Hasil untuk "Materials of engineering and construction. Mechanics of materials"

Marcel Dickmann, Ricardo Helm, Werner Egger et al.

We investigate the thermal evolution of implantation-induced defects in single-crystal CVD diamond using depth-resolved positron annihilation lifetime spectroscopy (PALS). Samples were implanted with 0.5MeV N+ ions at a fluence of 1×1014cm−2 and annealed between 600∘C and 1200∘C. We probe defect populations as a function of depth and quantify their types and concentrations. In the pristine material, small vacancies, predominantly divacancies, are detected at ∼ppm levels together with a low concentration of larger vacancy clusters. Nitrogen implantation increases the abundance of mono-/divacancies. In nitrogen-rich regions, fewer isolated vacancies are observed despite higher displacement damage. Upon annealing, small vacancies become mobile. In nitrogen-poor regions, they agglomerate and grow pre-existing clusters. In contrast, in nitrogen-rich zones, they are efficiently captured by substitutional nitrogen to form NV centers, which limits the formation of new vacancy clusters. At annealing above 1000∘C, positron annihilation occurs predominantly in perfect bulk or small open-volume defects consistent with NV center-related positron lifetimes. These results reveal a nitrogen content- and temperature-dependent competition between vacancy clustering and NV center formation.

Hyeonwoo Kim, Ho Lee, Kanghyeon Kim et al.

Chemical short-range order (CSRO) and grain boundary (GB) engineering are routes to enhance radiation damage tolerance in alloys. Here, we reveal that CSRO and GB interact in a sink-strength-dependent manner under irradiation in NiCoCr. Near a weak sink (Σ3 GB), CSRO reduces defect cluster growth by slowing interstitial diffusion and enhancing vacancy-interstitial recombinations. In contrast, near strong sinks such as Σ5 GBs, CSRO and GB act competitively for interstitial accumulation but synergistically to suppress large stacking-fault tetrahedra growth via enhanced recombination. Such mechanistic duality underscores the need for coordinated control of CSRO stability and GB sink strength to enhance radiation damage tolerance.

Mustafa Kurban, Beyza Furtana Yalcin, Mehmet Yilmaz et al.

This study integrates experimental and computational methods to evaluate the rejuvenation performance of an aged asphalt binder using two novel bio-based additives, 1T and 2T. The aged binder, sourced from reclaimed asphalt pavement (RAP), was modified with 25 wt% of each rejuvenator (denoted as 1T25 and 2T25, respectively). SARA (Saturates, Aromatics, Resins, Asphaltenes) fractionation and colloidal indices were used to assess compositional recovery. Both additives increased aromatic and resin contents while reducing asphaltenes. The 2T-modified binder achieved the highest colloidal stability (Ic = 0.29) and the most pronounced improvement in stability indicators (CI and Ic) among the tested systems. Complementary molecular dynamics (MD) simulations using the COMPASSII force field modeled the structural and thermodynamic behavior of RAP and rejuvenated systems. The 2T25 system exhibited higher density and more compact molecular packing, suggesting stronger cohesive organization and reduced free volume, whereas 1T25 showed greater molecular spacing and flexibility. RDF analysis and converged thermodynamic/structural trajectories (energy, temperature, cell length, and density stabilization) further supported rejuvenator-dependent rearrangement of packing during equilibration. Overall, MD acts as a mechanistic bridge that interprets experimental SARA/CI/Ic trends and supports design-oriented development of sustainable rejuvenators.

Song Zhao, Jian Ouyang, Wenting Yang

MAO Yongwen, LI Yong

Aiming at the issues of under-maintenance or over-maintenance in preventive maintenance of DSA200 type pantograph, a method was proposed to optimize inspection and maintenance parameters by using pantograph failure data.Firstly, the failure datas of the pantograph components were analyzed by using graph parameter method, which failure time distribution models were fitted.The failure datas were preliminarily determined to obey the exponential distribution，and the Bartlett value method was further used to verify the validity of the failure data obey exponential distribution.Secondly, based on the structure and working characteristics of pantographs, a reliability block diagram model with pantograph components in series was constructed.According to the characteristics of constant failure rate of pantograph components, the failure rate of pantographs was obtained.Thirdly, the minimum cost model of preventive maintenance and replacement of pantographs was established, and the optimal preventive maintenance interval and the optimal number of spare parts were obtained.Finally, the structure importance, probability importance and critical importance of pantograph components were analyzed by using fault tree analysis method, and the failure probability of pantograph and the key components in inspection and maintenance were obtained.The optimized pantograph inspection and maintenance parameters can provide scientific reference for maintenance personnel to improve their maintenance level and reduce maintenance costs.

