Simulation Of Uniaxial Compression Research Articles

A new combined finite-discrete element method for stability analysis of soil-rock mixture slopes

PurposeThe purpose of this paper is to propose a new combined finite-discrete element method (FDEM) to analyze the mechanical properties, failure behavior and slope stability of soil rock mixtures (SRM), in which the rocks within the SRM model have shape randomness, size randomness and spatial distribution randomness.Design/methodology/approachBased on the modeling method of heterogeneous rocks, the SRM numerical model can be built and by adjusting the boundary between soil and rock, an SRM numerical model with any rock content can be obtained. The reliability and robustness of the new modeling method can be verified by uniaxial compression simulation. In addition, this paper investigates the effects of rock topology, rock content, slope height and slope inclination on the stability of SRM slopes.FindingsInvestigations of the influences of rock content, slope height and slope inclination of SRM slopes showed that the slope height had little effect on the failure mode. The influences of rock content and slope inclination on the slope failure mode were significant. With increasing rock content and slope dip angle, SRM slopes gradually transitioned from a single shear failure mode to a multi-shear fracture failure mode, and shear fractures showed irregular and bifurcated characteristics in which the cut-off values of rock content and slope inclination were 20% and 80°, respectively.Originality/valueThis paper proposed a new modeling method for SRMs based on FDEM, with rocks having random shapes, sizes and spatial distributions.

Failure mechanism of a tunnel in a soil–rock mixture based on a new combined finite–discrete element method

The mechanical properties and failure characteristics of soil–rock mixtures (SRMs) directly affect the stability of tunnels constructed in SRMs. A new SRM modelling method based on the combined finite–discrete element method (FDEM) was proposed. Using this new SRM modelling method based on the FDEM, the mechanical characteristics and failure behaviour of SRM samples under uniaxial compression, as well as the failure mechanism of SRMs around a tunnel, were further investigated. The study results support the following findings: (1) The modelling of SRM samples can be achieved using a heterogeneous rock modelling method based on the Weibull distribution. By adjusting the relevant parameters, such as the soil–rock boundaries, element sizes and modelling control points, SRM models with different rock contents and morphologies can be obtained. (2) The simulation results of uniaxial compression tests of SRM samples with different element sizes and morphologies validate the reliability and robustness of the new modelling method. In addition, with increasing rock content, VBP (volumetric block proportion), the uniaxial compressive strength and Young’s modulus increase exponentially, but the samples all undergo single shear failure within the soil or along the soil–rock interfaces, and the shear failure angles are all close to the theoretical values. (3) Tunnels in SRMs with different rock contents all exhibit X-shaped conjugate shear failure, but the fracture network propagation depth, the maximum displacement around the tunnel, and the failure degree of the tunnel in the SRM roughly decreases via a power function as the rock content increases. In addition, as the rock content increases, such as when VBP = 40%, large rocks have a significant blocking effect on fracture propagation, resulting in an asymmetric fracture network around the tunnel. (4) The comparisons of uniaxial compression and tunnel excavation simulation results with previous theoretical results, laboratory test results, and numerical simulation results verify the correctness of the new modelling method proposed in this paper.

Research on ship-ice collision model and ship-bow fatigue failure Mechanism based on elastic-plastic ice constitutive relation

Collisions between sea ice and ships can damage the hull structure and pose a threat to crew safety in severe cases. The modelling of ice materials is crucial, but it is difficult to study ice-ship interactions. In this study, an ice constitutive model including the temperature factor was verified through experiments and numerical simulations of uniaxial and triaxial compression. Furthermore, the effects of salinity and porosity on the compressive strength of ice were studied using experiments and numerical simulations. The mechanical behaviour of sea ice was then simulated using the constitutive model mentioned above. A numerical model of collisions between polar ships and sea ice was established to investigate the ice-breaking processes of ships under different working conditions. The collision force and the level of structural damage were obtained. The influences of the initial pore size, hull speed, bow angle, and bow shape on the collision force and structural damage in the ship-ice collision process were analysed. Finally, fatigue damage to the bow structure at different ice thicknesses and speeds was calculated. The present results provide a reference for the structural design and optimisation of polar ships to a certain extent and improve the theory of ship-ice collisions.

