Friction and Wear Behavior of Resin/Graphite Composite under Dry Sliding

The friction and wear behavior of resin/graphite composite has been investigated using a pin-on-disc configuration under dry sliding condition. The results showed that the resin/graphite composite exhibited much better mechanical and tribological properties compared with the unimpregnated graphite. The friction coefficient was reduced by addition of furan resin, which could also prevent the"dusting" wear at loads more than 15 MPa. The steady and lubricated transfer film was easily formed on the counterpart surface due to the interaction of furan resin and wear debris of graphite, which was useful to reduce the wear rate of the resin/graphite composite. The composite is highly promising for mechanical sealing application and can be used at high load for long time sliding.     

Failure Mechanism of Laminated Damping Steel Sheet during Tensile—Shearing

The tensile-shear failure zone of the laminated damping steel sheet was investigated by scanning electron microscopy and X-ray photoelectron spectroscopy.It is found that there exists cohesive failure in polymer sandwich and sub-boundary failure between the steel sheet and the polymer.The sub-boundary layer is dominantly polymer material.The tensile-shear failure of the laminated damping steel sheet is a process during which the crazes form,grow up and merge into cracks.     

Dielectric,Electromagnetic Interference Shielding and Absorption Properties of Si3N4-PyC Composite Ceramics

Pyrolytic carbon（PyC） was infiltrated into silicon nitride（Si₃N₄） ceramics by precursor infiltration and pyrolysis （PIP） of phenolic resin,and Ni nanoparticles were added into the phenolic resin to change the electric conductivity of Si₃N₄-PyC composite ceramics.Dielectric permittivity,electromagnetic interference（EMI） shielding and absorption properties of Si₃N₄—PyC composite ceramics were studied as a function of Ni content at 8.2—12.4 GHz（X-band）.When Ni nanoparticles were added into phenolic resin,the electric conductivity of the prepared composite ceramics decreased with increasing Ni content,which was attributed to the decrease of graphitization degree of PyC.The decrease in electric conductivity led to the decrease in both permittivity and EMI shielding effectiveness.Since too high permittivity is harmful to the impendence match and results in the strong reflection,the electromagnetic wave absorption property of Si₃N₄—PyC composite ceramics increases with increasing Ni content.When the content of Ni nanoparticles added into phenolic resin was 2 wt%,the composite ceramics possessed the lowest electric conductivity and displayed the most excellent absorption property with a minimum reflection loss as low as -28.9 dB.     

Investigation of Sintering Technology for Composite of Stainless Steel and Partially Stabilized Zirconia

The sintering technology for mixed powedered extrusion rods of different proportions of stainless steel to magnesia partially stabilized zirconia(PSZ) was investigated..The effects of some sintering parameters including holding time ,atmosphere and protective gas pressure on shrinkage,relative density,micostructure,micro-Vickers hardness and compression strength of sintered samples were mainly researched.The experimental results are as follows(1)The shrinkage and the relative density of the sintered samples decrease as increasing stainless steel content in the composite,except for the xase containing 90 percent of stainless steel;(2)The porosity in PSZ matrix rises as increasing the stainless steel content in the composite;(3)Longer sintering holding time ,higher sintering vacuum and gas-pressure sintering process not only enhance the relative density ,but also improve microstructure of composite;(4)Micre-Vickers hardness of PSZ matrix decreases as increasing stainless steel content,while that of stainless steel particles in sintered samples varies unnoticeably.     

Compression Mechanical Behaviour of 7075 Aluminium Matrix Composite Reinforced with Nano-sized SiC Particles in Semisolid State

The 7075 aluminium matrix composite reinforced with nano-sized Si C particles was fabricated by ultrasonic assisted semisolid stirring method. The compression mechanical behaviour of the fabricated composite in semisolid state was investigated. The results show that the microstructure of the composite before semisolid compression consists of fine and spheroidal solid grains surrounded by liquid phase.Semisolid compression led to a nonuniform plastic deformation of solid grains. A slight plastic deformation occurred in the locations near the free surface due to the dependence of deformation on liquid flow and flow of liquid incorporating solid grains. However, obvious plastic deformation occurred in the central location and location contacting to die due to the contribution of plastic deformation of solid grains.The true stress–strain curve of the sample compressed at 500 °C consists of rapid increase of true stress and steady stage. However, rapid increase of true stress and decrease of true stress and steady stage are involved in the true stress–strain curves of the samples compressed at 550, 560, 570, 580 and 590 °C.The true stress–strain curve at 600 °C is similar to that at 500 °C. Apparent viscosity decreases with an increase of shear rate, indicating a shear thinning occurrence. When soaking time increases from 5 min to 15 min, the peak stress and steady stress decrease significantly. A further increase of the soaking time led to a slight change. Peak stress and steady stress increase with increasing volume fraction of Si C particles. A sudden increase or decrease of compression velocity led to a significant increase or decrease of the steady stress. The destruction of the samples compressed at solid state temperature mainly depends on cracks parallel to compression direction. However, the destruction forms of the samples compressed at semisolid temperatures consist of cracks parallel to compression direction and partial collapse. Increasing soaking time led to an obvious change of the destruction forms. Compression velocity affects slightly the macro appearance of the sample compressed at semisolid temperatures.     