Hongqiang Ma, Shaochen Zhang, Hao Fu et al.

Pitabash Sahoo, Ashutosh Dwivedi, Shivkumar M. Tuppad et al.

Boyoung Yoon, Yonghun Cho, Hyunwook Choo et al.

The study investigates the application of steel slag as an innovative material for compaction piles in the stabilization of soft soils, offering an eco-friendly alternative to conventional gravel compaction piles (GCPs). Through a comprehensive series of laboratory tests, field experiments, and numerical simulations, this study evaluated the performance, environmental impact, and long-term behavior of steel slag compaction piles (SSCPs). The key findings revealed that steel slag not only provides immediate soil improvement comparable to gravel but also exhibits significant time-dependent increases in strength and stiffness. Standard Penetration Test (SPT) N-ratios (N1/N0, where N1 = N value after improvement and N0 = N value before improvement) were similar for soils reinforced with SSCPs and GCPs after 0 months, but were about 30 % higher in SSCP-reinforced soils after 3 months. This increase was attributed to the cementation of steel slags, suggesting that the compaction pile with increased stiffness due to cementation acts as a compaction pile with an increased area replacement ratio (α). Environmental assessments confirmed that steel slag meets regulatory standards for soil contamination, positioning it as a sustainable option. Settlement analysis after embankment construction showed reduced and more uniform settlements with SSCPs, suggesting superior load distribution capabilities. Finite element analysis compared the behavior of SSCP-reinforced soils at varying α and stiffness of compaction piles, confirming that the cementation of steel slag produces an effect equivalent to increasing α in uncemented piles, thus enhancing the reinforcement effect.

Riccardo Antonello, Roberto Oboe, Daniele D’Elia et al.

The angular motion of quasi-static micromirrors used for raster scanning projection applications is typically affected by undesired oscillations related to high-frequency resonant modes triggered by the sawtooth-like driving signal. This paper proposes a novel closed-loop tracking controller for improving the linearity of the trace motion, and hence the image brightness. It includes a feedforward action to achieve the required tracking performance under nominal conditions, and a feedback control for robustness against disturbances and other nonidealities. Notch filtering prevents resonance-induced ringing. The simplicity of the architecture enables an easy implementation on FPGA or ASIC. Experimental tests carried out on two different micromirrors with Lead-Zirconate-Titanate (PZT) piezoelectric actuation and piezoresistive sensing demonstrate an average linearity of [Formula: see text] and reproducibility of [Formula: see text] for sawtooth reference trajectories with up to [Formula: see text] amplitude and 120 Hz frequency, thus meeting the performance requirements mandated by the standards for high-resolutions projection applications.

Сергій Орищенко, Віктор Орищенко

Під час робочого процесу навантажувач перемішується на майже горизонтальних майданчиках, допустимий ухил яких. Розрахунок поздовжньої стійкості навантажувачів ведеться з умови перекидання вперед з урахуванням того, що деформуються пневматичні шини, якщо пневмоколісний хід. Кут додаткового нахилу навантажувача вперед внаслідок деформації опор визначається співвідношенням сили тяжкості навантажувача з вантажем жорсткість ґрунту під переднім та заднім котками гусеничного ходу або радіальна жорсткість передніх та задніх пневматичних шин навантажувача на пневмоколісному ході; відстань між центром ваги навантажувача та вертикальною віссю, що проходить через точку перекидання. Тому при розрахунку поздовжньої стійкості гусеничного та пневмоколісного навантажувачів. Найменший запас поздовжньої стійкості має навантажувач у разі руху під ухил з одночасним гальмуванням машини та робочого обладнання при його опусканні. Положення робочого обладнання відповідає максимальному вильоту.

Jie Gao, Yonghua Zhai, Weihong Lu et al.

