干湿交替下黄土区苜蓿根系抗拔力学性能

[目的]研究黄土区干湿交替过程对草本植物根系抗拔力学性能的影响,以期为草本植物根系固土护坡工程提供一定的理论支持和依据。[方法]选取紫花苜蓿为研究对象,采用重塑土根系拉拔试验,研究苜蓿根系抗拔力学性能及其与根径、根长、土壤容重、干湿交替作用等影响因素的关系。[结果](1)苜蓿根系抗拔力学性能指标与根径、根长和土壤容重存在幂函数或指数函数关系。(2)相比未干湿交替试样,干湿交替试样根系抗拔力学性能指标均显著减小。(3)砂壤土中苜蓿根系抗拔力学性能指标均优于壤土,且干湿交替在砂壤土中对苜蓿根系抗拔力学性能指标的影响小于在壤土中的影响。(4)根径、根长及容重和干湿交替的耦合作用对根系抗拔力学性能指标有显著影响。[结论]在干湿交替作用下,根径、根长和土壤容重对苜蓿根系抗拔力学性能有一定影响。

CKBZ新型保温暖砖抗剪力学性能试验研究

对CKBZ新型环保暖砖的抗剪力学性能进行试验研究.暖砖抗剪试验共制作了8件暖砖试件,抗剪试验试件将在微机控制电液伺服压力机上进行,记录试件抗剪试验过程中的破坏规律和试件破坏时的荷载,对抗剪破坏荷载数据进行分析.通过抗剪破坏荷载数据分析结果与小型混凝土灌孔砌块砌体的抗剪性能相对比,提出适用于CKBZ新型保温暖砖的抗剪强度公式.

中介相沥青基碳纤维的力学性能

系统地论述了高性能中介相沥青基碳纤维的力学性能及其与原料、纺丝工艺、氧化/碳化/石墨化温度、纤维形状及尺寸、超分子结构和环境温度等之间的关系。与其它高级液晶聚合物纤维和PAN基碳纤维相比,中介相沥青基碳纤维显示较高的杨氏模量、抗压模量、抗张强度和抗压强度,最高可分别达1020GPa、770GPa、6.2GPa和3.5GPa。

热带雨林地区乔木树根力学性能试验研究

针对海南地区四类热带乔木树根进行室内抗拉、抗剪力学性能的研究;结合根簇形态特征,对四类树种单根力学性能进行分析。研究结果表明:随着根径增加,四类树种单根抗拉力明显增加,而单根抗拉强度则呈降低趋势;随根径的增加,树根抗剪力逐渐增加,单根抗剪强度则逐渐减小;树根在根系中的生长方向和分布密度对树根的力学性质产生影响,竖直向下生长的主根主要提供抗剪强度及抗拉强度,而与主根簇中主根夹角越大的树种,其侧根所提供的抗剪强度相应越小;结合边坡工程对植被的要求,认为小叶榄仁及凤凰木的各方面力学特征优于同试验的其它树种,表现出更好的工程适用性。

受阻胺抗氧剂对PA6工业丝热氧老化性能的影响

通过尼龙6(PA6)工业丝和添加质量分数为0.5%的受阻胺抗氧剂N,N′-二(2-萘基)对苯二胺(DNP)的尼龙6(PA6-DNP)工业丝的热性能和在热氧化过程中的力学性能的对比,研究了DNP对PA6工业丝的性能影响。结果表明:DNP不改变PA6工业丝的熔融温度,但会引起晶型的变化,对在氮气氛围下的热分解影响不大,对氧气氛围下的热氧化分解有抑制作用,分解温度提高了5.5℃;在高温热氧老化中,DNP的加入,PA6工业丝的断裂强度、断裂伸长率损失有所减少,初始模量没有变化。

