Simulation Of Uniaxial Compression Research Articles

Effect of joint angle in coal on failure mechanical behaviour of roof rock–coal combined body

Geological dynamic hazards during coal mining can be caused by the structural instability of a composite system of roof rock and coal layers, and joints in coal play a vital role in this structural instability. In this paper, uniaxial compression simulation tests on roof rock–coal combined bodies with a single joint at different angles in coal were conducted using PFC2D software. In particular, the effects of joint angle on the uniaxial compressive strength (UCS), acoustic emission (AE) and failure characteristics in a combined body were analysed. The results show the following. (1) The joint in coal causes a decrease in the UCS and crack initiation stress, and has promoting effects on the AE occurrence of the combined body. With an increase in the included angle α between the loading direction and joint plane direction, the UCS, AE occurrence time and crack initiation stress first decrease and then increase, presenting ‘V-shaped’ curves. The UCS and crack initiation stress at α of 45° are the lowest, and the AE occurrence time at α of 30° is the earliest. (2) The AE characteristics at α of 0°, 75° and 90° are basically consistent with those of the intact combined body, whereas at α between 15° and 60°, the intensity and frequency of AE events in the macro-failure stage are reduced by the joint in coal. (3) The failure of the combined body mainly occurs within the coal, whereas no apparent failure is observed for the roof rock. Only when α is between 15° and 45°, the roof rock near the bedding plane is destroyed by crack propagation in the coal. (4) Three typical failure modes (i.e. V-shaped shear failure cutting across the coal, shear failure partly along the joint plane direction and shear failure along the joint plane direction) are found for combined bodies with a single joint in coal.

Evaluation of Pore Size and Distribution Impacts on Uniaxial Compressive Strength of Lithophysal Rock

Discrete element method (DEM) has been extensively used for studying the properties of rock mass through numerical simulation, which includes bonded particle (or grain) model method (BPM) and discrete fracture network method. In this paper, utilization of BPM for modeling uniaxial compressive strength (UCS) of lithophysal rock is explored and associated stages are discussed and calibrated including generation of particles, sample scale, loading method, macro- and micro-parameters of BPM. In order to investigate the impacts of pore size and distribution of lithophysal tuff on UCS, various combinations of different pore sizes in one sample and different pore locations with the same pore size are simulated using BPM-DEM. The simulation results show that UCS significantly decreases due to the existence of pores with the same condition of porosity, and when the pore radii increase, the minimum value of UCS slightly declines. Moreover, combinations of different pore sizes in one sample show that greater proportion of small pore radii increases UCS of the sample, while the differences of UCS values decrease. Meanwhile, associated fracture has been observed to develop along the pore and generally tends to develop along the large pores at the edge of the sample in the process of uniaxial compression simulation, with relatively small associated UCS values.

Morphological similarity and structure-dependent scaling laws of nanoporous gold from different synthesis methods

Application of the foam scaling laws to the mechanical properties of nanoporous gold (np-Au) implicitly assumes geometrical similarity of structures of different relative density and synthesis methods. While the very few studies addressing the issue of geometric similarity during thermal coarsening show contradicting results, there are no studies covering np-Au from different synthesis routes. This paper performs quantitative morphological and topological comparison of np-Au of ca. 30% relative density synthesized by free and electrochemical corrosion methods, and thermally coarsened samples. Nanoindentation tests were performed to obtain elastic modulus and hardness. Uniaxial compression simulations of three-dimensional structures from FIB-nanotomography have been conducted using finite element analysis, and the results are compared with experiments. The three-dimensional np-Au structure has been quantified in terms of the ligament diameter and length distributions, ligament tortuosity, surface curvature distributions, structural anisotropy, nodal connectivity, and genus. Our results suggest that neither the synthesis route nor the thermal coarsening, to change length scale by up to a factor of 3, significantly altered the morphology and topology. The modulus and strength from both experiment and simulations exhibit a linear dependency on the scaled genus density, modifying the geometry-dependent prefactors in the Gibson and Ashby scaling relations.

