The mechanical response of the iron-hydrogen (Fe-H) system under triaxial tensile loading is systematically investigated using molecular dynamics simulations. The study focuses on how hydrogen concentration affects the stress state and void evolution and further explores its coupled effects with temperature. The results indicate that when the hydrogen concentration is less than or equal to 1%, hydrogen atoms impede dislocation motion, thereby retarding void growth by promoting dislocation entanglement and the formation of loop structures. Moreover, the evolution of void volume exhibits a typical three-stage characteristic: an initial slow growth phase, a rapid growth phase, and a decelerated growth phase after coalescence. In addition, the evolution of void surface area in the model essentially results from competition between two mechanisms: the decrease caused by void collapse and coalescence and the increase caused by void expansion. Cluster configuration analysis reveals that void formation around the clusters serves as a critical turning point for their structural stability, and the subsequent evolution of the voids leads to a substantial reduction in local structural stability. The analysis of the coupling effect between temperature and hydrogen concentration reveals that under high-temperature conditions, temperature plays a key role in determining the strength, while the strengthening effect of low hydrogen concentrations can be neglected. Additionally, at low temperatures, hydrogen concentration has a negligible effect on structure, but under elevated temperatures, increased hydrogen concentration markedly intensifies the degree of structural disorder.

In recent years, damage to buried pipelines caused by hydraulic engineering machinery such as backhoe excavators has become increasingly frequent. For unintentional excavation activities near deep-buried pipelines, there exists a continuous excavation process by the excavator that gradually reduces the overlying soil. To analyze the dynamic response characteristics of buried pipelines under multiple excavations by the excavator, a bucket-soil-pipeline model was established using the discrete element-continuous difference coupling method. The excavation process is completed through multiple excavations, progressively reducing the soil cover over the pipeline with each shovel. The research results indicate that during multiple excavation, as the soil cover decreases, both the excavation force and resistance acting on the pipeline increase with each shovel. The excavation force of the third shovel increases by approximately 2-3 times compared to the first two shovels. The stress on the pipeline exhibits an elliptical diffusion pattern that decreases outward, and the radial strain of the pipeline is symmetrically distributed along the horizontal plane of the axis, with strain increasing further from the axis. The pipeline's vibration acceleration fluctuates as the bucket approaches the pipeline, with a peak value of 4.23 m/s2 before contact and 17.26 m/s2 after impact. For a specific excavation condition, the study investigated the damage zoning of the pipeline by combining the analysis of pipeline vibrations and excavation loads. These results provide a reference for studying the noncontact damage mechanism of pipelines and offer insights for the prevention and control of third-party damage to pipelines.

This study employs large-scale molecular dynamics simulations to investigate the dynamic response of nanoporous nickel under impact loading, focusing on the influence of porosity and void distribution on stress, velocity, temperature, and density evolution over time, as well as on spalling strength. Results indicate that the presence of voids significantly weakens the impact strength of nanoporous nickel, with greater porosity leading to more pronounced weakening effects. Differences in void distribution affect the propagation characteristics of shock waves within the material. The study further discovered that both void collapse and spalltion induce localized high temperatures. Under identical impact conditions, spalling strength decreases with increasing porosity; even at the same porosity, varying void distributions cause fluctuations in spalling strength. Furthermore, this study revealed two synergistic mechanisms of void collapse—forward flow and lateral flow—and analyzed atomic displacement characteristics between voids under varying impact intensities: At lower impact intensities, atoms primarily fill adjacent voids bilaterally; at higher impact intensities, atoms migrate along the impact direction and participate in the collapse process.

An angular-dependent potential for the U-Nb system is developed based on an existing ADP for U and a new EAM potential for Nb, with flexible cross-interaction functions and alloy parameters fitted to experimental and first-principles data. This potential enables accurate prediction of phase transitions (alpha <-> gamma driven by solute concentration; alpha '' -> gamma under temperature in U-6Nb alloy), elastic properties, defect energetics, and mixing enthalpy. The melting points of U-Nb solid solutions is well reproduced. And the potential also well describes the temperature-dependence lattice parameter of gamma U-6Nb. Notably, it correctly predicts Hugoniot relations and equations of state up to similar to 90 GPa and resolves the alpha '' -> gamma transition under static high pressure. Combined with atomic simulations, we reveal a twinning-coupled alpha '' -> gamma transition of U-6Nb under high pressures: {112}(gamma) twins form via nanosecond-scale twinning precursors generated during the transient adiabatic compressions. The static phase transition pressure is predicted to be 54.5 GPa, comparable to 67.2 GPa by first-principles calculations. Besides, our result suggests that U-6Nb single-crystal would experience a nonlinear elastic relaxation before yielding plastically at 3.1 GPa (shear stress: 0.9 GPa). The results in this work help resolve long-standing discrepancies in understanding the abnormal shear stress relaxation mechanisms under high-pressure shock loading.

