Simulation Of Failure Process Research Articles

Triaxial compression test of MICP sand column and simulation of failure process

Microbially induced calcium carbonate precipitation (MICP) technology can induce calcium carbonate crystals with cementation and stable performance in the process of microbial metabolism or enzymization through the regulation of environmental factors MICP can be used as a cementing agent to cement cohesionless sand particles to form the materials with the characteristics of higher strength, better durability and environmental friendliness, as well as a good engineering application prospect. In this paper, the shear strength of sand column was tested by triaxial compression tests, and the strength index was obtained. In order to further study the micro-strength mechanism and the failure process, based on the discrete element method, a numerical model of MICP cemented sand column was established considering the factors of matrix soil particle gradation, particle morphology, content ratio of induced calcium carbonate, pore distribution characteristics, inter-particle cementation and so on. The failure process of MICP cemented sand column under load was analysed by numerical simulation, and the reliability of the numerical model was tested by combining with the stress intensity curve of samples under test conditions. The results indicate that compared with the actual triaxial tests of MICP cemented sand column, although there are deviations in stress and strain, cohesion and internal friction angle, the numerical simulation shows similar development law and intensity amplitude, and the same failure trend. The work in this paper verifies the reliability of the numerical model and provides a theoretical basis for the subsequent analysis of the factors influencing the geotechnical mechanical properties of biomineralized materials.

Аспекты численного моделирования процессов разрушения упруго-хрупких тел

Understanding the nucleation and evolution of microdefects in solid bodies is important to ensure the reliability and safety of critical structures and to identify their strength and deformation resources. In numerical modeling, failure zones can be represented as areas with significantly underestimated rigid characteristics by analogy with the method of variable elastic parameters used in solving the boundary-value problems of the theory of plasticity. However, the formal application of numerical algorithms of plasticity does not always lead to an adequate description of failure processes especially in elastic-brittle bodies. This paper considers some aspects of the numerical simulation of failure processes, such as the calculation of a stress-strain state after reducing the rigidity of finite elements under constant boundary conditions by organizing an appropriate iteration procedure, and the selection of the maximum number of finite elements fractured per iteration, the value of a loading step, and the discretization degree of the computational domain. The influence of the above aspects on the results of failure simulation is illustrated by comparing the numerical solutions to the problem of deformation of the strip made of elastic-brittle material with the edge stress concentrator, which were obtained by different algorithms. The loading diagrams were plotted, and the implementation of the post-critical stage at the macro level was demonstrated. Failure kinetics was analyzed for different variants of implementation of the iterative procedure and at a variable number of elements fractured per iteration. It has been found that, in order to get an accurate description of deformation and failure processes, the automatic selection of a loading step seems to be more reasonable. Analysis has indicated that the discretization degree of the computational domain has a strong impact on the modeling results. This suggests that the finite element size should correspond to a certain strength constant of a material having the dimensions of length.

A crystal plasticity-based microdamage model and its application on the tensile failure process analysis of 7075 aluminum alloy

In this study, a microdamage model by introducing the damage of crystal is proposed. Damage variables are defined for each slip system, and the damage-coupled crystal plasticity constitutive equations are derived by virtue of the concept of effective stress and the hypothesis of strain equivalence. A function of damage driving force is proposed by analyzing failure mechanisms. The damage evolution equation is then derived based on thermodynamics. After that, a differential evolution-based method is adopted for the calibration of the parameters, and a numerical simulation algorithm is implemented for the failure process simulation of a single crystal material for verification purposes. The proposed model and the corresponding numerical method are then applied to the failure process analysis of a polycrystalline material 7075 aluminum alloy. The EBSD observation is conducted to obtain the size and orientation of grains, which combines with the Voronoi diagram method to be the basis for establishing the polycrystal finite element model. Afterwards, the numerical simulation of the failure process of specimens under tension is conducted. The predicted results are in good agreement with the experimental observations. It indicates that the proposed model can well reflect the damage-softening effect from the microplasticity to the macroscopic deformation. Finally, the two damage mechanisms of grains in 7075 aluminum alloy are investigated based on the calculated result.