Strain rate dependence of tension and compression behavior in nano-polycrystalline vanadium nitride

Abstract We performed molecular dynamics (MD) uniaxial tension and compression simulations of nano-polycrystalline (npc) vanadium nitride (VN) with different strain rates to investigate strain rate effects and tension-compression asymmetry in npc VN. The Zener's familiar anisotropy index A of the polycrystalline VN model is 0.957, very closed to 1.0, demonstrating its elastic isotropy. The Young's modulus increases with the increase of strain rate. The yield strain, yield stress and flow stress increase in power form with the increase of strain rate. As the strain rate varies in the range between 5E8 and 1E9 s−1, strain rate effect becomes insignificant, and the corresponding loading can be regarded as quasistatic or low strain rate loading. Tension-compression asymmetry was observed and analyzed systematically. The elastic tension-compression asymmetry should be ascribed to the higher friction in compression, the asymmetry of interatomic potential, and the effect of cutoff distance in a MD simulation. While the plastic tension-compression asymmetry should mainly result from the different kinds of atomic interaction, intergranular fracture and dislocation glide. No distinct grain boundary sliding was found.

Mechanisms of compressive deformation and failure of porous bulk metallic glasses

Bulk metallic glasses (BMGs) are a new class of engineering materials having strengths as high as 10 times that of conventional steels, but show no significant plastic strain at fracture. By introducing pores, their strain to failure has been shown to improve under uniaxial compression. In this work, three-dimensional finite element simulations of uniaxial compression are carried out on Pd-based porous BMGs having a wide range of pore volume fraction (1.9%–60%) with emphasis on understanding the underlying deformation and failure mechanisms. The resulting stress–strain curves agree reasonably well with existing experimental results. The simulations clearly bring out different failure mechanisms in low porosity BMGs and high porosity BMG foams. For low porosity BMGs (below 20%), the deformation and failure involves nucleation of shear bands around the pore diameter, linking of the shear bands with adjacent pores finally leading to initiation of ductile cracking within the shear bands. For high porosity BMG foams, the mechanism of deformation involves reduction in porosity of the material, self-contact of the pores, and their collapse on themselves causing densification of the material leading to apparent hardening in the stress strain behavior. The effect of pore geometry is also studied by considering ellipsoidal pores of volume fraction 3% and 11%. For ellipsoidal pores, the failure mechanisms are found to differ significantly when the orientation of the major axis of the pore vis-a-vis the loading axis is changed.

Fracture of granular materials composed of arbitrary grain shapes: A new cohesive interaction model

Discrete Element Methods (DEM) are a useful tool to model the fracture of cohesive granular materials. For this kind of application, simple particle shapes (discs in 2D, spheres in 3D) are usually employed. However, dealing with more general particle shapes allows to account for the natural heterogeneity of grains inside real materials. We present a discrete model allowing to mimic cohesion between contacting or non-contacting particles whatever their shape in 2D and 3D. The cohesive interactions are made of cohesion points placed on interacting particles, with the aim of representing a cohesive phase lying between the grains. Contact situations are solved according to unilateral contact and Coulomb friction laws. In order to test the developed model, 2D uniaxial compression simulations are performed. Numerical results show the ability of the model to mimic the macroscopic behavior of an aggregate grain subject to axial compression, as well as fracture initiation and propagation. A study of the influence of model and sample parameters provides important information on the ability of the model to reproduce various behaviors.

Mechanisms of Plastic Deformation of Metal–Organic Framework-5

We use large-scale molecular dynamics simulations to investigate the mechanisms responsible for plastic deformation in metal–organic framework-5 (MOF-5). Simulations of uniaxial compression along [001], [101], and [111] directions reveal that structural collapse of {001} planes is responsible for irreversible deformation. The process involves slip along either one of the two ⟨100⟩ directions on the collapsing plane; this local shear process is due to the flexibility of the connection between of Zn–O clusters and 1,4-benzenedicarboxylate ligands. Thus, the collapse is driven both by compressive and shear stresses, and this fact explains the anisotropy in the mechanical response of this cubic crystal. The development of shear-collapse bands follows a nucleation and growth process with nuclei elongated along the slip direction and their subsequent growth in the directions normal to the slip and at much slower rates. This process is reminiscent of the glide of screw dislocations. Compression along the [101] a...