In the study of the dynamic evolution of Cu-Ni FGM NWs models, for the three functions P-FGM, E-FGM, and S-FGM, the trends of their density, temperature, velocity, and stress dynamic evolution are consistent. Throughout the impact loading process, the sample experiences a compression stage, followed by a stretching stage where the deformation gradually recovers. Finally, the tensile stress causes the sample to enter the spallation stage. In the study of the impact of the function parameter p on the model, for the P-FGM and E-FGM functions, the increase in p (the proportion of copper in the sample) leads to the formation of a denser compression zone under the impact wave, an increase in the number of voids, and a decrease in spalling strength and free surface velocity. In the S-FGM function, as p increases, under the impact loading, the model has higher density in the compression region, more voids, and lower spalling strength. At this point, the distribution of Cu dominates the influence on the sample.

Understanding the material response and material strength under dynamic loading is crucial for optimized design of advanced material serving in extreme conditions. Flow stress and spall strength are typical measured material strengths in shock loading. However, the correlation of the two strengths is not well understood. Here we use large-scale molecular dynamics simulations to demonstrate that flow stress and spall strength of nanocrystalline Cu have obviously different variation tendencies upon grain refinement at nanoscale. The flow stress reveals a transition from Hall-Petch (HP) to inverse Hall-Petch (IHP) behaviors as grain size decreases. The HP - IHP transition of flow stress is mainly attributed to the competition of grain boundaries strengthening effect by blocking and absorbing dislocations and the grain boundaries weakening effects including GB sliding and grain rotations. However, the grain size dependence of spall strength mainly shows an inverse Hall-Petch relationship, i.e., spall strength generally decreases as grain size decreases. This is mainly due to the role of grain boundaries as preferred void nucleation sites. For finer grain size, the larger volume fraction of grain boundaries and junctions facilitates damage nucleation and results in larger amount of voids and lower tensile strength.

Recently, oil and gas pipeline leaks in mountainous areas have occurred occasionally. A dynamic risk assessment system has been established to better understand and reveal the risk evolution of such accidents to monitor and predict the likelihood of pipeline leakage incidents. Using the bow-tie model, risk factors are identified, and accident consequences for buried aviation fuel pipelines in mountainous areas are analyzed. The GeNIe software is then used to transform the bow-tie model into a Bayesian network to analyze dynamic risks. The node variables in the model are examined before probability and sensitivity analysis, allowing for the identification of the key factors leading to pipeline leakage incidents. The research results indicate that the high-risk basic events, ranked from highest to lowest risk, are untimely handling, uneven ditch bottom, unintentional damage by personnel, mechanical damage during pipeline installation, failure to strictly enforce procedures, illegal construction, and untimely detection. Therefore, to prevent leakage accidents of aviation fuel pipelines in mountainous areas, it is essential to establish an efficient monitoring and response mechanism, leverage advanced technology to monitor pipeline conditions in real time, and ensure early detection and timely resolution of issues. Additionally, enhancing personnel safety awareness, strengthening pipeline quality reviews, and conducting regular inspections and maintenance of line markers (such as mileage piles, corner piles, signposts, and warning signs) are critical. Lastly, strict quality control and construction environment management should be implemented to optimize pipeline installation and maintenance processes, effectively reducing the risks associated with mechanical damage and terrain-related issues.

Hydrogen energy is increasingly becoming a critical component of China's energy structure due to its cleanliness, zero carbon emissions, high energy efficiency, and wide availability. Mixing hydrogen with natural gas in specific proportions and transporting it through the existing natural gas pipeline network is widely regarded as an economical and effective method of hydrogen utilization. However, pipeline failure due to hydrogen embrittlement (HE), especially in the girth weld zone, is a major challenge for hydrogen-mixed transportation. This paper investigates the hydrogen permeation behavior in various zones of the girth weld through electrochemical hydrogen permeation tests, elucidating the reasons for differences in hydrogen permeability coefficients and absorbed hydrogen concentrations in each zone. A compact tension (CT) specimen model based on the phase field method (PFM) was developed to simulate and fit the critical energy release rate of the X80 pipeline girth weld zone in a hydrogen environment. From the obtained force-displacement curves, the critical J-integral for each zone in a hydrogen environment was calculated, examining the fracture toughness variations of X80 pipeline steel base metal (BM) and weld metal (WM) under different hydrogen concentration conditions. Additionally, a quarter-pipe model of an X80 pipeline with a crack was developed using a phase field (PF) fracture model coupled with hydrogen diffusion, simulating the hydrogen-induced cracking phenomenon of the pipeline under actual working conditions. The study investigated the effects of internal pipeline pressure, initial hydrogen concentration, crack geometry, and defect types on the hydrogen concentration distribution at the crack tip and the PF value. Results indicated that before crack propagation, increasing internal pipeline pressure raised the hydrogen concentration at the crack tip, whereas after crack initiation, the hydrogen concentration at the crack tip decreased; increasing initial hydrogen concentration exacerbated the performance degradation of the girth weld zone; the sharper the crack geometry, the higher the hydrogen concentration at the crack tip and the more severe the damage at the crack tip. The models and analytical methods established in this study provide a theoretical basis and technical support for predicting and assessing the safety of pipelines under actual operating conditions. The research findings can guide and inform the design of safer hydrogen-mixed transportation systems.

