Dominant Deformation Mode Research Articles

Effect of deformation mechanisms on in-plane wave propagation in periodic cellular materials

Cellular solids’ acoustic properties, such as dispersion, direction dependence, and phase velocities, are inherently coupled to the dominant deformation modes in their ligaments. Understanding and exploiting this coupling can improve the design process of applications utilizing cellular solids’ acoustic properties. This work aims to provide insights into this coupling using finite element simulations. In particular, this work investigates the effect of the two main deformation mechanisms observed in cellular materials, i.e. bending and stretching, on the dispersive and direction dependent characteristics of 2D elastic waves traversing them. Two related honeycomb-based lattices are used in this work, namely a bending dominated lattice and a stretching dominated lattice. Results show that asymmetric waves in the bending dominated lattice are more direction dependent and less dispersive than in the stretching dominated lattice, whereas symmetric waves are generally independent of direction and dispersive in both bending and stretching dominated lattices. In addition, results show that phase velocities of symmetric and asymmetric waves scale linearly with relative density in the bending dominated lattice and nonlinearly with relative density in the stretching dominated lattice. Moreover, maximum phase velocities in the stretching dominated lattice are observed to be higher than in the bending dominated lattice.

Dynamic recrystallization of a wrought magnesium alloy: Grain size and texture maps and their application for mechanical behavior predictions

Effect of dynamic recrystallization (DRX) on the grain refinement and texture modification was studied by conducting a series of hot compression on AZ31B Mg alloy. Processing-grain size-texture maps were established as a function of temperature, strain rate, strain, and the Zener-Hollomon parameter (Z). Moreover, influence of simultaneous changes in the grain size and texture on tensile yield strength and ductility of the hot-worked Mg alloy was studied using the grain size and texture maps established. The processing-grain size map showed that the DRX grain size decreased with the increase in Z, also revealing various characteristics ranging from a grain growth, grain refinement, to a bimodal distribution of ultrafine grains and partially recrystallized grains. The effect of twinning on the grain refinement was also evident at high Z conditions. The processing-texture map revealed that the initial fiber texture was altered significantly to a shear, off-normal, or extension-twin texture with the increase in Z. The Schmid-factor maps were calculated to identify a dominant deformation mode during a subsequent tensile deformation of the hot-worked samples. Finally, a corresponding Hall-Petch relationship for each dominant deformation mode was used to establish tensile yield-strength maps, which agree well with the measured data.

Application of Molecular Dynamics Calculations to Elucidation of the Mechanism of Hydrogen-Induced Crack Initiation in Fracture Toughness Tests Using Tempered Martensitic Steels

It is well known that the presence of hydrogen deteriorates mechanical properties of steels, that appears as reduced fracture toughness, shorter fatigue lifetime, etc.; these phenomena are recognized as hydrogen embrittlement. The effect of hydrogen on crack initiation of fracture toughness test has been investigated using a combination of experimental and computational approaches. Tempered lath martensitic steel was subjected to fracture toughness test with monotonically rising load in air and high-pressure hydrogen gas. While crack propagated continuously within grains in air, cracking in hydrogen grew by linking isolated interface failure ahead of a main crack tip. Then, to understand the nucleation mechanism of isolated failure in the presence of hydrogen, the tensile simulations of twist grain boundaries (TGBs) rotated along <110> axis at various angles were conducted using molecular dynamics calculations. While the dislocation emission from TGB rotated 70° is dominant deformation mode in the absence of hydrogen, the rupture along TGB rotated 110° and 170° without stress relaxation due to dislocation emission is dominant deformation mode in the presence of hydrogen. As a consequence, it is indicated that the origin of hydrogen-induced isolated crack initiation in the vicinity of fatigue pre-crack is the rupture along the block boundaries within martensitic structure due to hydrogen-induced inhibition of dislocation emission from GBs.

