Time-dependent Damage Research Articles

Analysis of dynamic disturbance and multistage shear creep damage evolution law of the weak intercalated layers in slope under the influence of coupled damage effect

Based on the damage characteristics of multistage shear creep in weak intercalated layers (carbonaceous mud shale) of slopes under the influence of dynamic disturbance, the effective bearing area method was used. A new coupled damage equation (dynamic disturbance damage, shear creep damage, and initial damage) was established through further derivation, and its applicability was demonstrated. The calculation method for the relevant coupled damage degrees was also provided. Furthermore, by targeting the three coupled damage factors and extending the Kachanov damage law, a time-dependent damage evolution equation for weak intercalated layers under the influence of the three coupled damage effects was established. The influence of different dynamic disturbance intensities on the evolution of multistage shear creep damage in weak intercalated layers of slopes under the influence of coupled damage effects was analysed. The results show that the damage to the rock mass caused by dynamic disturbance mainly occurs in the low-frequency stage (40–80 Hz). The instantaneous damage caused by dynamic disturbance to the shear plane of weak intercalated layers is not only affected by the intensity of the dynamic disturbance but also limited by the magnitude of the shear creep load. The influence of the dynamic disturbance intensity on the entire process of multistage shear creep damage of weak intercalated layers was analysed. With increasing of dynamic disturbance intensity, the cumulative coupled damage at the end of shear creep at all levels gradually exhibits linear evolution. The time-dependent coupling damage evolution process of weak intercalated layers was quantitatively characterized.

Time-dependent damage characteristics of shale induced by fluid–shale interaction: a lab-scale investigation

The shale’s multi-scale mechanical behaviors were investigated to understand the time-dependent damage characteristics induced by shale–fluid interaction. The test results indicate that, as fluid–shale interaction proceeds, the mechanical strength of shale has undergone a weakened to an enhanced process as interaction proceeds, and the size distribution of fragments tends to be more uniform, leading to a positive correlation between the mechanical strength and fractal dimension. Within 2 weeks of fluid–shale interaction show a decreasing trend for the fractal dimension of fragments in post-failure and cause less than 2 mm for the dominant size of fragments. The dominant size increases to greater than 30 mm when the fluid–shale interaction is over 2 weeks. Finally, the correlation dimension associated with ring counts of acoustic emission (AE) at each loading stage is determined in terms of the G-P algorithm to predict the damage degree of shale.

A refined model for the flexural behavior of reinforced UHPC members under sustained loading

The long-term behavior of reinforced Ultra-High Performance Concrete (UHPC) members is significantly influenced by UHPC’s creep properties. To predict the long-term performance of structural members, it is essential to have both a material-level creep model and a constitutive model for structural analysis. This paper presents a refined model for the long-term performance of UHPC, incorporating critical nonlinear deformation mechanisms: instantaneous damage, plastic strain, creep strain, and time-dependent damage. The constitutive model for instantaneous damage and plastic strain mechanisms is based on experimental data from short-term cyclic loading tests on UHPC specimens. Additionally, the creep strain components and time-dependent damage evolution laws are derived from well-established linear and nonlinear creep models, validated for cementitious materials through extensive research. The model parameters were meticulously calibrated using creep damage test results from UHPC. The validation process included linear and nonlinear creep tests on UHPC cylinders under sustained stress levels ranging from 0.2fc to 0.66fc, creep failure tests on UHPC cylinders under sustained stress levels from 0.85fc to 0.95fc, and long-term bending tests of reinforced UHPC beams under sustained load. In the linear and nonlinear creep tests, comparison between the calculated ultimate creep coefficients and the experimental results demonstrates the model’s validity under low and moderate stress levels. In the creep failure test, a comparative analysis of strain evolution and creep lifetime between experimental and model results confirms the model’s validity under high sustained stress levels. Similarly, during the long-term bending test, simulated time-dependent displacement and compressive strain show good agreement with the experimental data, confirming the model’s accuracy in predicting the long-term performance of reinforced UHPC members. Furthermore, to streamline the constitutive model, the instantaneous damage effect was simplified and ultimately neglected. A comparison of simulation results between the original model and the simplified version demonstrates that disregarding the instantaneous damage effect is a safe approach for practical engineering applications.