Simulation of collapse failure process of rock slope based on the smoothed particle hydrodynamics method

The limit equilibrium method (LEM) or finite element method (FEM) for slope problems most frequently focusses on the stability analysis. There are, however, still some problems with the LEM or FEM when considering damage and failure evolution of a rock slope because of the distortion of mesh. In this work, a mesh-free particle approach, named the smoothed particle hydrodynamics (SPH) method, is presented and is improved to analyze the damage and failure process of a rock slope. In order to better describe the cause and mechanism of brittle failure for a rock slope, the plastic factor was suggested and introduced into the SPH algorithm, and the conservation equations of SPH for brittleness characteristics were obtained. Based on the variation of displacement and time, an effective criterion was proposed to define the factor of safety in SPH simulation. The Drucker-Prager Mohr-Coulomb strength criterion was implemented into the SPH algorithm to describe the elastic-plastic behavior. Then, three rock-slope models with different precast cracks were analyzed to illustrate the performance of the proposed method. It is shown that the proposed SPH algorithm can be effectively applied in the prediction of the deformation and failure process of rock slope.

Numerical Simulation of Deformation and Failure Process of Tunnel Surrounding Rock Based on Different Constitutive Models

Based on five different constitutive models, the progressive failure process of deep hard rock was simulated, and the plastic zone, shear strain increment high-value zone, horizontal displacement, and maximum principal stress distribution of surrounding rock were obtained. The calculation results show that the plastic zone of surrounding rock calculated by MCSS and HBSS models is mainly concentrated in the floor and vault of the cavern, and the sidewall is not damaged. There is no shear zone in the surrounding rock, and the magnitude of horizontal displacement is 10-4. In the L-CWFS model, the hysteresis cohesion of friction strengthening is weakened, and the initial friction angle is 0. The calculated plastic zone runs through the surrounding rock, and the whole section is destroyed. The order of magnitude of the horizontal displacement extremum is 10-3. The MC-HB model simulates the spalling failure of the side wall, and the strain localization of the side wall is not obvious, and no shear band is formed inside the surrounding rock deeply. The N-CWFS-TSS model simulates the buckling failure process of the straight wall plate crack. A shear band is formed at the bottom of the straight wall and penetrates into the interior of the surrounding rock. The strain localization is obvious and the order of magnitude of the shear strain increment is 10-2. The calculation results are consistent with the results of laboratory tests and field observations, and the failure mechanism of the compression-shear-tensile-shear composite in the progressive failure process of the surrounding rock is clarified.

Particle Flow Simulation of Failure Process of Defective Sandstone under Different Intermediate Principal Stress under True Triaxial Action

In order to explore the mechanical response characteristics of fractured sandstone under true triaxial different medium principal stresses, matdem particle flow software was used to study the mechanical response characteristics, fracture mechanism and damage evolution characteristics of sandstone specimens under the conditions of 30 MPa, 40 MPa and 50 MPa respectively. The simulation results are verified by true triaxial test. The results show that under true triaxial stress, the increase of medium principal stress is beneficial to increase the strength of sandstone. The fracture degree of the specimen increases with the increase of the intermediate principal stress, and finally the interlacing macroscopic cracks are formed. When the intermediate principal stress is perpendicular to the fracture strike, the fracture mode of sandstone is that the macroscopic fracture plane is perpendicular to the fracture strike, and the fracture mechanism of sandstone under true triaxial compression is mainly shear failure, accompanied by tensile failure. With the increasing of the intermediate principal stress, the fractal dimension of the fracture of sandstone specimen increases significantly and the degree of fracture deepens. Combined with the true triaxial test results, the rationality of particle flow simulation test is proved.

