Time-dependent Damage Research Articles

Transformation of classical PSA and DSA into the form of conditional event tree: An approach of human action in time dependent core damage risk

Although the accident progression in NPPs follows a dynamic trend, most industrial PSA studies used in the design process include static modeling with time-independent construction and without a well-defined linkage between the DSA and PSA. This is mostly due to the complicated methods for integration and post-processing procedures. This article aims to develop a straightforward combination process between DSA and PSA applicable in nuclear power plant safety analysis for considering the dynamic effects of operator task timing on the Core Damage Frequency (CDF). The case study is a Main Steam Line Break (MSLB) accident for a PWR. The combination approach includes a four-step procedure for the consideration of operator timing on the final core damage contribution. Thus, the CDFs are calculated based on different timings of human action, and the effects of timing on the CDF are presented in the form of a Conditional Event Tree (CET). According to the results, the total CDF is highly dependent on the HEP, and it can be reduced by providing additional time to the operator. The results also showed this additional time can be provided by the successful performance of the pressurizer safety valve as a passive device.

Effect of pesticides on erythrocytes of indigenous fish Labeo rohita

Single cell gel electrophoresis was used to observe the effect of bifenthrin and chlorpyrifos on Labeo rohita. The present work was planned to study the genotoxic effect of pesticide mixture on the major indian carp, L. rohita at sub-lethal concentration 33% LC50. First of all, 96-hr LC50 was determined for L. rohita, then fish was given sub-lethal environment for 70 days. Erythrocytes from blood were taken after each fortnight for the assessment of time dependent DNA damage (% damage), aggregate tail length of comets and genomic destruction. There was increase in damage up to 56 days and after that a slight decrease was observed in next fourteen days. After statistical analysis, it was concluded that the Single Cell Gel Electrophoresis may be implemented in ecofriendly observer courses in evaluation of toxicity.

A two-scale hydro-mechanical-damage model for simulation of preferential gas flow in saturated clayey host rocks for nuclear repository

Significant amounts of gases could be generated in the post-phase of radioactive waste repositories, which may deteriorate the integrity of natural host rocks. A safety issue related to the geological disposal facilities concerns the gas migration through saturated host rocks, of which the dominant process is mainly referred to the advective gas flow, accompanied by the formation of micro-fracturing that occurs at the applied gas pressure significantly lower than the minimum principal stress (compressive stress is regarded to be positive here). These fracture formed gas pathways are found to be highly localized and dynamically unstable, which may vary temporally and spatially within the clayey rocks. A multiscale model incorporating the evolving microcracks may be appropriate to address this specific rupture pattern. The model is developed from the periodically distributed microstructures with microcracks in a porous medium. The upscaling method based on the asymptotic expansions leads to the macroscopic hydro-mechanical (HM) governing equations coupled with the normalized microcrack length. Based on the micro-mechanical energy analysis, the time-dependent damage evolution law is constructed that accounts for the subcritical microcrack propagation. The local macroscopic response of the model is analyzed with emphasis on the influence of the microstructural size, the loading rate and the reference crack velocity, which are important factors influencing the localized pathways for gas migration. Two numerical examples of air injection tests on clayey rocks are presented where the highly localized gas pathways are explicitly simulated. The comparison between the model predictions and the experimental results provides in-depth understanding of gas induced fracturing process.

A New Approach to Characterise the Impact of Rock Bridges in Stability Analysis

Rock bridges have been the subject of considerable research since the 1970’s with a focus on developing methods to measure rock bridges and quantifying their role with respect to rock mass strength. In the literature, rock bridges are generally defined as a portion of intact rock separating discontinuity surfaces; however, whether a portion of intact rock resists failure and, therefore, represents a critical rock bridge depends on the failure mechanisms that may develop within the rock mass. The difficulty of defining what constitutes a rock bridge is associated with the challenge of measuring rock bridges in the field. This aspect is often ignored by engineers and practitioners, who fail to recognise that rock bridges could exist even within a rock mass characterised by fully continuous surfaces. Furthermore, field evidence of rock slope failure shows that rock bridges do not fail at the same time, and a simple definition of a rock bridge as the distance between existing discontinuities cannot account for progressive rock mass damage and changes in stresses within a rock mass. The authors suggest that the concept itself of rock bridges may be flawed, and more attention should be given to better understanding damage-related processes, including time-dependent damage in the context of engineered structures.