Numerical study of voids geometry effects on sandstone’s mesoscopic fracture Mechanism: Insights from acoustic emission and moment tensor inversion

In the field of rock mechanics, the study of void shape on the mechanical properties and fracture mechanisms of sandstone is crucial for the progression of rock engineering practices. In this study, PFC3D is utilized to conduct numerical simulations of uniaxial compression on intact rock and brittle rocks containing five different shapes of voids (including circular, inverted U-shaped, trapezoidal, rectangular, and square). By employing acoustic emission and moment tensor inversion techniques, the microscopic fracture mechanisms of rocks with different void shapes are revealed. Our key findings reveal: (1) The PFC3D’s Soft-Bond Model is adept at simulating acoustic emissions with high accuracy, facilitating an authentic reproduction of the uniaxial compression process in sandstone, including the nonlinear compaction stage. (2) The presence of hole defects markedly undermines the structural strength and deformability of the sandstone, with circular holes having minimal impact, whereas rectangular holes exert the most significant detriment. (3) A thorough analysis of fracture mechanisms demonstrates that specimens with hole defects primarily undergo initial tensile, remote cracks, V-shaped notch, and shear fractures, with shear fractures being pivotal in leading to specimen failure by rapidly evolving into macroscopic fractures that merge with V-shaped notches. (4) Acoustic Emission (AE) analysis highlights the distribution of tensile stress around the upper and lower extremities of the holes and shear stress along the left and right sidewalls, establishing shear stress as the dominant factor in the failure of specimens with hole defects.

Deformation mechanism and minimum energy path in Silicon–graphite composites with lattice defects

Edge-on atomic layers in layered solids undergo buckling, which creates a structure referred to as a “ripplocation.” A collective set of multiple ripplocations is referred to as a “ripplocation boundary.” In this study, in order to investigate the impact of lattice defects on ripplocation, we investigate the buckling deformation of graphene with lattice defects under confinement. To this end, we conducted confined uniaxial compression simulations by placing graphene sheets with various lattice defects between silicon atomic layers. Different types of lattice defects affect the mechanical properties of graphene, the results show that Young's modulus of graphene with the (1,0)_5 dislocation pair was the maximum at 494.6 GPa, whereas the Young's modulus of the (1,2)_10 dislocation pair was the minimum at 309.5 GPa. In addition, we employed a differential geometry method to study the out-of-plane deformation of a single-layer graphene system. Further, we used the nudged elastic band method for various types of lattice defects in graphene to uncover the minimum transition pathways, activation energy required to move from the (1, 0) dislocation pair to the (1, 1) pair is 44.916 eV. In particular, the results indicate that graphene with lattice defects exhibit kink deformation after buckling compared to that of perfect graphene. Our study not only explores the deformation of ripplocations and kink boundaries in layered solids but also provides a more comprehensive description influencing lattice defects on the nucleation mechanism and mechanical changes of ripplocations in graphene.

Mesoscale-based mechanical parameters determination and compressive properties of fully recycled coarse aggregate concrete

The use of recycled coarse aggregate (RCA) to prepare concrete can reduce the depletion of natural resources, such as sand and stone, and solve the issue of environmental pollution resulting from waste concrete materials. To promote the popularization of the RCA application, a study has been carried out on fully recycled coarse aggregate concrete (FRCAC), which is 100 % RCA replacement. The random convex polygon aggregate model was established using a self-compiled program. Then, A five-phase numerical model of FRCAC was proposed through the finite element software further developed, to realize the numerical simulation of uniaxial compression of FRCAC. The discount factor R between the mechanical parameters of the FRCAC mesoscopic components was determined by comparing the 8 groups of compressive strengths from the physical experiments with the 96 groups of compressive strengths from the numerical simulations. Meanwhile, the effects of RCA volume fraction, water-cement ratio (W/C) and mesoscopic composition on the compression performance of FRCAC were analyzed based on experimental and simulation methods. The result shows: 1) Simulation results exhibited good agreement with experimental results when the interface discount factor RITZ and the old mortar discount factor RM fell within the ranges of 0.45–0.55 and 0.8–0.85, respectively. 2) The compressive strength of FRCAC tends to decrease when W/C and the volume fraction of RCA rise, but the trend of declines is not constant. 3) The compressive properties of FRCAC were found to decrease with increased thickness of the old mortar and the interfacial transition zone, highlighting the necessity for pretreatment of RCA before its use. The findings of this research provide valuable insights and methodological references for the application and promotion of FRCAC and its mesoscopic models.

