Ti-Si-N超硬复合表面纳米压痕测量过程的有限元仿真

为了深入了解Ti-Si-N纳米复合表面的力学性能,尝试采用有限元方法对纳米压痕测量的加一卸载过程进行了模拟.详细介绍了该三维有限元仿真过程的各个细节,包括对标准Berkovieh压头的建模和相关参数的确定,以及对Ti-Si-N表面模型边界条件、压头与表面接触方式和加一卸栽方式的处理.采用有限元的非线性算法对一个Ti-Si-N表面纳米压痕测量的实验曲线进行了拟合.通过有限元仿真得到了Ti-Si-N样品的屈服极限和应力-应变关系.该研究表明,采用有限元仿真与纳米压痕测量相结合是研究纳米复合表面非线性塑性性能的有效方式.     

纳米压痕试验标准块均匀性的检验

应用显微维氏硬度计和纳米压痕仪,对高硬度钢样品（GCr15）和高纯度熔融石英分别进行了试验,得到该钢样品的弹性模量值和硬度值分别为238．140GPa和9．468GPa,高纯度熔融石英样品的弹性模量值和硬度值分别为71．386GPa和9．502GPa。按照标准块均匀性的统计检验方法对试验得到的数据进行了统计分析,发现高纯度熔融石英样品的均匀性比高硬度钢样品的均匀性高。     

纳米压痕试验方法测量不确定度简化评定

纳米压痕试验中对测试结果产生影响的因素很多,如果计算各个分项相当困难.采用重复性限和复现性限对熔融石英样品上的纳米压痕硬度和模量的标准不确定度进行了评定.     

两种微纳米硬度测试方法的比较

在对材料微纳米硬度测试中,可利用纳米压痕方法得到载荷-位移曲线,并用相关算法得到接触面积和硬度值;也可通过原子力显微镜测出压痕残余面积,由残余面积和最大载荷得到材料的硬度值.利用这两种方法对塑性材料单晶铝和脆性材料单晶硅做微纳米硬度测试试验,经过比较分析,这两种方法各有优势和不足,得到的材料微纳米硬度都有压痕尺寸效应,但第二种方法得到的微纳米硬度尺寸效应比第一种明显.     

基于小波变换的Nanoindenter图像处理

根据纳米压痕仪的特点,对小波变换应用于纳米压痕仪图像的降噪、增强及融合方法进行了阐述。采用纳米压痕仪对单晶Al进行纳米级压痕,利用纳米定位平台原位扫描技术获得了三维图像,使用bior3.3,coif2,sym8分别对所得图像进行降噪、增强、及融合处理。结果表明,利用小波变换对纳米压痕仪图像进行处理是有效的、可行的,图像质量得到明显提高。     

单晶铝纳米级硬度试验研究

使用纳米硬度计对单晶铝进行了纳米压痕试验,利用原子力显微镜对压痕形貌进行扫描并计算硬度值,重点观察和分析了纳米级条件下单晶铝的硬度性质,结果表明,当压痕深度小于2000nm时,单晶铝纳米硬度存在尺寸效应现象;从材料性质的角度分析了纳米硬度尺寸效应现象;探讨了纳米硬度和传统硬度本质上的区别,指出其根本原因在于不同尺度下人们对材料性质的关注点不同。     

仪器化压痕技术测试拉伸性能的重复性和准确性

采用新型便携式压痕仪和传统万能拉伸试验机两种测试仪器,对相同种类和尺寸的碳钢试块进行了拉伸性能测试,测试试块的屈服强度和抗拉强度,以验证仪器化压痕试验结果的重复性和准确性。结果表明:仪器化压痕技术测试屈服强度和抗拉强度的重复性较好,准确性较高;不同于现有的破坏性测试设备和评估方法,压痕系统使用无损害、经济和高效的仪器化压痕测试方法,可以通过评估从局部区域的纳米尺度到现有工业设施的宏观属性来提供可靠的解决方案。     

拉伸变形对电沉积镍镀层微观结构及力学性能的影响

采用电沉积法在低碳钢基体上制备了韧性较好的镍镀层,并对镀镍钢带进行了拉伸试验.通过扫描电镜(SEM)和X射线衍射(XRD)分别对镍镀层变形前后的表面形貌和织构进行了研究.用纳米压痕的方法对拉伸变形前后的镍镀层样品进行了载荷-深度曲线的测试,并测量了电沉积镍镀层变形前后的硬度与杨氏模量.结果表明,拉伸变形后的镍镀层表面粗糙度变大,出现起皱,但并没有产生新的织构,只是原有织构的强度发生了变化,其硬度和杨氏模量都明显减小.对于同一样品,加不同载荷会导致不同的压痕深度,随深度的增加,测得的压痕硬度和样式模量也有明显降低.     