A modified rigid-body-spring method for modeling damage and failure of brittle rocks subjected to triaxial compression

A three-dimensional modified rigid-body-spring method (3D mRBSM) is presented to simulate the progressive damage and failure process of rocks under triaxial compressive conditions. Different from the original RBSM model, the mRBSM employs spring-set groups distributed on interfaces between blocks to approximately describe the progressive failure process of micro-cracks without increasing the size of governing equations. Firstly, the basic equations of 3D mRBSM are derived. A new randomly distributed Voronoi-based mesh technique is proposed to reproduce homogeneous and isotropic rock materials. Then, relationships between macro and micro elastic parameters are established, and a calibration procedure for parameters of failure criterion is adopted based on the trial-and-error procedure. Lastly, the new model is applied to simulate pseudo triaxial and true triaxial compression tests on brittle rocks. Results show that the proposed model correctly captures common mechanical properties of brittle rocks, such as nonlinear stress–strain relationship, brittle-ductile transition, confining pressure dependence of failure mode and medium principal stress effect. The above research demonstrates that the mRBSM is successfully upgraded to three-dimensional version. The new method is a promising tool for simulation of deformation and failure process of rocks under true triaxial stress conditions.

A hybrid multi-phase field model to describe cohesive failure in orthotropic materials, assessed by modeling failure mechanisms in wood

Fracture mechanics is crucial for many fields of engineering applications, as precisely predicting failure of structures and parts is required for efficient designs. The simulation of failure processes is, both from a mechanical and a numerical point of view, challenging, especially for inhomogeneous materials, where the microstructure influences crack initiation and propagation and might lead to very complex crack patterns. The phase field method for fracture is a promising approach to encounter such materials, since it is able to describe complex fracture phenomena like crack kinking, branching and coalescence. Moreover, it is a largely mesh independent approach, given that the mesh is homogeneous in the area of the crack. However, the original formulation of the phase field method is limited to isotropic materials and does not account for preferable fracture planes defined through the material’s microstructure. In this work, the method is expanded to take orthotropic constitutive behavior and preferable directions of crack propagation into account. We show that by using a stress-based split and multiple phase field variables with preferable fracture planes, in combination with a hybrid phase field approach, a general framework can be found for simulating anisotropic, inhomogeneous materials. The stress-based split is based on fictitious crack faces and is, herein, expanded to support anisotropic materials. Furthermore, a novel hybrid approach is used, where the degradation of the sound material is performed based on a smooth traction free crack boundary condition, which proves to be the main driving factor for recovering commonly observed crack patterns. This is shown by means of a detailed analysis of two examples: a wooden single edge notched plate and a wood board with a single knot and complex fiber directions. In both cases, the proposed novel hybrid phase field approach is able to realistically reproduce complex failure modes.

Peridynamics simulation of impact failure in glass plates

This paper aims at presenting numerical simulation of dynamic failure process of Duran 50 glass plates subjected to high-velocity impact loads using a bond-based peridynamics (PD). In simulation, several affecting parameters including impact velocity, impact angle, impact contact area, glass plate thickness, and porosity percentage in glass plate are considered. The effects of these parameters on the damage, reaction force, and coefficient of restitution are examined. The functional relationship among the reaction force on bullet, the bullet velocity and the plate thickness is established. In addition, the functional relationship among the damage percentage of plate, the bullet velocity and the plate thickness is constructed. Thus, the reaction force on the bullet and the damage percentage of the plate can be directly evaluated with the functional relationships in the practice applications. PD simulated results are validated by existing experimental data with a good agreement. Through the simulated results, the following conclusions are obtained (1) a strong correlation exists between the coefficient of restitution observed experimentally and the model predictions; (2) the sensitivity to the velocity and sheet thickness in large-sized bullets is more than that in small-sized ones; (3) the damage, maximum reaction force, and coefficient of restitution almost change linearly with increasing the velocity, plate thickness and impact contact area; and (4) the effect of the porosity percentage on damage and reaction force is negligible.

A PD-FEM approach for fast solving static failure problems and its engineering application

A method of coupling of peridynamics (PD) and finite element method (FEM) for fast solving static failure problems is proposed. It is based on the force coupling method and adopts interface elements to couple the PD and FE subregions. By assembling the global matrix of the coupling model and using the adaptive dynamic relaxation (ADR) method to solve it, the static solution of elasticity and crack growth problems can be obtained quickly. By introducing short-range repulsive force and re-defining the coupling force, it is not only suitable for simulating tensile failure problems, but also suitable for compression failure problems. Through comparative analysis, the accuracy and effectiveness of this approach are verified. And then the method is successfully applied to simulate the excavation process of an underground cavern group, and the simulation of damage and failure process of engineering rock mass under complex tension–compression conditions has been realized. The stability characteristics of the surrounding rock are revealed by analyzing the damage and deformation evolution laws. It provides an effective numerical simulation method for predicting the excavation damage zone (EDZ) distribution characteristics and deformation law of the surrounding rock during the excavation of an underground cavern group. At the same time, compared with pure PD, the calculation efficiency is greatly improved, which is of great significance for the realization of engineering-scale simulation.