Evaluation of Compressive and Energy Absorption Characteristic of a Closed-cell Polymeric Foam subject to Dynamic Loading

Foamed plastics have been used in many engineering fields because of their superiority in low density, energy absorption, thermal insulation, and acoustic damping capacities. With foams, it is known that the microstructure of cells directly relates to macroscopic deformation behaviour. However, mechanical properties based on microstructures composed of non-uniform cells have not been fully understood. This study aims to clarify the mechanical properties grounded on microstructures of foamed plastics subjected to dynamic loading. The quasi-static and dynamic compression test was carried out using foamed plastic with anisotropy in the cell structure, then the strain rate dependence of deformation and energy absorption characteristics was investigated. It was confirmed that the local buckling of the cells was the dominant deformation mode in the plastic collapse of the test piece. It was also confirmed that cell buckling was initiated around the middle in the height after the plastic collapse, then propagated to the whole specimen in both the quasi-static and dynamic tests by using digital image correlation. The stress-strain relationships and the amount of absorbed energy showed strain rate dependence owing to the deformation mode in which the local buckling of the cells is dominant.

Deformation twinning in pure aluminum under ultrahigh strain rate: Dependence of strain rate and crystallographic orientation

Deformation twinning rarely occurs in single or polycrystalline aluminum due to its high stacking fault energy (SFE), even when deformed at low temperatures and/or high strain rate. Here we report electron back-scattered diffraction observations that provide evidence of deformation twinning in single crystal pure aluminum under shock loading. In addition, deformation twinning prefers to occur as twinning plane roughly paralleled to shear direction. Under shock loading, dislocation motion becomes jagged or even stopped, resulting in self-pinning. Then deformation twinning takes over as the dominant deformation mode. Our results provide a comprehensive understanding of the dynamic transition from dislocation slip to deformation twinning in pure aluminum under shock loading.

Polycrystalline Ni nanotubes under compression: a molecular dynamics study

Mechanical properties of nanomaterials, such as nanowires and nanotubes, are an important feature for the design of novel electromechanical nano-architectures. Since grain boundary structures and surface modifications can be used as a route to modify nanostructured materials, it is of interest to understand how they affect material strength and plasticity. We report large-scale atomistic simulations to determine the mechanical response of nickel nanowires and nanotubes subject to uniaxial compression. Our results suggest that the incorporation of nanocrystalline structure allows completely flexible deformation, in sharp contrast with single crystals. While crystalline structures at high compression are dominated by dislocation pinning and the multiplication of highly localized shear regions, in nanocrystalline systems the dislocation distribution is significantly more homogeneous. Therefore, for large compressions (large strains) coiling instead of bulging is the dominant deformation mode. Additionally, it is observed that nanotubes with only 70% of the nanowire mass but of the same diameter, exhibit similar mechanical behavior up to 0.3 strain. Our results are useful for the design of new flexible and light-weight metamaterials, when highly deformable struts are required.

Quantitative Investigation on the Slip/Twinning Activity and Cracking Behavior During Low-Cycle Fatigue of an Extruded Mg-3Y Sheet

The slip/twinning activity and cracking behavior of an extruded Mg-3Y sheet during strain-controlled tension-compression low-cycle fatigue (LCF) at room temperature were studied quantitatively and statistically by slip trace analysis and EBSD-based misorientation analysis combined with SEM. The twinned area fraction was 1.7 pct after 200 cycles indicating that twinning contributed limited plastic deformation, and only tension twins were observed. Among 989 grains analyzed, 11.4 pct grains exhibited observable slip traces. Basal slip, with a relative frequency of 81.4 pct, was the dominant deformation mode, and pyramidal II slip (12.4 pct) also exhibited a high activity. The slip-dominated deformation was responsible for the symmetrical hysteresis loops. Among the total 311 cracks observed after 200 cycles, 80.1 pct were intergranular and 19.9 pct were transgranular. The appearance of the two kinds of cracks was closely related. Persistent slip band (PSB, 13.8 pct) and twin (TW, 5.5 pct) were two key transgranular crack initiation sites. The PSB cracking fraction (cracked PSBs/total PSBs) for different slip modes followed pyramidal II (64 pct) > basal (36 pct) > prismatic (14 pct). Strain localization was likely to be responsible for the high cracking fraction of pyramidal II PSBs, which was consistent with their small normalized Schmid factors and the heterogeneous distribution of geometrically necessary dislocation density. Slip/Twinning transfers at grain boundary were also occasionally observed and they were closely associated with transgranular cracks.