Experimental Study on Non—proportional Multiaxial Strain Cyclic Characteristics and Ratcheting of U71Mn Rail Steel

An experimental study was carried out on the strain cyclic characteristics and ratcheting of U71Mn rail steel subjected to non-proportional multiaxial cyclic loading.The strain cyclic characteristics were researached under the strain-controlled circular load path.The ratcheting was investigated for the stress-controlled multiaxial circular,elliptical and rhombic load paths with different mean stresses,stress amplitudes and their histories.The experiment shows that U71Mn rail steel features the cyclic non-hardening/softening, and its strain cyclic characteristics depend greatly on the strain amplitude but slightly on its history.However,the ratcheting of U71Mn rail steel depends greatly not only on the values of mean stress and stress amplitude,but also on their histories.In the meantime,the shape of load path and its history also apparently influence the ratcheting.The ratcheting changes with the different loading paths.     

Microstructure and Performance of 2Y-PSZ／TRIP Steel Composites

2Y-PSZ/TRIP steel composites have been sintered by hot-pressing method. Their microstructure and mechanical properties were investigated by means of SEM, TEM, XRD and static tension, split Hopkinson pressure bar method. The results showed that the strength and elastic modulus of 2Y-PSZ/TRIP steel composites at room temperature decreased with the increase of 2Y-PSZ content. The main reason was that the combining strength was quite weak between the grains of ZrO2. Distortion induced martensite transformation and plasticity during the dynamic loading increased the strength and distortion capability of the composites. The transformation was carried out mainly through twins formation. The shape of martensite induced by distortion was lamellate with substructures of twins. The habit plane was near {259}γ with no mid-ridge and no explosion phenomena. The interface was straight between the austenite and martensite induced by distortion. The increase of 2Y-PSZ content, on the one hand, madethe composite dynamic flow stress improved. Thereby, the fracture strength was improved. On the other hand, it depressed both the distortion capability and the martensite transformation induced by distortion. This resulted in the decrease of dynamic fracture strength.     

Cracking Mechanism of Medium-High Carbon Steel during Hardfacing and Effect of Electrode Composition

In this paper,the temperature and stress fields during hardfacing and the crack mor-phology in welded specimens were studied by using a medium-high carbon steel 60CrMnMo, and a RE-doped electrode for cracking resistance has been developed.The temperature fields on the upper surface of simulated specimens during the hardfacing and the following colding were measured by a thermovision analyzer and the residual stress fields were determined by an X-ray stress analyzer. Both these fields have been simulated by usmg the FEM. The calculated re-sults of the temperature and the residual stress fields talhed with the measured ones quite well. The calcu-lations for establishing the influence of martensite transformation temperatures of the hardfacing metal on the stress distribution m simulated specimens show that,with their lowering,the peaks of tensile residual stress at dangerous positions reduce which is considered to be benefit to avoid the occurence of hardfacing cracks.It is shown that,by adding the RE-oxi     

Microstructure and properties of superplastic welding between 40Cr and CrWMn steels

Superplastic welding of tool steel and structural steel was investigated. The welding between 40Cr and CrWMn steels was carried out under the conditions of temperature 750~780℃, strain rate 2×10-4s-l, compressive stress 50-90 MPa for 3-5 min. The joints show similar strength to that of 40Cr steel and the good metallurgical joining is formed. The structural change occurring during Superpfastic welding was analyzed by metallography and distribution of carbon content in the vicinity of the welding joint was also determined. The mechanism of superplastic welding for steels is proposed to be the disappearance of original bond interfaces caused by atomic diffusion and the grain sliding.     

Microstructures and Mechanical Properties of Al/Mg Alloy Multilayered Composites Produced by Accumulative Roll Bonding

Al/Mg alloy multilayered composites were produced successfully at the lower temperature(280 C) by accumulative roll bonding(ARB) processing technique.The microstructures of Al and Mg alloy layers were characterized by scanning electron microscopy and transmission electron microscopy.Vickers hardness and three-point bending tests were conducted to investigate mechanical properties of the composites.It is found that Vickers hardness,bending strength and stiffness modulus of the Al/Mg alloy multilayered composite increase with increasing the ARB pass.Delamination and crack propagation along the interface are the two main failure modes of the multilayered composite subjected to bending load.Strengthening and fracture mechanisms of the composite are analyzed.     

