Underlying Damage Mechanisms Research Articles

A composite laser ablation diagnosis method based on multiple spectroscopic and imaging analyses

This study proposes a novel diagnostic approach for target ablation to comprehensively elucidate the physical mechanisms of laser ablation in aluminium alloys and stainless steel, precisely measure sample temperatures, and predict the ablation state. The method utilizes a spatially weighted emissivity model in conjunction with multispectral thermometry techniques to analyze spatial variations in temperature and emissivity distributions, facilitating the evaluation of target ablation status. Through a series of experiments, temperature data obtained using an enhanced weighted radiative spectral inversion technique were compared with temperatures recorded by thermal imaging cameras, confirming the effectiveness and accuracy of the weighted radiative spectral inversion method in multispectral thermometry. Additionally, a detailed examination of laser ablation in aluminium alloys and stainless steel was conducted to elucidate the underlying damage mechanisms. This refined approach establishes a solid groundwork for further investigation into the characteristics and dynamic Evolution of laser-damaged regions.

Extending the understanding of Shannon’s safe stimulation limit for platinum electrodes: biphasic charge-balanced pulse trains in unbuffered saline at pH = 1 to pH = 12

Objective.In neural electrical stimulation, safe stimulation guidelines are essential to deliver efficient treatment while avoiding neural damage and electrode degradation. The widely used Shannon's limit,k, gives conditions on the stimulation parameters to avoid neural damage, however, underlying damage mechanisms are not fully understood. Moreover, the translation from bench testing toin vivoexperiments still presents some challenges, including the increased polarisation observed, which may influence charge-injection mechanisms. In this work, we studied the influence on damage mechanisms of two electrolyte parameters that are differentin vivocompared to usual bench tests: solution pH and electrolyte gelation.Approach.The potential of a platinum macroelectrode was monitored in a three-electrode setup during current-controlled biphasic charge-balanced cathodic-first pulse trains. Maximum anodic and cathodic potential excursions during pulse trains were projected on cyclic voltammograms to infer possible electrochemical reactions.Main results.In unbuffered saline of pH ranging from 1 to 12, the maximum anodic potential was systematically located in the oxide formation region, while the cathodic potential was located the molecular oxygen and oxide reduction region whenkapproached Shannon's damage limit, independent of solution pH. The results support the hypothesis that Shannon's limit corresponds to the beginning of platinum dissolution following repeated cycles of platinum oxidation and reduction, for which the cathodic excursion is a key tipping point. Despite similar potential excursions between solution and gel electrolytes, we found a joint influence of pH and gelation on the cathodic potential alone, while we observed no effect on the anodic potential. We hypothesise that gelation creates a positive feedback loop exacerbating the effects of pH ; however, the extent of that influence needs to be examined further.Significance.This work supports the hypothesis of charge injection mechanisms associated with stimulation-induced damage at platinum electrodes. The validity of a major hypothesis explaining stimulation-induced damage was tested and supported on a range of electrolytes representing potential electrode environments, calling for further characterisation of platinum dissolution during electrical stimulation in various testing conditions.

Study on the effect of rubber content on the frost resistance of steel fiber reinforced rubber concrete

In cold areas, the steel fiber reinforced rubber concrete (SFRRC) pavement is exposed to natural environment and experiences varying degrees of damage from freezing and thawing. This can have a serious impact on the normal usage and safe operation of the pavement structure. This research examines the impact of varying rubber concentrations on multiple variables, such as the rate of mass reduction, relative dynamic modulus of elasticity, compressive strength, and thickness of the damage layer (Hf) during freeze–thaw (F-T) durability testing conducted on SFRRC. Furthermore, an analysis is conducted to determine the degradation pattern exhibited by SFRRC. The internal structure evolution and pore structure characteristics of SFRRC were examined using scanning electron microscopy and mercury intrusion porosimetry techniques, which revealed the underlying damage mechanism in SFRRC during F-T cycles. The results suggest that the addition of an appropriate amount of rubber can effectively enhance the frost resistance of SFRRC in water. A gradual improvement in the frost resistance of SFRRC is observed when increasing the rubber content from 0 to 10%. The optimal frost resistance is observed in SFRRC with 10% rubber content. However, when the rubber content reaches 15%, SFRRC exhibits significant degradation and lower level of resistance to freezing compared to SFRRC without rubber. Microcracks form within SFRRC due to the freezing–thawing forces experienced during the experiment, resulting in the development of a damage layer that extends from the surface to the interior. The compressive strength of the damaged layer significantly decreases as Hf increases. The addition of appropriate rubber in SFRRC improves its pore structure, leading to an increased proportion of harmless or less harmful pores and a reduction in average pore size, thereby significantly enhancing its frost resistance.