抗裂剂对钢壳混凝土收缩及热学性能的影响

为了解决钢壳混凝土自身的收缩变形及徐变造成的混凝土与钢管壁极易产生严重的脱空、脱黏问题,针对南京长江五桥索塔钢壳混凝土的无收缩、微膨胀要求,对混凝土配合比进行了研究,测试了标准混凝土力学强度。分别对20℃条件下C50混凝土的限制膨胀率、自生体积变形进行了测试,系统研究了具有温控效果的抗裂剂对C50混凝土的力学、恒温变形、热学性能及变温下的变形规律的影响。对不同掺量抗裂剂对C50混凝土力学性能的影响、限制膨胀率的影响、自生体积变形的影响、热学性能的影响进行了统计分析,模拟了某段塔柱温度历程的C50混凝土的变形。结果表明:索塔混凝土中未掺入适量的抗裂剂时,其绝湿条件下表现为收缩,钢索塔脱空的风险极大;掺入具有温控效果的抗裂剂的C50混凝土后期强度增幅超过基准混凝土;抗裂剂掺量较低时,抗裂剂产生的膨胀变形无法抵御混凝土的自收缩,掺入适量的抗裂剂后,混凝土绝湿限制条件下不收缩(具有一定的微膨胀性能);具有温控效果的抗裂剂,通过降低水泥水化热过程中加速期水化放热速率,可延长水泥水化加速期放热过程。总胶材450 kg/m^(3),水泥用量245 kg/m^(3),抗裂剂掺量为30 kg/m^(3)的C50混凝土能满足钢索塔不脱空的设计要求。

Mechanical Properties and Thermal Shock Resistance of SrAl_(2)Si_(2)O_(8) Reinforced BN Ceramic Composites

Hexagonal boron nitride(h-BN)ceramics have become exceptional materials for heat-resistant components in hypersonic vehicles,owing to their superior thermal stability and excellent dielectric properties.However,their densification during sintering still poses challenges for researchers,and their mechanical properties are rather unsatisfactory.In this study,SrAl_(2)Si_(2)O_(8)(SAS),with low melting point and high strength,was introduced into the h-BN ceramics to facilitate the sintering and reinforce the strength and toughness.Then,BN-SAS ceramic composites were fabricated via hot press sintering using h-BN,SrCO_(3),Al_(2)O_(3),and SiO_(2) as raw materials,and effects of sintering pressure on their microstructure,mechanical property,and thermal property were investigated.The thermal shock resistance of BN-SAS ceramic composites was evaluated.Results show that phases of as-preparedBN-SAS ceramic composites are h-BN and h-SrAl_(2)Si_(2)O_(8).With the increase of sintering pressure,the composites’densities increase,and the mechanical properties shew a rising trend followed by a slight decline.At a sintering pressure of 20 MPa,their bending strength and fracture toughness are(138±4)MPa and(1.84±0.05)MPa·m^(1/2),respectively.Composites sintered at 10 MPa exhibit a low coefficient of thermal expansion,with an average of 2.96×10^(-6) K^(-1) in the temperature range from 200 to 1200℃.The BN-SAS ceramic composites prepared at 20 MPa display higher thermal conductivity from 12.42 to 28.42 W·m^(-1)·K^(-1) within the temperature range from room temperature to 1000℃.Notably,BN-SAS composites exhibit remarkable thermal shock resistance,with residual bending strength peaking and subsequently declining sharply under a thermal shock temperature difference ranging from 600 to 1400℃.The maximum residual bending strength is recorded at a temperature difference of 800℃,with a residual strength retention rate of 101%.As the thermal shock temperature difference increase,the degree of oxidation on the ceramic surface and cracks due to thermal stress are also increased gradually.

Evolution of mechanical properties,localized corrosion resistance and microstructure of a high purity Al-Zn-Mg-Cu alloy during non-isothermal aging

The evolution of mechanical properties,localized corrosion resistance of a high purity Al-Zn-Mg-Cu alloy during non-isothermal aging(NIA)was investigated by hardness test,electrical conductivity test,tensile test,intergranular corrosion test,exfoliation corrosion test,slow strain rate tensile test and electrochemical test,and the mechanism has been discussed based on microstructure examination by optical microscopy,electron back scattered diffraction,scanning electron microscopy and scanning transmission electron microscopy.The NIA treatment includes a heating stage from 40℃to 180℃with a rate of 20℃/h and a cooling stage from 180℃to 40℃with a rate of 10℃/h.The results show that the hardness and strength increase rapidly during the heating stage of NIA since the increasing temperature favors the nucleation and the growth of strengthening precipitates and promotes the transformation of Guinier-Preston(GPI)zones toη'phase.During the cooling stage,the sizes ofη'phase increase with a little change in the number density,leading to a further slight increase of the hardness and strength.As NIA proceeds,the corroded morphology in the alloy changes from a layering feature to a wavy feature,the maximum corrosion depth decreases,and the reason has been analyzed based on the microstructural and microchemical feature of precipitates at grain boundaries and subgrain boundaries.

