Mechanical Damage Research Articles

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.

Wear, Material Transfer, and Electrocautery Damage Are Ubiquitous on CoCrMo Femoral Knee Retrievals.

Despite high total knee arthroplasty (TKA) survivorship after 10 years (92%-99%), a gap persists where patient satisfaction lags clinical success. Additionally, while cobalt chrome molybdenum (CoCrMo) use decreases in primary total hip arthroplasty, the alloy continues to be widely used in TKA femoral components. Invivo, CoCrMo degradation may be associated with adverse local tissue reactions (ALTR) and compared with the hip, the damage mechanisms that may release metal in the knee and the potential biological effects remain poorly understood. In this study, we characterized the damage on 50 retrieved CoCrMo femoral knee implants paired with 19 titanium alloy and 31 CoCrMo tibial baseplates. We asked (1) what damage modes can release CoCrMo debris invivo from femoral components and (2) how frequently does the damage occur? First, we developed a semiquantitative scoring system for abrasive wear. Then, we characterized damage modes on CoCrMo femoral implants using digital optical microscopy (DOM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). We found that wear, electrocautery damage, and Ti-6Al-4V material transfer were ubiquitous. Of the 50 CoCrMo femoral implants we investigated, we documented wear on 100% (n = 50/50), electrocautery damage on 98% (n = 49/50), and Ti-6Al-4V material transfer to the posterior condyles on 95% (n = 18/19). Our results suggest that these damage modes may be more prevalent than previously thought and may act as metal release mechanisms invivo.

Damage regularity and multifractal analysis of sol-gel reflection coating of KDP crystal under low UV irradiation flux.

This study employed multifractal analysis to investigate the changes in surface morphology of SiO2 anti-reflective coatings prepared on KDP substrates using the sol-gel method, under various conditions of ultraviolet (UV) irradiance. The coatings were successfully fabricated, and the chemical structure of the SiO2 sol was comprehensively characterized using Solid-State Nuclear Magnetic Resonance (SSNMR) technology. Under low UV irradiance (4 J/cm2), repeated experiments revealed a crack-induced mechanism of surface fatigue damage. Utilizing Scanning Electron Microscopy (SEM), the study discovered the induction effect of initial crack defects in UV-damaged coatings and established a damage model. Furthermore, Atomic Force Microscopy (AFM) was used to acquire images of the coatings' surface morphology at different damage levels, which were analyzed using the multifractal spectrum f(α). This analysis confirmed the multifractal nature of the coatings both before and after damage. This study identified significant effects of UV irradiation on the width of the multifractal spectrum and Δf, indicating that the SiO2 anti-reflective coatings exhibit multifractal characteristics under various damage states. The coatings displayed a pattern of decreasing and then increasing singularity spectrum width, height distribution unevenness, and surface roughness with increasing damage. This study demonstrates that multifractal analysis is an effective tool for describing the complexity of the surface morphology of sol-gel-derived anti-reflective coatings for the first time and for validating their multifractal properties across different stages of UV damage. HIGHLIGHTS: Damage dynamic process of KDP crystal sol-gel coating was described by SEM&AFM; The crack propagation mechanism of sol-gel coating under UV radiation is proposed; The damage evolution of sol-gel coating was described by multifractal analysis.

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.

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.

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.

Creep-fatigue interactive behavior and damage mechanism of TP321 stainless steel under hybrid-controlled conditions

In this study, Hybrid-controlled creep-fatigue (HCCF) tests were conducted on TP321 austenitic stainless steel under a variety of test conditions. The effects of strain amplitude, holding time, holding stress and temperature on the creep-fatigue behavior of TP321 austenitic stainless steel were not only analyzed in detail but also revealed the creep-fatigue damage interactive mechanism. The results demonstrated that a rise in test temperature and load holding time markedly induced creep deformation, resulting in a notable reduction in failure life. Additionally, an increase in test temperature led to the cessation of the cyclic hardening phenomenon. Secondly, the analysis of fracture morphology and X-ray computed tomography (X-CT) scanning results demonstrated that the transgranular cracks expanded inwards and connected with the intergranular voids under creep-fatigue interaction, forming a mixed intergranular and transcrystalline fracture mode. The presence of large creep cavities impeded the propagation of fatigue cracks when creep damage was the dominant phenomenon. Subsequently, the damage evolution mechanism was elucidated through microstructural analysis, which revealed that the impact of the slip bands on the triangular grain boundaries and the precipitation of carbides facilitated the nucleation of voids and the internal formation of intergranular microcracks, thereby causing creep-fatigue damage interaction. Finally, the TP321 austenitic stainless steel creep-fatigue damage interactive mechanism diagram was proposed in conjunction with the fracture morphological characteristics and microstructure.