Effects of aircraft operating fluids and environmental thermal fatigue on fly ash and steel slag based cementitious composites

This paper investigates the performance of concrete incorporating high-volume fly ash (HVFA) and steel slag aggregates against the detrimental effects of combined cycles of environmental thermal fatigue and exposure to leaked aircraft fluids. A total of 128 cubes and 90 prisms were cast for five mixes and exposed to 60, 120, 180, 240 and 300 combined cycles. The results demonstrate the positive effect of utilization of HVFA which reduces the total amount of portlandite available in the system. The SS aggregates demonstrate a strong interlocking with the surrounding matrix and supply the necessary portlandite for continued pozzolanic reaction. However, their reaction with aircraft fluids causes significant degradation to flexural strength initially, which is redeemed by pozzolanic reaction at a later stage. Hybrid basalt and polypropylene fibres were successful in enhancing the flexural strength and reducing the cracking. The mercury intrusion porosimetry revealed a reduction in pore volume because of HVFA. Scanning electron microscopy and differential scanning calorimetry were also employed to uncover the underlying mechanisms of damage and assess the performance of the cementitious composite.

Nerolidol rescues hippocampal injury of diabetic rats through inhibiting NLRP3 inflammasome and regulation of MAPK/AKT pathway.

Despite the observation of diabetes-induced brain tissue damage and impaired learning and memory, the underlying mechanism of damage remains elusive, and effective, targeted therapeutics are lacking. Notably, the NLRP3 inflammasome is highly expressed in the hippocampus of diabetic individuals. Nerolidol, a naturally occurring compound with anti-inflammatory and antioxidant properties, has been identified as a potential therapeutic option for metabolic disorders. However, the ameliorative capacity of nerolidol on diabetic hippocampal injury and its underlying mechanism remain unclear. Network pharmacology and molecular docking was used to predict the signaling pathways and therapeutic targets of nerolidol for the treatment of diabetes. Then established a diabetic rat model using streptozotocin (STZ) combined with a high-fat diet and nerolidol was administered. Morris water maze to assess spatial learning memory capacity. Hematoxylin and eosin and Nissl staining was used to detect neuronal damage in the diabetic hippocampus. Transmission electron microscopy was used to detect the extent of damage to mitochondria, endoplasmic reticulum (ER) and synapses. Immunofluorescence was used to detect GFAP, IBA1, and NLRP3 expression in the hippocampus. Western blot was used to detect apoptosis (Bcl-2, BAX, and Cleaved-Caspase-3); synapses (postsynaptic densifying protein 95, SYN1, and Synaptophysin); mitochondria (DRP1, OPA1, MFN1, and MFN2); ER (GRP78, ATF6, CHOP, and caspase-12); NLRP3 inflammasome (NLRP3, ASC, and caspase-1); inflammatory cytokines (IL-18, IL-1β, and TNF-α); AKT (P-AKT); and mitogen-activated protein kinase (MAPK) pathway (P-ERK, P-p38, and P-JNK) related protein expression. Network pharmacology showed that nerolidol's possible mechanisms for treating diabetes are the MAPK/AKT pathway and anti-inflammatory effects. Animal experiments demonstrated that nerolidol could improve blood glucose, blood lipids, and hippocampal neuronal damage in diabetic rats. Furthermore, nerolidol could improve synaptic, mitochondrial, and ER damage in the hippocampal ultrastructure of diabetic rats by potentially affecting synaptic, mitochondrial, and ER-related proteins. Further studies revealed that nerolidol decreased neuroinflammation, NLRP3 and inflammatory factor expression in hippocampal tissue while also decreasing MAPK pathway expression and enhancing AKT pathway expression. However, nerolidol improves hippocampal damage in diabetic rats cannot be shown to improve cognitive function. In conclusion, our study reveals for the first time that nerolidol can ameliorate hippocampal damage, neuroinflammation, synaptic, ER, and mitochondrial damage in diabetic rats. Furthermore, we suggest that nerolidol may inhibit NLRP3 inflammasome and affected the expression of MAPK and AKT. These findings provide a new experimental basis for the use of nerolidol to ameliorate diabetes-induced brain tissue damage and the associated disease.

