Intragranular Fracture Research Articles

Temperature-driven micro-fracturing in granite: The interplay between microstructure, mineralogy and tensile strength

High temperatures exert a significant influence on the mechanical and fluid flow properties of rocks and minerals. In crystalline rocks, differential thermal expansion of minerals is known to induce microfracture damage leading to changes in bulk volume and tensile strength. Here we report new data from thermally treated core samples of Devon Granite in order to constrain the interplay between tensile strength and thermally-induced damage with respect to the background mineralogy. A series of core samples was cyclically heated at temperatures ranging from 25 to 800 °C, with P-wave velocity and porosity measured after each cycle. Tensile strength decreased significantly from 9 MPa to less than 3 MPa as thermal treatment increased from 25 to 800 °C. The mechanical data were then compared to fracture density values obtained by optical maps of microfracture damage to assess the quantity and degree of linkage of intergranular and intragranular fractures using the FraqPaQ toolbox. The fracture density increased from 0.02 mm−2 to 2.0 mm−2 which is consistent with results obtained from direct physical parameters as calculated from elastic wave data. We conclude that the combined effects of thermal expansion and the α−β phase transition within quartz crystals has a pronounced effect on tensile strength.

Effect of high-pressure hydrogen environment in elastic and plastic deformation regions on slow strain rate tensile tests for iron-based superalloy A286

To investigate the effects of a high-pressure hydrogen environment in the elastic and plastic deformation regions, we performed slow strain-rate tensile tests of iron-based superalloy A286 at 150 °C by switching the atmosphere from 70 MPa hydrogen to air during the tests. The relationship between the nominal strain exposed to a hydrogen environment and the relative reduction in area (RRA) revealed that in the plastic deformation region, the RRA value decreased gradually depending on the nominal strain exposed to hydrogen, but in the elastic deformation region, the RRA value decreased rapidly. The RRA value further decreased when the stress cycle was applid in the elastic region. The fracture surface exhibited an intragranular slip plane fracture similar to that of the hydrogen-charged specimen. These phenomena suggest that the lattice decohesion theory is dominant in the elastic region, where hydrogen embrittlement occurs owing to an increase in the content of dissolved hydrogen.

Abu Hureyra, Syria, Part 1: Shock-fractured quartz grains support 12,800-year-old cosmic airburst at the Younger Dryas onset

A previous investigation revealed that shock-fracturing, a form of low-pressure shock metamorphism in quartz grains, can be produced during near-surface atomic airbursts and in cosmic impact structures, most likely at pressures lower than 8 GPa. This discovery implies that similar shock-fracturing may also form in quartz grains exposed to near-surface airbursts by comets and asteroids. Here, we investigate this hypothesis by examining quartz grains in a sedimentary profile from Abu Hureyra, a prehistoric archaeological site in northern Syria. This site was previously proposed to have experienced a nearby, low-altitude cosmic airburst at the onset of the Younger Dryas (~12,800 years ago). The Younger Dryas boundary layer (YDB) at Abu Hureyra has previously been shown to contain a rich assemblage of materials consistent in indicating a cosmic impact. These include anomalously high concentrations of melted micro-spherules displaying increased remanent magnetism; meltglass with low water content indicative of high-temperature melting; nanodiamonds, potentially including lonsdaleite; carbon spherules produced by biomass burning; black carbon or soot; total organic carbon; and abnormally high-temperature melted refractory minerals and elements, including platinum, iridium, chromite, and zircon. To further test this impact hypothesis, we searched for evidence of shocked quartz, a robust, widely accepted indicator of cosmic impacts. We used a comprehensive analytical suite of high-resolution techniques, including transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD), to examine and characterize quartz grains from the YDB layer at Abu Hureyra. Our analyses revealed the presence of quartz grains with sub-planar, sub-parallel, and sub-micron-wide intragranular fractures, most likely produced by mechanical and thermal shock or the combination of both. Furthermore, these fractures are typically filled with amorphous silica (glass), a classic indicator of shock metamorphism. Elemental analyses of the weight percentages of oxygen in the amorphous silica indicate that this could not have formed from the deposition of hydrated silica (e.g., opal and hyalite), which is enhanced in oxygen. Instead, the silica we observed is typically depleted in oxygen, consistent with melting under highly reducing conditions. The shock fractures in quartz grains also display Dauphiné twinning, which sometimes develops during the stress of high temperatures or pressures. This evidence is consistent with the hypothesis that the glass-filled fractures in quartz grains were produced by thermal and mechanical shock during a near-surface cosmic airburst at Abu Hureyra. These glass-filled fractures closely resemble those formed in near-surface atomic airbursts and crater-forming impact events.

