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

Xiuhua Liu, Peng Luo, Shuoyong Yang et al.

Zheng Wang, Tongge Cui, Bangbiao Wu et al.

The integration of face mask fibers (FMF) into cement materials has been proposed as a method to enhance material properties while mitigating pollution. Despite the validation of such advantages through extensive studies, the effects of mask fibers on the dynamic properties of the composite remain to be comprehensively investigated. This study examined dynamic tensile properties of cement mortar incorporating FMF at various volume percentages (0 %, 0.1 %, 0.2 %, 0.3 % and 0.5 %). X-ray Computed Tomography (CT) was utilized to assess specimen integrity. A split Hopkinson pressure bar (SHPB) system was employed to conduct dynamic Brazilian splitting tests, and quasi-static BD test was conducted for comparation. High-speed camera and digital image correlation (DIC) technology was used to analyse the specimen fracture during loading. Subsequently, both macro and micro-observations were made on the fragmented specimens. The results demonstrate that the inclusion of face mask generally reduces voids and microcracks within mortars, leading to material quality improvement for 8.6∼21.0 % characterized by CT value. As compared with the plain mortar, both the static and dynamic tensile strengths increase across all FMF mixtures, with the enhancement correlating with the material quality. The fracture energy density of the mortars showed significant improvement at higher loading rates (0.25–0.45 J/cm2 at 250 GPa/s), exhibiting pronounced rate sensitivity due to mask inclusion. The crushing pattern of the specimen also changes and shows certain microscopic characteristics. Based on these tensile properties, the optimum content of FMF is 0.3 %. These findings enhance the subsequent understanding of the effects of mask incorporation and provide a basis for determining the potential applications of such composite materials.

XU Xingxing, WANG Long, ZHANG Xiaofeng, LI Zhenhua, SHI Jianhui, YOU Lei, DING Qingyue, LU Yonghao

In order to evaluate the effect of scratch defects on the stress corrosion performance of 690TT alloy heat transfer tubes in a simulated high-temperature and high-pressure water environment of the secondary circuit， a nuclear power steam generator heat transfer tube was chosen as the research subject.A scratch device was used to create C-ring specimens with scratch defects on the surface of the tube.The stress corrosion behavior of the scratched 690TT alloy heat transfer tubes was investigated in the simulated secondary circuit high-temperature and highpressure water environment.The surface defect morphology， oxidation morphology， distribution of oxide elements and surface profile of the specimens before and after corrosion were analyzed using scanning electron microscopy (SEM)， transmission electron microscopy (TEM)， energy dispersive spectrometer (EDS)，Raman spectroscopy and white light interferometer.Results showed that in the simulated secondary circuit high-temperature and high-pressure water environment， spinel oxide and chromium-rich oxide were formed on the surface of the C-ring scratch groove under stress loading.Additionally， the particle size and quantity of the spinel oxide on the outer surface increased with the test duration.The scratching process led to the formation of mechanical microcracks in the scratch groove area， but after long-term immersion， these microcracks did not show significant propagation， indicating that the scratched 690TT alloy has a high resistance to stress corrosion cracking in the secondary circuit simulated environment.

Yanchi Chen, Xiang Chen, Han Chen et al.

In this work, we report a counter-intuitive activation of abnormal grain growth (AGG) in randomly-oriented fine grains (FGs) in an L-PBF Al–Mg–Sc–Zr alloy, which is unlikely from perspectives of curvature-driven grain growth, crystallographic texture or strain-induced boundary migration. The observed spontaneous AGG is understood in light of the growth instability of an arbitrary grain in an evolving particle-pinned polycrystalline aggregation. A generalized criterion for AGG is hence proposed, which efficaciously explains the observed susceptibility of FGs to AGG, the presence of multiple AGG activation sites, and the asynchrony of AGG activation.

David Valverde-Burneo, Natividad García-Troncoso, Ignacio Segura et al.