Landslide Failure Process Simulation with Automatic Remeshing in FLAC3D

Landslide is a serious geologic disaster, which remarkably influences the safety of lives and engineering activities. Numerical simulation is the most universal method to analyze the stability and influence of landslides. For the continuous mechanical modeling of deformation based on a mesh, most landslide deformation failures of a slope are based on the small strain mode instead of the large strain mode to avoid mesh distortion. However, the failure process and the morphological characteristics of different stages cannot be reflected. In this study, an automatic remeshing technology in Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) is developed to overcome this problem. With the built-in Python in FLAC3D, the mesh of the landslide is automatically updated with deformation. The strain and stress of the adjusted mesh are remapped from the old mesh to maintain the consistency of results. This method is extended to simulate the extremely large deformation in FLAC3D for the landslide failure process. With this strategy, 3D slopes with and without a large strain mode and automatic remeshing technology are compared to understand the failure process and eliminate or reduce threats of a landslide.

A robust multisurface return-mapping algorithm and its implementation in Abaqus

The simulation of complex material failure processes requires a precise differentiation of the involved failure mechanisms like fracture or plasticity. This is commonly achieved by using a so-called multisurface failure criterion, where each failure surface is related to a certain failure mechanism. In the case of plasticity, failure surfaces define the elastic domain of the material and any stress state outside of this domain is considered non-admissible and must be returned to the boundary of the elastic domain. So-called return-mapping algorithms are often used and well-studied methods for finding such valid stress states. However, their implementation in numerical simulation tools is often not robust and efficient enough for complex problems that involve sophisticated multisurface definitions. In this work, we present a multisurface return-mapping algorithm and its implementation in the finite element software Abaqus. We found that with additional and enhanced iterative solver methods, the classic Newton-Raphson-based implementation of the algorithm can be improved in order to find solutions to otherwise not returnable stress states. The added computational burden is minimal, as more stress states can be returned without reducing the size of the load increments. The paper focuses on the implementation aspects of such problems and offers the reader a thorough guide and the source code for an Abaqus implementation. We applied the algorithm to simulate the highly orthotropic behavior of wood, allowing us to predict plastic failure of various wooden structures and components.

Simulation of the Failure Process of Submarine Landslides on a Seabed by Coupled MPM

Mei, X.; Ma, G.; Hu, X.; Shi, B., and Huang, D., 2020. Simulation of the failure process of submarine landslides on a seabed by coupled MPM. In: Liu, X. and Zhao, L. (eds.), Today's Modern Coastal Society: Technical and Sociological Aspects of Coastal Research. Journal of Coastal Research, Special Issue No. 111, pp. 231–237. Coconut Creek (Florida), ISSN 0749-0208.Submarine landslides are large-scale natural marine disasters that commonly occur in coastal areas, which significantly threats important subsea infrastructures and offshore facilities. This paper presents a two-dimensional numerical model using the material point method and hydromechanical coupling to simulate a typical submarine landslide, named the Storegga Slide. The numerical simulation for modeling the submarine landslide, consisting of submarine clay with a strain-softening constitutive model, has provided information about the landslide failure process, as well as the failure mechanisms of retrogression deformation under the effect of water. The simulation reproduces the evolution process with a final deposit morphology, which is consistent with the previous investigation result. Based on the modeling, the landslide failure process, mechanisms, and plastic strain state are comprehensively discussed. It is found that because of the water effect, some distinct characteristics in the sliding process can be observed in submarine landslides: movement hinderance, a bulbous configuration, and high fluidization, which is valuable for disaster mitigation.

