摘要 ：

Traditional semiconductor used as channel materials in driving transistors suffer from significant performance degradation as the semiconductor thickness is reduced. The two-dimensional (2D) materials with smooth, dangling-bond-free surfaces, represented by graphene, can be alternatives. Graphene boasts several advantages, including structural stability, ultra-thin thickness, near-total transparency, exceptional flexibility, and high mobility. Therefore, graphene field-effect transistors (GFETs) in the paper are used to drive Micro-light-emitting diodes (Micro-LEDs), key elements in next-generation advanced displays due to their high resolution, high brightness, high contrast, etc. Importantly, this study addresses the two major bottlenecks i.e. Micro-LEDs' mass transfer and graphene transfer. That is, monolithically integrated devices of Micro-LED and its driver GFET are designed and fabricated, bypassing the issue of traditional Micro-LEDs' mass transfer. For the first time, transfer-free method by plasma-enhanced chemical vapor deposition (PECVD) is used to grow graphene directly on GaN Micro-LED samples and prepared graphene transistors. This approach avoids doping and damage to the graphene during the transfer process, significantly shortens the growth time, and improves the fabrication efficiency. The devices possess broad applications potential and compatibility with semiconductor planar processes. This study paves the way for the transfer-free growth of graphene and the integration of Micro-LEDs with 2D materials transistors.

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In the seismic mountainous regions such as western China, it is usuallly inevitable to construct tunnels near active fault zones. Those fault-crossing tunnel structures can be extremely vulnerable during earthquakes. Extensive experimental studies have been conducted on the response of continuous mountain tunnels under reverse and normal fault movements, limited experimental investigations are available in the literatures on mountain tunnels with special structural measures crossing strike-slip faults. In this study, a new experimental facility for simulating the movement of strike-slip fault was developed, accounting for the spatial deformation characteristics of large active fault zones. Two groups of sandbox experiment were performed on the scaled tunnel models to investigate the evolution of ground deformation and surface rupture subjected to strike-slip fault motion and its impact on a water conveyance tunnel. The nonlinear response and damage mechanism of continuous tunnels and tunnels incorporated with specially designed articulated system were examined. The test results show that most of slip between stationary block and moving block occurred within the fault core, and significant surface ruptures are observed along the fault strike direction at the fault damage zone. The continuous tunnel undergoes significant shrinkage deformation and diagonal-shear failure near the slip surface and resulted in localized collapse of tunnel lining. The segments of articulated system tunnel suffer a significant horizontal deflection of about 5°, which results in opening and misalignment at the flexible joint. The width of the damaged zone of the articulated system tunnel is about 0.44 to 0.57 times that of the continuous tunnel. Compared to continuous tunnels, the articulated design significantly reduces the axial strain response of the tunnel lining, but increases the circumferential tensile strain at the tunnel crown and invert. It is concluded that articulated design provides an effective measure to reduce the extent of damage in mountain tunnel. © 2024 Tongji University

关键词 ：

Earthquake engineering Strike-slip faults Fault slips Earthquakes Fracture mechanics Railroad tunnels Tunnel linings

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The poor adhesion of asphalt-granite limits the application of granite. This research aims to enhance the adhesion of asphalt and granite by establishing chemical connections between the hydroxyl groups on granite surface and the incompletely reacted isocyanate groups in polyurethane (PU) modified asphalt. For this purpose, end-capped PU modified asphalt (PUMA) was prepared, the adhesion mechanism between PUMA and granite was analyzed by Raman spectroscopy, the adhesion properties between PUMA and granite at different curing periods were evaluated by boiling and pull-out tests, and the wettability of PUMA on granite and its moisture sensitivity were evaluated using surface free energy (SFE) method. The findings suggested that the incompletely reacted isocyanate groups in PUMA can establish a chemical connection with the hydroxyl groups on the surface of granite. The adhesion between asphalt and granite can be greatly improved by the addition of PU, and this improvement is amplified as the curing time is extended. When the curing time is extended to 3 days, the fracture mode between asphalt and granite changed from adhesive failure to cohesive failure, and after 15 days of curing, the coating ratio of PUMA on granite following the water boiling test can be raised by 28.11% in comparison to the base asphalt. The water damage resistance of PUMA-granite system can be increased by adding PU and the adhesion work and combination ratio of the freshly prepared PUMA were increased by 55.91% and 79.45%, respectively, as compared to base asphalt. This study has great significance for enhancing the adhesion between asphalt and granite and encouraging granite application.

