Damage Law Research Articles

Feasibility Study of Material Deformation and Similarity of Spatial Characteristics of Standard Coal Rocks

The comparison between similar materials and original coal rock is the basis for similar simulation experiments in coal mines. The differences in mechanical properties, acoustic characteristics, and damage laws between similar materials and the original coal rock are of great significance for similar simulation research, to reveal objective laws. First, materials similar to coal rock with similar theoretical ratios were taken as the object of research, and the sand–cement ratio, the carbon paste ratio, and the water content were determined by multivariate linear regression to accurately match the ratios. Second, by using acoustic emission and digital scattering technology to explore the acoustic law, deformation characteristics, and spatial feature similarities of the materials similar to coal rock, the acoustic emission evolution law of the original rock was found to be the same as that of the similar materials. Digital scattering was able to describe the localization of strain in the similar materials, and the correlation between the overall deformation and the local deformation was explored. This indicates that materials similar to coal rock can effectively simulate the deformation of actual coal rocks. Lastly, these materials were found to allow effectively simulating the deformation characteristics and spatial properties of actual coal rock, which provides an important experimental means and method for similar research in the field of coal rock engineering.

Ballistic impact modeling of woven composites using the microplane triad model with meso-scale damage mechanisms

Existence of undulating fill and warp yarns in woven composite laminae introduces complex unit cell geometries and multi-scale interactions among the constituents. Due to these, the failure process involves various meso-scale constituent-level failure modes under complex loading scenarios such as ballistic impact. This can be challenging to model via conventional macro-scale damage tensor-based models. This challenge is tackled here via the adaptation of the previously developed multi-scale microplane triad model to ballistic impact of woven composites. The model can resolve meso-scale constituent level details (including yarn undulations) and predict not only the elastic constants of a woven lamina but also its fracturing behavior. In the present adaptation, only two damage laws are formulated, one for the fibers and one for the matrix. This enables the model to embody the correct values of the intralaminar mode I and II fracture energies of the woven lamina. The model is calibrated using constituent and lamina level test data, and then used to predict the ballistic impact behavior of a single plain-woven lamina under a wide range of projectile impact velocities. The model is demonstrated to predict very well the projectile residual (rebound and exit) velocities, the energy dissipation, the major failure modes of the lamina and the corresponding extent of damage, as well as the ballistic limit and deformation cone wave propagation speeds. The model’s simple, conceptually clear architecture, and computational efficiency represent a major advantage compared to existing damage tensor-based models. The model is also extended to multi-layer thick section woven laminate impact, where the analyses consider both intralaminar and interlaminar failures. The predictions are found to be comparable to those from MAT162, a commercially available material model in LS-Dyna, with much better computational efficiency. Via detailed sensitivity studies, it is demonstrated that the mode I and II intralaminar fracture energies of the lamina are a crucial model input, necessary for accurate predictions of ballistic impact. Not knowing these can introduce significant uncertainty and therefore, their characterization is an absolute must. Finally, the optimal meshing considerations as well as the advantages and limitations of the microplane triad model are discussed.

Study on the influence of injection pressure and frequency on the deformation and damage law of the surrounding rock in the old cavity of salt mine

AbstractThe long‐term cyclic gas injection and production mode of the gas storage will lead to accelerated deformation of the surrounding rock of the old cavity, and even the instability and failure of the cavity. Considering the geological conditions and cavity measurement data of the old cavity of the horizontal butted‐well in China, the deformation and failure characteristics of the long‐term cyclic injection‐production process of the surrounding rock of the old cavity under different internal pressure difference and injection‐production frequency are studied. The long‐term stability of the gas storage is predicted by six indexes: the deformation of surrounding rock, dilatancy safety factor, volume shrinkage rate, plastic zone volume, equivalent strain, and no tensile stress. The results show that with the increase of operation duration and cycle times, the deformation, volume shrinkage rate, and plastic zone volume of the surrounding rock gradually increase after the old cavity is reconstructed into the gas storage and the difference of results under different UGS and CAES gradually expands. The stability of the surrounding rock of the old cavity under the cycle action of CAES will be lower. The number of cycles has a limited impact on the stability of the surrounding rock of the old cavity, while the operation duration and injection‐production pressure are the main determinants of the stability of the surrounding rock of the old cavity. If the old cavity of the salt mine is reconstructed into CAES, the parameters such as the number of cycles, the operation duration, and the injection‐production pressure still need to be considered comprehensively. The research results can provide reference value for the reasonable design of the gas storage pressure range of the old cavity and the safety and stability evaluation of the surrounding rock.

