平点自冲铆接过程的数值模拟分析

为研究平点自冲铆接过程,以两层厚度均为1mm的铝板AL-1100以及材质结构为合金结构钢DIN 14NiCr14的半空心铆钉为研究对象,借助于有限元分析软件Deform-2D进行数值模拟并得到强度合适的接头以及冲头载荷随位移变化的曲线;选取接头自锁量和底部最小厚度作为评价指标,研究了不同铆钉高度对接头的影响。结果表明:平点自冲铆接技术是可行的;铆钉腿部的变形是引起冲头载荷迅速增加的主要因素;随着铆钉高度的增加,两个评价指标的变化曲线几乎呈线性关系。     

风载荷下机载复合材料天线罩强度有限元分析

机载天线罩对重量要求高,需要承受较大的风载荷,多采用复合材料以满足要求,因此需要对天线罩进行强度校核。文中针对某机载天线罩首先进行风载荷的计算流体动力学（Computational Fluid Dynamics, CFD）有限元仿真,然后利用ANSYS ACP进行复合材料结构铺层设计,进一步通过流固耦合方法在计算风压工况的条件下对天线罩强度进行分析,最后通过许用应力、变形情况以及复合材料多失效准则校核对天线罩结构设计安全性做出判断。该机载天线罩在要求的风载荷条件下满足使用要求。     

多途径提高冲头使用寿命的实验研究

冲头在冲裁金属零件时承受着较大的周期性冲击,导致冲头出现崩刃或折断两类主要失效形式。解决的主要方法：一是合理设计冲头的形状与结构,减少应力集中和冲击力的幅度;二是恰当地选用材料,并对材料进行合适的热处理,使材料具有良好的综合机械性能。通过对冲头刃口的改进,换用T8钢,对等温淬火的各种参数进行实验和优选,使材料淬火后得到下贝氏体组织,极大地改善了冲头抗冲击能力,有效提高了冲头的使用寿命。     

热锻模具的韧性要求

通过两类热锻模(精铸热锻模和锻造热锻模)的现场应用，分析热锻模的使用工况条件和失效机理，探讨了热锻模工况条件、失效形式、寿命与热锻模韧性的关系。结果表明：热锻模的脆性断裂是小能量多次冲击下的裂纹萌生、扩展至断裂，在热锻模生产和应用中不宜用冲击韧性作为韧性指标，片面地要求热锻模具有高的冲击韧性是不利的，锻模韧性要求应为多冲抗力，它是一定塑性的基础上以强度为主的韧性问题。     

离子增强沉积Ti/Mo多层膜对钛合金微动疲劳行为的影响

为提高Ti6Al4V钛合金微动疲劳抗力,利用离子增强磁控溅射沉积技术制备了不同结构的Ti/Mo金属多层膜,评价了膜层的结合强度、韧性、硬度等力学性能和摩擦学性能,对优选出的Ti/Mo多层膜进行微动疲劳试验.研究结果表明:离子增强磁控溅射沉积的Ti/Mo金属多层膜膜层结晶细致,膜基结合强度高,有效地提高了钛合金基材的耐磨...     

泡沫镍夹层结构自冲铆接头的成形特征及失效机理分析

为揭示泡沫镍夹层结构自冲铆接头的成形特征及失效机理,本文制备了以AA5052铝合金为基板,泡沫镍为夹层的自冲铆接头;采用理论分析与微观组织观察相结合的方法对夹层结构接头成形特征进行系统研究,通过拉伸-剪切试验研究接头的静失效载荷及失效位移,探究了接头的失效机理。结果表明:泡沫镍夹层可增大接头的钉脚张开度,并改善应力分布;铆接过程中泡沫镍能在铆接界面间形成牢固的自润滑物理吸附膜,可提高接头的耐腐蚀性;1mm泡沫镍夹层使接头静失效载荷增加了8.9%;随着泡沫镍夹层厚度的增加,接头的抗拉强度呈降低趋势;泡沫镍夹层结构自冲铆接头的失效模式为铆钉脱离下板,上板主要承受拉伸载荷,下板承受压缩载荷。     

