scholarly journals Investigation of Burn Cut Parameters and Model for One-Step Raise Excavation Based on Damage Evolution Mechanisms

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-16 ◽  
Author(s):  
Kai Liu ◽  
Jiadong Qiu
Keyword(s):  
Damage Evolution ◽  
Damage Zone ◽  
Damage Model ◽  
Threshold Value ◽  
Numerical Results ◽  
Good Effect ◽  
Charge Hole ◽  
Triangular Prism ◽  
Linear Charge Density ◽  
One Step

One-step raise excavation with burn cut is a kind of technology which use the drilling and blasting method to excavate the raise quickly. Due to the limitation of the free surface in burn cut, determination of cut parameters such as the length of burden and diameters of empty hole and charge hole is important to achieve a good effect of cut blasting. Meanwhile, the choice of the cut model is also crucial to form a proper opening. In this study, a modified Holmquist-Johnson-Cook (HJC) model, in which the tension-compression damage model and tension-compression strain rate effect model are considered, is embedded in the LS-DYNA software to investigate the damage evolution of rock in cut blasting. A simplified numerical model of burn cut is built in the LS-DYNA. The numerical results indicate that there is a threshold value of the burden length to maximize the opening. The empty hole has the effect of transferring blasting energy, and the effect becomes more obvious with the increase of the hole size. Moreover, the linear charge density of the prime cut hole can affect the compression and tension damage. Further, the comparison among four typical burn cut models are conducted based on numerical results. It demonstrates that triangular prism cut and doliform cut, which have more empty holes arrangement surrounding the prime cut hole, are better than spiral cut and diamond cut that with less empty holes locating one side of the prime cut hole in terms of energy efficiency and damage zone control.

Chip Morphology Studies Using Separate Fracture Toughness Values for Chip Separation and Serration in Orthogonal Machining Simulations

2018 ◽  
Author(s):  
Jaimeen Patel ◽  
Harish P. Cherukuri
Keyword(s):  
Damage Evolution ◽  
Damage Model ◽  
Equivalent Plastic Strain ◽  
Chip Morphology ◽  
Threshold Value ◽  
Threshold Values ◽  
Orthogonal Machining ◽  
Evolution Laws ◽  
On Chip ◽  
Chip Separation

It is well known that the chip morphology predictions in machining simulations depend on the separation criteria used for modeling chip formation. In this paper, we propose to use two different criteria for chip separation and serration along with the Johnson-Cook damage model. The threshold value for chip separation is determined from machining experiments using the methodologies discussed in Patel et al. [1]. In addition, two separate damage evolution laws for chip separation and serration are used. Our results indicate that the choice of the evolution law and the threshold values of Gc used for chip separation and serration have a significant effect on chip shape and other field variables such as the equivalent plastic strain, cutting force, temperature, etc.

scholarly journals A Modified Phase-Field Damage Model for Metal Plasticity at Finite Strains: Numerical Development and Experimental Validation

Metals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 47
Author(s):  
Jelena Živković ◽  
Vladimir Dunić ◽  
Vladimir Milovanović ◽  
Ana Pavlović ◽  
Miroslav Živković
Keyword(s):  
Phase Field ◽  
Damage Evolution ◽  
Deformation Gradient ◽  
Damage Model ◽  
Steel Structures ◽  
Plasticity Model ◽  
Metal Plasticity ◽  
Damage And Fracture ◽  
Von Mises ◽  
Von Mises Plasticity

Steel structures are designed to operate in an elastic domain, but sometimes plastic strains induce damage and fracture. Besides experimental investigation, a phase-field damage model (PFDM) emerged as a cutting-edge simulation technique for predicting damage evolution. In this paper, a von Mises metal plasticity model is modified and a coupling with PFDM is improved to simulate ductile behavior of metallic materials with or without constant stress plateau after yielding occurs. The proposed improvements are: (1) new coupling variable activated after the critical equivalent plastic strain is reached; (2) two-stage yield function consisting of perfect plasticity and extended Simo-type hardening functions. The uniaxial tension tests are conducted for verification purposes and identifying the material parameters. The staggered iterative scheme, multiplicative decomposition of the deformation gradient, and logarithmic natural strain measure are employed for the implementation into finite element method (FEM) software. The coupling is verified by the ‘one element’ example. The excellent qualitative and quantitative overlapping of the force-displacement response of experimental and simulation results is recorded. The practical significances of the proposed PFDM are a better insight into the simulation of damage evolution in steel structures, and an easy extension of existing the von Mises plasticity model coupled to damage phase-field.