Multiphysics simulations of uniaxial compression applied to various rock samples subject to microwave pretreatment

PurposeAmong the various applications involving the use of microwave energy, its growing utility within the mining industry is particularly noteworthy. Conventional grinding processes are often overburdened by energy inefficiencies that are directly related to machine wear, pollution and rising project costs. In this work, we numerically investigate the effects of microwave pretreatment through a series of compression tests as a means to help mitigate these energy inefficiencies.Design/methodology/approachWe investigate the effects of microwave pretreatment on various rock samples, as quantified by uniaxial compression tests. In particular, we assign sample heterogeneity based on a Gaussian statistical distribution and invoke a damage model for elemental tensile and compressive stresses based on the maximum tensile stress and the Mohr–Coulomb theories, respectively. We further couple the electromagnetic, thermal and solid displacement relations using finite element modeling.Findings(1) Increased power intensity during microwave pretreatment results in decreased axial compressive stress. (2) Leveraging statistics to induce variable compressive and tensile strength can greatly facilitate sample heterogeneity and prove necessary for damage modeling. (3) There exists a nonlinear trend to the reduction in smax with increasing power levels, implying an optimum energy output efficiency to create the maximum degradation-power cost relationship.Originality/valuePrevious research in this area has been largely limited to two-dimensional thermo-electric models. The onset of high-performance computing has allowed for the development of high-fidelity, three-dimensional models with coupled equations for electromagnetics, heat transfer and solid mechanics.

Bonded particle model for dilated polyhedron considering fracture modes and its application to lateral resistance of ballast bed in cold regions

Considering the spatial arrangement characteristics of bonded irregular particle systems, this paper first constructs irregular dilated polyhedron elements based on the Voronoi cutting algorithm and Minkowski Sum theory. Subsequently, by extending the traditional sphere-based BPM (Bonded Particle Model) to irregular particle elements, a novel dilated polyhedron bonding-breaking model considering different fracture modes is developed under arbitrary contact modes. A collision example between two bonded square particles and a rigid plate is adopted to verify the stability of the model. Later, the difference between the tensile-shear fracture mode and the mixed fracture mode with damage process for contact bond is compared by the discrete element simulations of the tension-fracture behavior between two bonded square particles and the uniaxial compression simulation of frozen ballast aggregate. Finally, the influence of section size on the lateral resistance of the ballast bed structure at low temperatures is discussed using the dilated polyhedron BPM. The results showed that the developed dilated polyhedron BPM considering different fracture modes can realize mechanical behaviours between bonded irregular particles. Compared with the tensile-shear fracture mode, the mixed fracture mode not only considers the combined effect of normal and tangential stress on the bond but also realizes the damage deformation and stiffness attenuation of the bond, which can achieve the “delayed” fracture effect. Meanwhile, the model also shows good reliability in analyzing large-scale engineering problems, such as the mechanical performance of low-temperature ballast beds. The research effectively develops the bonding and breaking model of irregular elements and provides a new perspective for the contact-bond-fracture behavior simulation of irregular granular materials.

Investigating strengthening and softening mechanisms in Al/Ni multilayers via molecular dynamics simulations of uniaxial compression

Due to their nanoscale features, nanometric multilayers can have a large variation in properties for varying bilayer heights. While the hardening at small feature sizes and the consequent softening at even smaller feature sizes have been observed for decades, the underlying mechanisms are still under debate. In this study, molecular dynamics uniaxial compression simulations are employed to study the mechanical properties of Al/Ni multilayers for bilayer heights h from 100 nm down to 5 nm. The effect of the microstructure on Young’s modulus and the yield strength was investigated. Furthermore, the mechanical properties of equiatomic and equivolumetric multilayers were compared. A comparison with experimental results from the literature showed good agreement. Both the hardening at intermediate bilayer heights as well as the softening at very small bilayer heights were observed. The results are discussed in the context of possible hardening and softening mechanisms. While the Hall–Petch effect with a h−1/2 scaling is not contradicted, it is shown that, although the underlying mechanisms are different, both the hardening as well as the softening are based on a general size effect with a scaling of ln(h)/h.