Investigation of damage mechanisms in thermomechanical fatigue of nickel-based single-crystal alloys

Thermomechanical fatigue (TMF) is essential for ensuring the safety and efficiency of various thermal engineering systems, however, the underlying damage mechanisms remain unclear. In the present work, a damage evolution model is used to quantify damage mechanisms in nickel-based single-crystal superalloy DD6. The isothermal creep-fatigue model combining the fatigue and creep damages is developed to elucidate their interactions and validated by the tension-dwelling experiments. Finally, the experimentally measured TMF damage is quantitatively decomposed into fatigue, creep and extra TMF components. Significant TMF damage in the in-phase TMF is identified, especially in the [001] specimens, potentially attributed to the non-isothermal creep or oxidation, while damage in out-of-phase TMF aligns with the spiking oxidation mechanism.

Damage mechanisms of spline teeth of friction plates under non-uniform impact

The fatigue fracture failure of friction plates seriously affects the safety of high-power density transmission systems due to the non-uniform impact with the inner hub. However, the crack initiation inducement and underlying damage mechanisms are still confused so far, which has critical significance for improving the service life. To address this problem, the matrix metallographic structure of friction plates was observed by Scanning Electron Microscope (SEM), which excludes internal defects within the organization. Then, an impact dynamic model was established to investigate the collision laws between spline teeth and the inner hub. The effect of the inner hub’s speed fluctuations on the impact force and acceleration was analyzed, and an analytical relationship between tooth root stress, impact force, and gear parameters was established. A large module simulation prototype test rig was designed based on the proposed equivalent model to verify the impact dynamic model. Results show that the majority of collisions between spline teeth and the inner hub are “catch-up collisions”, which well explains the non-uniform impact phenomenon. The “frontal collisions” will only occur when the speed of the inner hub is lower than that of the friction plate. The higher cumulative frequency of tensile stress on the pull side of spline teeth roots by “catch-up collisions” reveals the underlying mechanism for the differential extent of cracks’ damage. The minimum bending stress of the teeth root is 125.5 MPa at a pressure angle of 32°, which shows a linear increase with tooth clearance. The fatigue fracture of friction plates has been effectively suppressed after structural optimization.

Influence of the load frequency and moisture content on fatigue deterioration of high‐strength concrete

AbstractWith the expansion of offshore wind energy systems, the number of fatigue‐loaded concrete structures exposed to high moisture contents has significantly increased in the last decades. Investigations in the literature show a strong reduction of fatigue resistance with increasing moisture content of the concrete. However, a detailed quantified understanding of the influence of the moisture content and the underlying damage mechanisms is still lacking. In a conjoint project as part of the priority program SPP 2020 funded by the German Research Foundation (DFG), the water‐induced fatigue damage are investigated. In this paper, the results of compressive fatigue testes on high‐strength specimens with different moisture contents are presented. The cyclical loading was carried out at three different load frequencies and maximum stress levels, respectively. The results show that the damaging effect due to fatigue loading at high moisture content is more pronounced with decreasing stress levels and decreasing frequencies. Considering the strain development and acoustic emissions the results indicate that different damage mechanisms are acting with increasing moisture content of concrete. These mechanisms are elaborated in this paper.