scholarly journals Classification of extinction profiles for a one-dimensional diffusive Hamilton–Jacobi equation with critical absorption

2018 ◽  
Vol 148 (3) ◽  
pp. 559-574
Author(s):  
Razvan Gabriel Iagar ◽  
Philippe Laurençot
Keyword(s):  
Differential Equation ◽  
Ordinary Differential Equation ◽  
Jacobi Equation ◽  
Threshold Value ◽  
Monotonicity Property ◽  
Fast Diffusion ◽  
Extinction Time ◽  
One Step ◽  
Hamilton Jacobi Equation

A classification of the behaviour of the solutions f(·, a) to the ordinary differential equation (|f′|p-2f′)′ + f - |f′|p-1 = 0 in (0,∞) with initial condition f(0, a) = a and f′(0, a) = 0 is provided, according to the value of the parameter a > 0 when the exponent p takes values in (1, 2). There is a threshold value a* that separates different behaviours of f(·, a): if a > a*, then f(·, a) vanishes at least once in (0,∞) and takes negative values, while f(·, a) is positive in (0,∞) and decays algebraically to zero as r→∞ if a ∊ (0, a*). At the threshold value, f(·, a*) is also positive in (0,∞) but decays exponentially fast to zero as r→∞. The proof of these results relies on a transformation to a first-order ordinary differential equation and a monotonicity property with respect to a > 0. This classification is one step in the description of the dynamics near the extinction time of a diffusive Hamilton–Jacobi equation with critical gradient absorption and fast diffusion.

An improved nonlinear damage model of rocks considering initial damage and damage evolution

2020 ◽  
Vol 29 (7) ◽  
pp. 1117-1137 ◽  
Author(s):  
Wenlin Feng ◽  
Chunsheng Qiao ◽  
Shuangjian Niu ◽  
Zhao Yang ◽  
Tan Wang
Keyword(s):  
Damage Evolution ◽  
Least Squares Method ◽  
Damage Model ◽  
Creep Damage ◽  
Secondary Creep ◽  
Nonlinear Creep ◽  
Creep Failure ◽  
Initial Damage ◽  
Nonlinear Damage Model ◽  
Creep Damage Model

The experimental results show that the creep properties of the rocks are affected by the initial damage, and the damage evolution also has a significant impact on the time-dependent properties of the rocks during the creep. However, the effects of the initial damage and the damage evolution are seldom considered in the current study of the rocks' creep models. In this paper, a new nonlinear creep damage model is proposed based on the multistage creep test results of the sandstones with different damage degrees. The new nonlinear creep damage model is improved based on the Nishihara model. The influences of the initial damage and the damage evolution on the components in the Nishihara model are considered. The creep damage model can not only describe the changes in three creep stages, namely, the primary creep, the secondary creep, and the tertiary creep, but also reflect the influence of the initial damage and the damage evolution on creep failure. The nonlinear least squares method is used to determine the parameters in the nonlinear creep damage model. The consistency between the experimental data and the predicted results indicates the applicability of the nonlinear damage model to accurately predict the creep deformation of the rocks with initial damage.

Finite Element Modeling of Damage Formation in Rubber-Toughened Polymer

2005 ◽  
Vol 297-300 ◽  
pp. 1019-1024
Author(s):  
Mitsugu Todo ◽  
Yoshihiro Fukuya ◽  
Seiya Hagihara ◽  
Kazuo Arakawa
Keyword(s):  
Finite Element ◽  
Damage Zone ◽  
Damage Model ◽  
Crack Tip ◽  
Optical Microscope ◽  
Toughening Mechanism ◽  
Element Analysis ◽  
Zone Formation ◽  
Macro Scale ◽  
Rubber Toughened

Microscopic studies on the toughening mechanism of rubber-toughened PMMA (RTPMMA) were carried out using a polarizing optical microscope (POM) and a transmission electron microscope (TEM). POM result showed that in a typical RT-PMMA, a damage zone was developed in the vicinity of crack-tip, and therefore, it was considered that energy dissipation due to the damage zone development was the primary toughening mechanism. TEM result exhibited that the damage zone was a crowd of micro-crazes generated around rubber particles in the vicinity of notch-tip. Finite element analysis was then performed to simulate such damage formations in crack-tip region. Macro-scale and micro-scale models were developed to simulate damage zone formation and micro-crazing, respectively, with use of a damage model. It was shown that the damage model introduced was successfully applied to predict such kind of macro-damage and micro-craze formations.