Mechanical responses and stress distribution of rock-like specimen containing a spherical defect under uniaxial compression

Spherical defect is often seen in rock material, and the size and position of the defect seriously affect the stability of rock mass. In this study, a locating device for preparing spherical defects was designed. A series of uniaxial compression tests and simulations were conducted to study the influence of the defect size and location on the mechanical, micro-cracking, failure characteristics, and stress distribution of the sample containing a spherical defect. The results indicate that the uniaxial compressive strength (UCS) and Young’s modulus both decrease with increasing defect size. The location variation of the same-sized spherical defect has a significant influence on the UCS but hardly influences Young’s modulus. The closer the defect is to the boundary, the lower the UCS is. The acoustic emission (AE) monitoring results indicate that the damage point aggregates and expands around the defect, forming a failure surface in the later stage of specimen loading. The failure modes of the specimen are divided into tensile failure, shear failure, and tensile-shear failure. Laboratory test results match well with the numerical simulation results obtained through the PFC3D program. The numerical stress monitoring results indicate that there is significant stress concentration near the defect. And the concentrated stress at the defect boundary drops before the the model reaches its peak stress, which can be used to predict the failure of the defected rock mass. The research findings could supply a certain reference for stability analysis and control of rock material containing similar types of defects.

Research and analysis of the impact of the pore structure on the mechanical properties and fracture mechanism of sandstone

Rock pore structure, including porosity, pore size, and particle size, plays a crucial role in determining rock mechanical properties. This study investigates the impact of pore structure on rock mechanical properties through laboratory experiments and numerical simulation methods on sandstones with varying porosity and pore size. The pore structure characteristics of sandstone were determined using XRD, SEM, and NMR microscopic techniques. Additionally, the influence of rock porosity on rock mechanical properties was analyzed by combining Uniaxial compression test with DIC technology, revealing the fracture mechanism caused by porosity in rocks. Numerical models were constructed to simulate sandstones with different porosities and pore diameters, followed by uniaxial compression simulation tests to explore the influence of varying pore diameters on rock mechanical properties and the fracture mechanism. The study reveals the presence of four distinct pore types in the sandstone: micropores in the matrix (0–0.002 µm), intergranular pores (0.002–0.2 µm), dissolution pores (0.2–4 µm), and fracture pores (4–30 µm). Among these, intergranular pores and dissolution pores are the predominant types, accounting for approximately 92–96% of the total pore volume in the sandstone. It is observed that an increase in porosity leads to a decrease in the mechanical strength of sandstone and an increase in Poisson's ratio while keeping the pore size constant. Similarly, when the porosity remains constant, an increase in pore size results in a decrease in the mechanical strength and an increase in Poisson's ratio. Additionally, the study also finds that as the porosity and pore diameter of sandstone increase, the area of internal equivalent stress expands, leading to a shorter crack initiation time and accelerated crack penetration speed, ultimately resulting in a decline in the mechanical properties of sandstone. Numerical simulation experiments further demonstrate that large pores exhibit higher stress concentration compared to small pores, thereby exerting a more significant influence on the mechanical properties of sandstone.

A simplified numerical simulation of uniaxial compression for polyacrylonitrile fiber reinforced permeable concrete based on CT images

For fiber reinforced permeable concrete, numerical simulation method have been applied to reduce the time consumption of physical experiments and to study the mesostructure of the material. In this paper, polyacrylonitrile fiber reinforced permeable concrete (PANFRPC) is considered to consist of aggregate, mortar (containing fibers inside), interface transition zone (ITZ) and pores in 3D mesostructure model generated from computer tomography (CT) images. For the numerical simulation of the, material properties of each component in the model are assigned according to physical experimental results. The failure curve of the mortar in PANFRPC is determined by physical test results to reflect the effect of fibers. The simulation results show that the model has similar mechanical properties to the actual specimen and can be used to simulate the elastic stage of the uniaxial compression process and predict the strength with an error of less than 15% despite the simplification of fiber. the accuracy and reliability of the model have also been verified by the distribution pattern of vertical caraks and x-shaped shear cracks from macro and meso perspectives.

