Effect of fretting amplitudes on fretting wear behavior of steel wires in coal mines

Given that fretting wear causes failure in steel wires, we carried out tangential fretting wear tests of steel wires on a self-made fretting wear test rig under contact loads of 9 and 29 N and fretting amplitudes ranging from 5 to 180 μm. We observed morphologies of fretted steel wire surfaces on an S-3000N scanning electron microscope in order to analyze fretting wear mecha-nisms. The results show that the fretting regime of steel wires transforms from partial slip regime into mixed fretting regime and gross slip regime with an increase in fretting amplitudes under a given contact load. In partial slip regime, the friction coefficient has a relatively low value. Four stages can be defined in mixed fretting and gross slip regimes. The fretting wear of steel wires in-creases obviously with increases in fretting amplitudes. Fretting scars present a typical morphology of annularity, showing slight damage in partial slip regime. However, wear clearly increases in mixed fretting regime where wear mechanism is a combination of plastic deformation, abrasive wear and oxidative wear. In gross slip regime, more severe degradation is present than in the other regimes. The main fretting wear mechanisms of steel wires are abrasive wear, surface fatigue and friction oxidation.     

纤维组分比例对玄武岩/聚丙烯复合材料力学性能影响研究

采用非织造加工工艺,将玄武岩纤维和聚丙烯纤维通过开松混合后梳理成网,然后按照一定的尺寸制成预制件,使用模压成型工艺制备玄武岩/聚丙烯复合材料,研究不同比例的玄武岩纤维和聚丙烯纤维对复合材料力学性能的影响,并通过数学方差分析方法确定了影响因素的显著性.结果表明:当玄武岩纤维和聚丙烯纤维的比例为30/70时,复合材料的拉伸、弯曲强度和模量达到最高,最大拉伸强度、弯曲强度分别为92.998 MPa和156.134 MPa,最大拉伸和弯曲模量分别为3.400 GPa和1.288 GPa.     

Preparation and mechanical properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al laminated ceramic matrix composites

Three series of Al2O3/Al laminated ceramic matrix composites,named SPA,SPV and HP,were fabricated by different methods.SPA and SPV were prepared using Al2O3 slices and Al slurry via screen printing and subsequent heat treatment in air or vacuum.HP samples were made by hot pressing the layered stack of Al foils and Al2O3 slices.SEM and XRD were applied to analyze the microstructure and the interlayer crystal phase.The bending strength,fracture toughness and fracture work of the samples made by the three methods were measured and compared.The results show that the composites have much better toughness and higher fracture work than the Al2O3 slice.Among the samples made by the three methods,the samples made by hot pressing have the optimum mechanical performance.The displacement-load curves and fracture mechanism were analyzed.     

UHMWPE/Kaolin复合材料的物性研究--机械性能、耐磨性及其相关关系

按ASTM标准进行拉伸和缺口冲击强度试验，分析釜内聚合和机械混合两种方法制备的高岭土填充超高分子量聚乙烯基(UHMWPE／Kaolin)复合材料的机械性能，分别用MM200磨损试验机和MSH型腐蚀磨损试验机研究这两类复合材料的耐磨性．讨论UHMWPE／Kaolin的机械性能和耐磨性与制备方法和高岭土含量的关系．结果表明：UHMWPE／Kaolin的机械性能与制备方法显著相关，由于高度细化和均匀分散的高岭土颗粒的增强作用及较强的界面结合强度，釜内聚合方法制备的UHMWPE／Kaolin的综合性能比熔融机械混合方法制备的成分相同的复合材料的明显要好．进一步的数据分析发现，UHMWPE／Kaolin的耐磨性与机械强度综合指标有显著的相关关系．     

Fretting wear of steel wires in hoisting ropes

To investigate the fretting wear of steel wires in hoisting ropes, specimens were made of 6 × 19 point contact ropes. A model for the fretting wear was developed and a fretting wear test rig was designed in laboratory. A series of experiments were performed on this test rig. The wear volume was taken as a characteristic parameter to describe the fretting wear in relation to the contact load, reciprocating cycles and amplitude. Moreover, the wear mechanisms were discussed in the fretting process.     

Bonding mechanism of X10CrNi18-8 with Ni/Al_2O_3 composite ceramic by pressureless infiltration

An alloy steel/alumina composite was successfully fabricated by pressureless infiltration of X10CrNi18-8 steel melt on 30%(mass fraction) Ni-containing alumina based composite ceramic(Ni/Al2O3) at 1 600 ℃.The infiltration quality and interfacial bonding behavior were investigated by SEM,EDS,XRD and tensile tests.The results show that there is an obvious interfacial reaction layer between the alloying steel and the Ni/Al2O3 composite ceramic.The interfacial reactive products are(FexAly)3O4 intermetallic phas...     

