set stops growing before the secondary set starts growing, the result is a fully anisotropic fracture network; and if there is some overlap but the secondary set grows more slowly than the primary set, the result is a partially anisotropic fracture network. Although the applied horizontal strain rates are the key control on the relative growth rates of the two fracture sets, we show that the vertical effective stress, the initial horizontal stress, the elastic properties of the rock and the inelastic deformation processes, such as creep, grain sliding and pressure solution, all exert a control on the fracture growth rates, and that more isotropic fracture networks will tend to develop if the vertical effective stress is low or if the fractures are critically stressed prior to the onset of deformation. Thematic collection: This article is part of the Naturally Fractured Reservoirs collection available at: https://www.lyellcollection.org/cc/naturally-fractured-reservoirs

Second-order cone interior-point method for quasistatic and moderate dynamic cohesive fracture

Cohesive fracture is among the few techniques able to model complex fracture nucleation and propagation with a sharp (nonsmeared) representation of the crack. Implicit time-stepping schemes are often favored in mechanics due to their ability to take larger time steps in quasistatic and moderate dynamic problems. Furthermore, initially rigid cohesive models are typically preferred when the location of the crack is not known in advance, since initially elastic models artificially lower the material stiffness. It is challenging to include an initially rigid cohesive model in an implicit scheme because the initiation of fracture corresponds to a nondifferentiability of the underlying potential. In this work, an interior-point method is proposed for implicit time stepping of initially rigid cohesive fracture. It uses techniques developed for convex second-order cone programming for the nonconvex problem at hand. The underlying cohesive model is taken from Papoulia (2017) and is based on a nondifferentiable energy function. That previous work proposed an algorithm based on successive smooth approximations to the nondifferential objective for solving the resulting optimization problem. It is argued herein that cone programming can capture the nondifferentiability without smoothing, and the resulting cone formulation is amenable to interior-point algorithms. A further benefit of the formulation is that other conic inequality constraints are straightforward to incorporate. Computational results are provided showing that certain contact constraints can be easily handled and that the method is practical.

On the role of Cu-Zr amorphous intergranular films on crack growth retardation in nanocrystalline Cu during monotonic and cyclic loading conditions

In the present study, molecular dynamics simulation was used to investigate the influence of amorphous intergranular films (AIF) and its thickness on possible crack retardation in nanocrystalline Cu under tensile and cyclic loading conditions. Structural analyses were carried out based on different methods such as centro-symmetry parameter, common neighbor analysis, and atomic strain. Results showed that specimens with AIF thickness as small as 0.5 nm can restrict the propagation of both perpendicular and parallel cracks during uniaxial tensile deformation. By increasing the AIF thickness, the crack propagation was found to be further retarded due to crack tip blunting. Atomic strain analysis also revealed that thicker AIF localized the strain distribution more strongly thus inhibiting the nucleation of multiple intergranular cracks and subsequent rapid fracture. In case of cyclic loading, the strain was accumulated through the formation of twins/stacking faults when the AIF thickness was 0.5 and 1 nm, which can interact with the AIF and eventually cause the nucleation of voids/cracks. However, increasing the AIF thickness to 2 nm can restrict such mechanism as the strain was mostly accommodated by the amorphous phase.

Identify and Monitor Growth Faulting Using InSAR over Northern Greater Houston, Texas, USA

Growth faults are widely distributed in the Greater Houston (GH) region of Texas, USA, and the existence of faulting could interrupt groundwater flow and aggravate local deformation. Faulting-induced property damages have become more pronounced over the last few years, necessitating further investigation of these faults. Interferometric synthetic aperture radar (InSAR) has been proved to be an effective way for mapping deformations along and/or across fault traces. However, extracting short-wavelength small-amplitude creep signal (about 10–20 mm/yr) from long time span interferograms is extremely difficult, especially in agricultural or vegetated areas. This study aims to position, map and monitor the rate, extent, and temporal evolution of faulting over GH at the highest spatial density using Multi-temporal InSAR (MTI) technique. The MTI method, which maximizes usable signal and correlation, has the ability to identify and monitor faulting and provide accurate and detailed depiction of active faults. Two neighboring L-band Advanced Land Observing (ALOS) tracks (2007–2011) are utilized in this research. Numerous areas of sharp phase discontinuities have been discerned from MTI-derived velocity map. InSAR measurements allow us to position both previously known faults traces as well as nucleation of new fractures not previously revealed by other ground/space techniques. Faulting damages and surface scarps were evident at most InSAR-mapped fault locations through our site investigations. The newly discovered fault activation appears to be related to excessive groundwater exploitation from the Jasper aquifer in Montgomery County. The continuous mining of groundwater from the Jasper aquifer formed new water-level decline cones over Montgomery County, corroborating the intensity of new fractures. Finally, we elaborate the localized fault activities and evaluate the characteristics of faulting (locking depth and slip rate) through modeling MTI-derived deformation maps. The SW–NE-oriented faults pertain to normal faulting with an average slip rate of 7–13 mm/yr at a shallow locking depth of less than 4 km. Identifying and characterizing active faults through MTI and deformation modeling can provide insights into faulting, its causal mechanism and potential damages to infrastructure over the GH.