Characterization and Separation of Damage Mechanisms of Extruded Case-Hardening Steel AISI 5115 under Cyclic Axial-Torsional Loading

Due to the emerging relevance of topics such as climate change or scarcity of resources, the requirements for energy efficiency, emissions and resource conservation are increasing. In this context, components manufactured by metal forming offer a high potential for lightweight construction, cost effectiveness and resource efficiency. The defects resulting from forming processes e.g. in form of micropores and their growth are currently not taken into account. A commercial design is usually based on mechanical material properties and additional safety factors. The knowledge of the ductile forming-induced damage in the component design enables an improved design. In this study, the influence of different forming process parameters during full forward rod extrusion on the structural damage and the fatigue properties were investigated for the case-hardened steel AISI 5115 (16MnCrS5, 1.7131). The intention was to compare the fatigue properties of different damage states under cyclic axial and axial-torsional loading including the identification and separation of underlying damage mechanisms. A significant effect of superimposed cyclic torsional loading on cyclic axial properties and mechanisms was found, which was associated with a decrease of 38 % in the lifetime. Axial-torsional fatigue tests were conducted at various test temperatures to determine the effect of forming-induced damage and test temperature on the fatigue strength. In addition, differences in microstructure as a result of forming-induced and fatigue-induced damages were validated by using scanning electron microscopy.

The anisotropy of fracture toughness of an α+β titanium alloy by β forging

This study aims to investigate the anisotropic fracture toughness of an α+β titanium alloy processed by β forging. A typical basket-weave microstructure is observed, including the primary α (αp) phase, micron-scaled secondary α (αs) phase and residual β phase. The tensile test results show that the anisotropic strength results from the fine grain strengthening as well as the texture strengthening, and the plasticity difference is determined by the normal stress acting on the main crack in the fracture process. The orientation of the specimen also has a significant impact on fracture toughness. The corresponding toughening models of underlying damage mechanism with different orientations are proposed and discussed. It is found that the internal toughening mechanism is dominant, and external toughening mechanism also plays an important role in fracture toughness, including delamination and crack deflection caused by elongated β grains arrangement. Finally, the differences of J-integral resistance curves with different orientations are investigated in detail. The strength and fracture toughness values, KJIC (crack-initiation toughness) and KSS (growth toughness), are both highest when loading along radial direction (RD), and the positive effects of β grain morphology and two-phase texture on anisotropy of KJIC are summarized.

Durability of GFRP and BFRP reinforcing bars in simulated seawater sea sand calcium sulfoaluminate cement concrete pore solution

Thanks to the much smaller carbon footprint of calcium sulfoaluminate cement (SAC) concrete and the corrosion resistance of fiber reinforced polymer (FRP) reinforcement, FRP-reinforced SAC concrete can possibly replace conventional reinforced concrete in some cases. In this study, for the first time, the durability of glass FRP (GFRP) and basalt FRP (BFRP) bars, made with epoxy resin, is investigated in simulated pore solutions of concretes made with (a) SAC and fresh water, (b) SAC and seawater and sea sand. The bars were immersed in each solution and kept at constant temperature of 30 °C, 45 °C and 60 °C for up to 180 days. Bar samples were tested for their retained tensile strength and physiochemical degradation after 30, 60, 90, and 180 days of immersion. Scanning electron microscopy (SEM), X-ray dispersive spectroscopy (EDS), and Fourier transform infrared (FTIR) spectroscopy were used to identify the underlying damage mechanisms. Results show that solution (b) is less harmful to BFRP than solution (a), while the opposite is true in the case of GFRP. Both solutions caused the dissolution of the epoxy resin and the leaching of the Fe in the basalt fiber. Overall, GFRP exhibited higher durability than BFRP. Based on image analysis, the deteriorated zone within the bar cross-section is not a uniform ring, but its area correlates with the loss of tensile strength. Inspired by the Avrami-Erofe'ev Equation and the Eyring's Transition State Theory, a novel time-temperature-dependent FRP bar degradation model is proposed. The proposed model shows close agreement between the predicted and measured tensile strengths.