关键词 ：

Granite Polyurethane modified asphalt (PUMA) Interfacial adhesion End-capped polyurethane

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Understanding the time-dependent behavior of rocks has long been a critical challenge, hindered by complex multiscale failure mechanisms and time effects. Prolonged exposure to environmental factors such as groundwater and corrosive ions causes significant time-dependent behavior in the surrounding rock, posing potential risks to tunnel safety. In this study, the discrete element method was adopted to investigate the influence of environmental erosion on the time-dependent performance of rocks and mechanical response of tunnel linings at the structural level. To simulate rock erosion, an inhomogeneous erosion parallel bond model (IEPBM) was proposed, conceptualizing the erosion process as the gradual dissolution of bonding cementation between microscopic structures. The Weibull function was introduced to represent the inhomogeneous erosion of rock materials. The IEPBM was validated by comparing the simulation results with indoor tests, confirming the model's reliability. The model incorporated an updated bonding radius multiplier to simulate microstructural changes during erosion. Subsequently, the effects of the erosion degree, erosion rate, and inhomogeneity on the time-dependent mechanical behavior of the rock were explored. The results indicated that the creep behavior induced by environmental erosion was a macroscopic deformation process, with rock failure resulting from the accumulation of microscopic damage. The model successfully captured three creep stages: attenuation, stability, and acceleration. Additionally, erosion degree and rate significantly affected the multiscale creep properties of rocks, with highly inhomogeneous rocks potentially failing after relatively minor erosion. Finally, the time- dependent mechanical response of the tunnel lining owing to surrounding rock erosion was analyzed at the structural level. The erosion of the surrounding rock increases the stress on the lining, compromising the longterm safety of the tunnel structure and contributing to lining failures observed in modern tunnels.

关键词 ：

Environmental erosion Long-term safety Surrounding rock Tunnel Creep behavior DEM

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Manufactured sand (MS) was used to partially replace the traditional quartz sand (QS) to prepare a novel ultrahigh-performance manufactured sand concrete (UHPMC). To better understand the fracture damage mechanism of UHPMC, small-scale sample tensile tests were conducted to investigate the tensile behavior of three types of UHPMC (low strain hardening, low strain softening and high strain softening). Acoustic emission (AE) and digital image correlation (DIC) are employed simultaneously to monitor and assess the damage characteristics of UHPMC. The results indicate that the classical AE characteristic parameters (ringing counts, duration and bvalue) provide a satisfactory result in identifying the feature stages of low strain hardening and high strain softening. Based on the Gaussian mixture model (GMM) and support vector machine (SVM), an automatic probability classification algorithm has been developed that achieves the quantitative categorization of three UHPMC cracking types (shear or tensile cracks). Among them, tensile damage is dominant during the entire loading process, whereas shear damage, including aggregate dislocation and fiber debonding and pullout, accumulates during the hardening and softening stages. DIC visualization and AE source localization complement each other in identifying crack distribution, contributing to further revealing the tensile damage mechanism of UHPMC. The results obtained in this study can provide data and theoretical support for fracture damage characterization and health monitoring of ultra-high-performance concrete materials under tensile conditions.

关键词 ：

Fracture Small scale sample tensile testing Digital image correlation Acoustic emission technique UHPMC

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While drilling deep or ultra-deep wells in hard rock formations, there are significant problems such as easy wear of drilling cutters and a low rate of penetration (ROP), and rotary percussion drilling technology is one of the essential techniques for improving drilling efficiency. However, there is currently limited research on the compatibility of rotary percussion drilling tools, polycrystalline diamond compact (PDC) cutters, and hard rock formations. Considering the motion mechanism of rotary percussion drilling tools, a three-dimensional rock-breaking numerical model was established for different cutters (planar, axe-shaped, and triple-ridged) under impact loads. Penetration depths, cutting widths, and rock-breaking volumes of different cutters under static and dynamic load coupling were analyzed. Changes in tensile, compressive, and shear stresses during the cutter rock-breaking process were compared, revealing the different cutter rock-breaking mechanisms under impact loads. The cutter rock-breaking laws under different impact amplitudes and frequencies were analyzed quantitatively, and the differences in rock-breaking effects of different cutters under various geological conditions were assessed. The results indicated that cutter penetration depth during rotary percussion drilling could be increased by 16.04% compared to that during conventional drilling. Under the same impact load, the rock-breaking effects of different cutters on hard and soft rocks exhibited similar variation patterns. The penetration depth followed the order axe-shaped > triple-ridged > planar cutters, with an average tangential order of triple-ridged < axe-shaped < planar cutters. When drilling through hard rock, the average penetration depths of planar, axe-shaped, and triple-ridged cutters were 5.57, 6.06, and 3.91 mm, respectively. The average tangential forces were 670.57, 541.76, and 347.89 N, respectively. During the transition from soft to hard rock during drilling, the tangential forces of the planar, axe-shaped, and triple-ridged cutters increased by 8.41%, 3.21%, and 2.64%, respectively. The planar cutter experienced the most significant instantaneous tangential-force change and was more prone to impact damage. Increasing the amplitude of the axial stress waves helps enhance the penetration depth of the drill bit, whereas increasing the frequency of the stress waves can reduce the intensity of fluctuations during drill-bit penetration and increase drill-bit stability. The research results provide insights into optimizing drilling cutters and engineering parameters during rotary percussion drilling.