Non-Linear Creep-Relaxation Constitutive Damage Model for Aging Concrete

A thermodynamic constitutive damage model for plain concrete, and other quasi-brittle aging materials, under creep relaxation is developed. The model accounts for the anisotropic damage induced through a second-order tensor damage variable. The aging viscoelasticity of the material is considered through the theory of solidification for aging solidifying materials. The material is considered a viscoelastic-damageable material. The Helmholtz free energy, utilized in the formulation, is treated based on the representation theorem of coupled damage strain tensors and Volterra integral equations. The model can analyze time-dependent damage (tertiary creep) under constant loading and can account for damage due to cyclic creep. Theoretical case studies are considered to illustrate the applicability of the model. The determination of the functions and constants, representing the material behavior, as well as any experimental companion is proposed for further research.

Green Biosynthesis and characterization of organic Fructus mori-composite silver nanoparticles: Enhanced antioxidant and antibacterial activities

The bacterial resistance to antibiotics is becoming a major challenge worldwide. The novel antimicrobial silver nanomaterial without bacterial resistance has the hope of becoming a suitable substitute for antibiotics. However, it is necessary to produce nanosilver with appropriate size and better antimicrobial performance through a green and simple synthesis process. In the present study, Fructus mori-composite silver nanoparticles (M-AgNPs) were greenly biosynthesized using mulberry fruits (Fructus mori). Ultraviolet-visible (UV-vis) spectroscopy and X-ray diffraction (XRD) indicated the formation of M-AgNPs with face centered cubic structure. Fourier transform infrared (FTIR) spectroscopy confirmed reducing and capping effects of mulberry fruits' organic matter (polyphenols, flavonoids, etc.) on M-AgNPs. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) revealed that M-AgNPs were spherical and equably distributed, with a size of about 28 nm and an excellent stability. The antioxidant activity of M-AgNPs was evaluated by 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) assay, and the highest DPPH clearance rate was 84.69±3.68 %. M-AgNPs wrapped by biomolecules exhibited stronger antibacterial activity than chemically synthesized commercial nanosilver. M-AgNPs' diameters of inhibition zone against P. aeruginosa, E. coli and S. aureus were 13.9 ± 0.4, 12.2 ± 0.3 and 12.8 ± 0.7 mm, respectively. The minimal inhibitory concentrations of M-AgNPs against E. coli and S. aureus were 4 μg/mL and 16 μg/mL, respectively, and the minimal bactericidal concentrations were 4 μg/mL and 32 μg/mL, respectively. M-AgNPs showed time-dependent damage to the cell morphology of pathogens. Such biosynthesized organic silver nanoparticles have good prospects for biomedical applications.

Creep failure mechanism of -oriented thin-wall Ni3Al-based single crystal superalloys

Currently, thin-wall structures are widely employed in aviation engine turbine blades to enhance cooling efficiency. However, the mechanical properties of thin-walled structures exhibit significant sensitivity to thickness. This study investigates the creep behavior of a <111>-oriented Ni3Al-based single-crystal superalloy with different thicknesses (0.3, 0.5, 0.8 mm) at 1100 °C/137 MPa. The results indicate a significant reduction in creep life with a decrease in wall thickness. The mechanism of various influencing factors on different creep stages was analyzed from both microscopic and macroscopic perspectives combined with finite element modeling. The alteration in stress state from thick-wall to thin-wall influences the number of slip systems that are activated, which mainly affects the primary and steady-state creep stages. Surface oxidation as time-dependent damage leads to non-invasive crack formation, somewhat increasing the steady-state creep strain rate of thin-wall samples. The accumulation and propagation in varying wall thicknesses of cleavage microcracks primarily influence the steady-state and tertiary creep stages, respectively, thereby exacerbating the thickness debit effect.

