The use of XPS, FTIR, SEM/EDX, contact angle, and AFM in the characterization of coatings

Coatings are applied to surfaces for a variety of reasons: to enhance their appearance, to protect the substrate, to augment the adhesion to other layers, or to functionalize them for further reactions. To evaluate the efficacy of the coating, it is often necessary to analyze the substrate and the coating to ensure that the needed characteristics are present. To this end, the use of x-ray photoelectron spectroscopy (XPS), contact angle, and atomic force microscopy (AFM) can provide information about the surface composition, its morphology, and its ability to be wetted with various solvents. Scanning electron microscopy with energy dispersive x-ray analysis (SEM/EDX) and Fourier transform infrared spectroscopy (FTIR) can provide a clear picture of the near surface components as well as the continuity of coatings. All of these aspects are valuable in evaluating a coating and essential when problems are encountered. The application of these techniques to the analysis of coatings is discussed.     

Delamination during drilling in polyurethane foam composite sandwich structures

The objective of this paper is to study the influence of drilling velocity, feed rate, and flank length on the delamination of polyurethane foam sandwich structures. A Taguchi-based design of experiments was used to assess the importance of the drilling parameters, and scanning electron microscopy (SEM) was used to assess the damage from drilling. The drilling of sandwich structures results in significant damage caused by delamination and surface roughness around the drilled holes. The drilling process was evaluated based on a factor called the delamination factor, which is defined as the ratio of the maximum diameter of the damage zone, measured using SEM, to the standard hole diameter (drill diameter). Analysis of variance of the experimental results showed that cutting speed was the most significant parameter among the controllable parameters during drilling of sandwich specimens followed by flank length and feed rate. Finally, confirmation tests were performed to make a comparison between the experimental results and the correlation results. The damage mechanisms are explained using SEM.     

天然橡胶/顺丁橡胶共混物疲劳历程的研究

采用扫描电子显微镜、电性能测定和热重法等分析手段，研究了炭黑补强的天然橡胶／顺丁橡胶共混硫化胶的疲劳历程，探索了其内在的疲劳损伤机理。     

疲劳损伤定量分析与失效评估研究进展

本文对疲劳损伤定量分析的理论和模型、断口定量分析疲劳寿命、疲劳应力以及对工程构件安全使用具有重要意义的基于损伤容限设计思想的原始疲劳质量与失效评估技术的研究现状进行了分析.通过断口定量反推疲劳应力和疲劳寿命应用最多的是Paris公式,疲劳裂纹萌生寿命目前还无法直接从断口上反推出来,一般通过人为设定a0值的方法计算疲劳裂纹萌生寿命.相对而言,国外对在役构件的剩余寿命评估方面开展了较多的工作.本文分析比较了国内外在疲劳损伤定量分析与失效评估研究的侧重点和思路的异同,并指出了加强失效分析在产品设计、生产、使用和维护各个环节的应用力度及开展失效评估技术研究是失效分析领域发展的两个重要方向.     

TC17钛合金电子束焊接接头的疲劳裂纹扩展规律及疲劳剩余寿命

首先通过试验取得母材及焊接接头的疲劳裂纹扩展速率,然后结合TC17钛合金电子束焊接接头CTOD试验结果及裂纹容限计算值,以估算其疲劳剩余寿命.结果表明:在低应力水平或低△K下,TC17电子束焊缝的da/dN数据与母材的基本相当;然而随着应力水平的增加,焊缝的da/dN值越来越大.在初始裂纹尺寸相同的情况下,TC17合金电子束焊缝与母材疲劳裂纹扩展寿命曲线存在交叉点.当应力幅大于交叉点应力幅时,TC17母材疲劳裂纹扩展到临界裂纹尺寸的剩余寿命要高于相应焊缝的剩余寿命;当应力幅小于交叉点应力幅时,TC17母材扩展到临界裂纹尺寸的剩余寿命要低于相应焊缝的剩余寿命.     