Comparative study on the water droplet erosion behavior between stretched and casted aeronautical PMMA

Rain droplet erosion is a potential threat in aviation, especially for forward-facing components such as windshields of aircraft. To comprehend and mitigate such hazards, a comparative study was conducted on two kinds of commonly used aeronautical PMMA materials: casted and biaxially stretched. The study aimed to investigate the water droplet erosion (WDE) behavior and the underlying damage mechanism. A modified pulsed water jet erosion facility was constructed to mimic the impact of successive water droplets. The influence of impact velocity on the WDE behavior was explored and quantitative evaluations of volume loss, surface entrance area, and erosion depth were conducted. Results revealed that the increase in impact velocity leads to faster damage initiation and a larger erosion rate. Compared with the stretched sample, the casted sample exhibits higher erosion resistance. The stretched sample exhibits a funnel-shaped cavity with a flat bottom, while the casted sample shows a tapered crater with shallow depth. The cavity shape can influence the subsequent flow fields and stress distribution, thereby affecting the development of erosion entrance and depth. Microscopic analysis of the erosion cavities revealed different damage mechanisms at each stage of erosion. The stretched sample exhibited exfoliation of fine flakes and denudation of large pieces due to stress waves and lateral jet-induced shear, whereas hydraulic penetration had a more pronounced effect on the casted sample. The cushioning effect of the water film was also studied, noting a gradual reduction in its effectiveness with increasing impact velocity.

Study on rheological properties and damage mechanism of asphalt under acid-alkali precipitation corrosion

This research delved into the effects of pH precipitation on asphalt's rheological characteristics and damage mechanisms. We analyzed the shifts in asphalt's acid-alkali corrosion properties through macro and micro tests. To begin with, we conducted three cycles of bitumen corrosion tests using acidic, alkaline, and neutral solutions. Subsequently, the dynamic shear rheological test (DSR) measured the complex shear modulus, phase angle, and rutting factor before and after asphalt corrosion, revealing correlations between corrosion duration, temperature, and asphalt's rheological traits. Additionally, we evaluated post-corrosion changes in asphalt's functional groups through infrared spectrum testing, allowing us to deduce the underlying damage mechanism. Our results showed that asphalt's deformation resistance was directly related to soaking time and inversely related to temperature. The complex shear modulus exhibited an inverse relationship with temperature, while the phase angle demonstrated a direct proportionality to temperature variations. From a chemical perspective, acidic components within asphalt tend to dissolve and ionize, while alkaline substances undergo esterification and neutralization. Notably, asphalt modified with styrene–butadiene–styrene (SBS) exhibits enhanced resistance against acid and alkali corrosion, surpassing the performance of the 90# asphalt. Ultimately, this research established a theoretical framework for exploring acid-base precipitation resistance in asphalt binders, contributing to our understanding of asphalt's binder properties and broadening its applications.

Damage mechanisms and analytical model of CFRP laminate under low-velocity normal and oblique impacts

The present work investigates the energy absorption performance of carbon fibre-reinforced polymer (CFRP) laminates subjected to low-velocity normal and oblique impacts. Experimental tests are conducted on laminates exposed to varying impact energies at both normal and oblique angles. The numerical model is developed to simulate the dynamic response of the CFRP. The research employs a combination of experimental and numerical methods to reveal the underlying damage mechanisms. The changes observed in the oblique impact response are explained through an analysis of the damage mechanisms. Analytical models for each energy absorption mechanism are proposed based on the principles of energy conservation and the theory of large bending deformation of anisotropic materials. The energy absorption performance of the laminates under oblique impacts, considering rebound and penetration conditions, is discussed. It is found that the delamination is the primary energy absorption mechanism of CFRP laminate under rebound conditions, while elastic deformation of fibres is the primary energy absorption mechanism under penetration conditions. Furthermore, the energy absorption performance of the laminate is found to be affected by the peak force and effective thickness of the plate, which change with the oblique angle. This paper makes a significant contribution by utilising experimental, numerical, and theoretical approaches to gain insights into the damage mechanisms of laminates subjected to oblique impacts.

