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1.
《Soils and Foundations》2022,62(1):101103
The present study proposes a new elasto-plastic constitutive model that considers different types of hydrates in pore spaces. Many triaxial compression tests on both methane hydrate-bearing soils and carbon dioxide hydrate-bearing soils have been carried out over the last few decades. It has been revealed that methane hydrate-bearing soils and carbon dioxide hydrate-bearing soils have different strength and dilatancy properties even though they have the same hydrate contents. The reason for this might be due to the different types of hydrate morphology. In this study, therefore, the effect of the hydrate morphology on the mechanical response of gas-hydrate-bearing sediments is investigated through a model analysis by taking into account the different hardening rules corresponding to each type of hydrate morphology. In order to evaluate the capability of the proposed model, it is applied to the results of past triaxial compression tests on both methane hydrate-containing and carbon dioxide hydrate-containing sand specimens. The model is found to successfully reproduce the different stress–strain relations and dilatancy behaviors, by only giving consideration to the different morphology distributions and not changing the fitting parameters. The model is then used to predict a possible range in which the maximum deviator stress can move for various hydrate morphology ratios; the range is defined as the strength-band. The predicted curve of the maximum deviator stress obtained by the constitutive model matches the empirical equations obtained from past experiments. It supports the fact that the hydrate morphology ratio changes with the total hydrate saturation. These findings will contribute to a better understanding of the relation between the microscopic structures and macro-mechanical behaviors of gas-hydrate-bearing sediments.  相似文献   
2.
《Soils and Foundations》2022,62(3):101159
Suffusion erosion, characterized as the selective detachment and transportation of finer particles by seepage flow, is hazardous to the stability and serviceability of geotechnical structures. The removal of finer particles deteriorates the structure and fabric of the soil, leading to the degradation of its mechanical properties. Studies into the effects of suffusion on mechanical behavior have so far produced disparate results depending on the pre-erosion relative density of the specimens tested. To investigate this issue, small cyclic and monotonic loading tests were performed on intact and eroded gap-graded silty sand specimens in three dispersed density states, using a triaxial cell modified for the purpose of erosion. The variation of Young's modulus showed an inverse relationship with the pre-erosion density of the specimen, as the small strain stiffness decreased in the dense cases and increased in the loose cases. Conversely, Poisson's ratio increased in value as suffusion progressed regardless of the initial density of the specimens. In the contractive phase of monotonic loading, the densification of the coarse soil skeleton by the downward seepage flow resulted in a decrease in contractiveness and an increase in secant stiffness. In the dilative phase, the increase in porosity by the erosion of finer particles reduced the dilatancy and peak strength of the specimens. The results suggest that the pre-suffusion density determines the primary locus of affected mechanical behavior in triaxial compression, which shifts from the contractive phase to the dilative phase with the increase in pre-suffusion density. The critical state strength, inferred using stress–dilatancy theory, was largely unaffected by the erosion of finer particles. As the results indicate, pre-erosion density may be of practical significance in assessing the vulnerability to deterioration and collapse of geotechnical formations and structures subjected to suffusion erosion.  相似文献   
3.
《Soils and Foundations》2022,62(5):101206
Coral sand is one kind of the important building materials in coral reef engineering practice. The use of cement as a stabilizing agent can significantly improve the mechanical properties of coral sands and is widely applied in the subbase engineering construction in coral reef islands. Cement-stabilized coral sand structures may contain high contents of fine coral particles and salinity because of the high crushability of coral sands and the existence of seawater surrounding them. In this study, the effects of coral sand powders and seawater salinity on the dynamic mechanical properties of cemented coral sand (CCS) were investigated through the split Hopkinson pressure bar (SHPB) tests and Scanning Electron Microscope (SEM) analysis. It was found that the strength (i.e., the peak stress) of CCS specimens increased firstly and then decreased with the increase of powder content. The specimens reached the maximum peak stress when 3% powder content was included. The initial improvement of CCS strength was attributed to the pore-filling effect of coral powders, namely, the micro pores of the CCS specimens could be more effectively filled with higher percentages of coral powders being used in the experiments. However, excessive coral powders resulted in the reduction of specimen strength because these powders could easily be cemented into agglomerates by absorbing water from the specimens. These agglomerates could reduce the cementation strength between the coarse coral particles and the cement. Meanwhile, the peak stress of CCS specimens was found to be negatively correlated with the average strain rate and the ultimate strain. The degree of specimen fracture was found to be correlated with the amount of specific energy absorption during the tests. Furthermore, the “sulfate attack” caused by the inclusion of salinity of water had different influences on the CCS specimens with different coral powder contents. The ettringite and gypsum produced in “sulfate attack” could fill the pores and lead to cracking of the specimens, significantly affecting the specimen strength.  相似文献   
4.