Given the increasingly prominent problem of pipeline internal corrosion leakage in long-term service submarine oil and gas pipelines, this paper proposes a KPCA-ISSA-MKSVR combined prediction model for accurate internal corrosion rate prediction. The model uses kernel principal component analysis (KPCA) to reduce the dimensionality of influencing factors, improving computational efficiency. An improved sparrow search algorithm (ISSA) optimizes model parameters, employing a tent chaotic map and periodic nonlinear adaptive convergence factor to enhance exploration and search capabilities. Polynomial mutation disturbance is incorporated to prevent local optima traps. By leveraging mixed kernel support vector regression (MKSVR), which integrates multiple kernel functions, the model successfully captures the diversity and complexity of the corrosion data, solving the kernel function selection issue faced by traditional SVR models. In Example 1, the model reduced the mean absolute error (MAE) to 0.015, the root mean square error (RMSE) to 0.018, and the mean absolute percentage error (MAPE) to 0.546, and achieved an R2 of 0.991. In Example 2, the MAE decreased to 0.013, the RMSE to 0.017, the MAPE to 0.493, and R2 reached 0.994. The KPCA-ISSA-MKSVR strategy demonstrates superior accuracy in predicting internal corrosion rates, providing strong technical support for submarine oil and gas pipeline maintenance and safety management.

The whole process of pipeline–soil interactions between a landslide and a gas pipeline was simulated using the strength reduction method. The main purpose is to investigate how pipeline internal pressure, landslide displacement, crack depth ratio (the ratio of crack depth to wall thickness), crack aspect ratio (the ratio of crack depth to crack half-length), and reinforcement with anti-slide piles influence the J-integral of a circumferential crack in the pipeline under landslide impact. The simulation showed that increases in the landslide displacement, crack depth ratio, and pipeline internal pressure led to an increase in the maximum value of the J-integral at the crack leading edge. An increase in the crack aspect ratio reduced the maximum value of the J-integral. In addition, in the process in which the crack shape changed from semi-elliptical to semicircular, there was a critical crack aspect ratio at which the J-integral at the deepest point of the crack was equal to the J-integral at a point on the surface. The study also found that an increase in the number of anti-slide piles affected the location and distribution of the zone of maximum slippage and effectively reduced the maximum von mises stress and the J-integral at the crack tip. However, when the number and cross-sectional size of anti-slide piles exceed a certain threshold, further increasing or enlarging them barely affects the J-integral.

To ensure a thorough examination of the high-sulfur natural gas field station vent piping, it is proposed to use numerical simulation and field combination of methods, based on the wall liquid phase aggregation and droplet erosion of high-sulfur natural gas field station low-pressure vent pipeline corrosion simulation prediction technology to carry out a study, analyze the flow field situation and liquid phase deposition in different parts of the vent pipeline, to get the corrosion-prone parts, and compared with the on-site corrosion, the accuracy of 90% is reached. The accuracy reaches 90%. Verify the application of CFD simulation in the pipeline is not easy to detect the corrosion of the parts of the pipeline has a good prediction of corrosion prone to prioritize the corrosion-prone parts of the inspection, to prevent the occurrence of corrosion accidents.

Large quantities of spent lithium-ion batteries (LIBs) will inevitably be generated in the near future because of their wide application in many fields. It will cause not only resource waste but also environmental pollution if these spent batteries are not properly handled. Until now, the recycling of spent lithium manganate batteries has centered on high-valuable elements such as lithium; however, manganese element and current collector Al foil have not yet attracted wide attention. In this work, aluminum-doped manganese dioxide was synthesized by overall recycling cathode active materials and current collector Al foil from a spent lithium manganate battery. Employing such aluminum-doped manganese dioxide as the cathode material of aqueous Zn batteries, it displays better electrochemical performance than manganese dioxide prepared by only recycling the cathode active materials. The overall recycling not only simplifies the recycling process but also realizes high-value recycling of spent lithium manganate batteries. We offer new tactics for overall recycling of cathodes from spent LIBs and designing high-performance manganese dioxide cathodes for aqueous Zn batteries.