Assessment of Impact Resistance in Composite Sandwich Structures: An Experimental and Numerical Approach

Abstract: This paper presents an evaluation of the impact resistance of composite sandwich structures with regard to the type, design, and characteristics of impact in three parts. Structure consisting of lightweight core and reinforced face layers are widely used in all fields where high strength to weight ratios is desirable. It has established that carbon and glass fiber face sheets make quite different properties in impact absorption and structural resilience as foam or honeycomb cores. Both experimental and numerical formulations offer valuable results with few limitations toward the analysis of damage mechanisms within composite materials. A few suggestions for future work are related to further investigations of the constituent materials, improvements in numerical simulations, and the creation of purpose-oriented design recommendations for broader utilization of these structures in critical-end use applications

Improving shelf life and quality of guava fruit using an edible coating containing xanthan and pomegranate seed oil

ABSTRACT Guava, a tropical fruit, has a short shelf life due to its rapid ripening and susceptibility to various factors like water loss, mechanical damage, and cold storage. This study aimed to address this issue by using an edible coating containing xanthan and enriched with pomegranate seed oil to preserve guava fruit quality over 21 days at 5 ± 1°C and 85%-95% relative humidity, and a 5-day shelf life. The treatments significantly reduced fruit weight loss, with the oil treatment showing the least weight loss (2.18%). While the respiration rate increased during storage, the treated fruits exhibited a lower respiration intensity. Notably, treatments with oil and xanthan maintained greater firmness than that of the control. The antioxidant capacities of the treated fruits were significantly higher, with xanthan showing the highest value (96.8%). In contrast, the control group had a significantly higher total soluble solids (TSS)/titratable acidity (TA) ratio of 113.5. Principal Component Analysis (PCA) indicated that after 21 d, the control had high values of F1, associated with high TSS, respiration rate, weight loss, and TSS/TA. These findings suggest that pomegranate seed oil alone or Xan 0.2% + pomegranate seed oil effectively improve the shelf life and quality of guava fruit.

Damage Evolution and NOx Photocatalytic Degradation Performance of Nano-TiO2 Concrete Under Freeze–Thaw Cycles

The internal pore structure of nano-TiO2 concrete deteriorates gradually during freeze–thaw (F–T) cycles. The deterioration process can reveal the F–T damage mechanism and the deterioration law of photocatalytic performance. The evolution law of the pore structure of nano-TiO2 concrete during F–T damage was investigated. Moreover, this paper defined the microscopic F–T damage factor based on porosity and fractal dimension. The results showed that a 2% dosage of nano–TiO2 concrete had better frost resistance and lower porosity in this experiment. Its porosity only increased by 13.3% after 200 F–T cycles, which was much smaller than that of ordinary concrete. Furthermore, the presence of nano-TiO2 enhanced the volume fractal dimension of concrete pores larger than 100 nm, increasing the complexity of the pore structure and contributing to improved frost resistance. F–T damage led to a decrease in the photocatalytic performance of nano–TiO2 concrete. Still, it helped the nitrate on the surface of the concrete to dissolve and disappear more quickly under rainwater washout. Finally, a thermodynamic theory-based concrete F–T damage correction model was constructed, and the model was used to predict F–T damage values for some scholars. The results showed that the correlation between the model values and the experimental values was more than 0.95, which could accurately reflect the degree of F–T damage of concrete. In addition, a prediction model of photocatalytic NO reduction by nano-TiO2 concrete based on microscopic damage factor was established. It provides a theoretical basis for the application of nano-TiO2 concrete in the field of gas pollutant treatment.