BS600高强钢油罐车罐体轻量化研究

目的 为了有效降低油罐车的能源消耗和污染物排放,完成油罐车罐体减重30%的轻量化目标。基于有限元仿真与试验,验证使用高强钢替代罐体原材料实现油罐车轻量化方案的可行性。方法 利用ANSYS有限元软件,在3种不同工况下,对使用新材料的罐体进行强度、刚度分析;基于仿真结果,对3.5 mm厚的BS600高强钢板材进行焊接试验、金相组织观察以及拉伸试验,以评估BS600钢的焊接性能;对焊接后的BS600钢材进行小件和大件的弯曲试验,以验证BS600钢的弯曲性能。结果 在3种工况下,罐体的最大应力为288 MPa,小于材料的许用应力,罐体强度满足要求;罐体的最大变形量为5.92 mm,刚度满足要求;焊接后拉伸试样的抗拉强度为720～730 MPa,高于母材强度;焊接接头断口的断裂特性为韧性断裂与脆性断裂的混合断裂;弯曲后的小件BS600板材未出现裂纹,弯曲后的大件罐体焊缝缺陷数量较少,焊缝质量良好。结论 所设计的高强钢材料的厚度符合罐体各工况要求,高强钢的成形工艺可行性良好。罐体减重能达到30%,具有良好的工程应用价值。     

陶瓷棒填充点阵金属夹层结构的制备及抗侵彻实验

为提高轻量化复合装甲的抗侵彻能力,提出了内部填充陶瓷棒并由混杂短切玻璃纤维的环氧树脂封装的点阵金属夹层防护结构。首先,通过弹道冲击实验研究了陶瓷棒填充点阵金属夹层防护结构的抗弹丸侵彻能力;然后,结合失效模式和吸能效率,综合分析了该夹层防护结构的抗侵彻机制。结果表明:陶瓷棒填充点阵金属夹层防护结构的主要失效模式包括点阵金属结构和混杂填充材料的拉伸断裂、陶瓷棒的破裂、面板和背板的局部剪切破坏以及背板的总体弯曲变形。在球形弹丸侵彻过程中,由于点阵金属结构的塑性大变形和剪切扩孔、陶瓷棒和环氧树脂的断裂破坏以及面板的宏观弯曲变形,防护结构的抗侵彻能力得到大幅提高。研究结果可为新型轻质复合装甲的防护设计提供一定参考。      

U型钢板桩的冷弯性能

通过对钢板桩各弯弧位置进行力学检验,以及设计钢板桩锁口拉伸失效实验,并利用光学显微镜观察弯弧处的组织晶粒度变化,综合分析冷弯U型钢板桩的性能。结果认为生产冷弯钢板桩时,截面危险位置出现在内部,而非两端锁口最大弯弧角处;生产冷弯钢板桩时,每个弯弧外的表面晶粒沿宽度方向被拉长,弯弧的内表面晶粒沿厚度方向被挤压拉伸;钢板桩锁口的拉伸失稳过程出现两处明显失效,两种失效方式可用于不同用途的钢板桩冷弯性能检验。     

爆炸-轧制不锈钢／钢复合板复层表面裂纹分析

爆炸轧制不锈钢复合板技术工艺,实现了中薄复合板大面积复材无焊缝的要求,本文探讨了间隙对复合界面的影响及轧制过程中造成复层产生裂纹缺陷的原因,从而找出适合不锈铜／铜爆炸复合间隙的材料。     

取向碳纳米管膜/氰基树脂复合材料的制备与性能强化机制

以浮动催化化学气相沉积法(FCCVD)碳纳米管(CNT)膜为原料,通过氰基树脂溶液浸渍法制备CNT预浸膜,然后采用热辅助牵伸和热压固化的方法制备高取向CNT膜复合材料。详细分析了热处理的温度和树脂溶液浓度对CNT预浸膜拉伸性能的影响,从而得到合适的热辅助牵伸工艺,并考察固化工艺对复合材料性能的影响。在此基础上,从浸润特性、CNT取向程度和层间剪切性能方面揭示CNT膜复合材料力学性能的强化机制。结果表明与传统CNT膜牵伸工艺相比,CNT预浸膜热牵伸工艺更有利于制备高取向CNT膜复合材料。热牵伸的温度和树脂溶液的浓度是制备高取向、低孔隙CNT预浸膜的关键因素。通过固化工艺的改变可有效调控氰基树脂的反应程度碳纳米管薄膜/氰基树脂复合材料的拉伸性能。经高温后固化处理后,CNT膜/氰基树脂复合材料的拉伸强度和模量分别高达2 748 MPa和302GPa。优异的树脂浸润特性、层间剪切强度以及高的CNT取向度使CNT膜复合材料中CNT更有利于协同承载,从而提高其力学性能。     