Study on damage mechanism and damage distribution of the rear plate under impact of debris cloud

The debris cloud generated by the hypervelocity impact (HVI) of orbiting space debris directly threatens the spacecraft. A full understanding of the damage mechanism of rear plate is useful for the optimal design of protective structures. In this study, the hypervelocity yaw impact of a cylindrical aluminum projectile on a double-layer aluminum plate is simulated by the FE-SPH adaptive method, and the damage process of the rear plate under the impact of the debris cloud is analyzed based on the debris cloud structure. The damage process can be divided into the main impact stage of the debris cloud and the structural response of the rear plate. The main impact stage lasts a short time and is the basis of the rear plate damage. In the stage of structure response, the continuous deformation and inertial motion of the rear plate dominate the perforation of the rear plate. We further analyze the damage mechanism and damage distribution characteristics of the rear plate in detail. Moreover, the connection between velocity space and position space of the debris cloud is established, which promotes the general analysis of the damage law of debris cloud. Based on the relationship, the features of typical damage areas are identified by the localized fine analysis. Both the cumulative effect and structural response cause the perforation of rear plate; in the non-perforated area, cratering by the impact of hazardous fragments is the main damage mode of the rear plate.

Damage creep model and application for sandy mudstone considering the effect of immersion deterioration

Abstract Aiming at the problem of performance degradation and large deformation of sandy mudstone after immersion in water, the compression test is carried out. The damage and deterioration law of strength and elastic modulus of immersed rock mass is analyzed, and the function relationship between rock damage variable and soaking time is obtained by fitting. Combined with the Hoek-Brown criterion and Mohr-Coulomb criterion, the calculation method of instantaneous cohesion and instantaneous internal friction angle of damaged rock mass is derived based on the tangent method, and the equivalent Mohr-Coulomb criterion which can effectively characterize the nonlinear strength characteristics of damaged rock mass is given. Based on the built-in creep model Cvisc of Flac3D, a damage creep model is given by introducing the damage factor and nonlinear strength criterion of immersed rock mass, which is more suitable for describing the creep characteristics of immersed sandy mudstone. The validity of the model is verified by comparing with the measured results.

Damage degradation law of mechanical properties of sandstone under different water-rich states

Safety is the primary guarantee for achieving coal mine production. The degree of water in the overlying rock of the coal seam has a significant impact on the mechanical strength of the rock, which can lead to subsidence, roof collapse, and rock burst in the mining area. Therefore, it is important to study the law of water-rich damage and deterioration of coal seam overlying rock, as well as the characteristics of bursting liability to prevent and control mining disasters. This paper aims to investigate the change in compressive strength, elastic modulus, and bursting liability of coal measure strata under different water content and their relationship with lithology, particle size, pore characteristics, and mineral characteristics. We carried out uniaxial compression tests on drilled and prepared samples of coal measure strata in the east of Ordos City. We also monitored the acoustic emission characteristics of the rock failure process under different water content. The results demonstrate that, in the dry state, the compressive strength of siltstone >fine sandstone >medium sandstone >coarse sandstone. As the water content increases, the rock transitions from brittle to plastic, and the compressive strength, elastic modulus, and bursting liability gradually decrease. The stress-strain curve changes from a single peak to bimodal and multimodal, and the active degree of acoustic emission events decreases, especially the low-value ringing count. Calcareous cementation, clay minerals, and chlorite exhibit strong softening properties when subjected to water, while the grain skeleton (comprising quartz, feldspar, mica) and siliceous cementation displays weak softening properties in such conditions. The most significant is the mechanical strength deterioration of siltstone containing a clay matrix. The research findings can provide reference and theoretical support for safe mining practices in coal mines.