Turning nanopowder into nanomaterial: Effect of continuous SiC coating on mechanical properties of Si nanoparticle arrays

Atomistic simulations of quasi-static uniaxial compression and stretching of hybrid linear arrays of Si spherical cores with continuous crystalline SiC coatings are performed. The coating is modeled by overlapping shells of core-shell Si/SiC nanoparticles (NPs). The simulations reveal dramatic differences in the mechanisms of inelastic deformation, mechanical properties, and phase changes between the arrays without and with shell overlap. The arrays of NPs without overlap demonstrate purely ductile deformation behavior with relatively small modulus and strength but large ultimate strain. The arrays with continuous coatings show more brittle behavior with relatively small ultimate strain. At the maximum shell overlap, the compressive modulus exhibits a ten-fold increase compared to the arrays of NPs without overlap. The compressive deformation of individual Si/SiC NPs induces the formation of vast regions of β-Sn Si. In arrays with continuous coatings, such regions are not formed. These differences between the arrays of individual NPs and NP arrays with continuous coatings are caused by the formation of different patterns of slip and shear localization surfaces. At compression of individual NPs with 6H-SiC shells along the [001] direction, the slip system includes multiple parallel {0001} planes. In similar arrays with continuous coatings, the compression induces the formation of the {011¯1} slip planes that form a six-sided inverted truncated pyramid, which transform into a shear localization/fracture surface. The continuous SiC coating on Si NPs can increase the material modulus and strength a few times, turning a nanopowder into a porous nanomaterial with excellent mechanical properties.

Effect of residual mortar on compressive properties of modeled recycled coarse aggregate concrete

Based on the typical morphology of recycled coarse aggregate in reality and the ontological relationship of the existing recycled aggregate concrete (RAC) mesoscopic constituent materials, a finite element analysis model of recycled coarse aggregate that can take into account the factors of the amount and location of attachment of the residual mortar was developed to establish the Modeled Recycled Coarse Aggregate Concrete (MRCAC). Combined with the mesoscopic mechanical properties of MRCAC, a plastic damage intrinsic model was used in the numerical analysis of MRCAC under uniaxial compressive loading to study the damage characteristics and stress–strain relationships of MRCAC. In this paper, the Modeled Recycled Coarse Aggregate (MRCA) is established in the ABAQUS numerical analysis software by self-compiled Python script, and the uniaxial compression simulation of MRCAC is carried out. Compared with the existing idealized model recycled concrete and other forms of digital recycled concrete model, The results show that, on the premise of meeting the general law of existing research results, the development of cracks in MRCAC under load is directly related to the shape of residual mortar wrapping. The strength of MRCAC is minimally influenced by residual mortar adhesion amount; however, the coverage of residual mortar has a significant impact on its strength. The arrangement of MRCA may also play a role in the stress–strain relationship of MRCAC. Additionally, it should be noted that residual mortar adhesion amount and coverage are distinct concepts that affect the strength and strain of MRCAC independently. These findings highlight the need to differentiate between these two factors in further research.

Numerical Simulation and Field Test of a PDC Bit with Mixed Cutter Arrangement to Break Non-Homogeneous Granite