复合材料夹层板成形性的研究

本文通过弯曲实验对复合材料夹层板的成形性进行了研究。研究表明,和单层金属板相比,夹层板的成形有其特殊规律,胶膜和润滑条件对其成形有较大影响,在弯曲过程中往往会发生反向弯曲,工艺条件的改进可消除这种反向弯曲。     

橡胶/环氧树脂复合补强胶片的制备及性能研究

以丁腈橡胶、天然橡胶及环氧树脂共混制备高分子合金,采用压延法与玻璃纤维布复合成汽车用补强胶片。通过扫描电镜、热分析对高分子合金进行表征,用弯曲强度表征补强胶片对钢板的增强作用,用剪切强度表征丁腈橡胶/天然橡胶/环氧树脂复合材料与钢板的粘接性能。     

钢‒CFRP异质复合B柱的弯曲实验分析

目的 为提高B柱的抗弯性能,通常会在B柱上额外焊接补丁板,但同时也增加了B柱的重量。在原始B柱上铺设碳纤维增强复合材料(CFRP),获得钢?CFRP异质复合B柱,取消B柱的钢制加强板,实现B柱的轻量化。方法 通过热冲压制备原始B柱及带补丁板B柱,并以原始B柱为凹模,采用真空袋压工艺制备钢?CFRP异质复合B柱。基于2018版C?NCAP侧面碰撞实验要求,设计B柱三点弯曲夹具,进行原始B柱、带补丁板B柱及钢?CFRP异质复合B柱的三点弯曲实验,并对其重量及弯曲性能进行分析。结果 原始B柱重量4.1 kg,三点弯曲实验测得其刚度为0.763 kN/mm,最大载荷为21.59 kN,平均力为14.52 kN;带补丁板B柱质量为5.6 kg,三点弯曲实验测得其刚度为1.095 kN/mm,最大载荷为31.08 kN,平均力为18.38 kN;钢?CFRP异质复合B柱总质量4.7 kg,三点弯曲试验测得其刚度为1.071 kN/mm,最大载荷为31.76 kN,平均力为19.58 kN。结论 在保持刚度、最大载荷及平均力等弯曲力学性能不变的前提下,相对于带补丁板B柱,钢?CFRP异质复合B柱可以减轻质量0.9 kg,并且吸能更优,实现了B柱的轻量化。     

复杂载荷下钢带缠绕增强复合管力学特性

为研究海洋油气输送用钢带缠绕增强复合管在复杂载荷下的力学响应特性,考虑非线性接触,建立钢带缠绕增强复合管数值计算模型,研究由内外压、弯曲及拉伸载荷组合作用下钢带缠绕增强复合管的变形及承载性能。结果表明,压差(外压大于内压,≤2 MPa)越大钢带缠绕增强复合管的柔性越高。与纯弯曲相比,拉伸载荷和压差的附加联合作用使钢带缠绕增强复合管柔性降低;与纯拉伸相比,弯曲载荷和压差的附加联合作用则使钢带缠绕增强复合管抗拉承载能力降低。与单一载荷相比,复杂载荷下内、外聚乙烯(PE)管的高应力区位置及内层钢带对称应力分布的路径发生改变。钢带螺旋角度及摩擦系数越大,钢带缠绕增强复合管柔性越低;增大摩擦系数,钢带缠绕增强复合管承载能力提高。组合弯曲载荷下随着钢带螺旋角增大,钢带缠绕增强复合管屈曲时的临界弯矩呈非单调变化,存在极大值。研究结果可为钢带缠绕增强复合管的设计、制造及安全评价提供理论依据。      

铝/钢轧制复合有限元二次开发模拟与实验研究

目的 针对铝/钢两种金属性能差异大,轧制复合存在严重的变形不协调及结合强度低的问题,研究轧辊同径与异径及单辊驱动对复合板协调变形及结合强度的影响.方法 通过有限元二次开发进行模拟建模,并结合同步和异步轧制实验分析板翘曲机理.结果 与铝板接触的轧辊作为主驱动辊可使板变形更协调且结合强度更高,变形翘曲度为0.048,结合强度为34.2 MPa.结论 采用接触铝侧轧辊单侧驱动,双金属界面实现复合的位置更靠近轧辊出口,复合后的双金属界面间的剪应力和所受弯矩较小,制备的铝/钢复合板变形协调性更好,且结合强度更高.