Deformation behavior of cell walls in an additively manufactured hybrid metallic foam

A hybrid Al-Al3Ni metallic foam was synthesized in-situ via directed energy deposition (DED) of Ni-coated Al 6061 powder, without the need for a foaming agent. Three-dimensional characterization via X-ray computed tomography shows that the foam contains approximately 61.5 % porosity and a high volume fraction of the Al3Ni phase (∼60 vol. %) within the cell walls. This microstructure is notably distinct from the eutectic structure that is typically observed in conventionally processed Al-Ni alloys. To investigate the mechanical properties and deformation mechanisms of the Al-Al3Ni cell walls, in-situ micro-pillar compression was performed, and the results reveal a notable yield strength of 560 MPa and a compressive strain that exceeds 30 %. These properties are attributable to the presence of a high volume fraction of Al3Ni particles, in combination with the characteristics of the Al/Al3Ni interfaces. To provide insight into the deformation mechanisms in the cell walls we used in-situ mechanical testing, transmission electron microscopy and precession electron diffraction characterization, together with molecular dynamics simulations. Our results reveal two distinct mechanisms: uniform dislocation-based deformation of the Al alloy phase and localized deformation within the slip bands in the Al3Ni phase. The results further highlight the importance of the Al/Al3Ni interfaces in mechanical strengthening and the transfer of plastic deformation from the Al phase to the Al3Ni phase. At high mechanical loads, cracks form due to the large stress concentration at the slip bands and slip band intersections in the Al3Ni, giving rise to intragranular fracture of Al3Ni and finally interfacial debonding and cracking.

3D morphology and formation mechanism of fractures developed by true triaxial stress

As main part of underground rock mass, the three-dimensional (3D) morphology of natural fractures plays an important role in rock mass stability. Based on previous studies on 3D morphology, this study probes into the law and mechanism regarding the influence of the confining pressure constraints on 3D morphological features of natural fractures. First, fracture surfaces were obtained by true triaxial compression test and 3D laser scanning. Then 3D morphological parameters of fractures were calculated by using Grasselli’s model. The results show that the failure mode of granites developed by true triaxial stress can be categorized into tension failure and shear failure. Based on the spatial position of fractures, they can be divided into tension fracture surface, S-1 shear fracture surface, and S-2 shear fracture surface. Micro-failure of the tension fracture surface is dominated by mainly intergranular fracture; the maximum height of asperities on the fracture surface and the 3D roughness of fracture surfaces are influenced by σ 3 only and they are greater than those of shear fracture surfaces, a lower overall uniformity than tension fracture surface. S-1 shear fracture surface and S-2 shear fracture surface are dominated by intragranular and intergranular coupling fracture. The maximum height of asperities on the fracture surface and 3D roughness of fracture surface are affected by σ 1 , σ 2 , and σ 3 . With the increase of σ 2 or σ 3 , the cutting off of asperities on the fracture surface becomes more common, the maximum height of asperities and 3D roughness of fracture surface further decrease, and the overall uniformity gets further improved. The experimental results are favorable for selecting technical parameters of enhanced geothermal development and the safety of underground mine engineering.

Powder production of an equimolar NbTaTiZr high-entropy alloy via hydrogen embrittlement

Powder metallurgy methods such as additive manufacturing are often employed to fabricate bulk refractory alloys with high-melting temperature, nevertheless, it still remains a challenge to produce high-quality refractory high-entropy alloy (RHEAs) powders. In this work, we found that hydrogen absorption can embrittle the NbTaTiZr RHEA and promote intragranular fracture due to segregation of hydrogen atoms at grain boundaries. Synergistic effects of the hydrogenation temperature and time on the pulverization behavior of the NbTaTiZr RHEA were investigated, and the relation between grain sizes in the original ingots and particle sizes in the pulverized powders was explored. The present findings not only provide a highly efficient approach to produce high-quality powders of alloys with high-melting points, but also shed light into understanding hydrogen embrittlement of RHEAs.