Creep damage model of rock mass under multi-level creep load based on spatio-temporal evolution of deformation modulus

To study the damage characteristics of rock mass under multi-level creep load, damage variable D was defined based on the spatio-temporal evolution characteristics of deformation modulus E, and the Kachanov damage theory is used to describe the damage evolution, then the damage evolution equation of the rock mass under multi-level creep load is obtained. Combining the damage evolution equation with the Lemaitre strain equivalence principle, the creep damage constitutive model of rock mass under multi-level creep load considering initial damage is obtained. By comparing the results of uniaxial and triaxial tests with the calculated values of the model, the rationality, reliability, application range of the model proposed in this paper is verified. According to the results of parameter inversion, obtain the relationship between damage, stress and time. Results show that time and stress are the important factors influencing the damage of rock mass under multi-level creep loading, the damage increases with time and stress level. However, the influence of time and stress on damage has a significant stress response characteristics: under low stress, the instantaneous damage Dis caused by the instantaneous stress loading is the main reason for the damage. With the increase of the load level, the main cause of the damage gradually changes from the instantaneous loading of the stress to the creep accumulation of the damage, and the greater the initial damage, the higher the time-dependent damage DiT proportion in the global damage.

A two-scale time dependent damage model for preferential gas flow in clayey rock materials

Understanding of the gas migration within the host rock is critical for the safety assessment of a deep geological repository for radioactive wastes. However, localized gas flow in clayey host rock materials is a complex behavior associated with dynamic and unstable network of dilatant pathways, which are accompanied by micro-cracking that indicates macroscopic tensile fractures. The subcritical crack propagation at the microscale may represent the mechanism of time dependent damage observed at the macroscale. A two-scale damage model is developed in this study to explicitly simulate the preferential gas flow in clayey rock materials. A homogenization method based on asymptotic developments is employed to deduce the macroscopic damage behavior coupled with the poroelastic system, which initiates from the periodically distributed microstructures with micro-cracks. A time dependent damage evolution law is constructed based on the microscopic phenomena and the corresponding intrinsic permeability model is proposed which implicitly accounts for the fracture opening induced permeability change. The local macroscopic response of the model is analyzed and validated against the experimentally measured direct tensile strength, which illustrates the homogenized elastic and permeability coefficients, and highlights the influence of several parameters, i.e., the initial damage, the microstructural size and the strain rate. Numerical examples are presented in order to illustrate the global macroscopic response, in which a pure mechanical test, i.e., uniaxial tension test is simulated and verified against the laboratory results, then the simulation of preferential gas flow is illustrated together with the comparison of experimental explanation. The numerical results showed that the proposed two-scale model can explicitly simulate the gas induced fracturing, in which the damage propagation and the dilatant gas pathways are well captured.

Mechanical properties of rock salt under combined creep and fatigue

The mechanical performance of rock salt under combined creep and fatigue plays a critical role in the long-term stability and serviceability of underground compressed air energy storage (CAES). In the present study, laboratory tests were performed to investigate the impact of simultaneous creep and fatigue on the hysteresis behavior, deformability, progressive damage, cycling life, and fracture mechanism of rock salt. The strain-time curves undergo a three-phase (transient, steady-state and tertiary phase) S-shaped evolution, which is similar to that observed in pure creep or fatigue tests. It has been demonstrated that the presence of a stress dwelling period does not change the geometric similarity of the cumulative deformation curve, but may accelerate the accumulation rate of inelastic deformation, leading to a reduction in the cycling life of rock salt. The consistency between acoustic emission (AE) counting rate and the volumetric deformation indicates that micro-cracks are primarily generated during the loading period and grow stably during the stress dwelling period in rock salt within a single loading cycle. The cumulative cyclic damage and time-dependent damage in rock salt promote each other, which results in a notable positive interaction between them. The life of rock salt specimens can be reasonably predicted by employing a nonlinear cumulative damage rule that incorporates an interaction term. The logarithm of the deformation rate in the steady-state phase is linearly correlated with the logarithm of the creep or fatigue life, regardless of the loading history, and serves as an alternative approach for predicting the life of rock salt. It seems that the typical failure pattern tends to transform from multiple shearing to axial splitting as the creep load fraction increases. For rock salt in the combined creep and fatigue test, a mixed microcosmic intergranular and transgranular fracture was observed using a scanning electron microscope.