As the depth of petroleum drilling increases, the strata environment becomes more complex. The efficiency and lifespan of Polycrystalline Diamond Compact (PDC) drill bits fail to meet current drilling demands. However, the structure and arrangement of PDC cutters are valuable determinants of drilling efficiency, although related research still has gaps and deficiencies. This study focuses on PDC cutters in axe, triangular prism, and circular forms. It establishes an inhomogeneous granite model based on the actual measurements of granite and verifies the accuracy of this model through uniaxial compression simulation. Finite element models of three types of cutters in various combination schemes are constructed to examine rock-breaking effects, with the best scheme optimized using Box-Behnken response surface methodology. The rock-breaking process of the optimal PDC drill bit layout has been compared to that of a single cutter bit. Field drilling has demonstrated the effectiveness of a mixed cutter arrangement. The results show that the inhomogeneous granite model can be trusted. The optimal arrangement involves axe cutters in the front row and an alternate arrangement of triangular prism cutters and axe cutters in the back row. The optimal lateral and longitudinal distances for the triangular cutters from the front row of axe cutters are 10 mm and 7 mm, respectively, while those for the back row of axe cutters from the front row are 10.06 mm and 7 mm, respectively. The ROP standard deviation in the drilling process of mixed cutter bits decreases by 53.06% and 43.08% compared to axe and triangular prism cutter bits, respectively. The drilling efficiency increases by 16.8% and 16.6%, respectively, demonstrating higher efficiency and stability. Field drilling results indicate that a mixed cutter bit increases efficiency by 23.5% compared to a bit with only triangular prism cutters. This study posits that research on the combination schemes and parameters of PDC cutters can significantly enhance drilling efficiency, thereby reducing the drilling cycle and costs.

Mechanical Properties of Polymer Modified Concrete with Steel Fiber

For the concrete used in highway, bridge and other structures, the problems such as the premature failure of the surface material and the failure of the interface between the surface course and the base course have not been solved, and the research at home and abroad mainly focuses on the strength and durability of concrete. It is also considered that polymer modified concrete and fiber reinforced concrete can improve the strength and toughness of concrete. This paper mainly studies the compressive and flexural properties of polymer modified fiber reinforced concrete. The experiment found that the mix design of styrene butadiene lotion modified steel fiber reinforced concrete proposed in this paper was reasonable, and the flexural strength at the age of 3 days reached 6.321Mpa, which was 16.9% higher than that of plain concrete; based on the plastic damage model (CDP) theory of concrete, the constitutive model of polymer modified fiber reinforced concrete is established, and the cubic concrete model is simulated under uniaxial compression, and the influence of concrete mortar with different strength substrates on the stress-strain field of uniaxial compression simulation is further analyzed.

Experimental and numerical modeling of deformation-cracking mechanics of 3D-printed rock samples with single fracture

The analysis of mechanical response and deformation-cracking behavior contributes to the high-efficiency extraction of geo-energy and long-term safety of underground engineering structures. Compared to natural cores, the mechanical properties of 3D-printed samples made from quartz sand as raw material are relatively homogeneous, and can be used for quantitative studies on the influence of natural defects on the mechanical properties of rocks. In this work, 3D-printed samples with single fractures of different crack angles, lengths and widths were fabricated and used for uniaxial compression tests. Adopting the digital image correlation method, the stress-strain distribution during uniaxial compression tests were visualized, and the influence of prefabricated fracture characteristics (dip angle, length, and width) on the deformation-failure process were studied. An extended finite element method subroutine for ABAQUS® software was modeled and used for the uniaxial compression simulation, which was validated by experiments. Then, the influence of mechanical parameters (Young’s modulus, Poisson’s ratio, cohesion, and internal friction angle) on the deformation-cracking mechanics were simulated and studied. The results indicate that, compared to the intact sample, fractures reduce the sample strength. With the extension of fracture length and width, or the decline of fracture angle, both the peak strain and strength of the 3D-printed samples decrease. The splitting tensile failure, or shear failure, or both were determined for the 3D-printed samples with different fracture angles. For the same axial strain, the extension length of the new crack increases linearly with rising Young’s modulus and decreases linearly with increasing Poisson’s ratio. The initial strain of new cracks decreases linearly with increasing Young’s modulus, while little variations are found in samples with different Poisson’s ratio. For the same axial displacement load, the peak stress increases linearly with growing internal friction angle and cohesion. Cited as: Song, R., Tian, J., Wu, M., Liu, J. Experimental and numerical modeling of deformation-cracking mechanics of 3D-printed rock samples with single fracture. Advances in Geo-Energy Research, 2023, 8(2): 126-135. https://doi.org/10.46690/ager.2023.05.06

Mesoscopic Cohesive Crack Model of Microcapsule Self-Healing Concrete and Its Uniaxial and Triaxial Compression Simulation

