Failure mechanisms and damage evolution of hard rock joints under high stress: Insights from PFC2D modeling

It is very important to accurately determine the depth of excavation damaged zone for underground engineering excavation and surrounding rock stability evaluation, and it can be measured by acoustic test, but there is no quantitative method for analysis of the results, and it relies heavily on the experience of engineers, which leads to the low reliability of the results and also limits the application of the acoustic method. According to substantial field test data and the feedback of surrounding rock support parameters, the boundary method is proposed to determine the depth of excavation damaged zone in surrounding rock based on the relation between the ultrasonic velocity of measured point and the background wave velocity of rock mass. When the method is applied to the columnar jointed rock mass of Baihetan and the deep-buried hard rock of Jinping, the excavation damaged zone was well judged. The results in the Baihetan project show that the proposed method of determining excavation damage zone by the acoustic test can well demonstrate the anisotropy characteristics of the columnar jointed rock mass, and the damage evolution characteristics of jointed rock mass at the same position can also be obtained accurately. Moreover, the method also can accurately reveal the damage evolution process of the deep-buried hard rock under the condition of high ground stress, which proved the applicability of this method in jointed or nonjointed rock masses.

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A Method for Evaluating the Impact Wear Behavior of Multilayer TiN/Ti Coating

Coatings ◽

10.3390/coatings10020132 ◽

2020 ◽

Vol 10 (2) ◽

pp. 132 ◽

Cited By ~ 3

Author(s):

Xin Cao ◽

Weisheng Xu ◽

Weifeng He

Keyword(s):

Wear Behavior ◽

Failure Mechanisms ◽

High Stress ◽

Impact Wear ◽

Maximum Value ◽

Impact Peak ◽

Energy Dissipated ◽

The Impact ◽

Impact Zones ◽

Circular Cracks

An energy-controlled cycling impact test was applied to evaluate the impact wear behavior of hard coating. A multilayer TiN/Ti coating with a total thickness of ~10 μm, containing two TiN layers and two Ti layers, with the thickness ratio of these two kinds of the layers being 9:1, was chosen as the research object. The impact velocities were 60, 120, and 180 mm/s, and the impact cycles were 10, 102, 103, and 104, respectively. Damage morphology observation and numerical simulation were used to analyze the failure mechanisms. The results show that the contact time keeps almost constant under different impact velocities and cycles. Impact peak forces remain unchanged with increasing cycles at the same velocity, but they increase linearly with impact velocities, reaching a maximum value of 262.26 N at 180 mm/s. The energy dissipated rate (EDR) increases from 31.58% at 60 mm/s to 35.59% at 180 mm/s, indicating the degenerative toughness. Two impact-wear failure mechanisms are found in impact zones of the coating; these are peeling and circular cracks. Peelings are induced by cycling high-stress gradients in hard layers and interfaces. Circular cracks are caused by cycling tensile stresses in the form of fatigue at the edge of impacted pits.

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Experimental Investigation of Spalling Failure of D-Shaped Tunnel Under Three-Dimensional High-Stress Conditions in Hard Rock

Rock Mechanics and Rock Engineering ◽

10.1007/s00603-020-02280-3 ◽

2020 ◽

Cited By ~ 1

Author(s):

Xuefeng Si ◽

Linqi Huang ◽

Xibing Li ◽

Chunde Ma ◽

Fengqiang Gong

Keyword(s):

Experimental Investigation ◽

Hard Rock ◽

High Stress ◽

Three Dimensional ◽

Stress Conditions ◽

Spalling Failure

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Damage Evolution and Failure Mechanisms for APS-TBCS

Volume 1: Aircraft Engine; Ceramics; Coal, Biomass and Alternative Fuels; Manufacturing, Materials and Metallurgy; Microturbines and Small Turbomachinery ◽

10.1115/gt2008-50367 ◽

2008 ◽

Author(s):

Filippo Cappuccini ◽

Iacopo Giovannetti ◽

Suchismita Sanyal ◽

Massimo Giannozzi ◽

Santosh Kumar ◽

...

Keyword(s):

Bond Coat ◽

Gas Turbines ◽

Damage Evolution ◽

Failure Mechanisms ◽

Interface Roughness ◽

Atmospheric Plasma ◽

Turbine Engines ◽

Metallic Component ◽

Engine Efficiency ◽

Plasma Sprayed

Thermal barrier coatings (TBC-s) have been utilized in gas turbine engines for over two decades, primarily to protect the existing materials under the demands for higher temperatures and greater engine efficiency. Atmospheric Plasma Sprayed TBC, commonly used for hot combustion chamber components of advanced gas turbines, are exposed to thermo-mechanical loads, which may lead to failure in form of macroscopic spallations from the metallic component. The durability of TBC is limited by the interaction of different processes and parameters, such as bond coat oxidation, cyclic strains, visco-plastic and relaxation properties, interface roughness and others. In this work, the spallation failure mechanisms and damage evolution of APS-TBC system are investigated on samples aged by isothermal and thermal cycle tests using different time and temperatures exposures. Several parameters have been analyzed by SEM and a life prediction model approach for APS-TBC is being developed focusing on oxidation kinetics, identifying the parameters such as rumpling, bond coat oxidation, TGO thickness and interdiffusion of base metal elements which drive the oxide formation and TBC spallation mechanisms.