多层交替膜界限载荷研究

为了研究软硬交替多层表面膜在磨粒作用下的应力应变响应、膜层界面剥离和裂纹的产生及扩展的影响,采用大变形接触弹塑性有限元法对刚性基体上的TiN/Ti多层交替膜在法向压痕作用下的力学行为进行了模拟和分析,研究不同软硬膜层厚度比下,不同膜层的变形、界面切应力分布和表面张应力分布,分析得出界限载荷变化规律及参数分布对其影响情况.结果表明:当软层厚度小于或等于硬层厚度时,增加膜层总厚度可以明显增大多层膜层体系的界限载荷,而软层厚度大于硬层厚度时,增加膜层总厚度不但不能明显增加界限载荷,反而会因增大最大弯曲应力而使界限载荷变小;软硬层厚度比大,而膜层总厚度小的多层膜体系,具有相对较小的最大弯曲应力,因而能承受最大的界限载荷.     

展宽机织复合材料破片高速冲击仿真模拟研究

本文基于数值仿真方法研究了展宽平纹机织复合材料平板在金属破片高速冲击载荷作用下的失效行为。在显示动力学求解软件LS-DYNA~?中建立了平纹机织复合材料的宏观精细化有限元模型,通过多尺度分析计算得到单层机织复合材料的等效力学性能,采用经典的Chang-Chang失效准则评估复合材料靶板的冲击损伤和失效行为。通过平板高速冲击试验确定了材料在特定冲击条件下的临界穿透速度范围和典型破坏模式,并与数值仿真结果对比,验证了数值模型的准确性。在此基础上,采用所构建的冲击仿真模型研究了平纹机织复合材料在不同冲击速度(0.1～0.8 km/s)载荷下的侵彻失效特性。研究结果表明:展宽机织复合材料平板在承受高速冲击载荷过程中,中间层受压缩损伤区域较小,靠近边界层损伤区域较大;随着冲击速度的增加,机织复合材料平板受压缩损伤区域减小;在冲击速度为0.2～0.8 km/s下,平板吸收能量与破片冲击速度呈近线性关系。     

SiC/TC4复合材料涡轮轴渐进失效分析

为了研究SiC/TC4复合材料涡轮轴的失效行为,提出轴结构渐进失效分析方法,建立基于Hashin失效准则的层合板模型,并开展SiC/TC4层合板拉伸试验,对比试验与仿真得到的拉伸强度以验证计算方法的有效性.模拟涡轮轴结构在轴向拉伸载荷和扭转载荷下的损伤演化过程,预测失效强度.结果表明:0°铺层时涡轮轴的拉伸强度最大;4...     

层间增韧复合材料在静压痕力下的损伤阻抗和渐进损伤分析

在复合材料层合板层间植入韧性层是提高复合材料韧性和抗冲击能力的有效方法。为了研究层间增韧对层合板损伤阻抗的改善作用，文中通过准静态压痕试验研究层间增韧复合材料在准静态压痕力下的损伤和破坏行为，利用超声C扫描测量分层损伤面积。试验结果表明，层间增韧复合材料具有较高的分层起始载荷和分层起始能量，损伤阻抗显著提高。在相同的载荷水平下，具有较小的分层损伤面积。文中还采用有限元方法对层间增韧复合材料在静压痕力下的分层和铺层失效进行数值分析，有限元计算结果与试验结果吻合较好。     

Deposition of duplex Al2O3/TiN coatings on aluminum alloys for tribological applications using a combined microplasma oxidation (MPO) and arc ion plating (AIP)

Microplasma oxidation (MPO) has recently been studied as a cost-effective plasma electrolytic process to provide thick and hard ceramic coatings with excellent surface load-bearing capacity on aluminum alloys. However, for sliding wear applications, such ceramic coatings often exhibit relatively high friction coefficients against many counterface materials. Although coatings deposited by physical vapour deposition (PVD) techniques such as TiN coatings are well known for providing surfaces with a high hardness, in practice they often exhibit poor performance under mechanical loading, since the coatings are usually too thin to protect the substrate from the contact conditions. In this paper, these challenges were overcome by a duplex process of microplasma oxidation and arc ion plating (AIP), in which an alumina layer Al₂O₃ was deposited on an Al alloy substrate (using MPO as a pre-treatment process) for load support, and a TiN hard coatings were deposited (using AIP) on top of the Al₂O₃ layer for low friction coefficient. Microhardness measurements, pin-on-disc sliding wear tests, and antiwear tests using a Timken tester were performed to evaluate the mechanical and tribological properties. Scanning electron microscopy (SEM) was used to observe coating morphology, and to examine wear scars from pin-on-disc test. The research demonstrates that a hard and uniform TiN coating, with good adhesion and a low coefficient of friction, can successfully be deposited on top of an alumina intermediate layer to provide excellent load support. The investigations indicate that a duplex combination of MPO coating and TiN PVD coating represents a promising technique for surface modification of Al alloys for heavy surface load bearing application.     