Abstract: In practical engineering structures, concrete is usually under a multiaxial stress state. Therefore, it is significant to investigate the mechanical behavior of microcapsule self-healing concrete under triaxial compression. In this study, a three-dimensional mesoscopic cohesive crack model of concrete based on the cohesive element is established to simulate uniaxial compression tests and conventional triaxial tests of concrete with different microcapsule content. The result shows that when the uniaxial compressive loading reaches , a small number of microcracks start to appear, leading to the nonlinear behavior of the stress-strain curve. When the uniaxial compression is loaded near the peak point (), the internal cracks of the sample begin to increase sharply. Different from the crack of the sample in uniaxial compression concentrated in the interfacial transition zone, the crack of the sample in triaxial compression is scattered in the interior of the mortar and the interfacial transition zone, and the greater the confining pressure, the more crack in the mortar.

Micro-macro damage, deterioration and cracking of heterogeneous composite rock masses with non-penetrating cracks under uniaxial compression

Rock masses with non-penetrating cracks are widely found in nature. Their mechanical behavior plays a key role in rock engineering applications. However, previous studies have concentrated on the single lithologic layer, and few studies have reported the crack coalescence mechanism in heterogeneous composite rock mass with non-penetrating cracks (HCRC). In this study, uniaxial compression tests were performed on HCRC by discrete element numerical simulation experiments. Through the uniaxial compression simulation tests, the stress–strain variation and acoustic emission (AE) characteristics of HCRC are revealed. The instability and failure characteristics, energy evolution law and crack coalescence process of HCRC are also studied. And the influence of the crack numbers and crack positions (in weak body or strong body) on the mechanical behavior and failure processes in heterogeneous composite rock mass is investigated. The results show that the mechanical properties of HCRC are not all weakened with the increase of the crack numbers. As the number of cracks increases, the failure modes of the HCRC changes from brittle failure to ductile failure. The number of cracks will regulate the relative relationship between the strength of the two bodies of heterogeneous composite rock masses, so the crack coalescence forms, instability forms and failure characteristics of the HCRC will also change accordingly. If the number of cracks in the weak body is large, the damage of the HCRC mainly occurs in the weak body. The strong body produces a rebound energy release to the weak body, accelerating the destruction of the weak body. At this time, the overall strength of the HCRC is low. Conversely, increasing the number of cracks in a strong body will weaken the strength of the strong body. At this time, the strength difference between the strong body and the weak body decreases. The HCRC shows that the overall bearing capacity is not lower but becomes stronger. The research results provide a theoretical reference for the stability and disaster prevention of jointed rock mass engineering.

Unconventional dislocation starvation behavior of medium-entropy alloy single crystal pillars containing pre-existing dislocations

The excellent dislocation storage ability of bulk multi-principal element alloys (MPEAs) has been widely reported. To date, however, the underlying mechanisms of dislocation escape behavior in small-size face-centered cubic (FCC) MPEAs have rarely been studied. Here, we quantitatively control the initial dislocation densities (∼1015 m–2 and ∼1016 m–2) by large-scale molecular dynamics (MD) simulations and perform uniaxial compression simulations to compare the dislocation starvation behavior of CrCoNi with pure Cu single crystal pillars (SCPs). The analysis reveals that the CrCoNi SCPs with low initial dislocation density (∼1015 m–2) can continuously accommodate mobile dislocations, and the critical dimension for dislocation starvation is about 30 nm. In particular, the CrCoNi SCPs with chemical short-range ordering (SRO) exhibit better dislocation storage and multiplication abilities than the random solid solution (RSS) samples even when the initial dislocation density is low. However, the presence of a large number of pre-existing dislocation locks governs the strong dislocation multiplication ability of the small-size RSS CrCoNi SCPs, in obvious contrast to the deformation of all pure Cu SCPs which is completely dominated by intermittent mobile dislocation starvation. Most importantly, we reveal the fundamental physics for the good dislocation storage of CrCoNi SCPs at small sizes from the perspective of chemical heterogeneity. The new phenomena reported in this work provide a unique atomic-scale perspective for understanding the microscopic physical origin of the mechanical behavior of MPEAs and the discovery of extremely slow dislocation escape behavior in small-scaled pillars, providing a reliable basis for the development of the dislocation starvation model.