A unified stochastic damage model for concrete under monotonic and fatigue loading

This study proposes a unified concrete damage model that can be applied to both monotonic and fatigue loading scenarios. The proposed model adopts the framework of stochastic damage mechanics and considers the micro-spring in the micro-meso stochastic fracture model (MMSF) as an energy dissipation element. To describe the multiscale energy dissipation process of the micro-spring, the rate process theory and a crack hierarchy model are employed. It is found that the energy dissipation threshold is linked to the elastic strain energy of the micro-spring, and the derived fracture strain of the micro-spring in MMSF enables the proposed model to describe the damage evolution laws for both monotonic loading and fatigue loading. The underlying damage mechanisms associated with the two loading processes are analyzed in detail. Additionally, the energy dissipation analysis enables the definition of the corresponding micro-damage to the micro-spring, which leads to the demonstration of the nonlinear properties of the micro-spring's constitutive law. Finally, several numerical examples are presented to validate the model.

Quasi-Static and Dynamic Tensile Behavior of Water-Bearing Sandstone Subjected to Microwave Irradiation

Microwave irradiation on rocks before excavation is an effective method to reduce equipment wear and energy consumption during mechanical cutting. Rock mass excavation is usually carried out in a water-rich environment and exposed to dynamic loads, thus understanding the coupled effects of water content and loading rate on the mechanical behavior of rocks under microwave radiation is essential. In this study, sandstone samples with five levels of water content (from oven-dried to water-saturated) were exposed to microwave irradiation at a power of 700 W for 10 min. Brazilian disc tests were conducted on sandstone samples after microwave radiation under both quasi-static and dynamic loading conditions. Test results revealed that, with the increase of the initial water content, the microwave heating capacity of the rock is significantly improved. The surface temperature of the saturated samples is approximately 1.38 times higher than that of the dry ones. Moreover, weight, P-wave velocity, quasi-static and dynamic tensile strength of the rock decrease, while porosity and damage factor exhibit a similar growth law. Before microwave irradiation, the average value of the P-wave velocity and the quasi-static tensile strength of sandstone were about 2521.3 m·s−1 and 4.65 MPa. However, after microwave treatment, when the initial water content was 2%, 3%, 4% and 5.4%, the P-wave velocity decreased by 6.1%, 9.8%, 16.4% and 30.2%, while that quasi-static tensile strength reduced by 9.2%, 16.7%, 30.6% and 48.9%, respectively. For water-saturated samples under microwave irradiation, the porosity increases from 13.02% to 18.12% (showing an increase of 39.2%), and the damage value rises to 0.51. In addition, the dynamic tensile strength shows a significant loading rate dependence, and as the initial water content increases, also the dynamic increase factor (DIF) increases. At a given loading rate, the energy dissipation decreases with the increase of the initial water content, which indicates that the presence of water cause more significant damage to the rock when subjected to microwave radiation. Scanning electron microscopy (SEM) results indicate that the internal damage of the rock after microwave radiation is dominated by intergranular cracks, and crack density increases with increasing initial water content of the samples. The underlying damage mechanisms of microwave radiation on water-bearing sandstone were interpreted with the theory of pore water pressure and structural thermal stresses.

Photobiochemical mechanisms of biomolecules relevant to germicidal ultraviolet irradiation at 222 and 254 nm

To inactivate viruses and microorganisms, ultraviolet light in the short wavelength region is a promising candidate for mitigating the infection of disease. Germicidal mercury lamps emitting at 254 nm and KrCl excimer lamps emitting at 222 nm have sterilisation properties. In this work, wavelength dependence of the photobiochemical mechanisms was investigated with 222- and 254-nm irradiation to analyze the underlying damage mechanisms of DNA/RNA and proteins, using Escherichia coli, a protease, an oligopeptide, amino acids, plasmid DNA and nucleosides. The photorepair of damaged DNA and the “dark” reversion of the hydrates of uracil phosphoramidite coupling blocks were also investigated.