Time-dependent damage mechanism of rock deterioration under freeze–thaw cycles linked to alpine hazards

The unique natural environment of the alpine terrains along the Tianshan highway has led to the frequent occurrence of hazards. The typical hazards in this area, such as sliding collapse, have obvious time-dependent deformation characteristics, and the extreme climatic change causes rock mass deterioration under freeze–thaw cycles, which serves as an important factor that indirectly triggers hazards, while the relationship between the time-dependent characteristics of hazards and the damage characteristics of rock mass deterioration triggering hazards remains uncertain. A series of microscopic examination and macroscopic mechanical experiments were conducted on quartz sandstone from the Tianshan highway to study the mechanism. The experimental results show that the cyclic freeze–thaw action changed the microstructure of quartz sandstone and weakened its mechanical performance. The weakening effect on the long-term mechanical characteristics is much more remarkable than that on the short-term characteristics, and the failure modes become more complicated after long-term loading. Based on the experimental phenomenon, the mechanism was analyzed, and a new constitutive model was established to reflect the long-term mechanical characteristics of rock with freeze–thaw cycles and predict the deformation of an unstable rock mass during collapse. These results can provide a reference for alpine hazard prevention.

High temperature mechanical integrity of selective laser melted alloy 718 evaluated by slow strain rate tests

Strain rate dependent deformation behaviours of selective laser melted Alloy 718 (IN718) are systematically studied at 550 and 650 °C by slow strain rate testing, with a forged counterpart as a reference. Selective laser melted IN718 shows significant susceptibility to intergranular cavitation, resulting in ductility degradation with decreasing strain rate. Detailed fractography and cross section inspections are employed to identify the damage mechanisms. Creep rates are also estimated and compared with the conventional counterparts. The possible critical factors for the inferiority of time dependent damage resistance of selective laser melted IN718 are discussed.

A THERMODYNAMIC CONSISTENT ELASTOPLASTIC FRACTIONAL TIME-DEPENDENT DAMAGE MODEL FOR ROCK-LIKE MATERIALS

This paper aims at presenting a thermodynamically consistent elastoplastic fractional time-dependent damage model for describing short- and long-term behaviors of rock-like materials. The model utilizes generalized potential theory with a yield criterion, a non-associated flow rule and an isotropic plastic hardening function for describing the evolution of plasticity. A time-dependent Lemaitre-type damage is introduced through fractional derivative considering the short- and long-term evolution of microstructure, which leads to progressive degradation of elastic modulus and failure strength of material. In this context, both instantaneous and delayed deformations shall be well described within the unique constitutive model. For practical application, an efficient and convergent semi-implicit return mapping (SRM) algorithm involving a plasticity-damage decoupling corrector is developed. The proposed model is finally adopted to predict the mechanical and deformation behavior of several types of rocks under different loading conditions in conventional or quasi-static (different loading strain rate) triaxial compression tests, creep tests and relaxation tests. Comparisons between model predictions and experimental data demonstrate that the proposed model has the capability to reproduce main features of short and long-term behaviors of rock-like materials.

Damage development in neutron-irradiated concrete in a test reactor: Hygro-thermal and mechanical simulations

This paper reports the development of a 3D mesoscale hygro-thermal-mechanical simulation approach to predict damage in concrete irradiated in a test reactor. This framework, developed in MOOSE, considers the effects of elevated temperature, moisture content, and high neutron fluence (energy threshold, E > 0.1 MeV) on the mortar and aggregates separately. The first-stage simulation implements hygro-thermal analysis to determine the temperature and RH inside the specimen as a function of imposed radiation energy. These are used as inputs to the second stage, which considers radiation-induced volumetric expansion (RIVE) of aggregates, and creep, shrinkage, and stress-strain response of mortar to predict the expansion, stresses, and damage in specimens made using different coarse aggregates and subjected to different irradiation times. The irradiation time-dependent damage in the mortar is expressed using an isotropic damage parameter. This multi-physics model serves as a predictive tool for damage quantification in concrete due to neutron irradiation.