Study on mechanical properties of large deformation segmental cement-based honeycomb structure

Honeycomb structures provide a new means of controlling and supporting the tunnel envelope. However, traditional honeycomb structures have low strength and poor stability, and are prone to stress concentration and instability, further limiting their application in deep tunnel support projects. In this paper, a new type of segmental cementitious honeycomb structure is investigated, its performance under different loading rates is tested, and its application in deep large deformation tunnel support is discussed. Firstly, the honeycomb model was drawn and the honeycomb skeleton was prepared. Then, the cement suspension technique was optimised. Secondly, the effects of different loading rates on the performance of segmented cement-bonded honeycomb structures were investigated by laboratory experiments. The results show that when the loading rate is 3 mm/min, the structure has the maximum load capacity and the best energy absorption performance. It is worth noting that too fast or too slow loading rate will affect the performance of the structure. Finally, the damage mechanism of the segmented honeycomb structure was further investigated by using an acoustic emission system, and the acoustic emission characteristics showed that the segmented cementitious honeycomb structure firstly went through a relatively stable stage of microcrack development under the action of the loads in all bands, and then a large area of damage was observed in the top layer of the honeycomb skeleton when the peak load was reached, resulting in the collapse of the whole layer of the honeycomb structure, which led to the collapse of the whole layer of the honeycomb skeleton. This led to the collapse of the whole layer of the honeycomb structure and a significant decrease in the bearing capacity, which confirmed the layer-by-layer damage characteristics of segmental cementitious honeycomb structures. In addition, the RA-AF values show that the loading rate has little effect on the crack type, which is almost unchanged with the increase of loading rate. These studies verify the feasibility of using honeycomb structure to support roadway with fast deformation speed and large deformation. It is of great significance to guide the application of honeycomb structure in deep roadway support engineering.

Ultrasound evaluation of superficial lesions caused by ectoparasites in children.

Ectoparasites affect the skin, causing different clinical manifestations through direct mechanical damage, blood consumption, pathogen transmission, hypersensitivity reactions, or toxin inoculation. Dermatological ultrasound is the imaging modality of choice to evaluate these superficial lesions, detecting submillimetric alterations in a non-invasive and innocuous way. This review helps the radiologist describe the imaging findings of lesions caused by mosquitoes, myiasis, bees, spiders, and scorpions, with suggestive ultrasound patterns.

Semiconductor Laser Packaging Technology: Thermal Management, Optical Performance Enhancement and Reliability Studies

This review article presents a comprehensive and in-depth discussion of thermal management, optical performance enhancement, and reliability issues in semiconductor laser packaging technology. By synthesising existing literature and research results, the article presents a systematic summary of the research progress and practical applications of semiconductor laser packaging technology in these key areas. In the section on thermal management, the article reviews different heat sink technologies, packaging structures, and solid crystal materials with the aim of improving the thermal stability and long-term reliability of semiconductor la ser devices. In the section on optical performance enhancement, the article outlines beam shaping techniques and packaging technologies. It also addresses reliability issues in packaging, discussing optical mirror damage as well as stress and mechanical damage. The aim of this review is to provide assistance for the further development and application of semiconductor laser packaging technology, with the objective of promoting the rapid and healthy development of the laser industry.

Bridging Electrolyte Bulk and Interfacial Chemistry: Dynamic Protective Strategy Enable Ultra‐Long Lifespan Aqueous Zinc Batteries

The main bottleneck of rechargeable aqueous zinc batteries (AZBs) is their limited cycle lifespans stemming from the unhealthy electrolyte bulk and fragile interface, especially in the absence of dynamic protection mechanism between them. To overcome this limitation, benefitting from their synergistic physical and chemical properties, chitin nanocrystals (ChNCs) are employed as superior colloid electrolyte to bridge electrolyte bulk and interfacial chemistry for ultra‐long lifespan AZBs. This unique strategy not only enables continuous optimization of the electrolyte bulk and interfacial chemistry within the battery but also facilitates self‐repairing of mechanical damage both internally and externally, thereby achieving comprehensive, persistent, and dynamic protection. As a result, the modified Zinc (Zn) symmetric cells present high Zn plating/stripping coulombic efficiencies of 97.71% ~ 99.81% from 5 to 100 mA cm‐2, and remarkably service lifespan up to 8,200 h (more than 11 months). Additionally, the Zn//MnO2 full cell exhibits a high capacity retention of 70.1% after 3,000 cycles at 5 A g‐1. This dynamic protective strategy to challenge aqueous Zn chemistry may open up a new avenue for building better AZBs and beyond.

Bridging Electrolyte Bulk and Interfacial Chemistry: Dynamic Protective Strategy Enable Ultra-Long Lifespan Aqueous Zinc Batteries.