Effect of yttrium addition on dynamic mechanical properties, microstructure, and fracture behavior of extrusion-shear ZC61 + xY (x = 0, 1, 2, 3) alloys

In this study, extrusion-shear ZC61 + xY (x = 0, 1, 2, 3) magnesium (Mg) alloys were prepared by a novel severe plastic deformation method, i.e., extrusion-shear, which integrates direct extrusion with equal channel angular pressing. The effect of yttrium (Y) addition on dynamic mechanical properties, microstructure, and fracture behavior of ZC61 + xY (x = 0, 1, 2, 3) alloys was investigated by Split-Hopkinson Pressure Bar setup under a strain rate of 2100 s−1 along extrusion direction. With the increase in the content of added Y from 0 to 3 wt%, due to the strengthening of secondary phases and grain refinement, the yield strength of Mg alloys was enhanced from 142 to 342 MPa, and the ultimate compression strength of Mg alloys was improved from 582 to 701 MPa. During dynamic compression, the <c + a > pyramidal slip and extension twinning were the dominant deformation modes, which coordinated plastic deformation of ZC61 + xY (x = 0, 1, 2, 3) alloys. Analysis of the fracture behavior of four Mg alloys samples indicated that the fracture mode of ZC61 alloy was the brittle and melt mixed-mode; however, the fracture behavior of ZC61 + xY (x = 1, 2, 3) alloys was the brittle and ductile mixed fracture. With the increase of Y content from 1 to 3 wt%, the absorption energy density was observably increased, which was mainly responsible for the change of fracture mode from brittle fracture to ductile fracture.

Experimental and numerical investigation of compressive behavior of lattice structures manufactured through projection micro stereolithography

The present work focuses on investigating the effect of lattice geometry on compression behavior, deformation mechanism and energy absorption capability of 3D printed polymeric micro-lattice structures. The mechanical characteristics of lattice cores comprising of periodic body centered cubic (BCC) architecture unit-cells, printed with projection micro-stereolithography (PμSL) based 3D printing technique were experimentally and numerically examined. For a fixed mass and corresponding relative density of lattice, five variants of BCC lattice structures were built by varying unit cell size, numbers and its strut diameter. The quasi-static compression tests were performed to determine the load-displacement history, stress-strain curves and deformation modes of lattice structures. The experimental results show that number of unit cells with in a certain volume of lattice block can have significant effect on compression properties of lattice structure. Within the same geometric envelop and mass properties, the lattice containing higher number of cells with reduced strut diameter tends absorb more energy as compared to a lattice with fewer number of cells with increased strut diameter. The elastic modulus, collapse and plateau stresses of lattice increase while densification strain decreases with the increase in number of unit cells. Moreover, there exists a certain number of cells in certain volume of lattice structure for which the energy absorption is higher, after that number the effect not significant. The deformation behavior of lattice was inspected and bending dominant deformation modes were observed in all lattice structures. The lattice with small cells shows progressive layer by layer collapse while for larger cell sized lattice show signs of buckling effect with central localized deformation modes. Lastly, the experimental outcomes were numerically implemented in finite element (FE) solver LS-DYNA to model the compression process, collapse behavior and deformation modes of lattice blocks. The compression characteristics and collapse modes predicted by FE model were in good agreement with experimental findings.

Size-dependent deformation behavior of dual-phase, nanostructured CrCoNi medium-entropy alloy

The mechanical size effect of nanostructured, dual-phase CrCoNi medium-entropy alloy (MEA) was investigated by combining in-situ micro-compression testing with post-mortem electron microscopy analysis. The alloy possesses a superior yield strength up to ~4 GPa, primarily due to its hierarchical microstructure including column nanograins, preferred orientation, a high density of planar defects and the presence of the hexagonal close packed (HCP) phase. While the yield strength of the alloy has shown size-independency, the deformation behaviour was strongly dependent on the sample size. Specifically, with decreasing the pillar diameters, the dominant deformation mode changed from highly localized and catastrophic shear banding to apparently homogeneous deformation with appreciable plasticity. This transition is believed to be governed by the size-dependent critical stress required for a shear band traversing the pillar and mediated by the competition between shear-induced softening and subsequent hardening mechanisms. In addition, an unexpected phase transformation from HCP to face-centered cubic (FCC) was observed in the highly localized deformation zones, leading to strain softening that contributed to accommodating plasticity. These findings provide insights into the criticality of sample dimensions in influencing mechanical behaviors of nanostructured metallic materials used for nanoelectromechanical systems.