Numerical simulation of failure processes of heterogeneous rock specimens under assumption of invariant spherical stress during stress drop

Numerical simulation of failure processes of heterogeneous rock specimens under assumption of invariant spherical stress during stress drop

Seismic slope stability and failure process analysis using explicit finite element method

Earthquake is one of the primary factors that triggers the failure of slopes and the landslides in the mountainous area. In this study, an efficient method for the seismic slope stability analysis and seismic failure process simulation is proposed. The seismic slope stability and the failure process of a two-dimensional slope model are analyzed via the explicit finite element method with the influence of the dynamic mechanical behavior of soil and the frictional resistance characteristic of the slope rupture surface. A dynamic visco-elasto-plastic constituted model for soil is established and written in FORTRAN as a user subroutine of the finite element method code of ABAQUS. The validation of the visco-elasto-plastic constituted model and the explicit finite element method are compared with the experimental results and the implicit method. The seismic factor of safety and the sliding distance of the soil slopes under the natural earthquake conditions are calculated via the dynamic visco-elasto-plastic constituted model and the explicit finite element method. The influence of the ground motion characteristics on the seismic slope stability is analyzed in this study via the specified elastic response acceleration spectrum. The analysis results of this paper suggest that the seismic slope stability analysis and the progressive failure process of the slope under the seismic condition can be analyzed by the explicit finite element method efficiently. The results show that the dynamic mechanical behavior of soil and the ground motion characteristics are both critical influence factors for the seismic slope stability. The frictional resistance characteristic of the slope rupture surface is the principal influence factor for the sliding distance of the slope, and it also has more influence on the sliding distance of a high slope than that of the small slope.

Analysis of landslide stability under seismic action and subsequent rainfall: a case study on the Ganjiazhai giant landslide along the Zhaotong-Qiaojia road during the 2014 Ludian earthquake, Yunnan, China

In a strong earthquake, not only a large number of coseismic landslides are triggered, but relaxation and cracks in the rocks and soils are induced, which make these rocks and soils vulnerable to instability during subsequent rainfall; thus, strong earthquakes always have long-term effects on landslides. The geo-hazards along the Zhaotong-Qiaojia road in the 2014 Ludian earthquake (Ms 6.5) of Yunnan Province, China, were investigated, and the Ganjiazhai giant landslide was chosen as a case study. First, using the limit equilibrium analysis and Newmark method, the critical seismic intensity of the landslide before the earthquake was evaluated. Secondly, the dynamic failure process of the landslide under the measured ground motion was simulated with the discontinuous deformation analysis method. Lastly, based on stress–seepage coupling analysis and precipitation data from Ludian meteorological station, the stability of the landslide during subsequent rainfall after the earthquake was predicted. The results show that the critical seismic intensity was within degrees VIII–IX, which is consistent with the results of the earthquake damage investigation. The dynamic failure process can be divided into four stages, and four scarps formed; the potential sliding zones during the subsequent rainfall were at the first scarp and the fourth scarp, and their critical rainfall amounts were 35–40 mm and 55–60 mm, respectively. In this paper, failure process simulation and stability prediction of the landslide before, during, and after the strong earthquake are presented, which provide analysis methods for the dynamic stability of landslides in the meizoseismal area.

Numerical simulation of failure process of high-strength concrete using the discrete-element model

A two-dimensional mesoscopic model is presented for simulation of the failure process of high-strength concrete (HSC) confined by fibre-reinforced polymer (FRP). The model is based on the discrete-element method and modified rigid-body spring model, which were developed for simulation of the behaviour of normal-strength concrete, and is extended here to model HSC. Due to the fact that the mortar matrix and the interfacial layer in HSC are generally stronger than the strength of the aggregate, springs are designed in such a way that the crack can penetrate into the aggregate. To develop the confined model, FRP elements are connected to the basic model as rectangular elements, the connections of which are modelled together based on Hooke's law in cylindrical coordinates. Interfacial springs between FRP and concrete elements are designed based on the bond–slip model and the behaviour of concrete core under confining action provided by the FRP jacket. The failure behaviour of three unconfined and two confined HSC specimens was simulated by the proposed model. Analytical results are presented as stress–strain curves and crack modes, which were found to be in good agreement with experimental data.