关键词 ：

Numerical simulation PDC cutter Rock-breaking mechanism Parameter analysis

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The use of fiber-reinforced polymer (FRP) bars as a substitute for steel bars in concrete engineering structures is becoming increasingly popular. However, the impact resistance of concrete columns reinforced with GFRP bars (GFRP-RC) are still not clear enough. In this study, impact models for both reinforced concrete (RC) column and GFRP-RC column were generated through finite element (FE) software. Subsequently, the accuracy and effectiveness of these simulations were confirmed by comparing the simulation results with experimental data. Following this validation, the methodology was employed to analyze the impact performance of GFRP-RC columns having varying slenderness ratios. In addition, the effect of impact locations was discussed. The results show that the peak impact force of GFRP-RC and RC columns with different slenderness ratios and impact locations are similar, while the peak displacement and impact duration gradually increase with the increase in slenderness ratio. RC columns have a higher increase in impact duration than GFPR-RC columns. Impact duration and peak displacement tend to increase as the impact location gets closer to midspan. Shorter GFPR-RC columns fail along their entire height, while longer GFPR-RC columns tend to have local failure around the impact location, column foot, and column top. The failure mode of GFPR-RC columns is similar for impact locations ranging from h/8 to h/4, where the column failure occurs at the top and extends from the impact location to the column foot. At an impact location of h/2, GFPR-RC column failure occurs at all these three positions. The impact damage in shorter GFPR-RC columns is more severe compared to longer ones, resulting in a significant reduction of axial bearing capacity. Finally, an empirical model to predict the maximum deflection considering the effect of slenderness ratio and impact location was developed.

关键词 ：

Impact location Impact resistance GFRP-RC column Slenderness ratio

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The high water content of the surrounding rock in loess tunnels will lead to the deterioration of rock strength, causing deformation and damage to the initial support structure and thereby affecting safety during construction and operation. This article first analyzes the strength characteristics of loess under different water contents through indoor physical and mechanical tests. Secondly, based on numerical simulation results, the ecological environment, and design requirements, the water content threshold is determined. Finally, a reinforcement scheme combining surface precipitation measures and curtain grouting measures is proposed, and the reinforcement effect is analyzed based on on-site monitoring data. The results show that as the water content of loess increases, the cohesion, internal friction angle, and elastic modulus of the surrounding rock all decrease, leading to an increase in the sensitivity of the surrounding rock to excavation disturbances and a deterioration in strength. During the construction process, it shows an increase in the vault settlement and sidewalls' convergence. During the process of increasing the distance between the monitoring section and the palm face, the settlement and convergence of the tunnel show a rapid growth stage, slow growth stage, and stable stage. The water content threshold is determined to be 22%. The reinforcement scheme of combining surface precipitation measures with curtain grouting measures not only meets the requirements of the ecological environment but also makes the settlement and convergence values lower than the yellow warning deformation values required by the design.

关键词 ：

monitoring measurement loess tunnel countermeasures water content deformation law

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In the field of precision machining, with the popularity of brittle and hard materials such as infrared windows, has become difficult for conventional diamond grinding wheels to effectively perform high-quality machining. The structuring of traditional diamond grinding wheels using a pulsed laser is a key technology to effectively improve the grinding quality of grinding wheels. In this paper, three new shark fin diamond grinding wheels (SFSGW) with different slot widths are designed based on the excellent drag-reducing and channelizing properties of shark dorsal fins. The grinding performance of traditional grinding wheels (USGW) and SFSGW magnesium fluoride ceramics was compared. The effects of SFSGW on the surface quality, surface roughness and wheel damage of the workpiece were investigated. The results showed that the surface roughness of ceramics after grinding by SFSGW was reduced by 22.15 % compared with USGW, and the surface quality was better. Proper construction increases the material removal rate of the wheel and improves the wear resistance and service life of the wheel.

关键词 ：

Laser processing Wear resistance Shark fin-like structure Precision machining MgF(2)ceramics Surface roughnes

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Nowadays, with the continuous development of industrialization, liquid-filled pipeline is the most representative pipeline transportation system. The damage forms of pipes with cracks will affect the mechanical properties of reinforced concrete pipes to varying degrees and make their properties decline. We investigated the undamaged, damaged and liquid-filled reinforced concrete pipelines, and analyzed the propagation mechanism of piezoelectric sensing signals in reinforced concrete pipelines. When the ultrasonic guided wave touches the damaged position, part of the ultrasonic guided wave will reflect, while the other part of the guided wave will continue to propagate through the damaged position, which is the reflection and transmission phenomenon of the ultrasonic guided wave. The damage assessment of pipeline structure can be realized by using the reflection and transmission phenomenon of ultrasonic guided wave. The signals of undamaged hollow pipe and undamaged liquid-filled pipe were compared and compared undamaged signal and damaged signal in liquid filled pipeline. Based on pulse-echo method, the influence of damage on signal propagation in liquid-filled pipeline is obtained. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.

关键词 ：

Pipelines Reinforced concrete Ultrasonic waves Guided electromagnetic wave propagation Damage detection Wave transmission

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