Transition of dominant deformation mode in bulk polycrystalline pure Mg by ultra-grain refinement down to sub-micrometer

Magnesium (Mg) and its alloys usually show relatively low strength and poor ductility at room temperature due to their anisotropic hexagonal close-packed (HCP) crystal structure that provides a limited number of independent slip systems. Here we report that unique combinations of strength and ductility can be realized in bulk polycrystalline pure Mg by tuning the predominant deformation mode. We succeeded in obtaining the fully recrystallized specimens of pure Mg having a wide range of average grain sizes, of which minimum grain size was 650 nm, and clarified mechanical properties and deformation mechanisms at room temperature systematically as a function of the grain size. Deformation twinning and basal slip governed plastic deformation in the conventional coarse-grained region, but twinning was suppressed when the grain size was refined down to several micro-meters. Eventually, grain boundary mediated plasticity, i.e., grain boundary sliding became dominant in the ultrafine-grained (UFG) specimen having a mean grain size smaller than 1 μm. The transition of the deformation modes led to a significant increase of tensile elongation and breakdown of Hall-Petch relationship. It was quantitatively confirmed by detailed microstructural observation and theoretical calculation that the change in strength and ductility arose from the distinct grain size dependence of the critical shear stress for activating different deformation modes.

In-situ microstructural investigations of the TRIP-to-TWIP evolution in Ti-Mo-Zr alloys as a function of Zr concentration

Aiming at overcoming the strength-ductility trade-off in structural Ti-alloys, a new family of TRIP/TWIP Ti-alloys was developed in the past decade (TWIP: twinning-induced plasticity; TRIP: transformation-induced plasticity). Herein, we study the tunable nature of deformation mechanisms with various TWIP and TRIP contributions by fine adjustment of the Zr content on ternary Ti-12Mo-xZr (x = 3, 6, 10) alloys. The microstructure and deformation mechanisms of the Ti-Mo-Zr alloys are explored by using in-situ electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results show that a transition of the dominant deformation mode occurred, going from TRIP to TWIP major mechanism with increasing Zr content. In the Ti-12Mo-3Zr alloy, the stress-induced martensitic transformation (SIM) is the major deformation mode which accommodates the plastic flow. Regarding the Ti-12Mo-6Zr alloy, the combined deformation twinning (DT) and SIM modes both contribute to the overall plasticity with enhanced strain-hardening rate and subsequent large uniform ductility. Further increase of the Zr content in Ti-12Mo-10Zr alloy leads to an improved yield stress involving single DT mode as a dominant deformation mechanism throughout the plastic regime. In the present work, a set of comprehensive in-situ and ex-situ microstructural investigations clarify the evolution of deformation microstructures during tensile loading and unloading processes.

Microstructural dependence of the incipient to homogeneous flow transition in metallic glass composites

As ductile derivatives of amorphous alloys, metallic glass composites balance high strength with the ability to mitigate catastrophic shear localization, which has long plagued monolithic metallic glasses. In this study, we employ a bonded-interface indentation technique coupled with strain field mapping to identify the governing yield criterion in metallic glass composites as a function of their microstructural length scales. A crossover from the shear plane to maximum shear stress yield criterion is uncovered at a crystalline fraction of approximately 60%, thus signaling an effective transition from incipient to homogeneous flow as the dominant deformation mode of the composite microstructure.

Tungsten-based heterogeneous multilayer structures via diffusion bonding

Recent work has shown that tungsten (W) and other refractory metals with body-centered cubic (bcc) structures exhibit certain novel behavior when their grain size, d, is refined into the ultrafine (UFG, 100 nm < d < 1000 nm) or nanocrystalline (NC, d < 100 nm) regime. For example, it has been shown that bcc refractory metals with such microstructures show decreased strain rate sensitivity besides their elevated strength and vanishing strain hardening response. Consequently, under both quasi-static and high-strain-rate loading, plastic instability in the form of shear banding becomes the dominant mode of plastic deformation. Such behavior is long sought-after in certain applications. However, due to the technology used to refine the grain size (primarily severe plastic deformation), the inability to scale the dimensions of the material may limit wider use and application of UFG/NC bcc refractory metals. In this work, the feasibility was demonstrated of production of large-scale W parts using a diffusion bonding method. The microstructure, preliminary mechanical properties, and issues and challenges associated with the fabrication procedures were examined and discussed. It is envisioned that diffusion bonding may serve as a promising technology for scaled-up fabrication of UFG bcc refractory metals for the targeted application.