Development Characteristics and Distribution Patterns of Fractures in the Wufeng-Longmaxi Formation Shale in the Southwestern Sichuan Basin, China

Abstract As the important storage space and main seepage channel of the shale gas reservoirs, fractures control the migration, enrichment, and preservation of shale gas. Therefore, studying the development characteristics of fractures within shale is the key to the exploration and development of shale gas reservoirs. Based on core observation, microscopic thin section examination, field-emission scanning electron microscopy (FE-SEM) analysis, and three-dimensional seismic attribute analysis, this paper studies the development characteristics and distribution patterns of fractures in the Wufeng-Longmaxi Formation shale in the southwestern Sichuan Basin. The results show the following: (1) Both macrofractures and microfractures are developed in the Wufeng-Longmaxi Formation shale in the study area. On the macroscale, horizontal bedding fractures, low-angle slip fractures, vertical shear fractures, and high-angle fractures are mainly developed; on the microscale, intergranular fractures, intragranular fractures, abnormally high-pressure fractures, hydrocarbon generation shrinkage fractures, bedding fractures, etc. are mainly developed. These fractures of different scales work together to create an intricate fracture system within the shale. (2) Based on the 3D seismic attribute analysis, the distribution patterns of fractures was studied in the research area. It was found that nearly east-west-trending and nearly south-north-trending large faults were mainly developed in the Wufeng Formation and the Long-11 submember, with accompanying small faults and secondary fractures. From the bottom boundary of the Wufeng Formation to the top boundary of the Long-11 submember, the fault development shape is unchanged, and the secondary fractures are developed gradually densely, showing the characteristics of a zonal distribution in the entire study area. From the bottom boundary of the Wufeng Formation to the top boundary of the Long-11 submember, the development of microfractures shows variation in different zones. Microfractures are mainly developed around large faults, and the development range of microfractures decreases from bottom to top, but the development of microfractures is gradually intensive. The microfractures are densely distributed from the central to the southern part of the study area (gradually from convergence to divergence), are sparsely distributed in the western part of the study area, and are densely and widely distributed in the northern, northeastern, and northwestern parts of the study area. The research results can provide some guidance for the prediction of shale gas sweet spots in this area, which is beneficial to the further exploration and development of marine shale gas in this area.

Fracture behavior of Hastelloy X elaborated by laser powder bed fusion: Influence of microstructure and building direction

Laser Power Bed Fusion (LPBF) results in complex meso and microstructures, which significantly change the fracture mechanisms of Hastelloy X superalloys. This article aims to investigate the role played by original crack orientation (perpendicular or co-linear to sample lasing planes) on the fracture toughness values of LPBF HX. Single notched three-point bending samples were manufactured vertically (V) or horizontally (H) to estimate the fracture toughness for these two original crack directions. The highest value (about 1360 kJ/m²) is computed in V specimens with an original crack parallel to the lasing plane whereas a value of 1042 kJ/m² is estimated in H specimens with the second crack orientation. Compared to the values obtained in cast specimens, the fracture toughness of LPBF specimens is virtually 5–6 times higher. A non-self-similar cracking is specific to V specimens revealing a more tortuous crack path than in H specimens with self-similar cracking. In both cases, ductile failure is driven by both transgranular and intergranular modes. Nevertheless, the strong morphological texture contributes to promote intragranular fracture mode in V specimens which requires more energy than the one dissipated by an intergranular failure associated to H samples. Consequently, the fracture toughness is significantly higher in V specimens. • Fracture tests were conducted on Hastelloy X specimens elaborated by Laser Power Bed Fusion with two build directions. • In H specimens, intergranular fracture is dominant due to the grain boundaries aligned with the initial notch. • In V specimens, transgranular fracture occurs along with grain boundaries perpendicular to the initial notch. • The morphological texture is responsible for the fracture toughness anisotropy.

