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1.
The study of steels which guarantee safety and reliability throughout their service life in hydrogen-rich environments has increased considerably in recent years. Their mechanical behavior in terms of hydrogen embrittlement is of utmost importance. This work aims to assess the effects of hydrogen on the tensile properties of quenched and tempered 42CrMo4 steels. Tensile tests were performed on smooth and notched specimens under different conditions: pre-charged in high pressure hydrogen gas, electrochemically pre-charged, and in-situ hydrogen charged in an acid aqueous medium. The influence of the charging methodology on the corresponding embrittlement indexes was assessed. The role of other test variables, such as the applied current density, the electrolyte composition, and the displacement rate was also studied. An important reduction of the strength was detected when notched specimens were subjected to in-situ charging. When the same tests were performed on smooth tensile specimens, the deformation results were reduced. This behavior is related to significant changes in the operative failure micromechanisms, from ductile (microvoids coalescence) in absence of hydrogen or under low hydrogen contents, to brittle (decohesion of martensite lath interfaces) under the most stringent conditions.  相似文献   
2.
通过试验得出了C105混凝土100 mm×100 mm×100 mm立方体非标准试件抗压强度换算系数以及C105混凝土的标准方差和强度变异系数。采用理论计算,得到了棱柱体抗压强度与立方体抗压强度的比值αc1,并与试验实测平均值进行了比较,验证了理论计算方法的可行性。此外,通过对比分析,探讨了直接外延法和引用公式法两种C105混凝土设计参数计算方法的正确性,研究结果可为C105管桩混凝土的设计和应用提供参考。  相似文献   
3.
《Soils and Foundations》2022,62(5):101205
Global sustainable development faces challenges in greenhouse gas emission, consumption of non-renewable resource and energy, waste landfilling, and environmental pollution. Geotechnical engineering also faces similar challenges; for example, the use of cement and lime for stabilisation/solidification (S/S) of contaminated soil is associated with carbon dioxide (CO2) emission and consumption of limestone and energy. In this context, this study introduces a sustainable S/S method by using an industrial waste, ladle furnace slag (LFS), and a greenhouse gas, CO2, to replace common additives for S/S of lead (Pb)-contaminated soil. LFS was first mixed with Pb-contaminated soils and then CO2 was introduced into the soil for carbonation. The results showed that LFS-stabilised Pb-contaminated soils could achieve CO2 uptake up to 18% of LFS mass. After carbonation, the concentration of leached Pb from contaminated soils was reduced by three orders of magnitude than that without carbonation, demonstrating higher S/S efficacy than cement, lime, and magnesia. Additionally, this method can improve soil strength, as well as reduce non-renewable resource consumption, energy use, LFS landfilling, and additive cost.  相似文献   
4.
Tensile strain development in high-density polyethylene (HDPE) geomembrane (GMB) liner systems in landfills was numerically investigated. A new constitutive model for municipal solid waste (MSW) that incorporates both mechanical creep and biodegradation was employed in the analyses. The MSW constitutive model is a Cam-Clay type of plasticity model and was implemented in the finite difference computer program FLAC?. The influence of the friction angle of the liner system interfaces, the biodegradation of MSW, and the MSW filling rate on tensile strains were investigated. Several design alternatives to reduce the maximum tensile strain under both short- and long-term waste settlement were evaluated. Results of the analyses indicate that landfill geometry, interface friction angles, and short- and long-term waste settlement are key factors in the development of tensile strains. The results show that long-term waste settlement can induce additional tensile strains after waste placement is complete. Using a HDPE GMB with a friction angle on its upper interface that is lower than the friction angle on the underlying interface, increasing the number of benches, and reducing the slope inclination are shown to mitigate the maximum tensile strain caused by waste placement and waste settlement.  相似文献   
5.
通过成分优化(/%:0.35~0.46C,0.6~1.0Cr, 1.50~2.05Ni, 0.18~0.32Mo, 0.1V)、冶炼工艺(3 t VIM+ESR)以及热处理工艺(再次热处理工艺:850℃2 h水冷+590℃5 h水冷)的合理制定,获得了满足指标要求的紧固件用高强高韧SA-540合金钢材料。结果表明,为确保SA-540合金钢高温300℃规定塑性延伸强度Rp0.2≥860 MPa,室温抗拉强度应控制在1150~1170 MPa,仅有20 MPa的强度范围。对于经850℃2 h淬火/水冷+560℃5 h回火/水冷调质处理后室温抗拉强度超标的紧固件,可再次通过重新淬火并提高回火热处理温度(850℃2 h淬火/水冷+590℃5 h回火/水冷)使合金钢拉伸性能满足指标要求。SA-540合金钢淬火后随回火的温度升高,呈现抗拉强度和屈服强度下降、伸长率和断面收缩率增加的变化趋势。添加0.1%V的SA-540合金钢,可明显提高合金钢的强度和塑性指标,但低温冲击性能降低明显。  相似文献   
6.
