Mechanical Damage Research Articles

Exploring multi-scale damage mechanisms in 8Cr4Mo4V alloy by molecular dynamics simulations and experiments

8Cr4Mo4V, as an ideal choice for aeroengines bearing materials, involves multi-scale damage mechanisms during the process of material failure. Herein, we propose a multi-scale analysis method to explore the crack initiation and propagation damage mechanisms of 8Cr4Mo4V alloy. We find that different crystal orientations produce distinctly different damage mechanisms. The second phase doping also has different strengthening effects on the matrix conformed to cut-off and Orowan mechanism. Meanwhile, the study of the polycrystalline model verified inverse Hall-Petch relation at the micro-scale, where material strength decreases with grain refinement. Phase transitions caused by dislocations lead to stress concentration at specific grain boundaries, becoming the main inducer for the nucleation of initial voids. To address micro-to-macroscale-crossing issues, we constructed a large-scale mesoscopic molecular dynamics simulation and proposed an analytical formula to predict the relationship between average grain size and yield stress. Finally, we combine macroscopic experiments, crystallographic analyses, and atomic-scale characterization, verifying the combined action of dislocations and stacking faults leads to the failure of the material.

Study on the characteristics of CO2 fracturing rock damage based on fractal theory

CO2 fracturing is emerging as a carbon–neutral technology for underground excavation. Traditional studies on structural stability during excavation have largely focused on the vibration characteristics of rocks. However, the inherent damage in rock layers during CO2 fracturing poses significant challenges for understanding damage mechanisms under complex multi-field coupling. This study introduces a novel approach for calculating rock damage induced by CO2 fracturing.We developed a physical model of CO2 fracturing and applied a “two-stage effect” division method, creating a staged damage calculation model based on fractal damage mechanics theory. Experiments were conducted under combined dynamic and static loads to evaluate rock damage. A two-factor Analysis of Variance (ANOVA) was used to assess the significance of dynamic and static effects on the extent of rock damage.The findings revealed that static loads guide crack propagation direction, reducing the angle between the crack and vertical axis, while initial CO2 dynamic load pressure strongly influences crack patterns, with higher pressures resulting in more fractures. The extent of rock damage observed ranged from 0.680 to 0.845. Although dynamic loads showed no significant impact, static loads exhibited a notable effect, as indicated by a P-value approaching 0.01. This study’s fractal-damage calculation model provides a valuable tool for addressing stability concerns in structures affected by CO2 fracturing.

Size effect on CFST-column seismic performances at cryogenic temperature via mesoscale simulations

The macro-mechanical performances of CFST column at low temperatures can be significantly affected by three main factors: the change of meso-material properties, the filling and frost heave effects caused by pore ice, and the interaction between each meso-component. Therefore, a three-dimensional thermo-mechanical sequential coupling mesoscopic simulation method was established and verified by existing experimental results with the maximum errors within 10 %. The seismic performances of CFST columns with various cross-section sizes (200–800 mm) at different temperatures (20, −30, −60 and − 90 °C) were simulated and investigated, with focused on the damage mechanism and quantitative analysis of the low-temperature effect on various seismic performance indexes (i.e., hysteretic characteristic, nominal shear strength, ductility, energy dissipation and reparability) as well as the corresponding size effects. The results indicate that the low temperature can increase the nominal strengths (i.e., peak strength, yield strength and ultimate strength), but weaken ductility, energy dissipation capacity and reparability of CFST columns. With the increase of cross-section size, the reparability increases, while other seismic performance indexes decrease, showing the size effect, which tends to be more obvious at low temperatures. The size effect on peak strength at −90 °C is enhanced by 115.5 % than that at 20 °C, while 127.9 % for yield strength and 113.5 % for ultimate strength. Based on research results, a modified size effect formula for calculating shear strengths of CFST columns considering the influence of low temperature and structural size was developed, which can provide references for seismic design of large-sized CFST columns in extreme low temperature environments.