An isochronous stress ratio logarithmic strain curve based clay creep model considering the effects of hardening and damage

Creep is one of the typical mechanical properties of clay, and studying the creep mechanical properties of clay is of great significance to construction projects in clay sites. This study conducted creep tests on Chengdu clay and found that the soil mass underwent elastic deformation, decay creep deformation, steady-state creep deformation, and accelerated creep deformation. The isochronous stress ratio-logarithmic strain curves and their mathematical models were proposed to thoroughly analyze clay creep mechanical properties. Creep automatic feature points, such as linear elastic extreme point, initial yield point, long-term strength point, and plastic point, were identified on the curve. Considering the hardening and damage effects during creep loading, linear elastic and viscoelastic elements considering the time-dependent damage, a viscoplastic element considering the load hardening effect, and viscoplastic and plastic elements considering the load damage effect were established based on the element model and the Riemann–Liouville fractional derivative. Based on the mechanical properties of the whole clay creep process, the creep mechanical feature points, and the established element model, a clay creep model was proposed considering the hardening and damage effects. The rationality and regularity of the creep model were verified using the creep test data. This research accurately revealed the creep mechanical properties of clay and facilitated soil deformation prediction, thus providing technical guidance and references for construction projects in clay sites.

Time-dependent damage development during creep in carbon woven-ply polyphenylene sulfide laminates above the glass transition temperature

In order to understand the coupling between time-dependent behaviours (viscoelasticity, viscoplasticity) and damage mechanisms within carbon woven-ply polyphenylene sulfide (C/PPS) thermoplastic composites subjected to creep loadings at T &gt; Tg (Glass transition temperature), it is necessary to develop experimental protocols adapted to high temperature conditions. To this aim, the present study combines different complementary techniques (acoustic emission, edge replication, fractographic analysis, tomography) allowing in-situ analyses of the damage mechanisms that coexist and interact during the different phases of creep-type loadings. These techniques provide information to quantify and dissociate the different material behaviours (viscoelasticity, viscoplasticity, damage). Two main damage mechanisms are identified: intra-bundle cracking and inter-bundle cracking leading to extensive meta-delamination. Image analyses based on morphological operations allow the evaluation of the surface cracking density (intra- and inter-strand) from edge replicas. At macroscopic scale, the thermo-mechanical response is little influenced by the viscous behaviour of angle-ply C/PSS laminates though their thermo-mechanical behaviour is mainly driven by the PPS matrix. At micro and mesoscopic scales, the results clearly show the onset and propagation of time-dependent damage in C/PPS specimens. By implementing this protocol, the acoustic emission monitoring associated with the quantification of the cracking density proved to be relevant and complementary to study the coupling between viscous effects and damage within C/PPS laminates subjected to high temperature loading.

Evaluation of haematological, genotoxic, cytotoxic and ATR-FTIR alterations in blood cells of fish Channa punctatus after acute exposure of aniline

Aniline (C6H5NH2) an important intermediate in the organic and fine chemical industry, is ubiquitously used worldwide. It is one of the important building block for manufacturing of 4,4-methylene diphenyl diisocyanate (MDI), accelerators in rubber processing, dyes, tattoo inks, photographic chemicals, antioxidants, corrosion inhibitors, pharmaceuticals and antiseptics. The current study evaluated 96 h LC50 of aniline and based on this, two sublethal concentrations (4.19 mg/l and 8.39 mg/l) were selected for acute exposure studies in freshwater food fish Channa punctatus. Erythrocytes of fish are nucleated hence they play an important role in physiology, immune system, protein signalling and haemostatic condition along with respiration. Blood samples were collected after 24, 48, 72, and 96 h of exposure to study haematological, cytotoxic and genotoxic effects of sublethal concentrations of aniline in C. punctatus. Symbolic elevation in time and dose dependent DNA damage was observed by comet assay as well as micronuclei assay revealing maximum damage after 96 h of exposure. After aniline exposure, scanning electron microscopy and ATR-FTIR studies showed anomalies in structure and alterations in biomolecules of RBCs of aniline exposed group as compared to control group respectively. Semi prep HPLC studies revealed bioaccumulation potential of aniline in higher concentration exposed group.

Delayed fracture caused by time-dependent damage in PDMS

An experimental and theoretical study of delayed fracture of polydimethlsiloxane (PDMS) is presented. Previous works have demonstrated that delayed fracture in single edge notch specimens is caused by time dependent damage due to chain scission. Here we study the interactions between damage and the elastic field using different specimens and crack geometries with blunt and sharp cracks. Our experiments show that initial toughness is not well defined, as stable slow crack growth can occur over a range of applied loads. Our experiments demonstrate that there is a universal relation between crack growth rate and applied energy release rate. A model coupling the nonlinear elastic deformation and rate dependent bond scission is proposed and is in good agreement with experimental data.