基于高镍NCA811正极的21700锂离子电池在某装备上的应用研究

武器装备对储能电源的需求越来越向着更高比能量、极端温度条件、高抗力学等苛刻的应用要求发展。采用基于高镍NCA体系且已商业化应用的圆柱形21700锂离子电池作为对象,针对具体的实际应用工况,研究了单体电池及电池模组在某装备上应用的可能性。实验结果表明,圆柱形21700锂离子电池在电性能、极端温度条件、抗力学性能及安全性上均满足应用指标要求,可以用作该装备的储能电源。

Microstructure, mechanical and oxidation characteristics of detonation gun and HVOF sprayed MCrAlYX coatings

Microstructure, mechanical property and oxidation resistance of MCrAlYX coatings prepared by detonation gun (D-gun) and HVOF spraying were investigated. Lamellar microstructure and uniform microstructure formed in D-gun sprayed MCrAlYX coating and HVOF sprayed coating, respectively. Element redistribution and formation of new phase took place during the detonation process. Besides, the porosity of D-gun sprayed coating was much lower than that of HVOF sprayed coating. On the mechanical property, the micro-hardnesses of the two coatings were in the same level (~HV 910). However, D-gun sprayed MCrAlYX coating exhibited larger standard deviation of microhardness due to its lamellar microstructure, and exhibited better bend bonding strength owing to the existence of residual compressive stress between the layers and particles. Meanwhile, due to the much more compact microstructure, D-gun sprayed MCrAlYX coating showed superior oxidation resistance to the HVOF sprayed coating. The continuous dense protective layer can form earlier in D-gun sprayed coating and thus suppress further oxidation and control the oxide thickness at a relatively low level.

Tensile and wear properties of TiC reinforced 420 stainless steel fabricated by in situ synthesis

TiC particle reinforced 420 stainless steel matrix composites were fabricated, and the microstructure, tensile properties and wear resistance of the composites were studied. The experimental results indicate that the distribution of TiC particles with size of 5 to 10 μm in diameter is uniform if the volume fraction of TiC is lower than 6%. However, slight agglomeration can be observed when the TiC content exceeds 6%. With the increase of TiC content the tensile and yield strength of the composites prepared increases and reaches the maximum when the volume fraction of TiC increases to 5%. Further increase of TiC content causes reductions of yield and tensile strength. The ductility of the composites shows a monotone decrease with the increase of TiC addition. The introduction of TiC into 420 stainless steel results in significant improvement on wear resistance, which reaches a steady level when the volume fraction of TiC increases to 11% and does not show obvious variation if the TiC content is further increased.

Effects of T9I6 thermo-mechanical process on microstructure, mechanical properties and ballistic resistance of 2519A aluminum alloy

The effects of T916 thermo-mechanical process on microstructures, mechanical properties and ballistic resistance of 2519A aluminum alloy were investigated by optical microscopy （OM）, transmission electron microscopy （TEM）, tensile tests and ballistic resistance test. After T916 treatment, the yield strength, tensile strength and elongation rate of 2519A aluminum alloy reach 501 MPa, 540 MPa and 14%, respectively. And the ballistic limit velocity of 2519A-T916 alloy （30 mm in thickness） is 715 rn/s. The microstructure varies near the sidewalls of crater. The interrupted ageing contributes to these excellent properties of the alloy. During T916 process, the precipitation of Guinier Preston （GP） zone is finer and denser during the interrupted ageing, thus resulting in well precipitated strengthening phase.