应用纳米压痕法测定柱状纳米材料的力学特性（英文）

纳米压痕法在确定纳米结构材料,特别是具有较大高宽比的一维纳米结构/对象的力学特性时,若纳米结构沿压入方向的等效刚度远小于针尖-样品的接触刚度,应用常规数据分析(Oliver-Pharr)模型会导致较大的测量偏差.对常规Oliver-Pharr解析模型进行了推广,以补偿一维纳米材料等效刚度对测量结果的影响,进而提出了适用于此类测量对象的通用纳米压痕分析模型,并应用于分析柱状微纳米结构的准静态压痕测量数据.实验中应用原子力显微镜(AFM)定量测量了湿法刻蚀获得的一维单晶硅柱状结构的几何参数(包括硅纳米柱的直径和长度).实验结果表明,应用常规模型分析对较大高宽比的硅纳米柱(直径386 nm,长500 nm)的压痕数据会导致大于50%的偏差.应用修正模型分析实验数据时,测量结果不受被测对象几何参数的影响,因而可以有效提高应用纳米压痕法对微纳米结构材料,特别是一维材料的测量精度.     

微悬臂梁结构在微硬度试验力校准中的探索应用

正一、引言根据IS014577-1:2002《金属材料硬度和材料参数测量和确认试验%第1部分:试验方法》,硬度按照试验力和压痕深度被分为大硬度、微硬度和纳米硬度。试验力是硬度量值溯源的重要参数,通常试验力的力值通过标准测力仪进行溯源。对于微硬度和纳米硬度,由于其试验力范围的局限性,通常为5μN~1mN(0.05gf~10gf),超出了目前标准测力仪的有效量程范     

海洋浪溅区Zn涂层加速腐蚀实验模拟研究

采用RM-1型海洋加速腐蚀实验和连续中性盐雾实验模拟海洋飞溅区的腐蚀环境对电弧喷涂Zn涂层的加速腐蚀。同时采用灰色关联分析法和加速转换因子分析法对两种海洋加速腐蚀实验的模拟性和加速性进行了分析。结果发现:两种实验方法均能模拟海洋飞溅区的腐蚀环境,但RM-1型海洋加速腐蚀实验能较好地模拟浪花飞溅区的腐蚀情况,而连续中性盐雾实验对Zn涂层造成的腐蚀较为严重,其具有优良的腐蚀加速性。     

一种生物素改性聚乳酸生物材料的制备与性能研究

研究试图通过本体改性,将生物素接枝到聚乙二醇接枝聚乳酸(PPLA)上,以改善聚乳酸微球在药物缓释应用中血液循环时间短和无主动靶向性的缺点.在本实验室制备的聚乙二醇接枝改性聚乳酸的基础之上,采用N-羟基琥珀酰亚胺活化酯法,将生物素接枝到PPLA上,制备生物素改性聚乳酸(BPLA),通过茚三酮显色、核磁共振(1H-NMR)...     

Thermal shock cracking of lithium niobate single crystal

The quantitative estimation of failure stress of a lithium niobate (LN) single crystal due to thermal shock was investigated. Cylindrical test specimens were used in the thermal shock tests. The thermal stress of an LN test specimen under conditions of thermal shock cracking was calculated from a computer program which takes account of the crystal anisotropy, using the surface temperature measured in the thermal shock test. Four-point bending tests were also carried out to examine the relationship between the thermal shock cracking and the failure of a small test specimen due to mechanical load. LN single crystals fractured at the cleavage planes {0 1 1 2} in the thermal shock test and the four-point bending test. Although the failure stress data obtained from both tests obey the Weibull distribution, the Weibull distribution depends not only on specimen size but also on loading type. According to the Weibull distribution of thermal shock test data, if the normal stress σ_n acting on the cleavage planes {0 1 1 2} is lower than 10 MPa, the probability of thermal shock cracking becomes very small — less than 2%. This revised version was published online in July 2006 with corrections to the Cover Date.     

驻波管中的隔声量测试方法

本文探讨了在驻波管中采用吸声末端的小试样垂直入射隔声量测试方法 ,提出了驻波分离法 ,与直接比较法的测试结果进行了比较 ;并根据实验探讨了吸声末端的吸声性能对隔声量测试的影响。实验结果指明 ,吸声末端的吸声系数大于 0 .99时可使隔声量测试误差小于± 1dB。驻波分离法可提高测试精度 ,减少工作量     