Emphasizing the Creep Damage Constitutive Model of Hydro-Mechanical Properties of Rocks: A Case Study of Granite Gneiss

The constitutive model of rock materials can describe the mechanical behavior of rocks in creep tests. Also, it is one of the important means to study the deformation and strength characteristics of rocks in complex stress environments. This paper is based on the analysis of the porosity variation characteristics of the internal structure under the coupling effect of rock hydro-mechanical properties. The concept of the hydro-mechanical properties variable is proposed, and the relationship between the coupling variable, damage and plastic deformation is established. By introducing the coupling variable, instantaneous damage variable and time-dependent damage variable into the yield surface equation, as well as the plastic potential energy equation and the stiffness matrix of the elastic–plastic creep constitutive equation, a hydro-mechanical properties creep damage coupling model was established to simulate the creep mechanical properties of rock under coupling. Based on the triaxial creep test results of granite gneiss, the model parameters are determined. By comparing the test results with numerical results, it was revealed that the model can better describe the creep mechanical properties of rocks under the coupling effect of hydromechanical properties.

A novel time-dependent damage constitutive model for hard rock materials

The mechanical behavior of deep hard rocks plays a crucial role in the long-term safety and stability of engineering structures. This work focuses on studying the instantaneous and time-dependent fracture propagation of hard rock materials from a theoretical perspective. A new unified constitutive model, based on a modified Mohr–Coulomb (M-C) criterion, is proposed to accurately represent the short and long-term mechanical properties of hard rocks. To capture the strain hardening and strain softening behaviors, damage is utilized as an internal mechanism-driven variable, controlling the expansion and contraction of the plastic yield surface. Additionally, a combination of time-dependent damage law and viscoplastic theory is employed to account for nonlinear creep deformation characteristics. By considering the time-dependent effects, the model can be applied to both instantaneous loading and creep conditions. The general algorithm format is derived in detail, and an explicit integration algorithm is utilized to update the time-dependent damage evolution. Finally, the proposed model is validated by comparing its predictions with the short and long-term mechanical responses of Beishan granite and Rumei dacite. This comprehensive constitutive model improves our understanding of continuum damage mechanics and provides a scientific basis for analyzing and evaluating the long-term safety and stability of deep hard rock engineering projects.

Effect of sustained load on fatigue crack growth behavior of FGH96 at elevated temperature

Accurate prediction of fatigue crack growth behavior is crucial to damage tolerance assessment of turbine disk. Powder nickel-based superalloy is a kind of preferred material of turbine disk. For the purpose of better understanding the characteristics of its crack growth behavior under dwell fatigue conditions at elevated temperature, dwell fatigue crack growth tests of powder nickel-based superalloy FGH96 were conducted with compliance method at three temperatures (600℃, 650℃, 700℃) and multiple dwell time conditions (from 0 s to 60 s). The results show that sustained load can accelerate fatigue crack growth rate of FGH96 significantly at high temperature, and it is more pronounced with higher temperature and prolonged dwell time. At higher ΔK level, the acceleration effect brought by sustained load seems to diminish, this is ascribed to rapid crack growth rate which leads to insufficient time for time-dependent damage occurring at crack tip zone. The effect of temperature on dwell fatigue crack growth rate is more remarkable from 650℃ to 700℃, compared with that from 600℃ to 650℃. The fatigue crack growth resistance of FGH96 is sensitive to sustained load at 700℃, just 1 s dwell loading can produce remarkable acceleration effect on fatigue crack growth rate. The time-dependent crack extension in a loading cycle increases with dwell time in a decelerated manner. Finally, A phenomenological-based crack growth model considering time-dependent damage was proposed, the comparation between the proposed model and the experiment data confirms that it works well for a wide range of temperature and dwell time.