Numerical Simulation of Rock Failure Process with a 3D Grain‐Based Rock Model

A grain‐based rock model was developed and applied to study mechanical characteristics and failure micromechanics in thick‐walled cylinder and wellbore stability tests. The rock is represented as an assembly of tetrahedral blocks with bonded contacts. Material heterogeneity is modeled by varying the tensile strength at the block contacts. This grain‐based rock model differs from previous disk/sphere particle‐based rock models in its ability to represent a zero (or very low) initial porosity condition, as well as highly interlocked irregular block shapes that provide resistance to movement even after contact breakage. As a result, this model can reach higher uniaxial compressive strength to tensile strength ratios and larger friction coefficients than the disk/sphere particle‐based rock model. The model captured the rock fragmentation process near the wellbore due to buckling and spalling. Thin fragments of rock similar to onion skins were produced, as observed in laboratory breakout experiments. The results suggest that this approach may be well suited to study the rock disaggregation process and other geomechanical problems in the rock excavation.

GPGPU-parallelized 3D combined finite–discrete element modelling of rock fracture with adaptive contact activation approach

The combined finite–discrete element (FDEM) has become a well-accepted numerical technique to simulate the fracturing process of rocks under different loading conditions. However, the study on three-dimensional (3D) FDEM simulation of rock failure process is highly limited in comparison with that on two-dimensional (2D) FDEM simulations, which is due to the high computational cost of the 3D FDEM. This paper implements an adaptive contact activation approach and a mass scaling technique with critical viscous damping into a GPGPU-parallelized Y-HFDEM 2D/3D IDE code formally developed by the authors to further speed up 3D FDEM simulation besides GPGPU parallelization. It is proved that the 3D FDEM modelling with the adaptive contact activation approach is 10.8 times faster than that with the traditional full contact activation approach, while the obtained results show negligible differences. At least additional 25 times of speedups can be achieved by the mass scaling technique although further speedups are possible with bigger mass scaling coefficients chosen, which, however, will more and less affect the calculated results. Taking the advantage of the drastic speedups of the implemented adaptive contact activation approach and the mass scaling approach, the GPGPU-parallelized Y-HFDEM 3D IDE is then applied to model the fracture process of rocks in triaxial compression tests under various confining pressures. It is concluded that the GPGPU-parallelized Y-HFDEM 3D IDE is able to simulate all important characteristics of the complicated fracturing process in the triaxial compression tests of rocks including the transition from brittle to ductile behaviours of rocks with the increasing confining pressures. After that, some important aspects of the 3D FDEM simulation such as the effects of meshes, loading rates and model sizes are discussed. It is found that the mixed-mode I–II fractures are highly possible, i.e. very reasonable, failure mechanisms when unstructured meshes are used in the 3D FDEM simulation. For modelling rock fracture under quasi-static loading conditions using the 3D FDEM, the loading rate must be small enough, which is recommended to be no more than 0.2 m/s, to avoid its significant effects. Finally, it is concluded that the implementation of the adaptive contact activation approach and the mass scaling technique can further speed up 3D FDEM simulation besides the parallelization and the GPGPU-parallelized 3D IDE code with the further speedup is able to capture the complicated fracturing process of rocks under quasi-static loading conditions.

Simulating the Overtopping Failure of Homogeneous Embankment by a Double-Point Two-Phase MPM

Embankments are usually constructed along rivers as a defense structure against flooding. Overtopping failure can cause devastating and fatal consequences to life and property of surrounding areas. This motivates researchers to study the formation, propagation, and destructive consequences of such hazards in risk analysis of hydraulic engineering. This paper reports a numerical simulation of failure processes in homogeneous embankments due to flow overtopping. The employed numerical approach is based on a double-point two-phase material point method (MPM) considering water–soil interaction and seepage effects. The simulated results are compared to available laboratory experiments in the literature. It was shown that the proposed method can predict the overtopping failure process of embankments with good accuracy. Furthermore, the effects of the cohesion, internal fiction angle, initial porosity, and maximum porosity of soil on the embankment failure are investigated.