Shear creep behavior of red sandstone after freeze-thaw cycles considering different temperature ranges

A strong freeze-thaw (F-T) weathering effect influences the strength of rock in the high-altitude areas of the Qinghai-Tibet Plateau. To study the long-term deterioration characteristics of rock in an alpine F-T environment, shear creep experiments were conducted on red sandstone from the Sichuan-Tibet highway to analyze its shear creep characteristics under different temperature ranges. The results show that the rock’s stress level gradually decreases with increasing temperature under the same number of F-T cycles, while the creep displacement gradually increases. The long-term strength and long-term reduction factor present apparent decreasing trends with an increase in the F-T temperature range. The failure morphology evolves from shear failure with a single horizontal plane to that with multiple dipping shear planes. The greater the temperature range is, the greater the number of shear secondary cracks that intersect, resulting in more complicated failure morphologies. Then, a Burgers model considering F-T and time-dependent damage was established. The parameters of this model were identified via the experimental creep data of the red sandstone. The accuracy and applicability of the model were verified by comparing the experimental and model-predicted results. These results are significant for the construction of major engineering projects in the alpine region.

Insights into Unloading Relaxation Mechanism of Columnar Jointed Basalt at the Baihetan Left Dam Foundation

Columnar jointed basalt (CJB), characterized by unique geometric and geological properties, poses a great challenge for geotechnical designs due to its unloading relaxation and damage during excavation. In this paper, the geometrical structure and field failures of the CJB exposed on Baihetan left dam foundation were briefly presented. A systematic field test was conducted to study the excavation damage zone of the CJB on the dam foundation using ultrasonic P wave measurements. The excavation damage zone of the CJB not only showed time‐dependent damage in depth but also showed spatially inhomogeneous distribution in depth. Corresponding three‐dimensional numerical analysis was also carried out to analyze the unloading relaxation mechanism of CJB. The unloading relaxation of CJB on dam foundation was mainly caused by the joint opening under tension stress during excavation. The difference of excavation damage zone of the CJB located in different test zones was also discussed in this article.

Naphthalene-2-sulfonate induced toxicity in blood cells of freshwater fish Channa punctatus using comet assay, micronucleus assay and ATIR-FTIR approach

Present inquisition was undertaken to evaluate the genotoxicity of naphthalene-2-sulfonate (2NS), a sulfonated aromatic compound and a momentous intermediate involved in the synthesis of dyes and surfactants, in fresh water fish, Channa punctatus. After LC50 determination, two sublethal concentrations i.e. 2.38 g/15 g b.w. (1/4 of LC50) and 4.77 g/15 g b.w. (1/2 of LC50) were selected for studying acute exposure. For evaluating sub chronic exposure 1/10th (0.238 g/L) and 1/20th (0.119 g/L) of safe application rate (SAR) were reckoned. Blood samples were collected after 24, 48, 72, and 96 h exposure period to study acute effect, and after 30 and 60 days exposure period for sub-chronic effect. Symbolic elevation in time and dose dependent DNA damage was observed by comet assay as well as micronucleus test revealing maximum damage after 60 days of exposure. After cessation of exposure to 2NS, evident recovery was observed after 30 days. Along with comet assay and micronucleus test, spectroscopic evaluation of DNA damage was also noted using Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR). The biomolecular range (800 cm−1 - 1800cm-1) in lyophilized red blood cell’s extracted from 60 days exposed as well as control group exhibit significant alterations in their nucleic acid indicated through multivariate analysis i.e. Principal Component Analysis (PCA). Further structural analysis of erythrocytes in maximally damaged group using Scanning Electron Microscopy was performed. Thus the study proposed the genotoxic impact of 2NS which is further supported by other toxicity markers like ATR-FTIR and Scanning Electron Microscopy.