Evaluation of stress path and load rate effects on rock strength using compression testing data for Stanstead Granite

Compression testing schemes that induce failure in rock specimens primarily through a reduction in confining stress have become increasingly common in recent years. Despite this, the interpretation of the results from such studies are fraught with complications due to the large number of factors that can influence the outcome of such tests relative to standard compression tests that follow a loading path. Among these, unloading rate is especially significant, as it has the potential to both influence peak strength and total test time (i.e. time-dependent effects). In this study, we present a framework to convert unloading rates into equivalent loading rates to facilitate comparison with standard compression test results as well as comparisons across rock types. We then present the results of a suite of 39 compression tests, including strain-controlled standard UCS and triaxial tests, constant deviatoric stress unloading triaxial tests, diagonal stress path unloading triaxial tests, and load-controlled standard triaxial tests. Based on comparison of load-controlled and strain-controlled standard compression tests, it is concluded that strain-controlled tests produce appreciably lower peak strength values, even if relevant ISRM Suggested Methods and ASTM Standards are followed in both cases. Additionally, the different control modes produce different volumetric strain responses up to the point of peak strength. A detailed comparison of load-controlled test results from standard triaxial tests and unloading triaxial tests with failure points at σ3 ≈ 1 MPa reveals that diagonal stress path unloading tests produce comparable peak strength values to standard load-controlled tests. Although the observed trend in the constant deviatoric stress unloading triaxial test data corresponds to lower peak strength values than those obtained using standard load-controlled tests, we attribute this discrepancy to time-dependent damage effects and/or minor damage accumulation during the initial loading phase of the tests rather than to the difference in stress paths.

Time-dependent virtual crack model of rock with application to slope stability

Time-dependent deformation of rock involves the continuous to discontinuous deformation of joints, cracks, holes, and other defects under long-term stress conditions. Thus, it is of great significance to investigate the correlation between internal crack propagation in rock and external time-dependent damage and failure of rock to better understand the long-term stability of engineering rock mass. Here, we put forward a time-dependent virtual crack model to achieve the entire continuous-discontinuous time-dependent deformation progress of rock from the microscopic to the macroscopic scale. Simulated stress-strain curves for granite, including the mode of failure (axial splitting and Brazilian splitting), agree well with experimental data. We also used the virtual crack model to study the stability of one of the slopes of the Xiaowan Hydropower Station (China). The simulation results indicate that the weakly disturbed zone is the potential sliding surface, and that the deformation of the slope is similar to in-situ measurements. In the model, the vertical displacement decreased by 500 mm in 180 days and the axial strain rate decreased from 25 mm/d to zero, suggested that the slope is currently stable.

A local response function approach for the stress investigation of a centenarian steel railway bridge

Local stress concentrations in some specific geometric details often play an essential role in time-dependent damage propagation. However, measured strain or stress data are generally available in locations that are not the most critical ones. Proper numerical models are thus required to aid the damage severity assessment. In this paper, a surrogate model procedure based on the local response function method is proposed to accurately predict stress time histories in particular regions of bridges through a multiscale numerical analysis. The methodology is calibrated on the basis of direct strain measurements on a railway bridge in Vänersborg, Sweden. The bridge is currently monitored with a set of strain gauges, accelerometers, and an inclinometer allowing the investigation of its in-service conditions during the train passages and the lifting of the bascule truss. The results show the reliability of the method for stress prediction in specific regions of the bridge without the availability of directly measured data together with more detailed knowledge about the stress histories that could lead to fatigue or corrosion damage.

Roughness induced crack Closure: A review of key points

In this article we review and discuss the key points on the roughness induced closure (RICC) that is considered to affect crack tip shielding. While the RICC has been suggested as a mechanical obstruction in the wake of the crack during cyclic unloading for planar slip alloys at the threshold region, the emphasis on the access of the environment to the crack tip for an environmental damage was not considered. The question is how much the role of RICC alone versus the environment that can affect the overall damage needs some discussion. Dislocation-based models have indicated that the crack tip shielding effect from a single asperity is small. In addition, the location of such an asperity (rigid or deformable) behind the crack tip and multiple asperities also affects the shielding. Existing examples of threshold ΔKth data in a good vacuum (less than10-5 Pa) suggest that RICC is not a significant factor to reduce ΔKth with R in planar slip alloys at ambient temperature. The same alloy in moist air/dilute chemical environment do exhibit ΔKth reduction with R. This comparative observation indicates that the factor of environmental access dominates in the crack opening behind the crack tip affecting the near threshold region for fatigue damage. Near threshold region is where the time dependent environmental damage is significant.