Deformations of Ti-6Al-4V additive-manufacturing-induced isotropic and anisotropic columnar structures: Insitu measurements and underlying mechanisms

The deformations of isotropic and anisotropic Ti-6Al-4V columnar structures fabricated by additive manufacturing were extensively examined. The distinct texture and microstructure distributions were characterised. In situ X-ray diffraction measurements show different lattice activities resulting from the different microstructure distributions. Spatially resolved mapping revealed manufacturing-induced crystallite-orientation distributions that determine the deformation mechanisms. We propose a self-consistent model to correlate the multi-scale characteristics, from the anisotropic-texture-distribution microstructure to the bulk mechanical properties. We determined that basal and pyramidal slip activities were activated by tension deformation. The underlying additive-manufacturing-induced crystal plasticity plays a major role. We find that the texture development of the columnar structures and the distribution of crystallite orientation achieved by different processing conditions during additive manufacturing have important effects on the mechanical properties. The dominant deformation mode for the anisotropic Ti-6Al-4V columnar structure is basal slip, and that for the isotropic Ti-6Al-4V columnar structure is pyramidal slip. The difference may be important for determining the fatigue behaviour.

Influence of strain rate and temperature on the deformation mechanisms of a fine-grained Ti-6Al-4V alloy

Depending on their initial microstructure, titanium alloys, as the Ti-6Al-4V may have activation of different deformation mechanisms during hot forming processes. In this work, interrupted tensile tests and heat treatments are used to improve the understanding of the mechanical and microstructural behaviour of a fine-grained Ti-6Al-4V alloy at two temperatures (750°C and 920°C) and so for two different β phase fractions. The microstructural features like, α grain size and phase fraction, were determined by Scanning Electron Microscope (SEM) and image analysis. Moreover, evolution of the preferred crystallographic orientation of α grains and local misorientations between and inside grains were obtained by Electron Backscatter Diffraction (EBSD). The strain rate sensitivity parameter as well as the activation energy were deduced from mechanical tests. It appears, from all these microstructural and mechanical data, that several mechanisms are activated depending on the strain level and on the temperature range. At 750°C, for a high strain rate, the deformation is mainly controlled by dislocations activity in the α phase (texture changes, dynamic recrystallization) and, at very low strain rate, by probably GBS accommodated with dislocations activity into α (recovery) and β. On the contrary at 920°C, a clear decrease of the overall texture intensity associated with a high m value suggests that GBS is the dominant mode of deformation. Nevertheless, as the α∕β volume fraction is around 48%/52% at this temperature, not only the α phase but also the β phase as well as α∕α and β∕β boundaries might contribute to the flow behaviour. During long deformation time (low strain rate and high temperature), dynamic coarsening behaviour (both into α and β), that is controlled by bulk diffusion, can occur and modify the type, the distribution and decrease the number of α∕β, α∕α and β∕β boundaries. This can be partly related to the flow hardening observed at 920°C and 10−4s−1.

An Appraisal of Recent Earthquake Activity in Palghar Region, Maharashtra, India

The present study focuses on the recent earthquake activity in Palghar region, Maharashtra, India. Until 31 August 2019, a total of 4854 earthquakes have been located here, whose local magnitude (M L) varied from 0.1 to 4.1. Majority of the earthquakes (~94%) were located in the depth range 4-16 km. The precise earthquake relocations reveal two clusters. The N-S trending cluster north of 20.04°N extends to a depth of 10 km, whereas the NE-SW trending cluster to the south of 20.04°N extends to 16 km depth. The shallow northern cluster is noticed to be sandwiched between two mapped mafic intrusions, whereas the deeper southern segment shows earthquakes clustering around the mafic intrusion. The modelled composite focal mechanism solutions for both the north and south clusters suggest normal faulting with a minor strike-slip component as the dominant deformation mode for the Palghar region. From relocated seismici-ty, we have detected a deeper seismically active zone (with M > 3) at 4-16 km depth, occupying a crustal volume of 1440 km 3 (i.e. 20 km (in N-S) × 6 km (in E-W) and 12 km (in depth)) that dips toward 20°S and 70°W. This could be attributed to the large crustal stresses induced by the mafic intrusive body below the region.