Investigation of the nucleation, propagation and coalescence of hydraulic fractures in glutenite reservoirs using a coupled fluid flow-DEM approach

This paper presented a coupled fluid flow-DEM approach to investigate the nucleation, propagation and coalescence of hydraulic fractures in glutenite reservoirs, where embedded gravel causes strong stress concentration at the interfaces between gravel and matrix and significantly affects local mechanical response. The geometry heterogeneity induced by embedded gravel and multi-sized grains was accurately characterized in DEM, while a flow algorithm was used to model fluid flow. Gravel with different sizes and shapes were randomly embedded in specimens, the interaction mechanisms between propagating fractures and encountering gravel were investigated, and the effects of geo-stress difference, gravel strength and grain size distribution were studied. As can be expected, the macroscale fracture morphology is dominated by far-field geo-stress state, but the microscale mechanical responses of glutenite specimens under hydraulic loading are significantly affected by stress heterogeneity induced by the geometry heterogeneity. Due to the stress heterogeneity in the vicinity of a wellbore, multiple initiation points usually form, causing multi-branched fractures, but some of them are soon arrested by encountering gravel due to lack of sufficient energy for further propagation. When propagating fractures encounter gravel, four interaction patterns (attraction, deflection, penetration and termination) are observed, and then high energy is required for hydraulic fractures to propagate forward, this causes local stress reorientation and new initiation points, and finally complicated fracture morphology forms with branched fractures.

Effects of Intrinsic Properties on Fracture Nucleation and Propagation in Swelling Hydrogels.

In numerous industrial applications, the microstructure of materials is critical for performance. However, finite element models tend to average out the microstructure. Hence, finite element simulations are often unsuitable for optimisation of the microstructure. The present paper presents a modelling technique that addresses this limitation for superabsorbent polymers with a partially cross-linked surface layer. These are widely used in the industry for a variety of functions. Different designs of the cross-linked layer have different material properties, influencing the performance of the hydrogel. In this work, the effects of intrinsic properties on the fracture nucleation and propagation in cross-linked hydrogels are studied. The numerical implementation for crack propagation and nucleation is based on the framework of the extended finite element method and the enhanced local pressure model to capture the pressure difference and fluid flow between the crack and the hydrogel, and coupled with the cohesive method to achieve crack propagation without re-meshing. Two groups of numerical examples are given: (1) effects on crack propagation, and (2) effects on crack nucleation. Within each example, we studied the effects of the stiffness (shear modulus) and ultimate strength of the material separately. Simulations demonstrate that the crack behaviour is influenced by the intrinsic properties of the hydrogel, which gives numerical support for the structural design of the cross-linked hydrogel.

Mechanical responses of WSe2 monolayers: a molecular dynamics study

The mechanical responses of tungsten diselenide (WSe2) monolayers are systemically investigated using classical molecular dynamics simulation. The tensile behaviors of trigonal prismatic phase (h-phase) and distorted octahedral coordinated phase (t-phase) WSe2 in the armchair and zigzag directions are simulated, and the fracture strain, fracture strength and Young’s modulus are calculated under different temperatures, strain rates and vacancy defect ratios. The results show that, at 300 K and a strain rate of 1 × 10−4 ps−1, the fracture strength for h-WSe2 is 16.20 GPa under a 0.19 fracture strain in the armchair direction, while it is 15.74 GPa under a 0.21 fracture strain in the zigzag direction. For t-WSe2, the corresponding fracture strengths and strains have much lower values of 3.46 GPa and 0.06 for the armchair direction, and 3.66 GPa and 0.07 for the zigzag direction, respectively. The evaluated Young’s moduli in the armchair and zigzag directions are 119.73 GPa and 118.29 GPa for h-WSe2, and 68.57 GPa and 68.03 GPa for t-WSe2, respectively. Also, with the increased temperature, atomic thermal vibrations become stronger, which results in decreased fracture strains, fracture strengths, and Young’s moduli in the armchair and zigzag directions for both h-WSe2 and t-WSe2. When the defect ratio changes from 0% to 5%, the mechanical properties of WSe2 deteriorate due to the stress concentration, increased fracture nucleation and disorder of the W-Se bonds. However, in comparison with temperature and defect effects on mechanical properties, the strain rate effect is less significant.