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A statistical damage constitutive model considering whole joint shear deformation

International Journal of Damage Mechanics ◽

10.1177/1056789519900778 ◽

2020 ◽

Vol 29 (6) ◽

pp. 988-1008 ◽

Cited By ~ 26

Author(s):

Shijie Xie ◽

Hang Lin ◽

Yixian Wang ◽

Yifan Chen ◽

Wei Xiong ◽

...

Keyword(s):

Constitutive Model ◽

Damage Evolution ◽

Shear Stiffness ◽

Rock Joints ◽

Residual Phase ◽

Proposed Model ◽

Damage Constitutive Model ◽

Damage Theory ◽

Joint Shear ◽

Statistical Damage

The whole shear deformation of rock joints significantly affects the long-term behavior and safety of engineering projects. In this paper, a new damage constitutive model related to the Weibull distribution and statistical damage theory is proposed. This model considers the shear stiffness degradation, post-peak softening, and residual phase of rock joints in the whole shearing process. Main works include the three following aspects: First, the phase of initial damage is determined on the assumption that the joint shear failure is regarded as a result of damage evolution, according to the typical joint shear curve and the three-parameter Weibull distribution. Then, a statistical damage evolution model for the whole joint shearing process is introduced to make this model be capable of describing the residual phase of rock joints. Finally, a statistical constitutive model for the whole joint shearing process is proposed by statistical damage theory, and the calculated results of the models are compared to the experimental results. The results indicate that the proposed model shows a good agreement with the experimental examples, and the proposed model can distinctly reflect the effects of residual stress, peak stress, and shear stiffness. In addition, the model parameters can be mathematically confirmed and have distinct physical meanings.

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A multiscale computational method with inheriting simulation of moving trans-scale boundary for damage-induced structural deterioration

Engineering Computations ◽

10.1108/ec-06-2016-0219 ◽

2017 ◽

Vol 34 (5) ◽

pp. 1677-1699

Author(s):

Zheyuan Zheng ◽

Zhaoxia Li

Keyword(s):

Failure Analysis ◽

Damage Evolution ◽

Damage Mechanics ◽

High Stress ◽

Multiscale Simulation ◽

Computational Method ◽

Structural Failure ◽

Content Type ◽

Structural Deterioration ◽

Computation Efficiency

Purpose This paper aims to introduce a multiscale computational method for structural failure analysis with inheriting simulation of moving trans-scale boundary (MTB). This method is motivated from the error in domain bridging caused by cross-scale damage evolution, which is common in structural failure induced by damage accumulation. Design/methodology/approach Within the method, vulnerable regions with high stress level are described by continuum damage mechanics, while elastic structural theory is sufficient for the rest, dividing the structural model into two scale domains. The two domains are bridged to generate mixed dimensional finite element equation of the whole system. Inheriting simulation is developed to make the computation of MTB sustainable. Findings Numerical tests of a notched three-point bending beam and a steel frame show that this MTB method can improve efficiency and ensure accuracy while capturing the effect of material damage on deterioration of components and structure. Originality/value The proposed MTB method with inheriting simulation is an extension of multiscale simulation to structural failure analysis. Most importantly, it can deal with cross-scale damage evolution and improve computation efficiency significantly.

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Viscoelastic Damage Characteristics of Asphalt Mixtures Using Fractional Rheology

Materials ◽

10.3390/ma14195892 ◽

2021 ◽

Vol 14 (19) ◽

pp. 5892

Author(s):

Qipeng Zhang ◽

Xingyu Gu ◽

Zilu Yu ◽

Jia Liang ◽

Qiao Dong

Keyword(s):

Damage Evolution ◽

High Stress ◽

Creep Damage ◽

Asphalt Mixtures ◽

Creep Process ◽

Model Parameters ◽

Creep Tests ◽

Steady Stage ◽

Stress Levels ◽

Different Temperatures

The mechanical behavior of asphalt mixtures at high stress levels are characterized by non-linear viscoelasticity and damage evolution. A nonlinear damage constitutive model considering the existence of creep hardening and creep damage mechanisms in the entire creep process is proposed in this study by adopting the fractional rheology theory to characterize the three-stage creep process of mixtures. A series of uniaxial compressive creep tests under various stresses were conducted at different temperatures to verify the model. The results indicated that the model predictions were in good agreement with the creep tests. The relationship between the model parameters and applied stresses was established, and the stress range in which the mixture exhibited only creep consolidation was obtained. The damage to the asphalt mixture was initiated in the steady stage; however, it developed in the tertiary stage. A two-parameter Weibull distribution function was used to describe the evolution between the damage values and damage strains at different stress levels and temperatures. The correlation coefficients were greater than 0.99 at different temperatures, indicating that a unified damage evolution model could be established. Thus, the parameters of the unified model were related to material properties and temperature, independent of the stress levels applied to the mixtures.

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