Morphological changes in polycrystalline Fe after compression and release

Despite a number of large-scale molecular dynamics simulations of shock compressed iron, the morphological properties of simulated recovered samples are still unexplored. Key questions remain open in this area, including the role of dislocation motion and deformation twinning in shear stress release. In this study, we present simulations of homogeneous uniaxial compression and recovery of large polycrystalline iron samples. Our results reveal significant recovery of the body-centered cubic grains with some deformation twinning driven by shear stress, in agreement with experimental results by Wang et al. [Sci. Rep. 3, 1086 (2013)]. The twin fraction agrees reasonably well with a semi-analytical model which assumes a critical shear stress for twinning. On reloading, twins disappear and the material reaches a very low strength value.

Testing and numerical simulation of Holocene marine sand uniaxial compression along the Lithuanian coast

Compressibility of quartz sand from the Lithuanian coastal area in Klaipėda environs is investigated by testing and numerical simulation, with validation of obtained results. The shape of sand grains has been analysed with a scanning electronic microscope (SEM). The determined morphological parameters of sand grains are employed to create discrete models (particle models of grains) subsequently used for sand compression test numerical simulation via discrete element method (DEM) techniques. The background version of DEM and the numerical time-integration algorithm are implemented in original DEMMAT code. Compression tests have been realised by an oedometer device. Test versus numerical simulation results have revealed a dependence of significant compression curve character on the discretised shape of sand grains and Young’s modulus of particles.

Large-scale finite element analysis of human cancellous bone tissue micro computer tomography data: a convergence study.

The complex geometry of cancellous bone tissue makes it difficult to generate finite element (FE) models. Only a few studies investigated the convergence behavior at the tissue scale using Cartesian meshes. However, these studies were not conducted according to an ideal patch test and the postelastic convergence behavior was not reported. In this study, the third principal strain and stress, and the displacement obtained from human micro finite element (microFE) models of lower resolutions were compared against the model of 19.5 μm as a reference, representing the original spatial resolution of microCT data. Uni-axial compression simulations using both linear-elastic and nonlinear constitutive equations were performed. The results showed a decrease in percentage difference in all three values as the element size decreased, with the displacement converging the fastest among the three. Simulations carried out using a nonlinear constitutive equation however, failed to show convergence for the third principal strains and stresses. It was concluded that at the tissue level, Cartesian meshes of human cancellous bone tissue were able to reach a converged solution in all three parameters investigated for linear simulation and only in displacement for nonlinear simulation. These parameters can be used as references in the future for studies in local biomechanical behavior of human cancellous bone tissues with linear simulation. The convergence behavior for human cancellous bone tissue using nonlinear constitutive equations needs further investigation.

A semi-implicit integration scheme for a combined viscoelastic-damage model of plastic bonded explosives

This paper presents a new implementation of a constitutive model commonly used to represent plastic bonded explosives in finite element simulations of thermomechanical response. The constitutive model, viscoSCRAM, combines linear viscoelasticity with isotropic damage evolution. The original implementation was focused on short duration transient events; thus, an explicit update scheme was used. For longer duration simulations that employ significantly larger time step sizes, the explicit update scheme is inadequate. This work presents a new semi-implicit update scheme suitable for simulations using relatively large time steps. The algorithm solves a nonlinear system of equations to ensure that the stress, damaged state, and internal stresses are in agreement with implicit update equations at the end of each increment. The crack growth is advanced in time using a sub-incremental explicit scheme; thus, the entire implementation is semi-implicit. The theory is briefly discussed along with previous explicit integration schemes. The new integration algorithm and its implementation into the finite element code, Abaqus, are detailed. Finally, the new and old algorithms are compared via simulations of uniaxial compression and beam bending. The semi-implicit scheme has been demonstrated to provide higher accuracy for a given allocated computational time for the quasistatic cases considered here. Published 2014. This article is a US Government work and is in the public domain in the USA.