In the field of cancer therapy, inhibiting autophagy has emerged as a promising strategy. However, pharmacological disruption of autophagy can lead to the upregulation of programmed death-ligand 1 (PD-L1), enabling tumor immune evasion. To address this issue, we developed innovative ROS-responsive cationic poly(ethylene imine) (PEI) nanogels using selenol chemistry-mediated multicomponent reaction (MCR) technology. This procedure involved simple mixing of low-molecular-weight PEI (LMW PEI), γ-selenobutylacetone (γ-SBL), and poly(ethylene glycol) methacrylate (PEGMA). Through high-throughput screening, we constructed a library of AxSeyOz nanogels and identified the optimized A1.8Se3O0.5/siPD-L1 nanogels, which exhibited a size of approximately 200 nm, excellent colloidal stability, and the most effective PD-L1 silencing efficacy. These nanogels demonstrated enhanced uptake by tumor cells, excellent oxidative degradation ability, and inhibited autophagy by alkalinizing lysosomes. The A1.8Se3O0.5/siPD-L1 nanogels significantly downregulated PD-L1 expression and increased the expression of major histocompatibility complex class I (MHC-I), resulting in robust proliferation of specific CD8+ T cells and a decrease in MC38 tumor growth. As a result, the A1.8Se3O0.5/siPD-L1 nanogels inhibited tumor growth through self-inhibition of autophagy, upregulation of MHC-I, and downregulation of PD-L1. Designed with dynamic diselenide bonds, the A1.8Se3O0.5/siPD-L1 nanogels showed synergistic antitumor efficacy through self-inhibition of autophagy and prevention of immune escape.

Ahmed Abusultan, Heba Abunahla, Yasmin Halawani et al.

Abstract The adverse effect of ultraviolet (UV) radiation on human beings has sparked intense interest in the development of new sensors to effectively monitor UV and solar exposure. This paper describes a novel low-cost and flexible graphene oxide (GO)-based paper sensor capable of detecting the total amount of UV or sun energy delivered per unit area. GO is incorporated into the structure of standard printing paper, cellulose, via a low-cost fabrication technique. The effect of UV and solar radiation exposure on the GO paper-based sensor is investigated using a simple color change analysis. As a result, users can easily determine the amount of ultraviolet or solar energy received by the sensor using a simple color analysis application. A neural network (ANN) model is also explored to learn the relation between UV color intensity and exposure time, then digitally display the results. The accuracy for the developed ANN reached 96.83%. The disposable, cost-effective, simple, biodegradable, safe, and flexible characteristics of the paper-based UV sensor make it an attractive candidate for a variety of sensing applications. This work provides new vision toward developing highly efficient and fully disposable GO-based photosensors. Graphical Abstract

L.M.G. Silva, G.N. Leocádio, R.F.B. de Souza et al.

The performance of the electrospray technique was applied to obtain a gas diffusion layer (GDL) for a proton exchange membrane fuel cell. It was confirmed by confocal microscopy that polytetrafluorethylene (PTFE) was impregnated into the backbone, forming a dispersed layer of microscopic size homogeneously distributed over the substrate. The PTFE layer was characterized by infrared spectroscopy and thermogravimetric analysis. In this work, we demonstrated that the use of the GDL prepared by electrospray increases the maximum power of the H2/O2 fuel cell by about 10% and decreases the diffusion loss of the electrode owing to a better distribution characteristic hydrophobic coating with low impedance to gas diffusion. Thus, our method is promising for the development of fuel cells by the production of diffusion layers.

Jiaguang Zhu, Caifeng Chen, Ruifang Zhang

Polyvinylidene fluoride(PVDF) thin film with good electrical properties is usually used as a piezoelectric sensor or energy harvesting device. It has a broad potential application prospect in the fields of damage detection, structural vibration, medical devices, and artificial intelligence. In the work, PVDF/MWCNTs thin films were prepared by electroprinting method. The effect of the intercalation of MWCNTs on the β-PVDF formation and the mechanism of improving the electrical properties of PVDF piezoelectric thin films in the electroprinting process were discussed. The results show that the doping of MWCNTs promotes the crystallinity and the β-phase content of PVDF films in the electric field. With the increase of the amount of MWCNTs added, the piezoelectric and dielectric properties of the PVDF/MWCNTs thin film are correspondingly improved. However, the dielectric loss of the film is reduced. Due to the preparation and polarization of the film in the electroprinting process are unified, the PVDF piezoelectric film without poling shows excellent piezoelectric and dielectric properties.