Geogrid reinforcement can significantly improve the uplift bearing capacity of anchor plates. However, the failure mechanism of anchor plates in reinforced soil and the contribution of geogrids need further investigation. This paper presents an experimental study on the anchor uplift behavior in geogrid-reinforced soil using particle image velocimetry (PIV) and the high-resolution optical frequency domain reflectometry (OFDR). A series of model tests were performed to identify the relationship between the failure mechanism and various factors, such as anchor embedment ratio, number of geogrid layers, and their location. The test results indicate that soil deformation and the uplift resistance of anchor plates are substantially influenced by anchor embedment ratio and location of geogrids, whereas the number of geogrid layers has limited influence. In reinforced soil, increasing the embedment ratio greatly improves the ultimate bearing capacities of anchor plates and affects the interlock between the soil and geogrids. As the embedment depth increases, the failure surfaces gradually change from a vertical slip surface to a bulb-shaped surface that is limited within the soil. The strain monitoring data shows that the deformations of geogrids are symmetrical, and the peak strains of geogrids can characterize the reinforcing effects.  相似文献   
5.
A novel hierarchical structure of bimetal sulfide FeS2@SnS2 with the 1D/2D heterostructure was developed for high-performance sodium-ion batteries (SIBs). The FeS2@SnS2 was synthesized through a hydrothermal reaction and a sulphuration process. The exquisite 1D/2D heterostructure is featured with 2D SnS2 nanoflakes anchoring on the 1D FeS2 nanorod. This well-designed FeS2@SnS2 provides shortened ion diffusion pathway and adequate surface area, which facilitates the Na+ transport and capacitive Na+ storage. Besides, the FeS2@SnS2 integrates the 1D/2D synthetic structural advantages and synthetic hybrid active material. Consequently, the FeS2@SnS2 anode exhibits high initial specific capacity of 765.5 mAh·g−1 at 1 A·g−1 and outstanding reversibility (506.0 mAh·g−1 at 1 A·g−1 after 200 cycles, 262.5 mAh·g−1 at 5 A·g−1 after 1400 cycles). Moreover, the kinetic analysis reveals that the FeS2@SnS2 anode displays significant capacitive behavior which boosts the rate capacity.  相似文献   
6.
An experimental analysis regarding the distribution of the cutting fluid is very difficult due to the inaccessibility of the contact zone within the bore hole. Therefore, suitable simulation models are necessary to evaluate new tool designs and optimize drilling processes. In this paper the coolant distribution during helical deep hole drilling is analyzed with high-speed microscopy. Micro particles are added to the cutting fluid circuit by a developed high-pressure mixing vessel. After the evaluation of suitable particle size, particle concentration and coolant pressure, a computational fluid dynamics (CFD) simulation is validated with the experimental results. The comparison shows a very good model quality with a marginal difference for the flow velocity of 1.57% between simulation and experiment. The simulation considers the kinematic viscosity of the fluid. The results show that the fluid velocity in the chip flutes is low compared to the fluid velocity at the exit of the coolant channels of the tool and drops even further between the guide chamfers. The flow velocity and the flow pressure directly at the cutting edge decrease to such an extent that the fluid cannot generate a sufficient cooling or lubrication. With the CFD simulation a deeper understanding of the behavior and interactions of the cutting fluid is achieved. Based on these results further research activities to improve the coolant supply can be carried out with great potential to evaluate new tool geometries and optimize the machining process.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-021-00383-w  相似文献   
7.
8.
 板坯连铸结晶器液面的波动行为是结晶器内钢液流动、结晶器自身振动以及辊子挤压铸坯内部未凝固的钢液造成液面波动综合作用的结果。结晶器液位波动的稳定性对板坯连铸过程的卷渣行为有直接影响。在工业板坯连铸生产实践中,一般在结晶器某一区域(比如结晶器中部)利用放射源或涡流传感器检测液位波动来代表该工况下的整体波动水平。利用三维气液两相流动的数学模型研究了浇铸参数对结晶器液位轮廓的影响,浇铸参数包括拉速、吹氩流量、浸入式水口出口角度和浇铸断面。研究结果表明,结晶器不同宽度位置的波动幅值差异较大,且与工艺参数密切相关。液面的波峰与波谷之差随着拉速的增加在窄面附近逐渐增大,随着吹氩流量的增加在水口附近逐渐增大。在水口出口角度15°条件下,水口和窄面附近的液位波动均较大,而在水口出口角度45°条件下,仅在水口附近存在较大的液位波动。研究结果表明,使用板坯连铸常规的15°浸入式水口,当铸坯宽度大于800 mm时,结晶器液面检测需要在水口和窄面附近同时布置液位检测设备,以便更全面反应结晶器的真实液面行为,使液面波动对轧板表面质量指导性增强,有效提高连铸工艺的控制水平。如使用45°浸入式水口可以继续沿用原有的液位检测布置。  相似文献   
9.