This study shows that phosphogypsum (PG) can promote the recycling of waste crosslinking polyethylene (XLPE) cables with the solid-state shear milling (S3M) technology. As a kind of milling aid, phosphogypsum (PG) promoted molecular chain breaking and de-crosslinking. The mechanochemistry of co-milling promoted the uniform dispersion of PG in XLPE and the formation of Ca2+ coordinate covalent bonds. Coordinate covalent bonds improved the compatibility and toughness of the composite. The elongation and notch impact toughness of the composites with co-milled PG were 404.6

Vulcanized acrylonitrile-butadiene rubber (NBR)/poly (vinyl chloride) (PVC) blends are mainly served as insulation rubber-plastic materials. However, methods to reuse the waste NBR/PVC composites lack research. Here, we found that the mechanochemically modified waste NBR/PVC composites powders (WNPP) could be an alternative to fresh NBR. According to the results, the optimal replacement amount of WNPP for NBR was 20%, and the highest feasible proportion was 40%. WNPP treated by solid-state shear milling technology (S3M) would have a high degree of desulfurization, and the cross-linked chains within WNPP would be transformed into free chains. While co-vulcanizing, the sulfur agents and heat would induce the free chains of WNPP to react with the polymer chains of the NBR substrate, thereby generating dangling chains to form a robust interfacial layer. It was beneficial for the improvement of the mechanical properties of reclaimed products. And the strain of the excellent recycled sample (20C) reached 707%. Moreover, the modified WNPP in the co-vulcanized rubber represented heterogeneity because of the internal residual crosslinked network and the not-melting PVC plastic phase. Although the heterogeneity of WNPP damaged the continuity of the NBR matrix, it also brought a better hysteresis loss capability to the composite. In conclusion, this work expanded the mechanochemical application scope in recycling NBR/PVC wastes.

Cross-linked acrylonitrile-butadiene rubber (NBR)/poly(vinyl chloride) (PVC) blends are extensively served as commercial insulation foams. However, methods to reclaim the wasted NBR/PVC composites are usually inappropriate, causing severe pollution. Herein, we reported that the waste NBR/PVC composites powders (WNPP) with high thermal stability and degree of reclaiming were prepared by solid-state shear milling technology (S3M). Furthermore, the reclaimed products via thermoplastic re-processing had excellent mechanical properties, and the optimal stress and strain were increased by 208.2 % and 269.4 %, respectively, compared with the products made from virgin scraps. Through the investigation of each sample's molecular chains and thermal properties, it was found that when the cross-linked polar rubber-plastic composites are reclaimed, the molecular chains of the rubber phase would be close to each other. The interaction among polar groups would be enhanced, which is the main contributing factor limiting the movability of the polymer chains. And the interaction between the polar rubber and plastic phases would also increase, which is beneficial for the compatibility of the two phases. Moreover, there is a phase separation between the de-crosslinked continuous phase and the residual cross-linked network region for the re-processing products.

Vulcanized acrylonitrile-butadiene rubber (NBR)/poly (vinyl chloride) (PVC) blends are mainly served as insulation rubber-plastic materials. During manufacturing and use, amounts of waste NBR/PVC materials are produced. However, traditional methods of reusing waste are inappropriate. Herein, we innovatively proposed the utilization of mechanochemistry to induce the conversion of irreversible C-S cross-linked bonds in waste NBR/PVC insulation materials into dynamically reversible vitrimer-like network structures. The vitrimer-like structure endowed mobility to the global molecular chains in NBR/PVC materials. And thus, it was essential for the reclaimed products to eliminate the difference between the residual network within waste NBR/PVC materials and the devulcanized phase, improving the mechanical properties. More interestingly, waste NBR/PVC powder dynamically modified by trimethylsulfoniumiodide (TMSI) restored the ability to mix with other materials via thermal processing. The HNBR + CuSO4 compounds were then blended with the modified NBR/PVC powder to prepare mechanically excellent composites with optimum stress of 14.6 MPa and strain of 481.0%. The continuity of the matrix was critical to the mechanical properties of the recycled products, and solid-state shear milling (S3M) played a crucial role in this process, as characterized by various experiments.