Multiscale finite element analysis model of needle-punched carbon/carbon composites

The mechanical properties of matrix, fiber bundle, and chopped fiber felt are evaluated by means of micromechanical analysis. An equivalent matrix model composed of matrix and chopped fiber felt material is established, which together with fiber bundle is used as the basic component of single cell. Based on the mesostructural characteristics of NP C/C composites, the local structure is divided into five typical unit cells to characterize the five representative microstructures of NP C/C composites, and the mechanical properties of the five typical unit cells are calculated, respectively. According to the true distribution of needle holes, the five typical unit cells are arranged to form a representative volume element model of NP C/C composites. The Cai–Wu failure criterion is used to determine the failure of the five typical unit cells model, and the periodic boundary condition is applied to the tension and compression simulation of the NP C/C composites, the progressive damage law of the model is analyzed. The results show that the prediction of mechanical properties of the composites under unidirectional tensile load and unidirectional compression load are in good agreement with the experimental data.

Experimental study on mechanical damage characteristics of water-bearing tar-rich coal under microwave radiation

As a recognized special resource, tar-rich coal can extract the country's scarce oil and gas resources and generate semi-coke that can replace anthracite and coking coal. The tar-rich coal in northern Shaanxi is prominent, but due to the dense structure and high strength of tar-rich coal, it is easy to cause frequent dynamic disasters in coal mining. Therefore, the realization of pressure relief and disaster reduction has become the primary problem in mining tar-rich coal. There are many shortcomings in conventional pressure relief methods, so a new method of microwave-weakening coal is proposed. Through different water saturation treatments of tar-rich coal samples, the longitudinal wave velocity degradation trend and surface crack expansion law of water-bearing coal after microwave irradiation were analyzed, and the strength softening characterization and energy evolution relationship under the combined action of microwave and water were studied. Fractal dimension and its internal correlation based on the equivalent side length-mass of coal sample fragments. The experimental results show that: (1) Under the same microwave radiation condition, with the increase of water saturation, the deterioration trend of physical and mechanical parameters such as longitudinal wave velocity and peak strength is obvious. (2) After microwave radiation, the uniaxial compression results show that the coal sample is damaged by load, there is still a high residual strength, the ratio of elastic energy to dissipation energy decreases, and the possibility of rockburst of the coal sample decreases. The strength softening degree of coal specimen under the degradation of microwave and water is the highest, followed by microwave and water. (3) The fractal dimension is inversely proportional to the moisture content and microwave radiation intensity, and the fractal dimension has a significant positive correlation with the peak intensity and longitudinal wave velocity. The mechanical damage law of water-bearing tar-rich coal under microwave action is revealed, which aims to solve the problem of weakening and reducing the impact of hard coal on-site to a certain extent, ensure the safety of working face, and improve the mining efficiency of tar-rich coal. It provides basic theoretical support for microwave-assisted hydraulic fracturing technology and effective weakening measures for hard roof treatment.

Research on the Cumulative Damage Law of Surrounding Rock under Cyclic Blasting Action

In order to study the cumulative damage characteristics and laws of rock masses under cyclic blasting loads, based on the finite element software ANSYS/LS-dyna and the HJC constitutive model, a single blasting damage analysis is conducted first, and the accuracy of the results is verified. On this basis, numerical simulation studies on the cumulative damage of rock masses under cyclic blasting are carried out separately. The results indicate that the cumulative damage evolution cloud map of the rock mass under cyclic blasting is similar to that of a single blasting action, showing an inverse S-shape overall. The damage increment of the rock mass decreases with the increase of blasting times, and in the central area of the damage zone, the rock mass is particularly affected by the superimposed effect of cyclic blasting loads. Cyclic blasting fully reflects the accumulation of damage to the rock mass under multiple cyclic blasting loads, and there is a certain relationship between rock mass damage and the distance between the blasting centers. As the distance between the blasting centers increases, the amount and increment of rock mass damage generated by blasting continue to decrease.