Multiscale numerical scheme on shear failure feature of 3DOWC/Cs bar incorporating microlevel uncertainties and coupled constitutive behavior

In contrast to prevalently utilized carbon fiber reinforced plastics (CFRP), the carbon fiber reinforced carbon matrix composites (C/Cs) frequently present significantly divergent mechanics features. The current investigation dedicates to a robust multiscale finite element strategy on shear failure characteristics of three-dimensional orthogonal woven C/Cs (3DOWC/Cs) bolt bar together with relevant experimental measurement for validation, while the off-axial orientation sensibility of structural load-bearing performance and damage mechanism are systematically evaluated. In view of the complicated internal fabric architecture, the predictions are received via hierarchical numerical simulation at micro-, meso-, as well as macroscales. The random distributions of voids and fibers are incorporated to precisely capture the material properties, meanwhile the constitutive laws which embed the combining of Hashin and Puck criterions judging for yarn initial damage, multilinear rule for carbon matrix, and trilinear cohesive zone model (CZM) for interface, are implemented to render the coupling impacts of material behaviors. Besides, the extracted global load-displacement curves and local progressive failure morphologies from macroscale simulation are separately compared with experimental acquisitions to verify the accuracy of proposed modelling and to expose the damage mechanism of specimens with various off-axis angles. The contribution of this research lies in accurate quantification for microlevel uncertainties via modified stochastic algorithms, and applicable constitutive frame severally matching each material component to portray the distinctive mechanical particularities of 3DOWC/Cs.i

Leydig cells pyroptosis in testis mediates deoxynivalenol-induced male reproductive toxicity in mice

Deoxynivalenol (DON) is a toxic secondary metabolite produced by Fusarium spp. It is widely distributed among various cereals and has attracted much attention as a potential health threat to humans and domestic animals. However, the effects of DON on the reproductive systems of mammals are still ambiguous. In this study, the toxic effects of DON in the male reproduction of mice were investigated. The results showed that DON caused the shedding of sperm cells at all testis levels and the presence of inflammatory cells in the testicular interstitium. The rate of living sperm was significantly reduced, and the rate of sperm deformity was increased after DON exposure. The DON exposure resulted in decreased levels of testosterone (T) and increased levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in the serum. Measurements of oxidative stress markers showed that DON induced oxidative stress in mice testis. Meanwhile, DON triggered the assembly of NLRP3-ASC-Caspase-1 inflammatory complex and pyroptosis in both mice testis and TM3 cells, further causing the activation of GSDMD, promoting the leakage of inflammatory cytokines, including IL-1β and IL-18. Notably, the inhibition of oxidative stress was found to protect pyroptosis in TM3 cells exposed to DON. We identified a novel mechanism of reproductive damage induced by DON, demonstrating the activation of the canonical Caspase-1-dependent pyroptosis pathway and clarifying the protection of antioxidation against pyroptosis damage. Our discovery provided support for the risk assessment of DON and target exploration for clinical treatment related to pyroptosis.

Inhibition of ferroptosis attenuate lipopolysaccharide-induced early pregnancy loss by protecting against decidual damage of stromal cells

Endometrial decidualization is critical for successful embryo implantation. Dysregulation of the immune microenvironment can disrupt normal decidualization processes, potentially resulting in early pregnancy loss. Ferroptosis, a form of cell death dependent on iron and lipid hydroperoxides, is closely associated with inflammation. In this study, we developed an inflammatory early pregnancy loss model to elucidate the mechanisms of decidual damage induced by lipopolysaccharide (LPS) and to assess whether ferroptosis contributes to LPS-induced early pregnancy loss. Through in vivo experiments, we observed that embryo implantation was significantly inhibited and endometrial decidualization was impaired during LPS-induced early pregnancy loss. LPS exposure resulted in abnormal mitochondrial morphology, reduced antioxidant capacity, accumulation of reactive oxygen species (ROS) and disruptions in iron metabolism during decidualization in mouse endometrial stromal cells (mESCs). The administration of ferroptosis inhibitors, specifically ferrostatin-1 (Fer-1) and deferoxamine (DFO), effectively reversed embryo loss and mitigated the decidual damage associated with LPS-induced early pregnancy loss. Fer-1 and DFO exhibited resistance to ferroptosis during decidualization by modulating the antioxidant system and iron metabolism in mESCs, respectively. Our findings indicate that the inhibition of ferroptosis can confer protective effects against decidual damage during LPS-induced early pregnancy loss in mice.