Time-Dependent Deformation and Fracture Behavior of Fiber-Reinforced Ceramic-Matrix Composites under Stress-Rupture Loading at Intermediate Temperature

AbstractThe present study investigated the time-dependent deformation, damage, and fracture tendencies of fiber-reinforced ceramic-matrix composites (CMCs) that were exposed to stress-rupture loadi...

Assessing time-dependent damage to a cable-stayed bridge through multi-directional ground motions based on material strain measures

Investigations into previous earthquakes indicated that the seismic damage to bridges was closely related to the length of their service lives. Based on this observation, finite-element time-dependent models of a cable-stayed bridge with a single pylon and wide deck were established by considering the effects of concrete carbonization on various structural components. Ground motion records were selected and matched with the design spectrum of site classification Ⅰ. Different combinations methods of ground motions inputs were compared with respect to the strain distributions of critical elements, and the representative method was then determined according to the maximum responses. The strain limits of reinforcing steel and concrete were defined based on previous studies, and were used to identify the time-dependent damage states of critical elements under earthquakes. The incremental dynamic analysis (IDA) method was applied to comparatively investigate the effect of concrete carbonization on the seismic response of cable-stayed bridge. Using the defined strain limits, the effect of concrete carbonization on the time-dependent seismic damage to the cable-stayed bridge was also discussed. The results show that the strength of steel and concrete can decrease as much as 23.30% and 12.66% respectively due to the concrete carbonization. The coupling damage to the bridge is found under multi-directional ground motions. The pylon is the most critical element during three-way seismic waves, in which the base suffers the most serious damage, the deck-level section follows and the cable anchorage portion remains in slight damage state. Taking the concrete carbonization into consideration, the damage level of the pylon base increases significantly, and brittle failure may occur to the pylon base when subjected to earthquakes with high peak ground accelerations (PGAs). However, the damage levels of other critical portions of the pylon decrease when the concrete carbonization is considered.

A time-dependent vibration damping model of fiber-reinforced ceramic-matrix composites at elevated temperature

In this paper, a time-dependent vibration damping model of fiber-reinforced ceramic-matrix composites (CMCs) is developed. Considering time and temperature dependent interface damages of oxidation, debonding, and slip, the relationships between composite vibration damping, material properties, internal damages, oxidation duration and temperature are established. The effects of material properties, vibration stress, damage state, and oxidation temperature on time-dependent composite vibration damping and interface damages of C/SiC composite are discussed. The time-dependent composite vibration damping decreases with fiber volume, matrix crack spacing and interface shear stress, and increases with vibration stress. The experimental composite vibration damping and internal damages of 2D C/SiC composite for different oxidation duration t = 2, 5 and 10 h at elevated temperatures T = 700, 1000 and 1300 °C are predicted. When the oxidation duration was short (i.e., t = 2 h), the composite vibration damping decreased with temperature; however, when the oxidation duration was long (i.e., t = 5 and 10 h), the composite vibration damping decreased with temperature below 1000 °C, and increased with temperature to 1300 °C.

EFFECTIVENESS OF N-ACETYLCYSTEINE ON TITANIUM DIOXIDE NANOPARTICLES- INDUCED IMMUNOTOXICITY IN ADULT ALBINO RATS

Background: Titanium dioxide (TiO2) is a white pigment that can be used in paints, coatings, plastics, papers, inks, medicines, pharmaceuticals, food products, cosmetics, and toothpaste. Titanium dioxide nanoparticles (TiO2 NPs) have been reported to elicit various adverse cellular effects including oxidative stress and DNA damage. N-acetylcysteine (NAC) is an antioxidant and free radical scavenger used to combat oxidative stress-induced damage in various tissues. Aim of the Work: is to study the toxic effects of TiO2 NPs oral administration and the protective role of NAC on the immune system of adult male albino rats. Thirty adult male albino rats were divided into 4 groups: Group I subdivided into: Subgroup (A): negative control. Subgroup (B): positive control received 1 ml of 5% gum acacia solution by oral gavage once daily. Group II: gavaged orally 100 mg/kg NAC once daily. Group III:gavaged orally 1200 mg/kg titanium dioxide nanoparticles (1/10 LD 50) in 1ml of 5% gum acacia solution as a solvent once daily. Group IV: gavaged orally (100 mg/kg NAC then 1200 mg/kg TiO2 NPs once daily. After 6 weeks rats from each group and subgroup were subjected the following biochemical parameters: Tumor necrosis factor alpha and CBC with differential count. The rats were sacrificed and spleen was dissected and subjected to histopathological examination. Cell suspension from the spleen was examined to determine the extent of DNA damage through DNA extraction and gel electrophoresis. Conclusion: TiO2 NPs induced time dependent toxic effects and DNA damage in the spleen and administration of NAC with TiO2 NPs offers protection against their damaging effect. Recommendation: it is recommended to increase public awareness about health impact of TiO2 nanoparticles through nonessential drug additives, food colors, toothpastes etc.to limit their ingestion.