先进的电子断层扫描技术在材料科学中的发展——基于透射电子显微镜和扫描透射电子显微镜(英文)

介绍了基于透射电子显微镜和扫描透射电子显微镜的电子断层扫描技术在材料科学领域的最新进展。详细地描述各种电子断层扫描的类型:基于透射电子显微镜的断层扫描技术包括明场断层扫描、暗场断层扫描、弱束暗场断层扫描、环形暗场断层扫描和能量过滤断层扫描;基于扫描透射电子显微镜的断层扫描技术包括高角环形暗场断层扫描、环形暗场断层扫描,非共格明场断层扫描、电子能量损失谱断层扫描和X射线能谱断层扫描。报道了优化的倾转系列,比如双轴倾转、同轴倾转、锥形倾转以及等斜率倾转等。总结了先进的重构算法包括离散迭代重构技术、压缩传感算法以及等斜率算法。最后,提出了电子断层扫描技术在材料科学中的发展趋势。     

Study on Contact Fatigue Life and Failure Mechanism of Subquenched 42CrMo Steel

The effect of undissolved ferrite amount in subcritically quenched 42CrMo steel on contact fatigue properties and failure mechanism were studied. The amount of undissolved ferrite in the steel were 0%,3%,10%,15% and 20% in volume fraction, respectively. The experimental results show that the existence of undissolved ferrite can increase the contact fatigue life The contact fatigue life can be prolonged with increasing the amounts of undissolved ferrite The grain size can be fined by using subcritical quenching process and the area of phase boundaries can also be greatly increased. The stress relaxation and grain refinement due to occurring of plastic deformation are main reasons for improving the fatigue life. The existence of undissolved ferrite can increase the crack initiation period. Under the experiment conditions, when the amount of undissolved ferrite is 10%, the longest contact fatigue life can be the obtained.     

零件失效分析和抗疲劳设计

简单介绍了零件失效分析的作用及基本任务,指出疲劳失效是零件失效的主要形式之一.阐述了金属疲劳失效的外因和内因,并总结了三种典型的疲劳分析方法,以及如何在工程中使用这些方法.最后,详细论述了一体化疲劳耐久性工程的基本理念及其在产品开发中的作用,还概括性介绍了所涉及的一些主要工作任务,包括寿命目标的确定、数据采集、载荷分析...     

拖拉机二轴齿轮接触疲劳损坏的研究

针对拖拉机生产企业存在的零件生产质最问题,系统分析了拖拉机中央传动系统二轴18CrMnTi钢齿轮接触疲劳损坏的原因、类型、特征和形成机理,并进一步研究了齿轮接触疲劳损坏的影响因素,为生产企业采取针对性措施,改善二轴齿轮加工工艺提供了帮助.     

840D车轮辐板孔疲劳失效及裂纹容限研究

通过裂纹和断口的观察、理化检验、模拟仿真及其力学计算,分析了840D车轮辐板孔裂纹的特征、机理和原因.结果表明:裂纹属于高低周复合机械疲劳,裂纹主要在制动加机械载荷工况下萌生和扩展.统计分析确定了裂纹扩展速率,结合裂纹发展形态和理论计算给出了临界裂纹长度,进而评估出裂纹容限为20mm.     

Cavitation and grain boundary sliding during creep of Mg-Y-Nd-Zn-Mn alloy

Creep of squeeze-cast Mg-3Y-2Nd-1Zn-1Mn alloy was investigated at the constant load in the stress range of 30-80 MPa. Tensile creep tests were performed at 300℃up to the final fracture.Several tests at 50 MPa were interrupted after reaching the steady state creep;and another set of creep tests was interrupted after the onset of ternary creep.Fraction of cavitated dendritic boundaries was evaluated using optical microscopy.Measurement of grain boundary sliding by observation of the offset of marker lines ...     

某型号前轴疲劳试验及结果分析

为测试前轴的疲劳寿命,采用台架试验装置对某型号汽车前轴进行了试验,仅运行19.9万次就发生断裂。通过对断口的观察分析、断口部位的金相分析、硬度检测等方式,确定了前轴的失效模式,并对其断裂失效原因进行了分析。研究结果表明:汽车前轴的断裂性质为疲劳断裂,裂纹源起源于锻件飞边表面,该处存在较明显的沟槽;锻件表面的加工沟槽形成的附加应力集中是造成前轴疲劳断裂的主要原因;加工沟槽可能由于切边模的磨损而产生,因此切边模刃口需及时修整。     