The study of the adhesion of a TiN coating on steel and titanium alloy substrates using a multi-mode scratch tester

A titanium nitride (TiN) coating was deposited by magnetron sputter ion plating onto steel and titanium alloy polished substrates. The adhesion of the coating on each substrate material was investigated using a newly developed multimode scratch tester. Progressive loading scratch tests, constant load scratch tests, multiple scratch tests in the same track and indentation tests were all performed. It was shown that the modified scratch tester can be used to identify not only coating detachment during progressive load scratch tests, but also other failure events such as cracking and cohesive damage to the coatings. By using the additional modes of operation, it was possible to study the fracture mechanisms in more detail i.e. chipping in the scratch track was cohesive for the TiN coated steel and adhesive for the TiN coated Ti alloy.     

Experiences from scratch testing of tribological PVD coatings

The use of PVD coatings in tribological applications becomes more and more widespread. Thus also the need to fully understand the relationships between the intrinsic properties of the coating, the properties of the coating/substrate composite and the tribological performance of the composite in different tribological systems becomes increasingly pressing. One of the tools available for tribological characterization of coatings and coating/substrate composites is scratch testing. In the current paper, Uppsala University presents a selection of results from many years of scratch testing of PVD coated components. Applications range from adhesion assessment and coating quality determination to estimation of coating fracture resistance. Examples in the form of scratch studies of PVD coatings on various high speed steels and tool steels - including failure mode anaiysis in situ SEM - are given.     

Failure mode maps in the thin film scratch adhesion test

The scratch test has been used to assess thin coating adhesion for some time now. In this test a diamond indenter is drawn across the coated surface under an increasing load (either stepwise or continuous) until at some load, termed the critical load, L_c a well-defined failure event occurs; if this failure event represents coating detachment then the critical load can be used as a qualitative measure of coating-substrate adhesion. However, it is well known that a range of possible failure modes can occur and only some of these are dependent on adhesion. Other failure modes which depend on plastic deformation and fracture within the coating, rather than any adhesive failure at the coating substrate interface, may be just as useful in the assessment of coating quality particularly for tribological applications. In this paper the load regimes in which the main adhesion-related failure modes (spallation and buckling) occur as a function of coating thickness will be presented for thermally grown oxide and sputtered nitride coatings. The origin of the observed failure modes and the use of the scratch test to assess coating/substrate adhesion in a more quantitative fashion is discussed in the light of these observations.     

TiN薄膜的残余应力调控及力学性能研究

残余应力是制约物理气相沉积（Physical vapor deposition,PVD）硬质薄膜厚度的关键因素。采用多弧离子镀技术在高速钢基体上制备了厚度从3.7 m到15.5 m的TiN薄膜,结合曲率法和有限元法研究残余应力及结合性能随膜厚的变化规律。结果表明,随着膜厚的增加,基片弯曲程度加剧,而薄膜平均残余应力降低;膜层内残余应力的整体水平决定了界面切应力大小,薄膜结合性能随界面切应力的增加而降低。增加基体偏压、降低工作气压均导致薄膜内部残余应力的升高。当残余压应力较高时,TiN薄膜具有细小、致密的柱状晶结构,并呈现（111）择优取向,薄膜硬度及断裂韧度较高,耐磨性能良好。研究结果提示我们,通过残余应力的调控可提高硬质薄膜的力学特性。     

Characterization of multilayer pvd nanocoatings deposited on tungsten carbide cutting tools

The present trends in the coating technologies are gradient coatings, metastable coatings, multicomponaent coatings and multilayer or super lattice coatings. The physical vapour deposition (PVD) process is well-suited technology for these advanced coating technologies. The performance of the coated tools can be improved considerably using multi-layer micro and nanocoatings. The present paper discusses the deposition and characterization of multilayer TiN/Al₂O₃ coatings on cemented tungsten carbide cutting tools using reactive sputtering. The characterization of the coatings was carried out using X-ray diffraction (XRD) for phase analysis, chemical composition using EDAX, adhesion and toughness evaluation using Rockwell indentation test and surface roughness. It was observed that with decrease in thickness of each alumina layer to nanolevel in multilayer coating system results considerable improvement in final surface finish, adhesion and toughness of the coating. The experimental results are presented and analyzed in this paper.     