Complex Fracture Nucleation and Evolution with Nonlocal Elastodynamics

A mechanical model is introduced for predicting the initiation and evolution of complex fracture patterns without the need for a damage variable or law. The model, a continuum variant of Newton’s second law, uses integral rather than partial differential operators where the region of integration is over finite domain. The force interaction is derived from a novel nonconvex strain energy density function, resulting in a nonmonotonic material model. The resulting equation of motion is proved to be mathematically well-posed. The model has the capacity to simulate nucleation and growth of multiple, mutually interacting dynamic fractures. In the limit of zero region of integration, the model reproduces the classic Griffith model of brittle fracture. The simplicity of the formulation avoids the need for supplemental kinetic relations that dictate crack growth or the need for an explicit damage evolution law.

Outcrop evidence of polygonal faulting in Ypresian marine clays (Southern North Sea Basin) leads to a new synthesis

Layer-bound, polygonal fault systems (PFS) in marine, fine-grained sediments have been documented with seismic data over large areas in over 100 basins. The questions of how, when and how fast these muds broke without tectonic stress were still open. This study covered the missing observational length scales from 100 m to μms with a continuous range of outcrop observations and related lab results from two quarries in Ypresian marine unlithified swelling clays in the Belgian part of the North Sea Basin.The observed coeval dilatant hydrofractures and folded faults imply highly unstable and transitional tensile fracturing behaviour under shallow overpressure. The random fault plane orientations, radial striation vectors and conal micro-faults exclude far-field stress and slope instability as the driving force, and show that gravity was the major principal stress. A contributing driving force was overpressure in the oxidising fluviatile and lagoonal sands below, which further weakened its clayey caprock and supplied at least part of the water evacuating through it. This fracture water flow eroded and oxidised bits of wall clay and tell-tale microfossil mixtures along the way up. The sharp contrast of black gouge against barely stained wall clays implies that such dilatant fracture and fault growth was almost instantaneous. This resulted in winner-takes-all shear localisation along often razor-thin, slickensided fault mirrors. Faults that locked-up by different degrees of compaction folding and local rotational flow imply: 1) that this clayey mud was still an underconsolidated viscoplastic gel just prior to plastic faulting, capable of syneresis and therefore capable of supplying isotropic contractional stress; 2) not episodic growth but episodic nucleation of additional fractures and faults and punctuated dewatering along them, until the clayey gel matrix and the overpressure in it were fully deflated.

An in-situ study of stress evolution and fracture growth during compression of concrete

We experimentally correlate fracture nucleation with the evolution of aggregate stress tensors during the compression of concrete. The concrete sample, made with portland cement and single-crystal quartz aggregates, was compressed to failure in eight strain increments. X-ray computed tomography was used to determine the extent of fractures and their proximity to aggregates at each strain increment. Three-dimensional X-ray diffraction was simultaneously used to evaluate the full stress tensor in 30 to 40 individual aggregates at each strain increment. We found that a recently-developed mean-field model provides a good prediction of average aggregate stress tensors throughout the sample but does not predict the significant stress heterogeneity observed in individual aggregates, which are likely caused by aggregate interactions and may be responsible for fracture nucleation. Stress variations in aggregates after the nucleation of particular fractures suggest that fractures divided the sample into distinct load paths that experienced either an increase or decrease in compressive stress with further strain. We discuss extensions of the experimental measurements for quantifying specific failure processes in concrete, such as the fracture of the interfacial transition zone. We also discuss the applicability of the measurements to a broad range of other composite materials, and use of the measurements for developing and calibrating theoretical and computational models for composite strength.

How semi-coherent b.c.c. hydride interfacial interactions affect the inelastic deformation and fracture behavior of h.c.p. zirconium alloys

We analyzed how b.c.c. semi-coherent interfaces, within an h.c.p. matrix, have a central effect on the fracture of these multi-phase aggregates. We obtained 36 unique Orientation Relations (ORs) related to semi-coherent interfaces between the hydrides and the parent matrix, and calculated interfacial misfit strains between the matrix and hydride crystalline structures. We then coupled these microstructural interactions to a dislocation-density framework with a fracture nucleation and propagation approach to understand and predict different failure scenarios. The analysis indicates that misfit strains have a dominant mechanistic effect that is essential for an understanding of multi-phase crystalline aggregate behavior that spans different length scales.