Modeling of hydraulic fracturing in polymineralic rock with a grain-based DEM coupled with a pore network model

Rock is a typical heterogeneous material composed of inherent microstructures at the grain scale. In this paper, a grain-based discrete element model (DEM) coupled with a pore network model is developed to study the interaction behavior between hydraulic fractures and the inherent microstructures of rocks. The numerical model parameters are calibrated using the experimental results on Pocheon granite, and then the model is validated by the plane strain Khristianovic-Geertsma-de Klerk (KGD) analytical solution. The fracture propagation in polymineralic rock involves many unique phenomena at the grain scale, such as intragranular fractures splitting grains, intergranular fractures along grain boundaries, fluid lag, and rock fragments. Compared with high viscosity fluid, supercritical carbon dioxide (SC-CO2) driven fractures tend to separate grain boundaries with low local resistance and propagate less smoothly and continuously, more asymmetrically and tortuously. Furthermore, the uniqueness of microstructures controlled by mineral distribution can lead to large variability in fracture paths, but the fracture properties at the macro-scale have not much difference. As the intergranular bonding strength or average grain size increases, a transition from intergranular fracture-dominated to intragranular fracture-dominated is reported. In addition, it is found that the existence of weak grains can result in more intragranular fractures within weak grains and fewer intergranular fractures associated with weak grains. Rock fragments are likely created as a result of the interaction between hydraulic fractures and weak grains and grain boundaries. Our results show that the low-viscosity fracturing fluid and the strong micro heterogeneity of microstructures are prone to result in complex fracture propagation.

Molecular dynamics study on spallation fracture in single crystal and nanocrystalline tin

Spallation fracture in ductile metals with low melting points is an important scientific concern of dynamic fracture. Classical spallation and micro-spallation simulations of single crystal (SC) and nanocrystalline (NC) tin were carried out using non-equilibrium molecular dynamics at shock pressures of 13.5–61.0 GPa. The shock wave velocity had no effect on the waveform evolution in the SC Sn but not in the NC Sn. The front width of the stress wave in the classical spallation of the NC Sn was predominantly affected by grain boundary sliding. The atomic trajectory technique was first introduced to reproduce the evolutionary processes of void growth and coalescence quite effectively. In the classical spallation, the differences in void evolution behavior of SC and NC Sn were mainly reflected in nucleation position, spatial distribution, and growth zone, while their evolutionary behaviors were shared in the micro-spallation. In the NC model, for the classic spallation, voids mostly nucleated at grain boundaries and grew along grain boundaries, resulting in intergranular fractures; for the micro-spallation, voids nucleated at the grain boundary and inside the grain, resulting in intergranular, intragranular, and transgranular fractures. Furthermore, the void volume fraction followed the bilinear rise at the early nucleation and growth stages, and the critical transition point fundamentally signified the initiation of void nucleation to growth.

Underlying limitations behind impedance rise and capacity fade of single crystalline Ni-rich cathodes synthesized via a molten-salt route

Layered oxide LiNixMnyCozO2 (NMC) cathodes are often synthesized as polycrystalline secondary particles. Due to intergranular fracture stemming from volume changes of randomly oriented primary particles during charge/discharge, the synthesis of larger single-crystalline cathodes is of high interest. In this work, molten salt assisted growth of micron-sized Ni-rich crystals is achieved with excellent crystallinity, low cation mixing, and negligible impurities. However, electrochemical performance is compromised by high surface reactivity resulting in decomposition of electrolyte and subsequent formation of a thick CEI layer. While intergranular fracture is eliminated, planar gliding and severe intragranular fracture along the (003) plane occurs in the high voltage region within the first few cycles and is associated primarily with H2 to H3 structural transitions. In addition, H2 to H3 transitions are highly irreversible with cyclic voltammograms revealing polarization growth within <5 cycles. Subsequently, the single-crystalline material exhibited markedly reduced available capacity and enhanced capacity fade from sharp impedance growth compared to its polycrystalline counterpart. This work furthers a fundamental understanding into the limitations of single-crystalline Ni-rich cathodes, and the obstacles limiting the advantages offered by the single-crystalline morphology.