Simulation of Uniaxial Compression Based on Hamiltonian MPS Method with Wall Boundary Condition Using Penalty Method

Simulation of Uniaxial Compression Based on Hamiltonian MPS Method with Wall Boundary Condition Using Penalty Method

Numerical Modeling and Simulation of Uniaxial Compression of Aluminum Foams Using FEM and 3D-CT Images

The aim of this paper is to evaluate the elasto-plastic deformation behavior of open cell aluminum foams samples simulated under compressive loads and verified experimentally. Aluminum foams were fabricated from AlSiMg alloy by infiltration process with vacuum pressure. The samples geometry was obtained via 3D reconstruction using micro-computer tomography images. Solid representation of the samples was used for the numerical model based on Finite Element Method (FEM) where mechanical behavior was established. The material parameters were calibrated by experimental results and were used for setting up simulations. The compression test was carried out at room temperature and strain rate of 0.5mm.s-1. The average plateau stress and energy absorption per unit volume were evaluated from the measured stress-strain curves. The 3D FEM models were used to simulate the mechanical behavior of open cell aluminum foam and establish its stress - strain state. The experimental responses from the compression tests were in agreement with the obtained from the 3D numerical models. It was possible to determine by numerical models and experimental stress – strain curves, the mechanical behavior of the aluminum foams under study: the plateau stress and energy absorption increase with decreasing pore size and increasing density.

Numerical Simulation of Damage and Deformation Characteristics of Rock Mass with Transfixion Joint

Use FLAC3D, the interface command to define joint surface, set up rock mass models with 15 °, 30 °, 60 °, etc. different dip joint, and in accordance with the laboratory test data of rock and joint surface for a variety of strength and deformation parameters setting, carries on the numerical simulation of uniaxial compression. Got failure mode, plastic zone evolution and the stress strain curve of rock mass with different dip joint, and the result compared with the actual test has a higher similarity, to prove the feasibility of the numerical simulation method.

Mechanics of random discontinuous long-fiber thermoplastics. Part II: Direct simulation of uniaxial compression

The mechanical interactions between fibers in a dense random-fiber network transmit stress, cause fiber curvature, and influence fiber orientation in the processing of many types of composites. A few theories describe the mechanics of fiber networks, but almost no simulation results are available. Here, we report a direct numerical simulation of the mechanical behavior of random-fiber networks. The finite element method is used, and each fiber is represented by a small number of 3D beam elements. The calculations assume a periodic structure to avoid boundary effects, but within the unit cell, the fibers are placed randomly. A special algorithm that uses the random sequential adsorption process creates an initial structure of straight, random, nonintersecting fibers from which a unit cell with periodic boundary conditions is built automatically [A. I. Abd El-Rahman and C. L. Tucker III, “Mechanics of random discontinuous long-fiber thermoplastics. Part I: Generation and characterization of initial geometry...

Compressive consolidation of strongly aggregated particle gels

The compressive yield stress of particle gels shows a highly nonlinear dependence on the packing fraction. We have studied continuous compression processes, and discussed the packing fraction dependence with the particle scale rearrangements. The 2D simulation of uniaxial compression was applied to fractal networks, and the required compressive stresses were evaluated for a wide range of packing fractions that approached close packing. The compression acts to reduce the size of the characteristic structural entities (i.e. the correlation length of the structure). We observed three stages of compression: (I) elastic-dominant regime; (II) single-mode plastic regime, where the network strengths are determined by the typical length scale and the rolling mode; and (III) multi-mode plastic regime, where sliding mode and connection breaks are important. We also investigated the way of losing the fractal correlation under compression. It turns out that both fractal dimension $D_{\mathrm{f}}$ and correlation length $\xi$ start to change from the early stage of compression, which is different from the usual assumption in theoretical models.