SHEN Pin-hua, JIN Yu

The bivalent iron in potassium chloride zinc plating solution reduced the current density range, resulting in black barrel eye marks on barrel plating products. Hydrogen peroxide could oxidize them to much less harmful trivalent iron, but it also reduced the dispersion of plating solution and oxidized some brightener. Besides, hydrogen peroxide was listed in the list of dangerous chemicals, which was difficult for purchase and storage. In order to solve the problem in the process of potassium chloride zinc plating, a kind of iron remover DF (mainly divalent iron chelating agent) for potassium chloride zinc plating solution without hydrogen peroxide was developed. Besides, its application performance was characterized by Hull cell test.

Meng Ling, Xue Luo, Yu Chen et al.

F. Jamshidi, M. Dehestani

Kadhim Raheim Erzaij, Rouwaida Hussein Ali

Construction project costs are often related to the availability of construction materials and proximity to the work site. So this paper studied the effect of transportation of materials on the cost of construction projects in the desert and identified the increment percentages of materials cost in comparison with main cities and re-accounted the BOQ items prices in the desert cities. The results showed that the cost of some works may be doubled in the desert areas due to lack of construction materials and high transport costs.

Gangjin Chen, Jianfeng Zhang, Jianfeng Zhang et al.

Polymer electrets are increasingly getting application in a very wide range. However, its charge trapped mechanism is still poorly understood. It is always challenging how to improve its charge trapped ability and to enhance its performance stability. In this study, a charge trapped mechanism, quasi-dipole model, is proposed for semi-crystalline polymer electrets. Every grain of crystallite is viewed as a dipole based on the polarisation effect between crystalline and amorphous region when charged. The energy level of the charge trap has a dependence on the crystallite structure. The more regular the crystallite grain structure the better charge stability is. The melt-blown polypropylene (MBPP) electret fabrics with α or mesomorphic crystallite are used as the model material to verify the rationality of the mechanism. The experiment results from thermally stimulating discharge and X-ray diffraction proved that the charge-trapped stability could be improved by means of transformation from meso-crystalline to α crystalline structure. The MBPP fabric containing α-crystallite shows much better charge trapped performance than one containing mesomorphic-crystallite because of more regular structure in α crystallite. The findings not only present new insight into charge-trapped phenomena in polymer electrets, but also provide innovation for the processing technology of polymer electret materials.

Mateusz Wierzbicki, Sławomir Jaworski, Ewa Sawosz et al.

Abstract Antibacterial surfaces coated with nanomaterials, including silver nanoparticles, are considered effective alternative antimicrobial agents that can be used instead of antibiotics and chemical agents. However, reports of the potential toxicity of these materials raise questions about the safety of their use in biomedical applications. The objective of this research was to reduce the human cell cytotoxicity of silver nanoparticle-coated polyurethane foils by complexing silver nanoparticles with graphene oxide. The antimicrobial activity of nanoplatforms coated with silver nanoparticles, graphene oxide and the composite of silver nanoparticles and graphene oxide was assessed with Salmonella enteritidis. Cytotoxicity was analysed by an analysis of the viability and morphology of human fibroblasts, human umbilical vein endothelial cells (HUVECs) and chicken embryo chorioallantoic membrane. Additionally, the synthesis level of inflammatory proteins was examined for fibroblasts cultured on different nanoplatforms. The nanoplatform coated with the silver nanoparticles and graphene oxide composite showed strongest antibacterial properties, although nanoplatforms coated with only silver nanoparticles or graphene oxide also resulted in decreased S. enteritidis growth. Furthermore, a nanoplatform coated with silver nanoparticles and graphene oxide composite showed limited immunological stimulation and significantly reduced cytotoxicity towards fibroblasts, HUVECs and chicken embryo chorioallantoic membrane in comparison to the nanoplatform coated only with silver nanoparticles, due to the higher stability of the nanomaterials in the nanocomposite.