The crack initiation and strengthening mechanism in FGH96 solid-state diffusion bonding joint by quasi-in-situ SEM-DIC and EBSD

The crack initiation and strengthening mechanism of the FGH96 solid-state diffusion bonding joint at room temperature and 50 °C were investigated based on the interaction between microscopic strain concentration and microstructure features. Digital image correlation using SEM images (SEM-DIC) and electron backscattering diffraction (EBSD) technologies were applied. The results showed that the carbides, twin boundaries (TBs) combined with the grain orientation, and the high-angle grain boundaries (HAGBs) played a critical role in the crack initiations. At room temperature, the cracks initiated at the carbide/matrix interface due to the strain mismatch. Besides, the newly formed low-angle grain boundaries (LAGBs) or HAGBs in the grain interior, which were attributed to the direct or indirect inhibition (by forming the stress-affected regions) effect on the slip movements from TBs combined with grain orientation, were developed into cracks with deformation increasing. Moreover, some grain junctions with twin grains participation were also the crack origins due to the strain compatibility and adhesive failure. The cracks at different positions propagated and coalesced to lead to the intragranular fracture. At 650 °C, the effects of carbides, TBs, and grain orientation on the strain accumulation were weakened and contributed little to the crack initiation. The microscopic strain mainly accumulated along HAGBs, leading to the cracks originating along the HAGBs and the intergranular fracture. Due to the different deformation mechanisms, the relative tensile strength and elongation of the joint reached more than 90% at room temperature, while 79.36% and merely 24.4%, respectively, at 650 °C.

Small-scale analysis of brittle-to-ductile transition behavior in pure tungsten

l Small-scale and non-destructive approach to figure out the BDT behavior of pure W. l Development of practical fracture analysis diagram for estimating the BDT regime utilizing nano-indentation and atomistic simulation. l Good agreement between the present BDT prediction and direct observation of failure responses in macroscopic mechanical tests. l Lower pop-in activation energy and higher macroscopic shear strain rate in cold-rolled tungsten. l Decrease in BDT temperature after cold-rolling caused by the dominant presence of mobile edge dislocations. Tungsten as a material exhibits broad and increasingly important applications; however, the characterization of its ductile-to-brittle transition (BDT) is currently limited to large-scale scenarios and destructive testing. In this study, we overcome this challenge by implementing small-scale techniques to provide a comprehensive understanding of the BDT behavior of pure tungsten. In order to predict the failure mode at various temperature ranges, the practical fracture analysis diagram has been proposed to describe the resistance to shear flow and cracking behavior with temperature. High temperature nano-indentation tests have provided the inherent mechanical responses corresponding to the maximum shear stress at various temperatures, which is required for dislocation activities in an atomic scaled activation volume. On one hand, atomistic simulations have provided the temperature dependence of brittle fracture stress, where the atomic bonds break due to intergranular or intragranular fracture. We considered four tungsten specimens having various microstructures prepared using different processing conditions of cold-rolling and post-annealing, and their BDT ranges were inferred using the obtained fracture analysis diagram with the statistical data processing. The fracture analysis diagram of each specimen obtained were compared with the direct observation of fracture responses in macroscopic mechanical tests, which conclusively indicated that the small-scale inherent mechanical properties are greatly relevant to the macroscopic BDT behavior in pure tungsten. Based on the BDT estimations by small-scale characterization, we provided further insights into the factors affecting the BDT behavior of tungsten, focusing on the contributions of different types of dislocations. .

Chemo-mechanical modeling of inter- and intra-granular fracture in heterogeneous cathode with polycrystalline particles for lithium-ion battery

Evolution of complex fracture patterns during electrochemical cycling for the polycrystalline particulate cathode of lithium-ion batteries is found to be a primary reason towards capacity fading. Such fracture of a particles involves inter- and intra-granular crack propagation and often with its debonding from the binder. Till date, a comprehensive understanding of these fracture mechanisms under chemo-mechanical environment towards overall electrochemical response is lacking. In that context, a thermodynamically consistent multi-physics modeling framework is developed to account for strongly coupled chemo-mechanical environments and the evolution of arbitrary fracture within polycrystalline cathode particles embedded in the matrix. Specifically, a regular phase-field fracture variable is introduced for initiation and propagation of the inter- and intra-granular crack within the particle and debonding of the particle-matrix interface. Adopting two additional phase-field descriptors, grain boundaries and particle-matrix interfaces are expressed as diffused regimes. Thus, fracture energies of the grains, grain boundaries, and particle-matrix interface are suitably incorporated within the mathematical framework. Employing a finite element-based numerical scheme, the coupled governing equations are solved for three state variables: concentration, displacement, and phase-field damage. Various parametric studies are performed to investigate the effect of grain sizes, charge rates, and elastic modulus of the matrix on the interplay between the chemo-mechanical behavior and evolution of fracture, and ultimately their collective influences on the electrochemical response. Finally, the present findings offer predictive insights towards engagement of key fracture mechanisms for mechanical degradation of the polycrystalline cathode at electrode level.