Dynamic Mechanical Properties and Damage Evolution Behaviors of Ice-Rich Frozen Soil with Various Initial Moisture Contents

Dynamic Mechanical Properties and Damage Evolution Behaviors of Ice-Rich Frozen Soil with Various Initial Moisture Contents

Dynamic behavior of piled jacket offshore wind turbines based on integrated aero-servo-hydro-SSI-OWT model

Jacket foundation is typically the preferred choice for Offshore Wind Turbines (OWTs) erected in water depth varying from 40 m to 80 m. In this paper, an integrated dynamic analysis model is designed to study the coupling between aerodynamics, servodynamics, hydrodynamics, soil-structure interaction for piled jacket OWTs. The performances of the AeroDyn and ServoDyn modules are verified by FAST, showcasing their applicability under deterministic and stochastic environmental conditions. The OWT dynamic responses, especially for t-z modeling, stress-transfer mechanism and structural fatigue damage, are subsequently studied. The overall deformation of the jacket calculated by the nonlinear elastic t-z curve in the API guideline, is overwhelmed by the t-z curve formulated using bounding surface plasticity framework, due to the ignorance of the loading history effect. Accompanied by a “compressed-released-recompressed” stress-transfer process, the downwind tube would experience high stress level, hence necessitating more attention in the ultimate limit state design of piled jacket structure. Otherwise, the upwind tube seems to be more decisive to the fatigue limit state design of piled jacket structure, owing to severe fluctuation in structural stress caused by a “tensed-released-re-tensed” stress-transfer tendency.

Fragility analysis of tubular structures based on local-buckling driving variables

Performance-Based Earthquake Engineering (PBEE) is computationally demanding, due to the multiple high-fidelity nonlinear dynamic structural response analyses required to compute fragility curves. Local buckling of tubular steel structures is not properly characterized by typical Engineering Demand Parameters (EDPs) such as story drifts or plastic rotation angles. Targeting the two issues above, in this manuscript we propose using state variables based on Lumped Damage Mechanics (LDM) to characterize Local Buckling (LB) in PBEE. Hence, we propose an efficient and innovative procedure for the fragility analysis of complex tubular structures prone to fail due to local buckling. Moreover, local buckling produces a loss of stiffness, with loads transferred to intact or to less-damaged elements. Eventually, the structure forms a global collapse mechanism. Herein, we show how to identify the most likely global collapse mechanism in non-symmetrical tubular structures subjected to random seismic loading. This involves evaluating damage indices in different elements and their correlation, as well as identifying the combination of LB failures that are more likely to form a global collapse mechanism. Fragility curves characterizing the onset of LB at individual elements, and the most likely global collapse mechanism, are constructed. A simple frame structure is addressed, where the accuracy of the LB-LDM model is checked against experimental results. Another case study involving a non-symmetric tubular wharf illustrates the search for the most likely global collapse mechanism, and the derivation of its fragility function.

Crack evolution mechanism of stratified rock mass under different strength ratios and soft layer thickness: Insights from DEM modeling

Research on stratified rock masses, which are common geological formations, has primarily focused on their mechanical properties, while studies on crack evolution and microscopic damage mechanisms remain limited. This study addresses this gap by investigating the combined effects of strength ratios and soft layer thicknesses on the microcrack evolution mechanism of stratified rocks using the discrete element method (DEM). Through FISH language programming in the particle flow code (PFC), this study reveals the acoustic emission (AE) characteristics, crack initiation and propagation, damage degree, and final failure characteristics. The key findings are: (1) Higher strength ratios between the hard and soft components of stratified rocks make specimens more sensitive to increases in soft layer thickness. (2) Three types of AE events were identified: continuous active, intermittent active, and silent. (3) Cracks initiate at the interface between components and propagate along the interface into the rock matrix. The strength ratios determine the crack propagation path and the damage extent of the components. (4) The failure of stratified rocks is primarily controlled by the soft component. Crack connections typically form vertical and sub-vertical tensile failure planes in the hard component, and a shear failure surface with a “V”-shaped intersection in the soft component.