Strain-controlled fatigue testing of TRIP800 high-strength quenching and partitioning steel

In this paper, TRIP800 steel plates of thickness of 1.2 mm were subjected to the quenching and partitioning (Q&P) process and underwent strain-controlled fatigue tests. The respective experimental fatigue curves were plotted, and the influencing factors of fatigue resistance were identified and analysed, while the specimen fractographies were examined. The test results show that the existence of residual austenite inhibition of crack extension and strain induced the martensite phase transformation in the residual austenite. The residual compressive stresses improved the fatigue strength of Q&P steel plates under study. The fatigue fracture nucleation occurred in surface inclusions, the crack propagation zone exhibited the ductile fracture mode, while the transient area possessed the brittle fracture features.

Statistical physics perspective of fracture in brittle and quasi-brittle materials.

We discuss the physics of fracture in terms of the statistical physics associated with the failure of elastic media under applied stresses in presence of quenched disorder. We show that the development and the propagation of fracture are largely determined by the strength of the disorder and the stress field around them. Disorder acts as nucleation centres for fracture. We discuss Griffith's law for a single crack-like defect as a source for fracture nucleation and subsequently consider two situations: (i) low disorder concentration of the defects, where the failure is determined by the extreme value statistics of the most vulnerable defect (nucleation regime) and (ii) high disorder concentration of the defects, where the scaling theory near percolation transition is applicable. In this regime, the development of fracture takes place through avalanches of a large number of tiny microfractures with universal statistical features. We discuss the transition from brittle to quasi-brittle behaviour of fracture with the strength of disorder in the mean-field fibre bundle model. We also discuss how the nucleation or percolation mode of growth of fracture depends on the stress distribution range around a defect. We discuss the corresponding numerical simulation results on random resistor and spring networks.This article is part of the theme issue 'Statistical physics of fracture and earthquakes'.

A systematic study of internal gas generation in shale source rocks using analog experiments

A two-dimensional Hele-Shaw cell was created to study and visualize hydrocarbon source rock (i.e., shale) elastic-brittle fracture and fracture network propagation mechanisms triggered by internal gas generation and gas build up during maturation of organic components. An analog immature source rock was created using a mixture of gelatin, sugar, and live yeast in pre-determined proportions. This mixture was poured into the Hele-Shaw cell and allowed to gel. The internal gas generated as a result of sugar fermentation by yeast caused pressure build up within the gel that ultimately resulted in the activation of dissipation mechanisms such as gas diffusion and deformation of the gel matrix. These mechanisms are analogous to shale maturation and fluid generation. Image analysis was employed to study and characterize key events such as fracture nucleation, propagation, and coalescence versus time. Derivative parameters such as fracture growth rate, fracture tip pressure, and fracture spatial distribution, among others, were calculated using the image-sourced data and applying Linear Elastic Fracture Mechanics (LEFM) principles. Results showed that the experiments are repeatable within a consistent response range and additional parameters were identified to be useful input for numerical modelling, including nucleation sites, fracture merging angle, merging to nucleation ratio, and fracture connectivity. For a volume of about 100 cm3 of 11.6% wt. food-grade gelatin solution with 0.25% wt. yeast and a sugar/yeast ratio of 3, measured average total gas production was 35 cm3 (at standard conditions). On an average gelatin matrix area of 400 cm2, the average total fracture length and fracture density are 106 cm and 0.15 fractures/cm2, respectively. Average maximum calculated fracture tip pressure and maximum fracture velocity are 0.92 psi and 5.85 × 10−4 cm/s, respectively. Fracture connectivity was more frequent in the second half of the gas generation process and greater for the older and longer fractures. Average final fracture spacing was 4.42 cm. Connection angles between fractures tended to be closer to 0° than to 90°. Photoelasticity imaging techniques were applied to the experimental setup to visualize the stress field within the sample. The difference of principal stresses was estimated at 3.70 × 103 Pa for the tested material late in the maturation process. Results suggest interdependence of gas pressure, gas diffusion, and transient stress field states. The range of laboratory-scaled data are useful as benchmarking parameters for numerical modelling of source rock maturation including geomechanics.