Experimental study of the degradation of HDPE packaging under accelerated thermal aging

In this work, accelerated thermal aging at different temperatures was performed on high-density polyethylene (HDPE) bottles and specimens for food packaging. The degradation of HDPE was followed macroscopically by tensile and compression tests to evaluate the decrease in mechanical properties. The data obtained from these tests are used to calculate a new static damage law and the life fraction of this polymer. A prediction of the lifetime of HDPE was determined by thermogravimetric analysis (TGA) in dynamic mode. The evolution of the crystallinity rate during accelerated thermal aging was carried out using FOURIER transform infrared spectrometry (FTIR). The results obtained show a remarkable degradation of the mechanical properties in traction and compression by calculation of the static damage, and the physical and chemical properties by the analysis of the rate of crystallinity as well as the prediction by the law of Arrhenius.

Study on Cumulative Damage Law of Surrounding Rock Induced by Blasting during Tunnel Construction

The tunnel drilling and blasting method inevitably causes damage to the rock mass during the blasting process. This article takes a certain tunnel as the research object, proposes to simulate the process of continuous blasting and repeated blasting in each section of the tunnel, and quantifies the cumulative damage range of surrounding rock under each working condition. The results indicate that: (1) it is advantageous to use equivalent loads to simulate blasting loads when calculating large-scale blasting damage simulations; (2) The damage to surrounding rock caused by single cycle excavation of tunnels is caused by the superposition of multiple stages of delayed blasting, mainly influenced by adjacent auxiliary equipment.

Dynamic Analysis of the Guiding Shoe considering Contact Gap and Pose Disturbance

The pose disturbance of the guide shoe under complex working conditions can lead to collision, impact, and wear failure between the guide shoe and the pin row. To explore the damage law of pose disturbance on the guiding shoe, a rigid‐flexible coupling dynamic model of the walking mechanism considering the contact gap between the guiding shoe and the pin row was constructed. The contact characteristics of the guiding shoe under different poses were analyzed. The results indicate that the swing around the x‐axis has the most significant impact on the guiding shoe, with stress concentration primarily occurring near the corner of the trench. The posture of swinging solely around the y‐axis weakens the supporting effect of the guide shoe, resulting in stress concentration on the end face of the left side face. Swinging around the z‐axis results in stress concentrations on the upper faces of the shoe. Research shows that the angular velocity of the guiding shoe around the x‐axis and z‐axis is highly sensitive to variations in traction speed. In addition, an increase in lateral force weakens the support effect of the guiding shoe, resulting in elevated contact force on the lower side of the guiding shoe and increased y‐direction load on the walking wheel. The research results provide a reference for exploring the influence of walking unit postures on the failure of the guiding shoe and for improving shearer traction reliability.

Research on Cumulative Damage Induced by Cyclic Blasting of Tuff

This article establishes a numerical model for cumulative damage of surrounding rock that can simulate the characteristics of progressive cyclic blasting in tunnels based on explicit dynamics and “restart” technology, and conducts research on the cumulative damage law of surrounding rock induced by tunnel blasting. The results show that: (1) considering the characteristics of progressive cyclic blasting in tunnels, the degree and range of surrounding rock damage are significantly increased compared to single blasting, with an increase of about 50%; (2) the amount of damage caused by blasting in the surrounding rock follows a Boltamann function (S-shaped curve) evolution feature as the distance between the blasting centers increases. In practical applications, when evaluating the degree and range of damage to the surrounding rock at the current location, additional cumulative damage caused by adjacent footage cycles should be considered, and the damage value can be 1.5 times the damage value of the current single blasting condition

Research on Damage Evolution Law of Glazed Hollow Beads-Cement/Sodium Silicate Grouting Materials under Different Cycles of Loading and Unloading.

With the depletion of shallow resources, deep resource mining has become a trend. However, the high temperature and complex stress environment in deep mines make resource extraction extremely challenging. This paper developed a thermal insulation grouting material made of glazed hollow beads, sodium silicate, and cement and tested the compressive strength, gelation time, and stone rate under various curing days in light of the issue of high temperature heat damage in high ground temperature mines and the impact of mining on roadway grouting bolt support. Fatigue strength, fatigue deformation, load-residual strain, energy evolution and microscopic features were studied and analyzed in relation to the damage law of graded cyclic loading and unloading under the number of varying cycles. The findings demonstrate that cyclic loading and unloading strength is lower than uniaxial compressive strength. The fatigue strength is significantly decreased when the number of cycles reaches its limit. Residual strain is less sensitive to changes in stress than load strain. The fitting correlation coefficients of total output energy and elastic energy are higher than 0.71.