Application of Multifunctional Wellbore Cleaning Fluid in the Removal of Residual Drilling Fluids in Ultra-Deep Wells: Research Progress and Prospects

Developing ultra-deep wells presents a significant challenge in current petroleum exploration and production. Ensuring the cleanliness of the wellbore is a crucial aspect of safeguarding the development process. Removing contaminants from residual drilling fluids is vital to ensure unobstructed production pathways in ultra-deep wells, thereby achieving secure operational environments. This paper analyzes the primary residual components of drilling fluids in post-drilling operations of ultra-deep wells. It also explores the synergistic damaging mechanisms of residual drilling fluids on casing-ion corrosion and abrasive wear. Moreover, we summarize the technical challenges involved in the flushing and treatment of ultra-deep wellbores. Drawing from global developments in flushing fluids for ultra-deep wellbores, this study investigates the performance and on-site applicability of various flushing fluids. The findings indicate that the flushing of ultra-deep wellbores necessitates the development of fluid systems tailored to different well conditions and residual components. Adaptable flushing fluids exhibit suitability across diverse operational scenarios. Furthermore, understanding the mechanisms of flushing fluids provides novel perspectives for their future development. Presently, research on the mechanisms of flushing fluids predominantly relies on experimental observations and theoretical simulations. This study analyzes the future directions of flushing fluid research by summarizing and synthesizing existing technical challenges. In conclusion, as discussed in this study, the tailored technology for flushing wellbores lays a fundamental groundwork for large-scale flushing and treatment of ultra-deep wells, thus offering a foundational contribution to the field.

Molecular dynamic simulations of displacement cascades in Molybdenum and Molybdenum-Rhenium alloys

Molybdenum-Rhenium (Mo-Re) alloys are considered core materials for advanced nuclear reactor components due to their excellent mechanical properties, machinability, and resistance to irradiation damage. However, irradiation-induced embrittlement and phase precipitation at high temperatures, along with transmutation nuclides, have hindered their broader application. To address this, we developed a Mo-Re interatomic potential using the Finnis-Sinclair formalism, facilitating molecular dynamics simulations to study primary irradiation damage. Systemically primary irradiation damage simulations for Mo and Mo-Re alloys have been performed. It’s found that there were more Frenkel-pair defects produced during the stage of thermal spike in Mo-Re alloys but fewer defects survived at the end of the cascade compared to Mo. In addition, the number of large-size interstitial clusters and dislocation loops was higher in Mo-Re alloys than in pure Mo with the same PKA energy. This is mainly attributed to the fact that Mo-Re alloys have lower thermal conductivity, while the binding energies of interstitial clusters and dislocation loops with sizes less than 100 in Mo-Re alloys are comparable to those of pure Mo, resulting in higher defect composites and larger defect sizes in Mo-Re alloys. These findings provide valuable insights into the primary damage mechanisms in Mo-Re alloys under irradiation, offering a foundation for developing kinetic models to simulate radiation-induced microstructural evolution.

Exploring mechanical properties and cracking behavior of AC-13 and OGFC-16 aggregate-segregated asphalt mixtures