Numerical and experimental study on seismic behavior of concrete-filled T-section steel tubular columns and steel beam planar frames

The seismic behavior of planar frames with concrete-filled T-section columns to steel beam was experimentally and numerically studied. A finite element analysis （FEA） model was developed to investigate the engineering properties of the planar frames. Two 1：2.5 reduced-scale specimens of T-section concrete-filled steel tubular column and steel beam of single-story and single-bay plane frames were designed and fabricated based on the design principles of strong-column, weak-beam and stronger-joint. One three-dimensional entity model of the investigated frame structure was built using a large-scale nonlinear finite-element analysis software ABAQUS. Experimental results show that the axial compression ratio has no effect on the failure mode of the structure, while with the increase of axial compression ratio and the dissipated energy ability increasing, the structural ductility decreased. The results from both experiments and simulations agree with each other, which verifies the validity and accuracy of the developed finite element model. Furthermore, the developed finite element model helps to reflect the detailed stress status of the investigated frame at different time and different positions.

Modeling hot strip rolling process under framework of generalized additive model

This research develops a new mathematical modeling method by combining industrial big data and process mechanism analysis under the framework of generalized additive models(GAM)to generate a practical model with generalization and precision.Specifically,the proposed modeling method includes the following steps.Firstly,the influence factors are screened using mechanism knowledge and data-mining methods.Secondly,the unary GAM without interactions including cleaning the data,building the sub-models,and verifying the sub-models.Subsequently,the interactions between the various factors are explored,and the binary GAM with interactions is constructed.The relationships among the sub-models are analyzed,and the integrated model is built.Finally,based on the proposed modeling method,two prediction models of mechanical property and deformation resistance for hot-rolled strips are established.Industrial actual data verification demonstrates that the new models have good prediction precision,and the mean absolute percentage errors of tensile strength,yield strength and deformation resistance are 2.54%,3.34%and 6.53%,respectively.And experimental results suggest that the proposed method offers a new approach to industrial process modeling.

Microstructure,anticorrosion,biocompatibility and antibacterial activities of extruded Mg−Zn−Mn strengthened with Ca

To find suitable biodegradable materials for implant applications,Mg−6Zn−0.3Mn−xCa(x=0,0.2 and 0.5,wt.%)alloys were prepared by semi-continuous casting followed by hot-extrusion technique.The microstructure and mechanical properties of Mg−6Zn−0.3Mn−xCa alloys were investigated using the optical microscope,scanning electron microscope and tensile testing.Results indicated that minor Ca addition can slightly refine grains of the extruded Mg−6Zn−0.3Mn alloy and improve its strength.When 0.2 wt.%and 0.5 wt.%Ca were added,the grain sizes of the as-extruded alloys were refined from 4.8 to 4.6 and 4.2μm,respectively.Of the three alloys studied,the alloy with 0.5 wt.%Ca exhibits better combined mechanical properties with the ultimate tensile strength and elongation of 334 MPa and 20.3%.The corrosion behaviour,cell viability and antibacterial activities of alloys studied were also evaluated.Increasing Ca content deteriorates the corrosion resistance of alloys due to the increase of amount of effective cathodic sites caused by the formation of more Ca2Mg6Zn3 phases.Cytotoxicity evaluation with L929 cells shows higher cell viability of the Mg−6Zn−0.3Mn−0.5Ca alloy compared to Mg−6Zn−0.3Mn and Mg−6Zn−0.3Mn−0.2Ca alloys.The antibacterial activity against Staphylococcus aureus is enhanced with increasing the Ca content due to its physicochemical and biological performance in bone repairing process.

Effects of SiC interfacial coating on mechanical properties of carbon fiber needled felt reinforced sol-derived Al2O3 composites

3D carbon fiber needled felt and polycarbosilane-derived SiC coating were selected as reinforcement and interfacial coating,respectively,and the sol-impregnation-drying-heating(SIDH)route was used to fabricate C/Al2O3 composites.The effects of Si C interfacial coating on the mechanical properties,oxidation resistance and thermal shock resistance of C/Al2O3 composites were investigated.It is found that the fracture toughness of C/Al2O3 composites was remarkably superior to that of monolithic Al2O3 ceramics.The introduction of SiC interfacial coating obviously improved the strengths of C/Al2O3 composites although the fracture work diminished to some extent.Owing to the tight bonding between SiC coating and carbon fiber,the C/SiC/Al2O3 composites showed much better oxidation and thermal shock resistance over C/Al2O3 composites under static air.