Mechanism of Time-Dependent Instability of Deep Soft-Rock Roadway and Crack-Filling Reinforcement Technology

Soft broken surrounding rock exhibits obvious rheological properties and time-dependent weakening effects under the action of deep high-ground stress, leading to the increasingly prominent problem of sustained large deformation in deep roadways. In this study, with the II5 Rail Rise in Zhuxianzhuang Coal Mine as an example, the mechanism and control technology of time-dependent damage and instability in a deep soft-rock roadway were explored through a field observation and numerical simulation. The research results show that the range of the loose circle in the deep fractured surrounding rock can reach 3.0 m. The expansion of shallow and deep cracks causes the primary plastic deformation and secondary rheological deformation of the surrounding rock, with the rheological deformation rate increasing by 21.4% every 55 days on average, which ultimately induces the instability and failure of the surrounding rock. Based on the mechanism of roadway instability, a control technology of high-preload bolt + deep- and shallow-borehole crack filling was proposed. The technology reduces deformation and ensures the stability of the roadway surrounding rock by inhibiting the propagation of deep and shallow cracks and reinforcing the surrounding rock.

Coupled Two-Phase Flow and Elastodamage Modeling of Laboratory and In Situ Gas Injection Experiments in Saturated Claystone as a Potential Host Rock for Nuclear Waste Repository

Understanding gas migration behavior in host rocks is of importance to the safety evaluation of deep geological repositories for nuclear waste. Experimental results reported in the literature show that gas flow in saturated claystone is through a highly localized network of dilatant pathways and that water is barely displaced. To explain the specific gas migration behavior, a two-scale approach is developed. A subcritical criterion for microcrack propagation is proposed to represent the time-dependent damage at the macroscale. The passage from microscale to macroscale is implemented through an asymptotic homogenization method. The solid mechanics is coupled with the fluid flow through pore pressure variation and an intrinsic permeability model, which implicitly accounts for the fracture opening induced permeability change. The developed model is tested against both laboratory and in situ gas injection experiments in the literature. Some key experimental findings, such as the development of preferential gas pathways and the fully saturated state are explicitly captured by the poroelastic damage model. Model results explain that the highly localized fracture pathways are the major places where gas and water interact with each other, and as a result the whole rock is almost kept fully saturated, which helps us get in-depth understanding of this gas transport mechanism.

Research on creep characteristics of loading and unloading of hard Flint limestone

The hard Flint limestone of Shuibuya hydropower station underground construction cavern is utilized as a research object to investigate the creep problem caused by excavation of rock masses such as caverns. In order to perform a triaxial compression grade-unloading creep test, the actual adjustment path of stress during excavation of underground cavern surrounding rock is used. Limestone under different confistiff pressures is then evaluated. Based on the Nishihara model, the elastic damage element considering time-dependent damage is introduced, and the unloading creep constitutive model of stiff Flint limestone is established and verified by experiments. The results show: 1) Deformation and creep strain appear at all stress levels. 2) As the unloading amount increased from 2 to 4 MPa, the quasi-destructive stresses of the samples were smaller from 83 to 79 MPa, indicating that the unloading amount affected the final creep damage strength of the rock samples. In other words, the higher the unloading amount, the lower the ultimate creep failure strength. 3) When entering the accelerated creep stage, the axial and lateral creep strains of the sample increase non-linearly, and the rupture duration of the sample is very short. Therefore, the creep deformation and creep rate characteristics of this stage should be paid attention to in practical engineering. 4) Different from the loading stress path, the failure mode of the Flint limestone rock sample is different. When the unloading amount is 2 and 4 MPa, the creep failure mode of the Flint limestone rock sample is shear failure, showing a significant oblique section crack. 5) The non-linear creep model curve of aging damage and the fitting effect of the unloading creep test curve are acceptable. The rationality of the established non-linear creep model is illustrated.