Damage Evolution and Failure Modeling in Unidirectional Graphite/Epoxy Composite

2001 ◽  
Author(s):  
G. P. Tandon ◽  
R. Y. Kim
Keyword(s):  
Damage Evolution ◽  
Failure Modes ◽  
Epoxy Composite ◽  
Damage Model ◽  
Tensile Loading ◽  
Unidirectional Composite ◽  
Concentric Cylinder ◽  
Failure Modeling ◽  
Stress Levels

Abstract A study is conducted to examine and predict the micromechanical failure modes in a unidirectional composite when subjected to tensile loading parallel to the fibers. Experimental observations are made at some selected stress levels to identify the initiation and growth of micro damage during loading. The axisymmetric damage model of a concentric cylinder is then utilized to postulate and analyze some failure scenarios.

Ductile Damage Model Based On Void Growth Analysis for Application to Ductile Crack Growth Simulation

2021 ◽  
Author(s):  
Takehisa Yamada ◽  
Mitsuru Ohata
Keyword(s):  
Crack Growth ◽  
Void Growth ◽  
Damage Evolution ◽  
Damage Model ◽  
Crack Growth Resistance ◽  
Growth Behavior ◽  
Ductile Crack ◽  
Growth Simulation ◽  
Crack Growth Simulation ◽  
Ductile Crack Growth

Abstract The aim of this study is to propose damage model on the basis of the mechanism for ductile fracture related to void growth and to confirm the applicability of the proposed model to ductile crack growth simulation for steel. To figure out void growth behavior, elasto-plastic finite element analyses using unit cell model with an initial void were methodically performed. From the results of those analyses, it was evident that the relationships between normalized void volume fraction and normalized strain by each critical value corresponding to crack initiation were independent of stress-strain relationship of material and stress triaxiality state. Based on this characteristic associated with void growth, damage evolution law was derived. Then, using the damage evolution law, simple and phenomenological ductile damage model reflecting void growth behavior and ductility of material was proposed. To confirm the validation and application of proposed damage model, the damage model was implemented in finite element models and ductile crack growth resistance was simulated for cracked components were performed. Then, the simulated results were compared with experimental ones and it was found that the proposed damage model could accurately predict ductile crack growth resistance and was applicable to ductile crack growth simulation.

Modeling the Fatigue Damage Evolution in Welded Joints

2017 ◽  
Author(s):  
Zbigniew Mikulski ◽  
Vidar Hellum ◽  
Tom Lassen
Keyword(s):  
Crack Initiation ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Damage Evolution ◽  
Threshold Value ◽  
Phase Model ◽  
Two Phase ◽  
Initiation Phase ◽  
Weld Toe ◽  
Small Cracks

The present paper presents a two-phase model for the fatigue damage evolution in welded steel joints. The argument for choosing a two-phase model is that crack initiation and subsequent crack propagation involve different damage mechanisms and should be treated separately. The crack initiation phase is defined as the number of cycles to reach a crack depth of 0.1 mm. This phase is modelled based on the Dang Van multiaxial stress approach. Both a multiaxial stress situation introduced by the acting loads and the presence of the multiaxial welding residual stresses are accounted for. The local notch effect at the weld toe becomes very important and the irregular weld toe geometry is characterized by extreme value statistics for the weld toe angle and radius. The subsequent crack growth is based in classical fracture based on the Paris law including the effect of the Stress Intensity Factor Range (SIFR) threshold value. The unique fatigue crack growth rate curve suggested by Huang, Moan and Cui is adopted. This approach keeps the growth rate parameters C and m constant whereas an effective SIFR is calculated for the actual stress range and loading ratio. The model is developed and verified based on fatigue crack growth data from fillet welded joints where cracks are emanating from the weld toe. For this test series measured crack depths below 0.1 mm are available. The two-phase model was in addition calibrated to fit the life prediction in the rule based S-N curve designated category 71 (or class F). A supplementary S-N curve is obtained by the Random Fatigue Limit Method (RFLM). The test results and the fitted model demonstrated that the crack initiation phase in welded joins is significant and cannot be ignored. The results obtained by the Dang Van approach for the initiation phase are promising but the modelling is not yet completed. The fracture mechanics model for the propagation phase gives good agreement with measured crack growth. However, it seems that the prediction of crack retardation based on a threshold value for the SIFR gives a fatigue limit that is overly optimistic for small cracks at the weld toe. The threshold value has been determined based on tests with rather large central cracks in plates. The validity for applying this threshold value for small cracks at the weld toe is questioned. As the present two-phase model is based on applied mechanics for both phases the parameters that have an influence on the fatigue damage evolution are directly entering into the model. Any change in these parameters can then be explicitly taken into account in logical and rational manner for fatigue life predictions. This not the case with the rule based S-N curves that are based on pure statistical treatment of the bulk fatigue life.