The study of flow behavior and governing mechanisms of a titanium alloy during superplastic forming

TA15 (Ti–6Al–2Zr–1Mo–1V) is a near-α titanium alloy and has wide applications in the aerospace industry because of its high strength to mass ratio, good weldability, and superior creep resistance at high temperatures up to 550 °C, compared to other titanium alloys. This study investigates the flow behavior and microstructural evolution as functions of temperatures and strain rates during deformations under the superplastic conditions at 880 °C/0.01s−1, 900 °C/0.01s−1, 880 °C/0.001s−1, and 920 °C/0.0005s−1. Results showed that this alloy exhibit excellent superplastic behavior for all selected temperatures and strain rates. The maximum tensile elongation of 1450% is achieved at 880 °C with a strain rate of 0.001s−1. Flow softening is observed under deformation conditions of 880 °C/0.01s−1 and 900 °C/0.01s−1, while strain hardening is observed at deformation conditions of 880 °C/0.001s−1 and 920 °C/0.0005s−1. These complex flow behaviors are rationalized by characterizing the underlying microstructures on the interrupted tensile samples using electron backscatter diffraction (EBSD) and backscattered electrons (BSE). The geometrically necessary dislocations (GNDs) density, which is caused by lattice rotation and misorientations and plays a vital role in the plastic constitutive behaviors, was for the first time, systematically revealed. Together with other key microstructures, i.e. grain sizes, texture, phase fractions, the results show that the dominant deformation mode changes at initial, intermediate, and final stages of the deformation. The probable deformation mechanisms, such as grain boundary sliding (GBS) under different deformation conditions, are discussed in terms of grain morphology, GNDs, and texture evolution. Also, it is observed that the β-phase transformation is accelerated during deformation and contributes to the enhancement of superplasticity.

Dynamic collapse of metal self-similar hierarchical corrugated sandwich plates subject to shear and compression coupled loading

Analysis of dynamic collapse response of metal self-similar hierarchical triangular corrugated sandwich plates subject to the shear loading and the shear coupled with compression is conducted. The initial collapse modes of the triangular corrugated sandwich cores are identified, in which different shear or shear-compression coupled impact velocities and various slenderness ratios of the large and small struts are considered, i.e. Euler buckling of large struts, Euler buckling of small struts, the wrinkling of large struts, the mode of combined Euler buckling of small struts with the wrinkling of large struts, and the mode of combined Euler buckling of large struts with the wrinkling of large struts. The collapse mechanism maps are then figured out with the axes representing the slenderness ratios of the large and small struts for hierarchical corrugated sandwich cores under single shear loading and combined shear and compression. In particular, the theoretically predicted collapse mechanism maps are in good agreement with the numerical results at applied velocity V0 = 1 m/s under the single shear loading and the shear coupled with compression. It is demonstrated that the velocity has insignificant influence on the dominant deformation mode of self-similar hierarchical corrugated sandwich plates for the cases of velocities V0 = 1 m/s and 10 m/s under the single shear loading and the shear coupled with compression. The designed self-similar hierarchical corrugated sandwich core has better energy absorption than traditional corrugated sandwich core subject to the single shear loading.

Accounting for Small-Scale Heterogeneity and Variability of Clay Rock in Homogenised Numerical Micromechanical Response and Microcracking

Clayey rocks have a complex microstructure with multiple characteristic lengths. Deformation under mechanical loading generally induces damage by microcracking, which essentially concerns the scale of mineral inclusions embedded in the clay matrix. The modelling of these materials is considered within the framework of a double scale approach, by numerical homogenisation, of the squared finite element method type. This allows a heterogeneous microstructure of the material to be taken into account and a distribution of morphological properties to be introduced. Emphasis is placed on the generation of microstructures satisfying experimental observations, and keeping a certain simplicity to fit into the framework of double scale modelling. The material characteristics and behaviour are defined at the grain scale: the mineralogical properties include the mineral phase proportions and the grain morphology, while the material constituents are represented by elastic grains separated by damageable cohesive crack models. Then, the overall microscale behaviour of the material under solicitation is derived from equilibrated elementary area (EA) configuration and computational homogenisation. The variability of the material response is studied with regard to small-scale aspects as microstructure variability, microstructure size, grain angularity, and properties of grain contacts. Deformation analyses at grain contacts emphasise a dominant shear deformation mode and the development of decohesion between grains. The latter induces microfaulting processes across the entire EA and strain softening of the overall response. Moreover, the improvement of microscale behaviour modelling opens new possibilities for more realistic multi-scale modelling and upscaled behaviour of heterogeneous rocks.