Investigation on Zener-Hollomon Parameter in the Hot Compressive Deformation Behavior of SWRCH 35K

The hot compressive deformation behavior of SWRCH 35K was studied with uniaxial hot compression simulation tests at 923 ~ 1223 K and strain rate of 0.01 ~ 20 /s. The results show that the hot compressive deformation activation energy was 408 kJ/mol and the rang of deformation stored energy was 10 ~ 50 J/mol. The quadratic fitting expression between deformation stored energy and Zener-Hollomon parameter (Z) was established and the deformation stored energy was considered to increased with increasing Z or with lower deformation temperature and increasing deformation rate.

Effect of Different Strain on Microstructure Evolution of Medium Carbon Steel

Uniaxial hot compression simulation experiment at 700°C with different true strain was carried out to study the microstructure evolution of medium carbon steel, the predominant mechanism on the cementite softening has been explored, the experimental results show that the volume fraction of deformation induced ferrite (DIF) increased with increasing true strain and even exceeds the equilibrium content. With the increase of DIF, more and more carbon atoms congregated in the boundaries such as the interface of DIF and the interphase of DIF/deformation austenite. Carbon congregation provides the right carbon content and the optimized microstructure for divorced decomposition during the process of controlled cooling. Therefore spherical or rod-like cementite and degenerated pearlite can be obtained.

Numerical Simulation of Marine Recycled Concrete Specimen Based on ABAQUS

Based on ABAQUS, this article builds up a dispersion cracking model and carries out the numerical simulation of the influence of sea water erosion depth and intension upon marine recycled concrete specimen. Compared with stress-strain curve from the experiment, it can be easily found that the experimental results match well with that of simulation through the numerical simulation of uniaxial compression on average concrete, recycled concrete corroded by seawater and the same concrete after vacuum pumping, which shows two kinds of curves stay close to each other. From the results of the simulation, strain develops from the edges to the middle of the cube until it runs through the whole section, which basically corresponds with the outcome observed in the experiment.

Mechanism for amorphization of boron carbide B4C under uniaxial compression

Boron carbide undergoes an amorphization transition under high-velocity impacts, causing it to suffer a catastrophic loss in strength. The failure mechanism is not clear and this limits the ways to improve its resistance to impact. To help uncover the failure mechanism, we used ab initio methods to carry out large-scale uniaxial compression simulations on two polytypes of stoichiometric boron carbide (B${}_{4}$C), B${}_{11}$C-CBC, and B${}_{12}$-CCC, where B${}_{11}$C or B${}_{12}$ is the 12-atom icosahedron and CBC or CCC is the three-atom chain. The simulations were performed on large supercells of 180 atoms. Our results indicate that the B${}_{11}$C-CBC (B${}_{12}$-CCC) polytype becomes amorphous at a uniaxial strain s $=$ 0.23 (0.22) and with a maximum stress of 168 (151) GPa. In both cases, the amorphous state is the consequence of structural collapse associated with the bending of the three-atom chain. Careful analysis of the structures after amorphization shows that the B${}_{11}$C and B${}_{12}$ icosahedra are highly distorted but still identifiable. Calculations of the elastic coefficients (${C}_{ij}$) at different uniaxial strains indicate that both polytypes may collapse under a much smaller shear strain (stress) than the uniaxial strain (stress). On the other hand, separate simulations of both models under hydrostatic compression up to a pressure of 180 GPa show no signs of amorphization, in agreement with experimental observation. The amorphized nature of both models is confirmed by detailed analysis of the evolution of the radial pair distribution function, total density of states, and distribution of effective charges on atoms. The electronic structure and bonding of the boron carbide structures before and after amorphization are calculated to further elucidate the mechanism of amorphization and to help form the proper rationalization of experimental observations.