Failure Predictions for DP Steel Cross-die Test using Anisotropic Damage

2011 ◽  
Vol 21 (5) ◽  
pp. 713-754 ◽  
Author(s):  
M. S. Niazi ◽  
H. H. Wisselink ◽  
T. Meinders ◽  
J. Huétink
Keyword(s):  
Strain Rate ◽  
Damage Evolution ◽  
Damage Model ◽  
Anisotropic Damage ◽  
Continuum Damage ◽  
Anisotropic Plasticity ◽  
Continuum Damage Model ◽  
Damage Models ◽  
Isotropic Damage ◽  
Failure Predictions

The Lemaitre's continuum damage model is well known in the field of damage mechanics. The anisotropic damage model given by Lemaitre is relatively simple, applicable to nonproportional loads and uses only four damage parameters. The hypothesis of strain equivalence is used to map the effective stress to the nominal stress. Both the isotropic and anisotropic damage models from Lemaitre are implemented in an in-house implicit finite element code. The damage model is coupled with an elasto-plastic material model using anisotropic plasticity (Hill-48 yield criterion) and strain-rate dependent isotropic hardening. The Lemaitre continuum damage model is based on the small strain assumption; therefore, the model is implemented in an incremental co-rotational framework to make it applicable for large strains. The damage dissipation potential was slightly adapted to incorporate a different damage evolution behavior under compression and tension. A tensile test and a low-cycle fatigue test were used to determine the damage parameters. The damage evolution was modified to incorporate strain rate sensitivity by making two of the damage parameters a function of strain rate. The model is applied to predict failure in a cross-die deep drawing process, which is well known for having a wide variety of strains and strain path changes. The failure predictions obtained from the anisotropic damage models are in good agreement with the experimental results, whereas the predictions obtained from the isotropic damage model are slightly conservative. The anisotropic damage model predicts the crack direction more accurately compared to the predictions based on principal stress directions using the isotropic damage model. The set of damage parameters, determined in a uniaxial condition, gives a good failure prediction under other triaxiality conditions.

scholarly journals Realization of Lasing Emission from One Step Fabricated WSe2 Quantum Dots

Nanomaterials ◽  
2018 ◽  
Vol 8 (7) ◽  
pp. 538
Author(s):  
Pengpeng Ren ◽  
Wenfei Zhang ◽  
Yiqun Ni ◽  
Di Xiao ◽  
Honghao Wan ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Transition Metal Dichalcogenides ◽  
Laser Cavity ◽  
Threshold Value ◽  
Gain Medium ◽  
Excitation Wavelength ◽  
Excitation Threshold ◽  
Ultrasonic Probe ◽  
Metal Dichalcogenides ◽  
One Step

Two-dimensional (2D) transition-metal dichalcogenides (TMDCs) quantum dots (QDs) are the vanguard due to their unique properties. In this work, WSe2 QDs were fabricated via one step ultrasonic probe sonication. Excitation wavelength dependent photoluminescence (PL) is observed from WSe2 QDs. Room-temperature lasing emission which benefits from 3.7 times enhancement of PL intensity by thermal treatment at ~470 nm was achieved with an excitation threshold value of ~3.5 kW/cm2 in a Fabry–Perot laser cavity. To the best of our knowledge, this is the first demonstration of lasing emission from TMDCs QDs. This indicates that TMDCs QDs are a superior candidate as a new type of laser gain medium.

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