This research focused on developing an innovative multifunctional cementitious material with both conductive and auxetic properties simultaneously. This novel cement-based metamaterial has different applications, ranging from piezoresistivity to structural energy dissipation. The cementitious composite (CC) with an auxetic structure were produced using additive manufacturing techniques. The study involved analyzing different cementitious compositions, including Ultra High-Performance Concrete (UHPC) formulation tailored for both high strength and workability, and flexible mortar. Both types of composites were combined with two types of fibers: recycled carbon and Polyvinyl Alcohol (PVA). Uniaxial compression tests, conductivity, piezoresistivity by load cycles, and Digital Image Correlation (DIC) analysis were carried out on the auxetic cementitious composite (ACC). Among these tested cementitious composites (UHPC and flexible mortar) reinforced with PVA and recycled carbon fibers, only the flexible mortar with carbon fibers achieved the desired multifunctional properties. This success with flexible mortar and carbon fibers suggests promise for this combination. Conversely, UHPC composites with PVA fibers, with or without additional carbon fibers, failed to achieve the targeted functionality. As a result, both piezoresistivity and auxetic properties were achieved. From the auxetic behavior results, the Poisson’s ratio reached -67.5%. This implies that if compressed longitudinally, the specimen is shortened transversely (auxetic behavior) by up to 67.5%. This finding stands out compared to traditional construction materials like concrete and steel, which typically exhibit much lower strain recoveries (15–30%). On the other hand, the specific deformation energy absorption of the auxetic specimen reached 0.076 Jcm3. Moreover, the resistivity reached the small magnitude of 0.15 Ωm at 50 Hz, proving to be a conductive composite. The gauge factor of 4.26 indicates that it can be used as a self-sensing concrete. This innovative cementitious composite opens new possibilities for future applications that require materials with conductive and auxetic behaviors.

Sergi Parareda, Daniel Casellas, Marc Mares et al.

Determining the fatigue behaviour of metallic materials using standardised testing methods is costly and time-consuming. Therefore, several methods have been proposed to shorten the testing time and improve the fatigue optimisation of materials and components. This work presents a new fatigue testing method based on fatigue damage monitoring that allows determining the fatigue resistance in a short time and with few specimens. The presented method, named as the stiffness method, monitors the inelastic strains as an indicator of fatigue damage evolution. Strain measurements were carried out by digital image correlation techniques and showed to effectively follow damage evolution during fatigue tests. Results are convincing and more evident to obtain and discuss than other monitoring techniques, like temperature dissipation. In addition, the method overcomes the main limitations of the existing fast testing methods by avoiding the utilisation of complex apparatus, like infrared cameras or acoustic emission sensors. The approach has been validated in ten different metallic materials, as titanium and aluminium alloys, carbon steels, and stainless steels. The estimated fatigue limit was compared with values obtained following standardised tests, showing excellent agreement. Results allow pointing out the stiffness method as an efficient and effective tool for rapidly determining the fatigue behaviour of metallic materials.

Jiasi Luo, Wanting Sun, Dingshan Liang et al.

Heterogeneous crystalline-amorphous nanostructures have been documented to show superior strength-ductility synergy via the co-deformation cooperative effects of nanograins and amorphous grain boundaries. In this work, a facile laser surface remelting technique with rapid cooling rate was successfully developed to fabricate a ∼ 100 μm-thick gradient nanostructured layer accompanied by phase decomposition on a TiZrHfTaNb0.2 high-entropy alloy, where a ∼ 5 μm-thick crystalline-amorphous nanostructured top surface layer with an average grain size of ∼ 7 nm was obtained. Such crystalline-amorphous nanostructured layer shows an ultrahigh yield strength of ∼ 6.0 GPa and a compression strain of ∼ 25 % during the localized micro-pillar compression tests. The atomic observations reveal that co-deformation cooperative mechanisms include the well-retained dislocation activities in nanograins but crystallization in amorphous grain boundaries, which subsequently lead to the grain coarsening via grain boundary-mediated plasticity. This study sheds light on the development of high-performance high-entropy alloys with novel crystalline-amorphous nanostructures and provides significant insight into their plastic deformation mechanisms.

Shigang Chen, Soe Ring Jeong, Shanwen Tao

Aqueous rechargeable lithium-ion battery (ARLiB) is of specific importance due to the low-cost, environmental-friendly properties. Recently, its energy denisty and cyclic life have been significantly enhanced, demonstarting the potential for real applications. The improvement on key materials of ARLiB, ranging from cathode, anode and electrolyte, can finally ameliorate coresponding performance of full cell. Hereon, the cathode materials of ARLiBs are summerized as spinel oxides, layered oxides, olivine polyanion compounds olivine and Prussian blue analogues, while anode materials are classified into vanadium-based, polyanion, titanium-based and organic ones. Meanwhile, the strategies for better aqueous electrolytes are discussed from the aspects of salt concentration, solvent and interface. In the last part, issues challenging the commercialization of ARLiBs are provided as well as the suggestions for future research and development.

Sasitha C. Abeyweera, Matas Simukaitis, Qilin Wei et al.