Effectiveness of AMDAL Implementation in Protecting Environmental Damage Due to Industrial

To prevent environmental damage due to industrial activities in Indonesia, AMDAL is an essential document to prepare. AMDAL has an instrument that aims to prevent environmental damage and prevent environmental damage (Law No.32 of 2009). In making and implementing AMDAL, we must pay attention to ecological sustainability so that we do not cause significant impacts that are harmful to current and future generations. This research aims to find and collect information coherently and comprehensively regarding the effectiveness of AMDAL implementation in preventing environmental damage due to industrial activities in Indonesia. This research uses a literature study method on activities that are organized systematically and scientifically using an interdisciplinary and even multidisciplinary approach to answer the effectiveness of AMDAL implementation in preventing environmental damage due to industrial activities in Indonesia. The results of this study indicate that the effective implementation of AMDAL activities is significant and must be implemented by all businesses, companies, and industries. AMDAL is one of the requirements in environmental permits to prevent ecological damage and pollution around the activities of these companies, businesses, and industries.

Study on reasonable anchorage length based on failure mechanism of the bolt anchorage system

In addition to analysing the mechanism of failure of the prestressed rock anchor anchor system and investigating the appropriate depth for fixing the rock anchors, theoretical equations were derived to calculate the rock anchors' axial force, ultimate capacity, and the interfacial shear force in the elastic phase. These equations are then used to analyse the pressure distribution within the rock bolt anchorage section and to investigate the effect of interfacial shear strength, shear stiffness, and anchorage length on interface failure. Drawing on the findings from both field-based rock bolt pull-out tests and numerical simulations, analyzed the failure mechanism of the anchor system, and proposed a reasonable anchor length design method for rock bolt. The results show that there is a strong dependence between ultimate load carrying capability of rock bolts and interfacial shear stress and shear rigidity, and that increasing the anchorage length and reducing the interface shear stiffness can avoid the stress concentration phenomenon. The primary factor leading to the anchor system failure is secondary interface failure. The evolution law of interface damage is that the damage occurs first at the initial position. As the interface damage location changes, the peak shearing stress moves towards the bottom of the anchored section. The engineering application results verified the feasibility of a reasonable anchorage length calculation method and rock bolt design process. The findings of this paper can be used as a basic reference for determining rock bolt anchorage support parameters during the design and construction of underground engineering projects.

Compressive study on recycled concrete: experiment and numerical homogenization modelling

This paper describes a study of recycled concrete under compressive loads. The study was conducted in two main parts. In the first part, experimental tests were carried out on concrete samples with varying levels of substitution (25%, 50%, and 75%) with recycled aggregate in order to measure the mechanical properties of the recycled concrete. In the second part of the study, a nonlinear homogenization model was developed on the basis of a classical secant approach to predict the behavior of recycled concrete. In this model, we assume that the behavior of the mortar phase, the concrete, and the recycled aggregates follow Mazars damage law. Comparison with the experimental data shows that the proposed homogenization model is accurate and efficient in predicting the correct nonlinear behavior of the recycled concrete. By better understanding the properties and behavior of recycled concrete, it will be possible to develop more effective methods for incorporating recycled materials into concrete structures.