The main bottleneck of rechargeable aqueous zinc batteries (AZBs) is their limited cycle lifespans stemming from the unhealthy electrolyte bulk and fragile interface, especially in the absence of dynamic protection mechanism between them. To overcome this limitation, benefitting from their synergistic physical and chemical properties, chitin nanocrystals (ChNCs) are employed as superior colloid electrolyte to bridge electrolyte bulk and interfacial chemistry for ultra-long lifespan AZBs. This unique strategy not only enables continuous optimization of the electrolyte bulk and interfacial chemistry within the battery but also facilitates self-repairing of mechanical damage both internally and externally, thereby achieving comprehensive, persistent, and dynamic protection. As a result, the modified Zinc (Zn) symmetric cells present high Zn plating/stripping coulombic efficiencies of 97.71% ~ 99.81% from 5 to 100 mA cm-2, and remarkably service lifespan up to 8,200 h (more than 11 months). Additionally, the Zn//MnO2 full cell exhibits a high capacity retention of 70.1% after 3,000 cycles at 5 A g-1. This dynamic protective strategy to challenge aqueous Zn chemistry may open up a new avenue for building better AZBs and beyond.

Clues to transcription/replication collision-induced DNA damage: it was RNAP, in the chromosome, with the fork.

DNA replication and RNA transcription processes compete for the same DNA template and, thus, frequently collide. These transcription-replication collisions are thought to lead to genomic instability, which places a selective pressure on organisms to avoid them. Here, we review the predisposing causes, molecular mechanisms, and downstream consequences of transcription-replication collisions (TRCs) with a strong emphasis on prokaryotic model systems, before contrasting prokaryotic findings with cases in eukaryotic systems. Current research points to genomic structure as the primary determinant of steady-state TRC levels and RNA polymerase regulation as the primary inducer of excess TRCs. We review the proposed mechanisms of TRC-induced DNA damage, attempting to clarify their mechanistic requirements. Finally, we discuss what drives genomes to select against TRCs.

Mechanical properties and damage characterization of cracked granite after cyclic temperature action

Due to the unique geographical environment of the plateau, large-scale damage and destruction of fractured surrounding rock often occur during geotechnical engineering construction as a result of high-temperature cycles. Therefore, this study aims to investigate the mechanical properties and damage characteristics of fractured granite under the influence of cyclic temperature, uniaxial compression tests were conducted on granite specimens with pre-existing fractures at cyclic temperatures of 30 °C, 50 °C, 70 °C, 100 °C, and 130 °C. The study integrated analyses of characteristic stress, acoustic emission parameters, damage variables, fractal dimensions, and SEM to explore the mechanical properties and damage features of granite. The results indicated that at a 45° fracture inclination and a temperature of 70 °C, granite exhibited a distinct turning point in mechanical properties and damage characteristics. At the same cyclic temperature, granite with a 45° pre-existing fracture showed significant decreases in peak stress, elastic modulus, and σci/σm ratios, with the AE b-value drop point noticeably earlier, and both cumulative AE ring count and total energy reduced. The damage variable quickly reached its maximum, and the development of internal microcracks in the specimen is highly orderly. At the same fracture inclination, peak stress, elastic modulus, and σci/σm slightly increased at 70 °C, while AE ring counts and total energy were lower, indicating the degree of internal thermal damage in the specimen has significantly decreased, and the development of internal microcracks in the specimen has shown a marked reduction in orderliness. These findings provide theoretical insight into the meso-damage and failure mechanisms of granite influenced by different cyclic temperatures and fracture inclinations.

Study on Acoustic Emission Characteristics and Damage Mechanism of Wind Turbine Blade Main Spar with Different Defects

This paper aimed to understand the AE signal characteristics and damage mechanism of wind turbine blade main spar materials with different defects during the damage evolution process. According to the typical delamination and wrinkle defects in wind turbine blades, the GFRP composite with defects is artificially prefabricated. Through acoustic emission experiments, the mechanical properties and acoustic emission characteristic trends of wind turbine blade main spar composites with different defects under tensile loading conditions were analyzed, and the damage evolution mechanism of different defects was explained according to the microscopic results. The results show that the existence of artificial defects will not only affect the mechanical properties of composite materials but also affect the damage evolution process of the materials. The size and location of delamination defects and the different aspect ratio of the wrinkle defects have a certain influence on the damage mechanism of the material. K-means cluster analysis of AE parameters identified the damage models of GFRP composites. The types of damage modes of delamination defects and wrinkle defects are the same, and the range of characteristic frequency is roughly the same. This study has important reference significance for structural damage monitoring and damage evolution research of wind turbine blade composites.