Evaluation of adhesion/cohesion bond strength of the thick plasma spray coatings by scratch testing on coatings cross-sections

The possibility of adhesion/cohesion bond strength evaluation of thick plasma spray coatings with scratch tester, according to the ISO working draft (ISO/WD 27307), was analyzed and compared with the standard test method (ASTM C 633). Four different coatings deposited with atmospheric plasma spraying were used. The results showed that scratch testing could be used as an efficient method for evaluation of thick plasma spray coatings cohesion. It is a relatively easy and quick test method, and for practical application it could be also used as a supplement of some standard test method as a coating characterization and quality control technique.     

Deformation–wear transition map of DLC coating under cyclic impact loading

A new deformation–wear transition map of hydrogen-free amorphous carbon coating (commonly known as Diamond-Like Carbon (DLC) coating) on tungsten high speed steel (SKH2) substrate under cyclic impact loading has been proposed to clarify the interactions of the operating parameters, deformation and wear. The study was carried out using an impact tester, under lubricated conditions over a wide range of impact cycles, and applied normal loads. SKH2 discs were coated with thin DLC films using a Physical Vapor Deposition (PVD) method. Tungsten (W) was used as an interlayer material. The DLC coated disc was impacted repeatedly by a chromium molybdenum steel (SCM420) pin. All impact tests were conducted at room temperature. It has been suggested that the deformation–wear transition map is an easy way to illustrate the impact wear mechanisms of DLC coating, as shown by its transition zones. Initially, the DLC coating only follows the plastic deformation of the substrate until several impact cycles. Then, a suppression of plastic deformation of the substrate is taking place due to the decreasing contact pressure with impact cycles to the yield point. Wear of the DLC coating becomes dominant when the critical limit of maximum normal impact load and impact cycles is exceeded. From experimental observations, some degradation of the DLC coating occurs within the wear zone.     

Functional behaviour of PVD coatings under sliding and rolling stress conditions

Whereas wear-resistant PVD coatings are well established in the field of metalcutting, and the functional and tribological behaviour of these coatings is well known under such conditions, PVD coatings are used only occasionally in mechanical engineering. The reason for this seems to be the lack of information concerning the functional behaviour of these coatings in closed tribosystems. To evaluate new areas of application together with optimised coating compounds, model wear tests were performed under sliding, rolling and slip-rolling stress conditions. In addition, the test parameters, such as sliding speed, load, ambient temperature, and number of revolutions were varied, as were the coating compounds and their thicknesses. The results obtained show that friction and wear of PVD coatings are both strongly influenced by the kind of stress and the test parameters themselves. Coatings that perform well under certain test conditions can break down quickly under some other stress conditions. TiN coatings, for example, which display low friction and wear under sliding friction, fail under rolling conditions very shortly afterwards.     

Rolling contact fatigue performance of detonation gun coated elements

Rolling contact fatigue performance of thermal spray coatings has been investigated using an experimental approach. A modified four ball machine which simulates a rolling element bearing was used to examine the coating performance and failure modes in a conventional steel ball bearing and hybrid ceramic bearing configurations. Tungsten carbide (WC-15% Co) and aluminium oxide (Al₂O₃) were thermally sprayed using a super D-Gun (SDG2040) on M-50 bearing steel substrate in the geometrical shape of a cone. A coated cone replaced the upper ball that contacts with three lower balls. The rolling contact fatigue (RCF) tests were performed under immersed lubricated conditions using two different lubricants. Fatigue failure modes were observed using a scanning electron microscope. Microhardness measurements of the coating and the substrate and elastohydrodynamic fluid film thickness results are included. The results show the requirement for significant optimization of the coating before use in rolling element bearing applications. The coating was fractured in a delamination mode. Test results show an optimization in coating process is required before these coatings can be used for rolling contact applications. WC-Co coatings perform better than Al₂O₃ coatings in rolling contact.