Abstract Selective reduction of CO2 into liquid products such as ethanol through electrochemical catalysis is promising in storing renewable energy in more deliverable chemicals and balancing the carbon footprint in the environment. However, the lack of efficient catalysts for electrochemical CO2 reduction reaction (eCO2RR) makes the promise challenging because the formation of C2+ alcohols requires coupling reactions between the shallow reduction intermediates and deep reduction intermediates that are usually difficult to form on uniform catalyst surfaces simultaneously with appropriate transient kinetics. Herein, we report a new strategy for synthesizing bimetallic nanostructures with high densities of interfaced Ag/Cu boundaries, which facilitate the coupling reaction of the high‐oxidation‐number intermediates (CO) formed on the Ag surface and the low‐oxidation‐number intermediates (CHx) formed on the Cu surface. The synthesis relies on the electrochemical reduction of bilayered nanoplates made of silver thiolate and copper thiolate, resulting in Ag/Cu nanostructures exposing Ag surface, Cu surface, and the Ag/Cu interfaced boundaries. Balancing the accessible surface areas of the Ag surface, Cu surface, and Ag/Cu boundaries is beneficial for maximizing the activity and selectivity of eCO2RR towards ethanol production. Faradaic efficiency of forming ethanol has been observed as high as about 50% using the Ag/Cu nanostructure catalyst with molar ratio nAg:nCu of 1:1. Moreover, the promoted coupling reaction at the Ag/Cu boundaries and surface modification with thiolate anions significantly suppress the undesirable hydrogen evolution reaction, particularly at high cathodic potentials, maintaining high energy efficiency for eCO2RR.

Noura Sinno, Medhat H. Shehata

Sandeep Singh

Min Chen, Xuefeng Zhang, Xuan Xiao et al.

Herein, the effect of adding VC with different contents and Mo _2 C, WC and TaC on the core-rim structure evolution of TiC-based cermets was investigated using x-ray diffraction, scanning electron microscopy and energy-dispersive spectroscopy. Results show that the added secondary carbides exhibiting the same crystal stucture as TiC are prone to solid dissolution in TiC grains and change the core-rim stuctures of TiC-based cermets. With the addition of only VC, (Ti,V)C is the main component in the black core-grey rim structure and increasing the VC content is beneficial for promoting the dissolution process of cores. With the addition of multiple carbides, the core-rim structure in cermet Ta-7 is effectively improved, showing a high percentage of white core-grey rim structures, and the mechanical properties are improved.

Josefa Virginia da Silva Souza, Manoel Ribeiro da Silva, Marcos Antonio da Silva Costa

The aims of this work were to develop a magnetic carrier system consisting of microspheres made of gelatin for controlled release of doxorubicin and to investigate the ability of fructose, glucose, genipin and 1-ethyl-3(3-dimethylaminopropyl)carbodiimide (EDC) as crosslinking agents of gelatin microspheres. In addition, we also investigated the changes in the microspheres’ magnetic properties produced by using magnetite incorporated by three different methods and the doxorubicin release performance by using a constant, oscillating or no external magnetic field. The system obtained with fructose as crosslinker (low toxicity) was superparamagnetic, with high saturation magnetization and release profiles that could be controlled. Among the crosslinkers studied, genipin was the most efficient to reduce the solubility of the gelatin microspheres in water. When ferrous chloride was employed in magnetite synthesis, the Ms showed the highest values (61.6 emu/g), and its use in magnetic gelatin microspheres allowed the production of systems with high magnetization (29.6 emu/g).

ZHI Sheng-xing, LI Xing-gang, YUAN Jia-wei et al.

The Gleeble-3500 thermal simulation tester was used to perform hot deformation behavior on the extruded AZ40 Mg alloy to analyze the trend of the true stress-strain curve after compression and to obtain the influence of the flow stress on the deformation temperature and strain rate. Subsequently, the constitutive equation was constructed for extruded AZ40 alloy based on the hyperbolic-sine relationship, and the thermal processing map of extruded AZ40 alloy was established based on the dynamic material model (DMM), thereby estimating the processing range of extruded AZ40 alloy. The results show that the rheological curve of extruded AZ40 alloy is characterized by obvious dynamic recrystallization. Furthermore, during the compression process, the peak stress of extruded AZ40 alloy decreases with the increase of deformation temperature, while increases with the increase of strain rate. Moreover, the proportion of dynamic recrystallized grains (DRGs) decreases with the increase of the strain rate under the same deformation temperature condition; while the DRGs size increases with the increase of the deformation temperature under the same strain rate condition. The coarse uncrystallized grains show obvious crystallographic orientations of 〈10<span style="border-top: 1px solid; padding-top: 0px;">1</span>0〉‖ND and 〈2<span style="border-top: 1px solid; padding-top: 0px;">1</span><span style="border-top: 1px solid; padding-top: 0px;">1</span>0〉‖ND, while crystallographic orientation of DRGs is random distributed. Finally, through thermal processing map and tissue analysis, the optimal processing window was identified as <i>T</i>=573 K, $\dot \varepsilon $=0.1 s^-1.