《Ceramics International》2022,48(3):3544-3553
In this study the effects of thermal shock on the impact damage resistance, damage tolerance and flexural strength of Nextel 610/alumina silicate ceramic matrix composites were experimentally evaluated. Composite laminates with balanced and symmetric layup were gradually heated to 1200°C in an air-based furnace and held for at least 30 min before being removed and immersed in water at room temperature. The laminates were then subjected to low velocity impacts via a hemispherical steel impactor. The resultant damage was characterized non-destructively, following which the laminates were subjected to compression tests. Three-point bend tests were also performed to evaluate the effect of thermal shock on the flexural strength and related failure modes of the laminates. Thermally shocked laminates showed smaller internal damage and larger external damage areas in comparison to their pristine counterparts. For the impact energy and resultant damage size considered, the residual compressive strengths for the thermally shocked and pristine laminates were similar.  相似文献   
7.
《Ceramics International》2022,48(21):31245-31254
Optimization binding system for refractory castables is significant to enhance the service performance. Hydrotalcite has been considered a promoter for high-temperature performance of basic castables, however, its binding property remains to be improved before practical application. In this work, the thermal activated Mg–Al hydrotalcites were incorporated in magnesia castables, and the mutual influence of pre-calcination temperature on the hydration, microstructure, and strength of castables was investigated. The obtained results indicated that the reconstruction of calcined hydrotalcite took place in the hydration process and effectively motivated the hydrolysis. Hydrate was thus promoted and a relatively dense microstructure of magnesia castables was confirmed by X-ray computed tomography analysis. Hydrotalcite pre-calcinated at 300 °C contributed to the highest early strength for castable, and the high-temperature properties also performed better than that of other pre-calcinated hydrotalcite-adding. The enhancement mechanisms of calcined hydrotalcite were attributed to the two following reasons: (ⅰ) the modified microstructure of magnesia castables from the early stage by hydration process, (ⅱ) the further enhanced sinterability inspired by the appropriate thermal activation effect.  相似文献   
8.
Polycrystalline mullite fibers and novel zirconia-toughened mullite (ZTM) fibers with average diameters between 9.7 and 10.3 μm containing 3, 7 and 15 wt.-% tetragonal ZrO2 (ZTM3, ZTM7, ZTM15) in the final ceramic were prepared via dry spinning followed by continuous calcination and sintering in air. A shift in the formation of transient alumina phases and tetragonal ZrO2 to higher temperatures with increasing amounts of ZrO2 was observed. Concomitantly, the mullite formation temperature was lowered to 1229 °C for ZTM15 fibers. X-ray diffraction revealed formation of the desired tetragonal crystal structure of ZrO2 directly from the amorphous precursor. Room temperature Weibull strengths of 1320, 1390 and 1740 MPa and Weibull moduli of 9.5, 7.1 and 9.0 were determined for mullite, ZTM3 and ZTM15 fibers, respectively. Average Young’s moduli ranged from 190 to 220 GPa. SEM images revealed crack-free fiber surfaces and compact microstructures independent of the amount of ZrO2.  相似文献   
9.
High-entropy alloys (HEAs) are composed of multiple principal elements and exhibit not only remarkable mechanical properties,but also promising potentials for developing numerous new compositions.To fully realize such potentials,high-throughput preparation and characterization technologies are especially useful;thereby,the fast evaluations of mechanical properties will be urgently required.Revealing the relation between strength and hardness is of significance for quickly predicting the strength of materials through simple hardness testing.However,up to now the strength-hardness relation for HEAs is still a puzzle.In this work,the relations between tensile or compressive strength and Vickers hardness of vari-ous HEAs with hundreds of compositions at room temperature are investigated,and finally,the solution for estimating the strengths of HEAs from their hardness values is achieved.Data for hundreds of different HEAs were extracted from stud-ies reported in the period from 2010 to 2020.The results suggested that the well-known three-time relation (i.e.,hardness equals to three times the magnitude of strength) works for nearly all HEAs,except for a few brittle HEAs which show quite high hardness but low strength due to early fracture.However,for HEAs with different phase structures,different strengths should be applied in using the 3-time relation,i.e.,yield strength for low ductility body-centered cubic (BCC) HEAs and ultimate strength for highly plastic and work-hardenable face-centered cubic (FCC) HEAs.As for dual-phase or multi-phase HEAs,similar 3-time relations can be also found.The present approach sheds light on the mechanisms of hardness and also provides useful guidelines for quick estimation of strength from hardness for various HEAs.  相似文献   
10.
This study describes the synthesis of ceramics, in which a micrometre-sized Al2O3–ZrO2 nanopowder was used as an oxide base for the hardening of the materials. To a suspension of this mixed metal oxide, the pore-forming crystallisation additives camphor and carbamide were added to produce ceramics with thin permeable pores. Camphor crystallised in the oxide suspension in the form of single pentagonal stars and сarbamide crystallised in the form of thin elongated needles. The use of the different crystallisation additives allowed the formation of ceramics after sintering that have both permeable and complex pore morphologies, where anisotropic properties were observed using carbamide as an additive but not when camphor was used. The total porosity of the resulting ceramics was 51.3%, with a compressive strength in the range of 17.3–92.3 MPa.  相似文献   
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