Natural fractures and their contribution to tight gas conglomerate reservoirs: A case study in the northwestern Sichuan Basin, China

Well-developed natural fractures in the tight gas conglomerate reservoirs of the northwestern Sichuan Basin, China, are proved to greatly contribute to the porosity and permeability of such reservoirs. Natural fractures can be storage space for hydrocarbons in the reservoir and also serve as fluid flow conduits. Outcrops, cores, and image logs were assessed in order to understand the natural gas production from the tight conglomerate reservoirs. Based on the type of interaction between fractures and clast grains, here we present three types of fractures in the conglomerate tight gas reservoirs: intergranular fractures, intragranular fractures, and grain-edge fractures. These fractures may be tectonic, diagenetic, or combined tectonic-diagenetic. Factors affecting natural fracture development in conglomerates include composition of grain and interstitial material, grain size, contact behavior of grains, and structural position. Well-developed open fractures make up over 70% of the porosity within the tight conglomerate reservoir, while the local permeability can be 3-5 orders higher than that of the matrix reservoir. Natural fractures can also significantly impact the natural gas productivity from individual wells. Production data suggests that higher natural fracture intensity correlate with higher natural gas productivity from wells. Compared with the intensity of intragranular fractures and grain-edge fractures, the high intensity of intergranular fractures shows a notably stronger correlation with high gas productivity. The impact of fractures on natural gas productivity varies greatly with fracture orientation. East-West fractures are predominant flow channels under the existing East-West stress field, contributing significantly to gas production. Northeast-Southwest-oriented fractures are of secondary importance.

Revisiting the capacity-fading mechanism of P2-type sodium layered oxide cathode materials during high-voltage cycling

P2-type sodium layered oxide cathode (Na2/3Ni1/3Mn2/3O2, P2-NNMO) has attracted great attention as a promising cathode material for sodium ion batteries because of its high specific capacity. However, this material suffers from a rapid capacity fade during high-voltage cycling. Several mechanisms have been proposed to explain the capacity fade, including intragranular fracture caused by the P2-O2 phase transion, surface structural change, and irreversible lattice oxygen release. Here we systematically investigated the morphological, structural, and chemical changes of P2-NNMO during high-voltage cycling using a variety of characterization techniques. It was found that the lattice distortion and crystal-plane buckling induced by the P2-O2 phase transition slowed down the Na-ion transport in the bulk and hindered the extraction of the Na ions. The sluggish kinetics was the main reason in reducing the accessible capacity while other interfacial degradation mechanisms played minor roles. Our results not only enabled a more complete understanding of the capacity-fading mechanism of P2-NNMO but also revealed the underlying correlations between lattice doping and the moderately improved cycle performance.

Diverse effects of intragranular fractures on reservoir properties, diagenesis, and gas migration: Insight from Permian tight sandstone in the Hangjinqi area, north Ordos Basin