部分充填混凝土钢箱连续梁抗弯性能研究

为研究部分充填混凝土钢箱连续梁抗弯性能,对2个两跨部分充填混凝土钢箱连续梁和1个空钢箱连续梁试件进行了静力试验研究,获得了试验梁变形发展、截面应变发展、破坏特征等方面试验数据.试验结果表明,部分充填混凝土连续钢箱试验梁的极限承载力是钢箱连续试验梁的1.9倍,延性也增加了大约5倍.提出了部分充填混凝土钢箱连续梁截面抗弯强度计算公式,计算结果与试验结果吻合良好.利用计算公式对连续梁截面强度影响的主要参数进行了分析,表明增大受拉区钢箱翼板厚度,对于提高梁的抗弯承载能力效率最高.     

Processing and properties of 2D SiC/SiC composites by precursor infiltration and pyrolysis

Two-dimensional plain-weave silicon carbide fiber fabric reinforced silicon carbide (2D-SiC/SiC) composites were molded by stacking method and densified through precursor infiltration and pyrolysis (PIP) process. SiC coating was deposited as the fiber/matrix interphase layer by chemical vapor deposition (CVD) technique. Fiber/matrix debonding and relatively long fiber pullouts were observed on the fracture surfaces. Additionally, the flexural strength and elastic modulus of the composites with and without fiber/matrix interphase layer were investigated using three-point bending test and single-edge notched beam test. The results show that the fiber fraction and the porosity of 2D-SiC/SiC composites with and without coating are 27.2% (volume fraction) and 11.1%, and 40.7% (volume fraction) and 7.5%, respectively. And the flexural strength and elastic modulus of 2D-SiC/SiC composites with and without coating are 363.3 MPa and 127.8 GPa, and 180.2 MPa and 97.2 GPa, respectively. With a proper thickness, the coating can effectively adjust the fiber/matrix interface, thus causing a dramatic increase in the mechanical properties of the composites. Foundation item: Project(NCET-07-0228) support by the New Century Excellent Talents in University     

非傅立叶模型层状复合陶瓷结构热传导分析

用非傅立叶热传导模型分析层状复合陶瓷结构的温度场,并与单热涂层结构的结果进行比较,同时进一步研究了夹层热物理性能参数对温度场的影响。研究表明：夹层可以有效地减缓内部结构的温度变化,夹层热物理性能参数（如：松弛时间、声速）对结构层的温度场有明显影响。     

Microstructures and Mechanical Properties of Ceramic/Metal Gradient Thermal Barrier Coatings

1　IntroductionCeramicthermalbarriercoatings (TBCs)sprayedonmetalsubstrateshavebeenusedtoincreasethetempera turelimitsandtodecreasetheheatrejectionforgastur bineanddieselengines .However,themismatchbetweenceramicsandmetalwillcausethermalstresseswhichmayleadtocrackandspallofthecoatings .Functionalgradi entmaterials (FGMs)areanewconceptionfordesigningtheceramic metalthermalbarriercoatings ,whichhasgradientmicrostructureaswellasgradientmaterialprop ertiesandcangreatlydecreasethethermalstresses[…     

Tribological properties of self-lubricating laminated ceramic materials

In order to improve the tribological properties of ceramic composites, Al2O3/TiC-Al2O3/ TiC/CaF2 self-lubricating laminated ceramic composites were prepared by vacuum hot pressing sintering. Experiments were conducted to get mechanical properties and the friction and wear properties were also measured with friction and wear tester. The worn surfaces were observed by scanning electron microscope （SEM） and energy dispersion spectrum （EDS）. The wear resistance properties and the self-lubricating effect of ceramic composites were analyzed. Results show that the Al2O3/TiC-Al2O3/TiC/CaF2 self-lubricating laminated ceramic composites layers are well-defined with a higher bonding strength and the mechanical performances are uniform enough to overcome the anisotropy of weak laminated ceramic composites. In addition, the fracture toughness of Al2O3/TiC layers is also improved. Its friction coefficient and wear rates decrease with the increase of rotation speed and load. Al2O3/TiC-Al2O3/TiC/CaF2 self-lubricating laminated ceramic composites have good wear resistance because of the tribofilm formed by the CaF2 solid lubricants. The wear mechanisms of Al2O3/TiC/ CaF2 layers are abrasive wear and Al2O3/TiC layers are adhesive wear.     

Artificial neural network modeling of mechanical properties of armor steel under complex loading conditions

An artificial neural network (ANN) model is established to predict plastic flow behaviors of the 603 armor steel,based on experiments over wide ranges of strain rates ( 0.001 - 4 500 s -1 ) and tempera...     