Use of DC voltage fluctuation method to investigate real-time Mode I and Mode II subcritical crack growth behavior in gypsum rock

Subcritical crack growth strongly influences the mechanical behavior of rock and the precursory phase of geohazards and catastrophic failure. In earlier studies, indirect measuring methods were used to investigate the subcritical crack growth behavior of rock materials. However, these methods cannot fully reflect the whole process of subcritical crack growth of geomaterials. Therefore, in this study, a new method (DC voltage fluctuation method) was developed which can monitor the whole process of crack growth and measure the crack growth rate in real time. This method is based on the monitoring principle of change in voltage caused by the change in resistance. Then, the whole processes of Mode I and Mode II subcritical crack growth of gypsum specimen were monitored in real time by the self-designed fracture strain gauge, which consists of 10 breakable resistance wires, and a DC voltage signal monitor. Furthermore, using the measured crack growth rates and the stress intensity factors of varying crack path lengths, the parameters of the modified Charles model were fitted. The results show that: (1) the subcritical crack growth process mainly includes three stages: cracking latent period (primary stage), steady-state crack growth stage (secondary stage), and accelerated crack growth stage (tertiary stage). The cracking latent period lasts for the largest proportion of the entire fracture process duration. The duration of each stage decreases gradually with increasing applied load. (2) In the steady-state crack growth stage, both Mode I and Mode II crack growth rates increase with increasing applied load. However, the crack growth rates in the accelerated stage are basically the same with increasing applied load. When a specimen is subjected to a given constant applied load, the subcritical crack growth rate of Mode II is higher than that of Mode I in the secondary and tertiary stages. (3) The parameters A and n of the subcritical crack growth model (modified Charles model) (secondary stage) increase with increasing external applied load. The parameters are closely associated with the size of fracture process zone at the crack tip. The results of this study can provide a deeper insight into the macroscopic failure of rock, and also provide the parameters for the time-dependent damage evolutional process of underground constructions.

Complete slaking collapse of dike sandstones by fresh water and prevention of the collapse by salt water

Slaking is a well-known process, in which the surface of rock masses consisting of rocks such as mudstone, shale, etc. show rapid and complete disintegration when they are subjected to drying and then wetting with fresh water. On the other hand, dried sandstones even if they contain clay minerals such as smectite, etc., usually do not exhibit complete disintegration when they are soaked in fresh water. Instead, they usually show a strength decrease. Their slaking durability is tested by rotating them in a drum which is partially immersed in fresh water and eventually measuring the decrease in weight. On the other hand, it was found that some of the Paleogene sandstones from Kushiro Coal Mine in Japan, were completely disintegrated when they were immersed in fresh water followed by drying, but they were not collapsed when saline water was used instead of the fresh water. It was also shown that sandstones containing calcite did not show the complete breakdown even in fresh water. To understand the complete collapse of sandstones in fresh water and prevention of the collapse by salt water, sandstones sampled from Neogene dikes and Cretaceous at the mine were immersed in pure and salt water with Shikotsu welded tuff for comparison. Only dike sandstones showed a complete collapse in pure water and 3% salt water. Dike sandstone further showed severe time-dependent damage in salt water whose salinity was less than 7%. The results were explained by the dissolution of halite, swelling pressure of montmorillonite, osmotic pressure, etc.