1000 MPa级双相钢的疲劳性能

对1000 MPa级双相钢板进行了一系列疲劳试验,并对试验数据进行拟合处理,得出了双相钢的疲劳寿命经验公式,然后对疲劳断口进行了扫描分析。最终发现：在加载频率为8 Hz的拉-拉疲劳试验条件下,DP1000钢板的疲劳极限是680 MPa;双相钢的疲劳断裂主要是主裂纹扩展到一定程度后失稳断裂,二次裂纹萌生但未形成扩展。钢板的疲劳裂纹源与扩展区有明显的韧性断裂特征,瞬断区失稳发生脆性断裂。     

Fatigue behavior of friction stir spot welded AZ31 Mg alloy sheet joints

The fatigue behavior of friction stir spot welded (FSSW) AZ31 magnesium alloy sheet joints was investigated by tension–compression of fatigue test. The results suggest that all the fatigue failures occur at the stir zone of the FSSW AZ31 sheet joints, and all cracks initiate at the stir zone outer edge between the upper and lower sheet. When the cycle force equals 1 kN, the crack propagates along the interface of heat-affected zone and thermo-mechanical zone, simultaneously across the direction of force; while the cycle force equals 3 kN, the crack propagates along the diameter of stir zone and shear failure occurs finally. Moreover, the transverse microsections indicate that there is a tongue-like region at the outer edge of stir zone between the two AZ31 sheets, and the direction of tongue-like region is toward outside of the stirred zone and all fatigue cracks initiate at the tongue-like region.     

强度为600MPa TRIP钢板的疲劳性能研究

通过对1.5mm厚的TRIP600 MPa钢板进行系列疲劳试验,对试验数据进行拟合处理,用扫描电镜观察疲劳断口形貌.结果表明,在加载频率为8Hz、R=0的高周拉-拉疲劳试验条件下,TRIP600钢板的疲劳极限为460 MPa;S-N曲线拟合的经验公式为:lgN=51.1625-16.8574 lgσ;钢板的疲劳源多位于表面下的夹杂物处,裂纹的扩展区为韧性断裂,瞬断区为脆性断裂.     

大型宽厚板轧机万向节疲劳失效分析

某宽厚板轧机主传动系统的万向节发生多次断裂事故。本文对万向节失效进行分析、主传动系统动力学仿真、万向节有限元模拟以及疲劳强度计算,计算结果表明：疲劳强度安全系数偏低,仅为1．03,是万向节疲劳失效的主要原因。     

Corrosion of Type 7075-T73 Aluminum in a 10% HNO3 + Fe2(SO4)3 Deoxidizer Solution

Localized corrosion damage in Type 7075-T73 aluminum was investigated for a HNO₃ + Fe₂(SO₄)₃ deoxidizer solution which is frequently used for surface pretreatment prior to anodizing. The corrosion damage was quantified in the time domain using the electrochemical noise resistance (Rn) and in the frequency domain using the spectral noise impedance (Rsn). The Rsn was derived from an equivalent electrical circuit model that represented the corrosion cell implemented in the present study. These data are correlated to scanning electron microscopy (SEM) examinations and corresponding statistical analysis based on digital image analysis of the corroded surfaces. Other data used to better understand the corrosion mechanisms include the open circuit potential (OCP) and coupling-current time records. Based on statistical analysis of the pit structures for 600 and 1200 s exposures, the best fit was achieved with a 3-paramater lognormal distribution. It was observed for the 1200 s exposure that a small population of pits continued to grow beyond a threshold critical size of 10 μm. In addition, significant grain boundary attack was observed after 1200 s exposure. These data are in good agreement with the electrochemical data. Specifically, the Rn was computed to be 295 and 96 Ω-cm² for 600 and 1200 s exposures, respectively. The calculated value of Rsn, theoretically shown to be equal to Rn in the low frequency limit, was higher than Rn for a 1200 s exposure period. However, better agreement between the Rn and Rsn was found for frequencies above 0.01 Hz. Experimental results on the measurement performance for potassium chloride (KCl) saturated double-junction Ag/AgCl and single-junction Hg/Hg₂Cl₂ reference electrodes in the low-pH deoxidizer solution are also compared.