表面活性剂协同超声分散制备还原氧化石墨烯＠月桂酸Ｇ棕榈酸复合相变材料及其表征

相变储能材料因能有效地解决能量供求中时间和空间不匹配的矛盾而备受关注。本实验首先采用熔融共混法制得月桂酸(LA)-棕榈酸(PA)低共熔混合物后,将其与还原氧化石墨烯(RGO)混合,通过超声分散制得还原氧化石墨烯@月桂酸-棕榈酸(RGO@LA-PA)复合相变材料。FT-IR、Raman、SEM、DSC和形貌稳定性的分析结果表明,RGO与LA-PA是以物理方式结合,所添加的RGO能对材料形成均匀包覆,仅1%(质量分数)的RGO就能使其导热系数提升20%为0.426 W·m-1·K-1,相变潜热为159.9 J·g-1,起始分解温度提高2 ℃;经100次热循环后,其相变潜热仅下降2%,说明RGO包覆相变材料后提高了其导热性能,改善了其渗漏现象,同时该复合相变材料还具有良好的热稳定性。     

Mechanical properties of a low-pressure-plasma- applied Co-Cr-Al-Y coating

The low pressure plasma spray process was used to deposit coatings of a Co- 29Cr-6A1-1Y alloy onto IN-738 test specimens and to make free-standing deposits from which specimens were machined. Tensile tests, stress rupture tests and high cycle fatigue test were run on the coated specimens from room temperature to 870°C and results showed no significant effect of the coating process. A strain-to-coating-cracking test was also run on coated specimens and a coating ductile-to-brittle transition was found between 760 and 870°C. Free-standing Co- 29Cr-6Al-1Y tensile specimens were machined from the thick low-pressure- plasma-sprayed deposits. The tensile properties of these deposits were measured from room temperature to 980°C and results showed that the tensile strength of the deposits ranged from 50% above to 100% below the strength of cast IN-738, while elongation went from 0% to 130%. It is shown that the low pressure plasma process produced clean low defect coatings which perform well in mechanical cycling. However, it is also shown that the Co-29Cr-6Al-1Y coating, at low temperatures (less than 540°C), has relatively low ductilities which could cause early cracking in high strain level testing or service conditions. Some scanning electron microscopy replica and metallographic evaluations are also presented to illustrate the tensile cracking behavior of the coating.     

Über die Abschätzung des Größeneinflusses bei unregelmäßig beanspruchten Bauteilen

The Estimation of the Size-Effect of Parts under Random Loading The scatter of the number of cycles N to initiate a crack in randomly loaded specimens can be described by the Weibull-formula (Eq. 1) where P_B is the probability of crack initiation, N_v and m are constants and A/A₀ is the magnification factor. Notched specimens of different size (Fig. 1) were tested either under a Gaussian type or under a flight-by-flight random sequence. The elastic stress-concentration factor of the geometrically enlarged specimens was K_t = 2.5. In each case of test conditions only four specimens were used to determine the scatter of the number of cycles to crack initiation. On the basis of the test results of one specimen size the constants N_v and m of the Weibull-formula (Eq. 1) were determined. If the magnification factor of another specimen size is inserted into Eq. (1) a prediction of the distribution of N can be made. In practice the prediction is often necessary on the basis of a smaller test piece. The test results of the smaller specimens (size I or II) were therefore used to predict the test results which were obtained with the larger specimens. The comparison of the predicted values with the corresponding test results shows a relatively good agreement although there were used only four test results for the prediction.     

Holographic recording of cosmic ray tracks in BEBC

We report on a successful test of holography in the Big European Bubble Chamber (BEBC) at CERN, which was filled with a heavy neon—hydrogen mixture. During the test of a modified in-line scheme we photographed bubble tracks longer than 1 m, which were produced by cosmic rays. The smallest bubbles, which were recorded with excellent contrast, had a diameter of ? 120 μm. This presents an improved resolution of a factor of five compared to photos taken with conventional cameras.     

Multi-step Load Impression Creep Tests for a 1/2Cr1/2Mo1/4V Steel at 565°C

Abstract: Impression creep tests under multi-step load conditions were performed for a service-aged 1/2Cr1/2Mo1/4V steel at 565°C, corresponding to uniaxial stresses in the range of 100–150 MPa. Results of the tests have shown that the minimum creep strain rate data of the material, produced from the creep curves obtained under different load histories, are in good agreement. The results obtained indicate that the results from a multi-step load test of an impression creep specimen, which is particularly useful when the test material is very limited, can be used to obtain the secondary creep properties for a material from a very small test sample.     

Sensitivity of electrode contact solutions and contact pressure in assessing electrical resistivity of concrete

This paper covers some aspects of the development of a simple and robust electrical resistivity test method which has the potential for assessing the durability of concrete. A simple low frequency AC end-to-end resistivity test was adopted as a laboratory test method and has the potential of being preferred as a quality control test in readymixed concrete plants. The test method forgoes the need for cast-in place electrodes or silver paint for electrode-concrete interface. The work presented here examines the sensitivity of electrode contact solutions and contact pressures at the electrode-concrete interface with the use of synthetic sponges. Five concretes conforming to C32/40 compressive strength class in BS EN206-1/BS 8500-1 made from five different cement types were investigated and the work highlighted the need for using a reference conductive contact solution and a contact pressure.