S. Sanchez, G. Gaspard, C.J. Hyde et al.

Components manufactured by laser powder bed fusion (LPBF) are limited by their performance for use in critical applications. LPBF materials have microstructural defects, such as suboptimal grain size and morphology, and macroscale anomalies, such as lack of fusion. This results in LPBF components performing below their wrought counterparts for various mechanical properties, such as creep which has seldom been researched. To understand the creep behaviour of LPBF alloy 718, parts were fabricated using different scanning strategies and build orientations and creep tested at 650 °C under a 600 MPa load. Heat treatment increased the creep life by a factor of 5, confirming its necessity. The build orientation and stress state were shown to be determining factors in the creep failure mechanisms. The Meander scanning strategy resulted in a 58% increase in creep life compared to the Stripe strategy, due to the detrimental effects of the numerous laser overlapping regions in the Stripe strategy. For a given strategy, a 24% increase in creep life compared to wrought alloy 718 was observed, indicating that LPBF has the potential to surpass wrought material properties. As a result of this work, it is possible to propose build strategies for high temperature creep applications.

LIU Wei-wei, LIU Shi-zhong, LI Ying et al.

DD6 single crystal superalloy specimens were prepared by spiral crystal selection method. After standard heat treatment the long term aging at 980 ℃ was performed for 2000 h. The influences of the microstructural evolution and mechanical properties of DD6 single crystal superalloy after long term aging at 980 ℃ were studied. The results show that with the prolongation of long term aging time, the size of γ' phase in the alloy increases. After long term aging for 2000 h, the size of γ' phase is about 1 <i>μ</i>m, and there is no TCP phase precipitation,which shows that DD6 alloy has good microstructural stability. The stress rupture life of sample after long term aging for 2000 h is 180.16 h at 980 ℃/243 MPa, which is 56.3% of heat treated state, and 144.42 h at 1070 ℃/130 MPa, which is 35.31% of heat treated state. The fracture mode is microvoid coalescence fracture. The tensile strength and yield strength of the alloy after long term aging for 2000 h are reduced by 5.55% and 5.88% at 760 ℃, and 11% and 10.59% at 980 ℃, respectively.

Arief Suriadi Budiman

谢集祥, 罗钢, 刘浏 et al.

Based on the structural parameters and cooling conditions of Liansteel slab caster, a numerical model of solidification & heat transfer during steel Q235B 230 mm x 1280 mm slab continuous casting is established. The temperature distribution of slab and the variation of shell thickness are studied, and the effects of superheat and casting speed on the temperature of slab and the position of solidification end are also studied. It is concluded that with the increase of superheat and casting speed, the temperature at the center and comer of billet increases as a whole. With the same other parameters, the solidification end and the disappearance position of liquid phase move backward 0. 38 m and 0. 31 m respectively with every 10℃ of superheat increase, and the solidification end and the disappearance position of liquid phase move backward 2. 06 m and 1.4 m respectively with every 0. 1 m/min increase of casting speed. Through numerical simulation, the variation of slab temperature and solidification end position are mastered.

Zizhao Zhang, Xiaoli Guo, Qianli Lv et al.

Because of the arid climate and fragile ecological environment in Xinjiang, China, land reclamation should be carried out after mining. The core of land reclamation is the water content of the surface covering soil. In this paper, the law of water distribution in reclamation reconstructed soil of nonmetal mines in Xinjiang was studied. In order to obtain the law of water distribution in reconstructed soil, we set up an observation system of the neutron probe and tensiometer. The neutron probe was used to monitor the soil water content. The tensiometers were used to obtain the matrix potential of soil for verifying the water distribution in reconstructed soil. Volumetric water content and matrix potential of reconstructed soil during 1-year period of management and irrigation were obtained by long-term monitoring. After one year’s field in situ test, 2424 sets of neutron probe data and 1368 sets of tensiometer data were obtained. By studying the above parameters, we summarized the law of water distribution in reconstructed soil of variable thickness and degree of compaction with nonmetallic waste rock filling. The results showed that covering soil was helpful to retain water content. Whether the soil was compacted or uncompacted, the soil water content at the depth of 10 cm was less than that at other depth of reconstructed soil because it was greatly affected by meteorological factors. The water content of reconstructed soil at 30 cm depth was greater than that at other depths. Under the influence of factors such as the thickness and compaction of the soil, the response time of soil water content and matrix potential to each irrigation infiltration was different. According to the characteristics of reclamation-vegetation such as alfalfa growth in Xinjiang, the thickness of surface reconstructed soil should be not less than 50 cm. Over time, soil that was compacted once was better for the vegetation. The research results could provide a reference for the land reclamation of nonmetallic mines in Xinjiang, China.