With the progress of nanotechnology, the application of functionally gradient materials (FGMs) has shifted from traditional applications to complex micro nano electronic and energy conversion devices. Therefore, it is very important to study the mechanics of different FGMs nanostructures for exploring the feasibility of their different applications. In this study, we used molecular dynamics (MD) simulation to study the mechanical properties of Au-Ag functionally graded nanowires (NWs) with radial gradient distribution. For the FGMs NWs considered, the radial distribution of Au-Ag alloy follows power function, exponential function and S-shaped function. Our results show that the distribution function parameters play an important role in adjusting the mechanical properties (elastic modulus and ultimate tensile strength) of FGMs. The study also shows that the power function and exponential function have a great influence on the mechanical properties of materials, and the S-shaped function has a relatively small influence than the other two functions. In addition, we found that the time to reach the peak value of total dislocation length lags behind the time to reach the ultimate tensile strength, and the dislocation density is unevenly distributed throughout the system. In the subsequent process of dislocation annihilation, the dislocation annihilation is more obvious in the region with higher dislocation density. Moreover, we consider the effect of strain rate on the crystal structure change of FGMs NWs. At low strain rate, the transformation of crystal structure type is reversible. With the increase of strain rate, this reversible trend gradually decreases until reversible change phenomenon no longer occurs.

Aramid fiber is widely used in aerospace, machinery, construction, and other fields for its high strength, high elastic modulus, lightweight, and superior comprehensive performance. However, because aramid fiber is difficult to be melted and reprocessed, efficient and environmentally friendly recycling of aramid fiber waste (AFW) is an urgent and challenging issue. In this work, we reported a facile way to recycle AFW for the preparation of friction-resistant polyoxymethylene (POM)/AFW composites. The ultrafine AFW powder with 64.69 mu m in size was fabricated by solid state shear milling (S3M) technology, which broke the amide bond due to the strong compression and shearing during milling. With the increase of milling cycles, the roughness and active groups on the surface of AFW were increased, which was contributed to improving the compatibility between AFW and POM matrix. The morphology observation indicated a good dispersion of AFW in POM. The mechanical property test results showed that the flexural strength increased from 52.69 MPa to 80.12 MPa with 20 wt.% AFW. As a friction modifier, the addition of AFW could improve the tribological properties of POM/AFW composites, and the coefficient of friction (COF) and wear rate of composites with 20 wt.% AFW could decrease by 53.02% and 69.52%, respectively. The S3M technology presented in this work is an efficient and industrialized strategy for AFW recycling to prepare value-added products, which has great potential in the engineering application field.

With good insulation, cross-linked polyethylene (XLPE) cables are widely used as an important basic material for power transportation. Due to being insoluble and infused, the cross-linked network structure caused a challenge in the recycling of waste XLPE, which is usually treated by incineration and landfilling. In this research, XLPE was part-de-cross-linked via solid-state shear milling (S3M) technology, but the resulting powder was difficult to process. In order to improve the re-processability of XLPE, asphalt with a similar structure was added during the thermoplastic processing. To deeply understand the influence of asphalt on the matrix, the compatibility, dispersion, and rheological properties of the composites were characterized. Due to the good compatibility between de-cross-linked XLPE and asphalt, the viscosity of the composites decreased significantly. Some sea-island structures also formed in composites, which increased the toughness of the composites, so the elongation at break reached as high as 322%. The use of asphalt to achieve the processing performance of part-de-cross-linked XLPE powder was highly effective. Furthermore, the prepared composites showed potential application in the field of waterproofing, which could recycle waste XLPE cables on a large scale.

Fracture research of natural gas pipelines with cracks is an important part of pipeline integrity evaluation. Based on the cohesive zone model (CZM), a numerical analysis is conducted of the dynamic fracture of X80 steel pipelines under explosion load. The factors considered include the crack propagation length, crack propagation velocity, dynamic crack tip opening angle (CTOA) and gas pressure. The results show that the whole cracking process can be divided into three stages: rapid cracking, stable propagation, and deceleration and stop cracking. When in the rapid cracking stage, the axial cracking of the pipeline is dominant. However, in the stable propagation stage, lateral expansion plays a more significant role. Besides, there exist upper limits on the length and velocity of crack propagation. In addition, it is also found that the time for the inflection point of rapid cracking and stable propagation is later than that to reach the velocity peak. The dynamic CTOA decreases with axial crack propagation, and the steady-state value of the CTOA is positively correlated with the load. The high-pressure gas escapes from the pipeline along the crack, resulting in the increase of air pressure outside the pipeline. Moreover, the peak pressure outside the pipeline is approximately linear its the initial crack length. The present research on the dynamic fracture mechanics behavior of the pipeline provides a necessary supplement for the test.