Aggregate segregation compromises the homogeneity of asphalt pavement, which diminishes the road performance of the asphalt mixture. The segregation behavior and damage mechanism of asphalt mixture are complex. To investigate the mechanical properties and cracking behavior of asphalt mixtures with varying degrees of aggregate segregation, the dense-graded asphalt mixture with the nominal maximum size of 13.2mm (AC-13) and Open Graded Friction Course with the nominal maximum size of 16.0mm (OGFC-16) with varying degrees of segregation were designed. Indirect tensile test and the digital image correlation (DIC) technology was employed to analyze the strain distribution and strain evolution at the crack initiation point within the asphalt mixtures. The parameters were also proposed to evaluate the resistance to cracking for the segregated asphalt mixtures at a mesoscopic scale. The results show that increased segregation of coarse aggregates in AC-13 mixtures leads to decreased indirect tensile strength, lower maximum tensile strain along the horizontal direction (E11), and reduced failure displacement. Conversely, segregation of fine aggregates in OGFC-16 mixtures results in increased tensile strength, maximum strain, and failure displacement. Higher amount of coarse aggregates in the asphalt mixture contributes to a more intricate strain distribution and a greater number of strain peaks. Dense-graded mixtures show larger strain concentration zones prior to cracking, while smaller stress concentration zones are observed in open-graded mixtures. The horizontal strain-time curve displays distinct stages of stable growth, rapid growth, and rapid decline. Aggregate segregation results in more intricate crack patterns with larger inclination angles, influenced by the random distribution and shapes of coarse aggregates. Novel indexes such as strain uniformity (P1,2) and strain density during crack development (DW) effectively evaluate mesoscopic cracking resistance of asphalt mixtures. The results offer valuable insights into cracking behavior and improve evaluation methods for the mechanical performance of aggregate-segregated asphalt mixtures.

An adaptive SBFEM based on a nonlocal macro/meso damage model for fracture simulation of quasibrittle materials

An adaptive scaled-boundary finite element method (SBFEM) is proposed to simulate the crack damage and propagation of quasibrittle materials on the basis of a nonlocal macro/meso damage model. The mesoscopic damage is defined by the deformation of the material bond between the two pairs in the model. First, the structure is discretized via an arbitrary polygon–quadtree mesh. During the damage propagation process, the damage value in each damaged element is determined by the model. Once the damage of an element reaches the damage threshold, the damaged element automatically undergoes mesh refinement until the refined mesh size meets the minimum mesh size requirement. This refinement strategy does not require manual intervention and is automatically implemented by computational software, greatly enhancing the computational efficiency of crack simulation. The transition elements between the refined area and the original elements are discretized using elements with a 2:1 size ratio, ensuring the high quality and efficiency of the automatically subdivided mesh. The nonlinear damage problem is solved iteratively via the arc-length method. The accuracy and efficiency of the proposed algorithm are verified through three numerical examples. The results also indicate that our method is not sensitive to mesh configurations, as commonly encountered in classic local damage mechanics. Moreover, increasing the mesh density results in smoother crack paths and higher computational accuracy.

Fabrication of flexible photo-responsive mesh with reversible wettability and enhanced mechanical damage resistance for efficient oil/water separation

Fabrication of flexible photo-responsive mesh with reversible wettability and enhanced mechanical damage resistance for efficient oil/water separation

ANALYSIS OF THE IMPACT OF CROSS-SECTION DAMAGE ON THE STRENGTH AND DEFORMABILITY OF BENT REINFORCED CONCRETE ELEMENTS

The article analyzes defects and damage in reinforced concrete structures, particularly physical, biological, and chemical, with an emphasis on the impact of prolonged operation and aggressive environmental conditions. Research shows that mechanical damage, such as spalling and potholes, significantly reduces the load-bearing capacity of structures and causes complex deformations. Relevant directions in scientific research have been identified, particularly regarding the behavior of damaged reinforced concrete beams under load, which require further development and improvement of methods for assessing residual load-bearing capacity. The article emphasizes the need for additional experimental studies and the use of modern software for more accurate methods of predicting and calculating reinforced concrete structures.