钢水余热烧结衬瓷铸钢件的耐磨性

为了将纳米陶瓷粉与其它金属粉料制成复合粉料，借助一种高温胶(自行研制的新产品)将陶瓷复合粉料粘结在铸型(铁型或砂型)的工作表面上，然后将钢水浇铸到型腔中，利用钢水余热将陶瓷复合粉料烧结在铸钢件表面上.结果表明：钢水余热烧结衬瓷技术保证了浇铸时产生较少的气泡，且衬瓷面平整，达到了可以应用的程度.试样的耐磨性有了较大的提高，主要是因为复合陶瓷粉分布均匀，增强了耐磨性.面扫描和线扫描成分分析表明：即使衬瓷层厚度达到200μm，如果表面层的氧化铝颗粒分布不均匀，也不能提高耐磨性.显微组织分析表明，衬瓷层显微组织致密，衬瓷层与基体结合强度高.     

Microstructure and properties of SiC gradiently coated Cf/C composites prepared by a RCLD method

The SiC gradiently coated carbon fiber/carbon (Cf/C) composites were prepared by a two-step rapid chemical liquid depo-sition (RCLD) method. The microstructure and properties of the composites were investigated using X-ray diffraction, scanning elec-tron microscopy together with energy dispersive X-ray analysis, bending tests, and oxidation tests. The experimental results show that the surface layer of the composites is composed of SiC, pyrocarbon, and carbon fibers. Their inner area consists of pyrocarbon and carbon fibers. The SiC content gradiently decreases with increasing distance from the outer surface to the center of the compos-ites. Furthermore, the thickness of the SiC layer increases with increasing tetraethylorthosilicate content and deposition time. SiC coatings have no significant influence on the bending strength of the composites. However, the oxidation resistance of the compos-ites increases with increasing thickness of the SiC layer.     

Fabrication and properties of Al matrix composites strengthened by in situ alumina particulates

New aluminum matrix composites strengthened by Al2O3 particulates through stirring cast by adding NH4Al（SO4）2 to the molten aluminum have been fabricated. TEM observation shows that in-situ Al2O3 particulates are generally spherical and they are uniformly distributed in the Al matrix. Dry sliding wear test results show that the volume loss of the unreinforced Al matrix is about three times that of the Al2O3 reinforced metal matrix composite （MMC） and the volume loss of the MMC fabricated by adding Al2O3 is larger than that of the MMC by adding NH4Al（SO4）2. Lubricating sliding wear test results show that the volume loss of the MMCs increases more slowly than that of the matrix with the increasing of the load.     

一种新型冷轧变形钢筋的力学性能试验分析

对一种新型冷轧变形钢筋进行金相分析和力学性能试验。结果与热轧圆盘母材和I型冷轧扭钢筋作了比较，表明其抗拉强度，表面强度比热轧圆盘母材提高了20％以上，而伸长率δ5大于9．05％，与I型冷轧扭钢筋相比，其塑性性能获得提高。     

Evaluation of statistical strength of bamboo fiber and mechanical properties of fiber reinforced green composites

Green composites made from bamboo fibers and biodegradable resins were fabricated with press molding.On the basis of the Weibull distribution and the weakest-link theory,the statistical strength and distribution of bamboo fiber were analyzed,and the tensile strength of green composites was also investigated.The result confirms that the tensile statistical strength of fiber fits well with two-parameter Weibull distribution.In addition,the tensile strength of bamboo fiber reinforced composites is about 330 MP...     

竹纤维/水泥复合材料力学性能和耐久性的试验研究

利用竹纤维制备了水泥基复合材料,采用正交试验法得到了纤维掺量、纤维长度、减水剂和水灰比四个因素的最佳试验条件.在此基础上测试了该复合材料在不同龄期抗压强度和抗折强度.针对竹纤维的机械性能在碱性水泥浆中会逐渐恶化的缺点,对竹纤维表面预涂了乳液并进行了耐久性对比测试.结果表明,加入预处理的竹纤维制备出的水泥基复合材料的力学性能和耐久性得到了显著改善.     

Microstructure of Steel Fiber Reinforced Polymer—cement—based Composites

Mercury intrusion porosimetry was used to measure the pore structure of steel fiber reinforced polymer-cement-based bomposite.The results indicate that the large pore volume decreases by 57.8%-51.2% and by 87.1%-88% with the addition fo steel fibers and polymers respectively.When both steel fibers and poly-mers are simultaneously added, the large pore volume decreases by 88.3%-90.1% .As a surface active materi-al ,polymer has a favorable water-reduced and forming-film effect, which is contributed to the decrease of the thick-ness of water film and the improvement of the conglutination between the fibers and the matrix.Polymers could form a microstructure network.This network structure and the bone structure of cement hydration products penetrate each other and thus the interpenetrating network with sticky aggregate and steel fiber inside forms.