Mixed mode fracture of geometrically similar FRUHPC notched beams with the localizing gradient damage model

A localizing gradient damage model is proposed in this paper to capture the mechanisms underlying the fracture of fiber reinforced ultra-high performance concrete (FRUHPC): (i) an initially expanding damage process zone due to the formation of numerous fine cracks, each widening up slowly due to the fiber bridging effect; (ii) a gradual formation of a localized macroscopic crack, when at least one of the fine cracks has opened up sufficiently to trigger a fiber pull-out process. Restricting to tensile-shear dominated failures in monotonic loadings, the simplest form of damage model is adopted, where an isotropic damage variable is driven by a strain-like variable. The performance of the proposed localizing gradient damage model is first demonstrated by comparing the damage evolution process against the corresponding intensity of acoustic emission (AE) events obtained experimentally, for a notched FRUHPC beam in three-point bending. It was shown that the model is able to reproduce the slightly widening fracture process zone (FPZ) during strain hardening, as well as the eventual localized damage process zone during strain softening. Specifically, during strain hardening, the proposed localizing gradient damage model predicts an energy dissipation bandwidth that compares well with the AE energy maps, together with a consistent propagation of crack front. With a correct description of the underlying damage mechanisms, the predictive capability of the proposed model is next demonstrated through the mixed mode fracture of a series of geometrically similar FRUHPC notched beams. Since the specimens are of the same casting batch as those in the three-point bending test, the numerical material parameters calibrated earlier are adopted directly for the mixed mode fracture tests. Without any further undue calibrations, the localizing gradient damage model is shown to predict well the structure responses and size effect of the series of geometrically similar FRUHPC notched beams in mixed mode fracture.

Effect of shock-flame interactions on initial damage characteristics in highway tunnel under hazmat tanker truck accident

Hazardous materials road transportation (HMRT) accidents are the main hazards of highway tunnels, and the damage evolution process subject to catastrophic consequences have gained significance due to increasing accidental events. This study presents the scene reconstruction referenced with actual case of methanol tanker truck explosion in highway tunnel and integrates it with effecting parameters such as location, causation, consequence, time series data, tunnel structure, hazmat properties, emergency. In this work, the damage characteristics caused by tanker truck explosion are discussed by comparing with different traffic situations inside the highway tunnel. The results indicate the strength of shock wave is enhanced as the traffic flow grows, especially in the ceiling and ground of tunnel, the peak overpressures are significantly higher than that in other areas. With the increasing of the traffic vehicles in tunnel, the process of the explosion overpressure changing in tunnel can be categorized in five stages. This study presents the predictive model relating with explosion specific impulse, which can be better presented in impulse changes in tunnel with the minimum degree of fitting is 0.9139. By comparison between different traffic situations in tunnel, it reveals the formation of precursor shock wave enhances the flame propagation, and the accelerated flame in turn strengthens the overpressure, indicating the underlying damage mechanism. This study contributes to better understanding multi-factor damage mechanism of HMRT accident in highway tunnel, and further optimizing HRMT accident detections and emergency plans.

Influence of cooling speed on the physical and mechanical properties of granite in geothermal‐related engineering

AbstractIn deep‐earth engineering, the high earth temperature can significantly affect the rock's mechanical properties, especially when the rock is cooled during the construction process. Accordingly, whether the cooling speed affects the mechanical and physical properties of rocks is worth to be investigated. The present study explored the influence of the cooling rate on the physical and chemical properties of granite heated at 25–800 °C. The mechanical and physical properties involved in this study included uniaxial compression strength, peak strain, modulus, P‐wave velocity, mass and volume, the change of which could reflect the sensitivity of granite to the cooling rate. Acoustic emission (AE) monitoring, microscopic observation, and X‐ray diffraction (XRD) are used to analyze the underlying damage mechanism. It is found that more AE signals and large‐scale cracks are accounted for based on the b‐value method when the specimens are cooled by water. Furthermore, the microscopic observation by polarized light microscopy indicates that the density, opening degree, and connectivity of the cracks under water cooling mode are higher than that under natural cooling mode. In addition, the XRD illustrates that there is no obvious change in mineral content and diffraction angle at different temperatures, which confirms that the change of mechanical properties is not related to the chemical properties. The present conclusion can provide a perspective to assess the damage caused by different cooling methods to hot rocks.