Effects of niobium addition on microstructure and properties of CPM121 powder metallurgy high-speed steel

Massive vanadium additions as hard phases in powder metallurgy high-speed steels(PM HSS)lead to higher cost and bad machinability.In this study,ultrahigh alloy PM HSS with CPM121(10W-5Mo-4Cr-10V-9Co,wt.%)as the basic composition,was directly compacted and activation sintered with near-full density(>99.0%)using pre-oxidized and ball-mixed element and carbide powders.Niobium-alloyed steels(w(V)+w(Nb)=10 wt.%)show higher hardness and wear resistance,superior secondary-hardening ability and temper resistance.But excess niobium addition(>5 wt.%)leads to coarsened carbides and deteriorated toughness.EPMA results proved that niobium tends to distribute in MC carbides and forces element W to form M6C and WC carbides.Further,the role of rotary forging on properties of niobium-alloyed steels(S3)was researched.After rotary forging with deformation of 40%,the bending strength and fracture toughness of niobium-alloyed steels could be further improved by 20.74%and 43.86%compared with those of sample S3 without rotary forging,respectively.

Effect of T6I6 treatment on dynamic mechanical behaviour of Al-Si-Mg-Cu cast alloy and impact resistance of its cast motor shell

The effect of T6I6 treatment on the dynamic mechanical and microstructure behaviour of Al-Si-Mg-Cu cast alloy was investigated using split Hopkinson pressure bar(SHPB), transmission electron microscopy(TEM), and highresolution transmission electron microscopy(HRTEM). Besides, the impact resistances of T6I6 and T6 motor shells of new energy vehicles made of Al-Si-Mg-Cu cast alloy were compared using a trolley crash test. The results indicated that the main strengthening-phases of the T6 peak-aged and T6I6 peak-aged alloy were GP zone and β″ precipitates. T6I6treatment can increase the density and size of β″ precipitates in peak-aged alloy and enhance both its tensile strength(σb)and elongation(δ). The dynamic toughness values of T6I6 samples are 50.34 MJ/m^(3) at 2000 s^(-1) and 177.34 MJ/m^(3) at 5000 s^(-1) which are 20% and 12% higher than those of T6 samples, respectively. Compared with a T6 shell, the overall deformation of T6I6 shell is more uniform during the crash test. At an impact momentum of 3.5×10;kg·m/s, the T6I6shell breaks down at 0.38 s which is 0.10 s later than the T6 shell.

Preparation of three-dimensional braided carbon fiber reinforced mullite composites from a sol with high solid content

To prepare the three-dimensional braided carbon fiber reinforced mullite （3D C/mullite） composites, an Al2O3-SiO2 solwith a solid content of 20% （mass fraction） and an Al2O3/SiO2 mass ratio of 2：1 was selected as the raw material. Characteristics andmullitization of the sol were analyzed throughly. It is found that the formation of mullite is basically completed at 1300℃ and thegel powders exhibit favorable sintering shrinkage. The 3D C/mullite composites without interfacial coating were fabricated throughthe route of vacuum impregnation-drying-heat treatment. Satisfied mechanical properties with a flexural strength of 241.2 MPa anda fracture toughness of 10.9 MPa·m1/2are obtained although the total porosity reaches 26.0%. Oxidation resistances of the compositesat 1200, 1400 and 1600 ℃ were investigated. Due to the further densification of matrix, the 3D C/mullite composites show tiny massloss and their mechanical properties are well retained after oxidation at 1600 ℃ for 30 min.

The application of nanotechnology in the improvement of dental composite resins

In this paper, nanotechnology for the improvement of dental composite resins has been reviewed in the background of the existing shortcomings, focusing on the improvement for polymerization shrinkage, anti-bacterial properties and mechanical properties of composite resins. The results show that the use of nanotechnology and nano materials can be an effective method to improve the performance of dental composite resins in a various ways. At last, the paper also discusses the perspective about the dental composite resins.