Dynamic mechanical properties and damage constitutive modelling of paste phyllite under triaxial impact testing

Dynamic mechanical properties and damage constitutive modelling of paste phyllite under triaxial impact testing

Inventário e Análise da Arborização de praças no município de Campo Belo, MG

Due to the population growth in urban areas, it is necessary to rethink city planning. Parks, as accessible green spaces, play an important role in providing leisure, social interaction, education, and ecosystem services, contributing to improving quality of life.he objective was to carry out a qualitative and quantitative inventory of trees located in Cônego Ulisses and Menotti d’Áurea squares in Campo Belo, Minas Gerais. On-site data collection included identification, measurement (DBH, height, and cankers), and visual assessment (inadequate pruning, mechanical damage, apparent nutritional deficit, and pests). By cross-referencing the data, a classification of the trees' phytosanitary status was conducted. A total of 257 trees were found, with 70% belonging to native species and classified as large-sized. Only 3.5% of the trees showed apparent nutritional deficits. Regarding pests, 4.66% suffered attacks by termites, 5.44% by borers, and two individuals were attacked by caterpillars. It was observed that 10.89% had larger canker dimensions. It was noted that 43.97% of the trees were pruned irregularly, outside of the recommended technical standards, and three species suffered mechanical damage due to vandalism. It was identified that 52% of the trees classified under criterion III (precarious tree) were Pau Ferro. The inventory in the squares showed a predominance of native species, but planning for the planting of new specimens should respect specific diversity criteria. Monitoring needs to be carried out, and replanting planning should prioritize the replacement of precarious trees. Training should be provided for professionals performing pruning, and environmental education strategies should be developed for the population.

Viral hepatitis A in children: a false prosperity?

The article presents current data on the state of the issue of Hepatitis A (HA) in children in the Russian Federation and describes clinical and epidemiologic features of rare cases of severe course of the disease, as well as pathogenetic mechanisms of liver damage mediated by cell immune response. Objective. To identify clinical and epidemiologic features of the modern course of HA and its outcomes in children of Saint Petersburg within the period of 2018— 2023. Materials and methods. The study included 89 children diagnosed with HA, undergoing treatment at the Children's Research and Clinical Center for Infectious Diseases from 2018 to 2023. The analysis of disease progression in this group of patients was presented using clinical-anamnestic, epidemiologic, biochemical, virologic and instrumental data. Results. The analysis of infection sources showed a high frequency of HA infection within the family (44.9 ± 0.8%) and significantly less in childcare facilities and schools (7.9 ± 1.0%). The frequency of children with unidentified sources of infection remained high (47.2 ± 0.7%). One-third of all disease cases were imported from southern regions. Most hospitalized children had icteric HA (64.0 ± 0.6%) of moderate severity (79.8 ± 0.5%). Severe HA was observed in 6 patients (6.7 ± 1.0%). During the study, 17 patients (19.1 ± 0.9%) had a prolonged, complicated course of the disease, including ascites and aplastic anemia (12.6 ± 2.2%). Ascites was found in 4 patients with severe severity and in 5 patients with moderate severity of HA. Conclusions. Currently, there is an upward trend in the incidence of HA in the Russian Federation and Saint Petersburg, especially among schoolchildren (56.2%). A rather high frequency of severe (6.7%) and complicated forms (19.1%) of the disease is observed, and the growth of ascites and aplastic anemia cases in HA draws particular attention.

Damage Characteristics and Mechanical Properties of DD6 Single‐Crystal Alloy Based on Crystal Plasticity Theory under Uniaxial Tensile Conditions

Herein, the mechanical behavior and damage characteristics of DD6 nickel‐based single crystal alloy under different crystal orientation conditions are studied based on the theory of crystal plasticity coupled with damage constitutive equations using the crystal plasticity finite‐element method. The results indicate that the crystal plastic finite‐element model coupled with damage constitutive equations can well describe the entire deformation process from elasticity to damage. Under the reference orientation condition, the damage starts from the center position inside the test specimen and extends to the surrounding areas. The stress value in the damaged area decreases gradually from the periphery to the center of the test specimen, and an external stress reduction zone is formed. The crystal exhibits the best elasticity properties in the [0, 1, 1] orientation and the best plasticity properties in the [0, tan22.5°, 1] orientation. As the rotation angle of crystal orientation increases, the damage zones of X‐Z, Z‐Y, and X‐Y sections all exhibit clockwise rotation characteristics.