Development of process design tools for extrusion-based bioprinting: From numerical simulations to nomograms through reduced-order modeling

The planning of a bioprinting procedure requires the definition of several process variables. In extrusion-based bioprinting these are, for instance, the printing pressure, the nozzle diameter, the target extrusion velocity and/or mass flow rate. They should be properly set in order to allow printability of the bio-ink, as well as to ensure high cell viability at the end of the process. In fact, printing procedures expose cells to shear and extensional stresses that can lead to mechanobiological damage mechanisms. Bioprinting planning is then a challenging task since process variables are closely interconnected each other through the physical response of bio-inks. Non-Newtonian characteristics of bio-inks, together with possible complex geometries of the extruding system, generally introduce a strong non-linear coupling among process variables. To date, the bioprinting planning in laboratory practice is generally performed via expensive and time-consuming trial-and-error procedures. The aim of this work is the development of novel methodological approaches for an informed definition of printing process variables such to guarantee target conditions of the outcome. The non-linear coupling among dominant process variables is described via a semi-analytical approach, calibrated through high-fidelity numerical solutions and defined via a reduced-order modeling strategy. A cell damage law depending on bioprinting conditions is also introduced, generalizing state-of-the-art approaches on the basis of available experimental evidence. The proposed framework allows to build operative nomograms, whose practical utility is confirmed via some exemplary applications. The latter address the prediction of extrusion velocity, mass flow rate and cell viability, when both the printing pressure and nozzle diameter vary within typically-adopted ranges. The analyzed case studies highlight soundness and effectiveness of such a modeling strategy in providing a clear and straight pathway for planning and setup of bioprinting processes.

Gas explosion impact behavior and disaster analysis based on structural failure: Numerical modeling

For gas leakage explosion accidents that occur in high blockage environments, the failure of building structures often leads to the evolution of explosion waves becoming unpredictable, resulting in the amplification of accident consequences. In this paper, a severe gas leakage and explosion accident in Beijing is analyzed using computational fluid dynamics (CFD) method, and the disasters of the accident are evaluated based on the evolution of physical quantities. The laws of propagation and impact damage of explosion waves based on structural failure are also summarized. Based on the numerical analysis results, the explosion of 4.0–4.1 m3 combustible gas is sufficient to destroy a large number of walls with a maximum indoor overpressure of 1.130 bar and create a high-pressure injury area of 10 m and a high-temperature injury area of 14 m outdoors. The impact behaviours of explosion waves are closely related to the building structures and obstacle characteristics. Structures whose spatial direction is the same as the propagation direction of the initial wave suffer less damage, and similar obstacle characteristics on both sides of structures reduce damage. The disorder of gas explosion intensity leads to the unpredictable failure direction and process of building structures, and the collapse direction of component may be opposite to the path of initial explosion wave; Outdoors, the gas flow rate of several hundred meters and the peak dynamic pressure of 0.5 bar caused all the glass of two buildings to break. Therefore, a reasonable pressure relief area and sufficient safety distance become the key measures to prevent and mitigate the disaster of civil explosion accidents. The research results can provide scientific basis for the investigation and loss prevention of explosion accidents, as well as safety assessments in the process industries.

Continuum damage mechanics of cyclic viscoplasticity using asymptotic numerical method

Conscious efforts on reduction of greenhouse gas emissions have led to an energy transition to renewable energy, however uncertainties of renewable energy production have resulted in higher thermal cycling demands from conventional power plants. Thermal load cycling at high temperature regions of steam turbine components leads to enhanced creep-fatigue damage accumulation. It is well established that such damage mechanism is numerically best predicted by unified constitutive modeling including damage as a variable as per the formalism of continuum damage mechanics at an expense of considerable computational efforts using finite element analysis. In this paper, the non-iterative Asymptotic Numerical Method (ANM), currently limited to partial cycle analysis with linear hardening plasticity model, is proposed for the first time to address cyclic viscoplasticity problems including damage capable of handling multiple cycles and most generalized loading conditions. Regularization techniques additionally necessary to implement loading-unloading-reloading criteria and advanced constitutive models etc. are presented. The constitutive model chosen for the formulation includes the non-linear multiple back stress variable modified Chaboche model to include damage combined with modified Chaboche-Rousselier isotropic hardening model to include damage, power law for viscoplasticity, Lemaitre’s damage potential and Kachanov-Rabotnov’s creep damage law. The method is verified with defined error measures and then applied to two high pressure steam turbine rotors, one with and another without thermal stress relief groove (TSRG) at the inlet under service type loading conditions to study the beneficial effect of the TSRG on creep-fatigue damage evolution. The accumulated errors of the proposed ANM and computational time are compared to a conventional Newton-Raphson solution.