张宁飞  崔志强  王婕  侯清宇  黄贞益 《钢铁》2022,57(10):170-177
 为了分析硅镍合金化奥氏体基低密度钢在中温环境下的拉伸变形行为,采用Instron电子拉力试验机对Fe-28.64Mn-8.99Al-1.68Si-1.39Ni-1.0C(Mn29Al9Si2Ni,质量分数/%)低密度钢在23~300 ℃下进行了温拉伸试验,研究了该钢的温拉伸力学行为,并采用SEM、TEM和热力学计算对该钢的强韧化机制进行了研究。结果表明,随着应变的增加,温拉伸应力-应变曲线主要包括弹性变形、均匀塑性变形和断裂等几个过程,没有明显的屈服现象。随着温度的提高,该钢的强度逐渐降低,塑性(断后伸长率)先增加后减小再升高,于200 ℃时出现塑性低谷,此时该钢的应力-应变曲线和应变硬化率曲线均具有明显的锯齿状特征,应变硬化率随应变的增加变化不大。而该钢在其他温度下的应力-应变曲线和应变硬化率曲线没有发现明显的“锯齿状”特征,应变硬化率随应变的增加而平缓下降。试验钢在23~300 ℃下的主要强韧化机制为κ-碳化物强化、应变强化、孪生诱发塑性和动态应变时效强化。较低温度下位错可动性较差对孪生诱发的促进作用、镍元素和硅元素对孪生的抑制作用、较高温度下孪生现象的减弱和温度对动态应变时效的促进或抑制作用等使得试验钢在23、100和300 ℃时存在明显的孪生诱发塑性,而在200 ℃时存在明显的动态应变时效强化的主要原因。动态应变时效强化是该钢在200 ℃时出现塑性低谷的主要原因。  相似文献   
10.
彭宁琦  付贵勤  杨建华  周文浩  朱苗勇 《钢铁》2022,57(12):152-160
 针对Q690q耐候桥梁钢,利用MMS-300热模拟试验机进行焊接热循环过程模拟试验,研究了10.5~114.9 kJ/cm热输入下粗晶热影响区(CGHAZ)、细晶热影响区(FGHAZ)和不完全相变热影响区(ICHAZ)的微观组织以及冲击韧性、硬度的变化情况,并观察了冲击断口形貌,然后采用优选的焊接热输入,进行了免预热的药芯焊丝熔化极气体保护焊(FCAW)和埋弧焊(SAW)的焊接工艺评定试验。结果表明,热输入较低时,CGHAZ和FGHAZ主要生成板条马氏体组织、ICHAZ出现岛状的M/A组元,其冲击韧性低、硬度高;热输入较高时,CGHAZ主要生成大尺寸的粒状贝氏体、准上贝氏体或上贝氏体组织,同时大尺寸的块状M/A组元数量不断增加、尺寸变大,其冲击韧性显著降低。FGHAZ生成较多多边形或准多边形铁素体、珠光体等高温转变组织,其硬度降低明显。ICHAZ除生成准多边形铁素体、无碳化物贝氏体和退化珠光体外,回火索氏体基体组织中的碳化物颗粒尺寸不断变大,其强韧性不断降低;热输入为18.2~25.7 kJ/cm时,CGHAZ以板条束细小且异向的板条贝氏体为主、FGHAZ形成细小均匀的板条贝氏体和粒状贝氏体组织、ICHAZ主要为细小的回火索氏体和板条贝氏体组织等,试验钢热影响区各亚区均具有高冲击韧性和与母材相当的硬度。因此,优选焊接热输入应控制在18.2~25.7 kJ/cm范围内。采用(22±1) kJ/cm的焊接热输入,开发的40 mm厚Q690q耐候桥梁钢板在免预热焊接条件下的FCAW和SAW焊接接头均具有良好的可焊性和焊接性能,热影响区的强韧性与母材相差不大。从而成功实现了Q690q耐候桥梁钢免预热焊接的实验室尝试。  相似文献   
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