Elastic-plastic properties of thin film on elastic-plastic substrates characterized by nanoindentation test

To characterize the elastic-plastic properties of thin film materials on elastic-plastic substrates,a simple theory model was proposed,which included three steps:dimensionless analysis,finite element modeling and data fitting.The dimensionless analysis was applied to deriving two preliminary nondimensional relationships of the material properties,and finite element modeling and data fitting were carried out to establish their explicit forms.Numerical indentation tests were carried out to examine the effectiveness of the proposed model and the good agreement shows that the proposed theory model can be applied in practice.     

Identification of Logarithmic-Type Creep of Calcium-Silicate-Hydrates by Means of Nanoindentation

Abstract:  In order to relate the complex macroscopic behaviour of concrete with finer-scale properties of cement paste, aggregates, porous space, etc. multiscale models are developed. Here, in addition to homogenisation schemes establishing the relation between the properties of the constituents, e.g. matrix and inclusions, and the properties of the composite material, experimental methods for identification of finer-scale properties are required. Recently, the elastic properties of the main clinker phases in ordinary Portland cement (OPC) and calcium-silicate-hydrates (CSH) were identified by nanoindentation (NI). In this paper, the NI technique is extended towards identification of the viscous, time-dependent behaviour of CSH, i.e. the main finer-scale binding phase in OPC-based material systems. Hereby, a logarithmic-type creep behaviour is identified, corresponding perfectly to the creep behaviour encountered for mortars and concrete.     

QUASICONTINUUM METHOD SIMULATION OF THE INITIAL PLASTIC DEFORMATION OF SINGLE CRYSTAL Cu IN NANOINDENTATION

采用准连续介质方法模拟了纳米压痕实验中单晶Cu初始塑性变形过程. 采用3种不同宽度的纳米尺度压头, 得到了载荷-压痕位移关系曲线, 确定了 3种不同宽度压痕下位错发射的临界载荷. 临界载荷的大小与能量理论的预测结果基本一致. 通过对压头下方位移场的分析, 揭示了加载过程中位错形核的力学特征和微观结构特征; 得到了压头下方几何必需位错密度增加的一般规律. 定性地分析了卸载过程中位错的运动与湮灭.     

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。     

Particle shape effects on ductility of SiC particle reinforced LD2 matrix composites investigated by AFM based nanoindentation

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Pseudoelasticity of Metal Nanoparticles Is Caused by Their Ultrahigh Strength

An assembly of hemispherical Ag nanoparticles is prepared by solid‐state dewetting of thin Ag film deposited on the sapphire substrate. The in situ nanomechanical compression testing of the particles with a flat diamond punch inside the scanning electron microscope demonstrates the deformation behavior typical for the nucleation‐controlled plasticity: high elastic deformation followed by an abrupt particles collapse. The latter is associated with the dislocations nucleation in otherwise pristine particle. The average contact pressure in the contact zone at the onset of dislocation‐controlled plasticity is about 8 GPa, and does not depend on particle size. This observation supports the hypothesis that the pseudoelasticity of much smaller Ag nanoparticles is intrinsically related to their ultrahigh strength. A stress‐induced diffusion along the particle–substrate and particle–punch interfaces is identified as a factor controlling the pseudoelastic deformation. The corresponding diffusion model allows estimating the room‐temperature self‐diffusion coefficient of Ag along the Ag–W and Ag–zirconia interfaces, which is quite close to the estimated value of the grain boundary self‐diffusion coefficient in Ag. Based on this finding, the map of pseudoelastic deformation of crystalline materials is proposed.     

纳米压入测试中面积函数测量方法综述

在纳米压入法材料力学性能测试中,面积函数的准确测量对保证测量结果的准确性非常重要。本文对纳米压入测试中常用的面积函数确定方法进行了分类介绍,并对各种方法的特点进行了分析,指出了为提高纳米硬度和弹性模量等力学性能参数的测量准确性对面积函数进行校准的必要性。     

基于纳米压痕的氧化镓不同晶面的蠕变特性

使用Berkovich压头,采用恒载荷法对氧化镓的(100)及(010)晶面进行纳米压痕试验,通过数据拟合获得氧化镓晶体的蠕变应力指数.单晶氧化镓(100)晶面的蠕变应力指数范围在15.5～27.8,(010)晶面的蠕变应力指数范围在46.1～63.4.纳米压痕法能够有效测量氧化镓的蠕变变形量;氧化镓的2个晶面均呈现了...     

广西河池红层泥岩力学特性的纳米压痕试验研究

为了系统表征广西河池地区红层泥岩中各矿物组分的力学性质,采用纳米压痕测试技术,测试了红层泥岩样品在4种峰值荷载下的力学性能,并结合X射线衍射仪和光学显微镜等设备,将每个测点结果依次对应到各矿物组分上。结果表明：广西河池地区红层泥岩内部具有高度的非均质性,主要成分以SiO₂、Al₂O₃、Fe₂O₃为主,所含矿物组分主要包括石英、斜长石、白云母等。黏土矿物和各种矿物组分呈紧密、无规律排列。单次纳米压痕试验的泥岩荷载-压入深度曲线的离散化程度较高,但每组荷载下的12个测点的平均最大压入深度和塑性变形满足荷载越大则压痕深度越大的基本规律。当峰值荷载较小时,泥岩中各测点的弹性模量和硬度体现了良好的线性相关性。泥岩中的石英成分强度最高,力学性能最好,斜长石次之;白云母和黏土矿物的力学性能最差。同时,红层泥岩内部表现为多孔隙、多裂缝结构,导致黏土矿物的平均弹性模量低于其他类岩石的水平,这也是导致红层泥岩易开裂、遇水易崩解的原因。