As petroleum industry tilts towards unconventional petroleum resources, the significance of fractures in exploration and development becomes increasingly prominent. In this study, thin sections and scanning electron microscopic (SEM) observation, porosity and permeability measurement, mercury injection porosimeter (MIP) and computerized tomography (CT) analysis were carried out to investigate the morphology and development characteristics of intragranular fractures, and their effects on physical properties, reservoir diagenesis, and gas migration of the He-1 Member tight sandstones in the Hangjinqi area. Results show that the tight sandstones have intergranular and intragranular dissolved pores, intercrystalline pores and heterogeneous distributed intragranular fractures. The average porosity and permeability of the tight sandstones with intragranular fractures are 12.76% and 4.70 × 10−3 μm2, while those lack of fractures are 6.06% and 0.574 × 10−3 μm2, respectively. The fracture density increases with the enlargement of clastic-grain size and the content of rigid grains. Results indicate that the intragranular fractures greatly enhance permeability, but they have limited direct contribution to total porosity. And the sandstones rich in intragranular fractures have a more homogeneous and connective pore structure with larger radius of pore throat. Intragranular fractures are beneficial to the latter feldspar and debris dissolution caused by organic acids derived from hydrocarbon generation in coal-bearing strata. The dissolved pores directly enhance the porosity of tight sandstones compared to intragranular fractures, and together they form a percolation network to increase permeability. Faults mainly control the lateral petroleum migration from the south to the north, and intragranular fractures affect the local accumulation of gas. This study helps to illustrate the influences of intragranular fractures on reservoir properties, diagenetic difference, and gas migration of the He-1 Member tight sandstones in the Hangjinqi area, and can guide the evaluation and exploration of tight sandstone reservoirs in the Ordos Basin and other basins with similar settings around the world.

Petrography and diagenetic evolution of the Barail sandstones of Naga Schuppen belt, North East India: implication towards reservoir quality

Rock-thin section, scanning electron microscopy and X-ray diffraction analyses have been employed to describe in detail the mineralogical constituents, diagenetic alterations and their impact on reservoir quality of Oligocene Barail sandstones of Naga Schuppen belt, North East India. The Barail Group comprises of alternate beds of hard and compact sandstones with siltstone, shale, carbonaceous shale, and a few thin intermittent coal seams in the upper part of the rock sequence. Petrographic analysis indicates that quartz (42.02–55.02%) is the most dominant mineral constituent followed by rock fragments (6.85–15.67%) and feldspars (0.00–1.97%) with different types of cement in the studied sandstones. Quartz overgrowth, formation of pseudo matrix, authigenic growth of secondary mine­rals and precipitation of clay within the pore spaces tend to reduce the primary and secondary porosities of the rocks. However, in certain samples, the grain coating restricts or hinders cementation and preserves porosity during deep burial, but decreases permeability at pore throats. Partial dissolution and intragranular fracturing of the framework minerals provide sites for pore growth. Pyrite framboids and iron oxides inhibit quartz cementation, but infill pore spaces. The present study shows that original pore morphologies, as well as secondary porosities within the sandstones tend to be destroyed to a large extent by the diagenetic processes

Fracture-induced aging anomalies in LiNi0.6Mn0.2Co0.2O2 electrodes

The gradual loss of capacity and increase in the cell impedance are the mainstream of aging patterns for the lithium-ion batteries and mainly result from the depletion of cell’s cyclable-lithium reservoir. The irreversible drain from this reservoir is well understood and originates from the phenomena such as electrolyte oxidation and reduction at the electrode/electrolyte interfaces. There is, however, limited knowledge about the circumstances leading to the recuperation of misplaced lithium, gain in cell’s energy, and impedance drop. Here, we showcase that the intragranular fracture induces a peculiar aging behavior in the LiNi0.6Mn0.2Co0.2O2 electrodes. Fracture enables an alternative path for the (de)insertion of lithium from the hard-to-reach center of the secondary particles by lithium pore-wall flux instead of solid-state diffusion. The possible consequences are the energy recovery and decrease of the charge-transfer resistance in the electronically well wired electrodes.

Surface and Subsurface Damage Caused by Bullet Impacts into Sandstone

The shift of armed conflicts to more urbanised environments has increased the risk to cultural heritage sites. Small arms impacts are ubiquitous in these circumstances, yet the effects and mechanisms of damage caused are not well known. A sandstone target was shot under controlled conditions to investigate surface and subsurface damage. A 3D model of the damaged block, created by structure from motion photogrammetry, shows that internal fracturing was at least as extensive as the visible surface fractures. Backscatter electron imaging of the damaged surface shows a shift from intragranular fracturing and grain size reduction at &lt;5 mm from the impact point to primarily circumgranular fracturing and grain ‘plucking’ at 20 mm from the impact point. Internal fracture intensity decreased with distance from the centre of the crater. Volumes around the impact point are therefore at greater risk of subsequent weathering deterioration, but significant damage extends to the periphery of the target, rendering whole blocks vulnerable. The surface crater, despite being one of the most conspicuous aspects of conflict damage, has many times less area than internal and surface fractures.