Fracture behavior of transversely isotropic rocks with discrete weak interfaces

SummaryAnisotropic rocks have gained increasing attention due to the development of unconventional oil and gas reservoirs. This type of reservoir requires complex engineering procedures from drilling to completion, and the mechanical properties of the rocks play a significant role. One of the most important characteristics of unconventional formations is the presence of well‐defined layers, which greatly modify both elastic and fracture properties of the rocks. Rock elastic response is direction dependent, commonly described as vertically transversely isotropic (VTI), meaning that there is an isotropic plane of symmetry with respect to the vertical direction. Between layers, calcitic veins or ash beds alter the rock's properties substantially. These interfaces, which can have low or no cohesion at all, act as preferential planes for fracture nucleation and propagation, affecting the rocks strength. In this work, the fracture behavior of VTI rocks with weak interfaces is studied using numerical simulations of brazilian tests. A hybrid discontinuous Galerkin–cohesive zone model was used to simulate fracture initiation and propagation on discs in the presence of weak planes. With this approach, we determined the effective brazilian test strength of the rocks under different conditions, namely, relative angles between layers and the loading direction, densities, and cohesion of weak interfaces. Shear reactivation of the interfaces is analyzed using the Mohr‐Coulomb failure criterion and Mohr circles.

Lattice rotations in precipitate free zones in an Al-Mg-Si alloy

Scanning precession electron diffraction and automated crystal orientation mapping in a transmission electron microscope (TEM) have been applied to quantitatively study the crystal orientation of precipitate free zones (PFZs) of four GB regions in an AA6060 alloy in peak aged condition (temper T6) after uniaxial compression to 20% engineering strain. The PFZ width in the alloy was found to be w = 170 ± 40 nm. The results show that some PFZs develop significant misorientations relative to their parent grain, and represent, to the best knowledge of the authors, the first quantitative evidence of this. This misorientation may either be constant inside a particular PFZ, making it appear like a band or a very elongated subgrain, or be partitioned in discrete regions with a diameter comparable to the PFZ width, making the former PFZ into a collection of small grains. The band-like PFZ observed in this work had a misorientation relative to its parent grain of ≈ 7°, while the grain-like PFZ had grains with misorientations between ≈ 12° and ≈ 20° relative to its parent grain. The other PFZs that were observed had only limited misorientations relative to their parent grains, and had either dislocations perpendicular to the GB plane or a dislocation wall at the transition region. A general TEM study of the material at various engineering strains was also conducted and suggests that grain-like PFZs are more frequent for larger strains, indicating that the different PFZ features are likely due to different strain localisation in individual PFZs. This localisation is expected to be influenced by the orientation of the loading axis relative to crystal orientations and GB planes. It is also suggested that the different PFZ features engender different work hardening rates and possibly affect nucleation of intergranular fracture. The results support previous studies on the microstructure evolution of PFZs in age-hardenable aluminium alloys during deformation.

The configurational-forces view of the nucleation and propagation of fracture and healing in elastomers as a phase transition

In a recent contribution, Kumar et al. (J Mech Phys Solids 112:523–551, 2018) have introduced a macroscopic theory aimed at describing, explaining, and predicting the nucleation and propagation of fracture and healing in elastomers undergoing arbitrarily large quasistatic deformations. The purpose of this paper is to present an alternative derivation of this theory—originally constructed as a generalization of the variational theory of brittle fracture of Francfort and Marigo (J Mech Phys Solids 46:1319–1342, 1998) to account for physical attributes innate to elastomers that have been recently unveiled by experiments at high spatio-temporal resolution—cast as a phase transition within the framework of configurational forces. A second objective of this paper is to deploy the theory to probe new experimental results on healing in silicone elastomers.

Numerical modelling to predict fracturing rock (Thanet chalk) due to naturally occurring faults and fluid pressure

Outcrop mapping of a chalk cliff and wavecut platform in Thanet, Southeast England show a complex fracture pattern that seems to be controlled by meso-scale strike-slip faults within the chalk. The response of these faults to changes to in situ stress and fluid pressure is thought to control the nucleation and propagation of fractures in the chalk. In this study the DEM (Discrete Element Method) technique has been employed as a follow up to previous field and numerical (boundary and finite element method) investigations to ascertain the role of the faults in the initiation and nucleation of fractures The role of fluid pressure, in-situ stress, and fault geometry are recognised as focal factors. The generation of localised areas of tensile stresses due to fluid pressure and stress perturbations have been shown to cause the initiation of fractures around the fault bends. For releasing bends, localised tensile stresses tend to occur along the central segment of the fault bend, whereas for restraining bends, tensile stresses are more likely to develop on the outer edges of the fault bend. The dissimilarity in the fracturing process due to differences in the geometry of pre-existing faults demonstrates the significance of both fault geometry and fluid behaviour in controlling fracturing.