基于微纳米压入法的高熵合金柏氏矢量研究

采用微纳米压入法对CoCrFeNiMn高熵合金进行多种应变率下的压入测试研究,实验获得了材料硬度与压深之间的关系并通过计算分析得到了其不同工况下的柏氏矢量值,探究了压入深度和应变率对柏氏矢量的影响．实验结果表明,所测材料柏氏矢量值在一定范围内呈现出一定的波动性,随着压深的增大,柏氏矢量表现出尺寸效应,即柏氏矢量随压深呈增加趋势;并且在同等压深下,柏氏矢量存在率效应,随着应变率的增加,柏氏矢量值先减小后增加,柏氏矢量从滑移主导向原子失配主导的转变是其率效应转变的主要原因．     

Probe Indentation: A Mesoscale Approach to Characterise Powder Systems: Experimental Investigation of Monomodel and Bimodal Diameter Distributions of Glass Spheres

An experimental study investigating a novel power characterisation method is investigated. The scope of this experimental work is to assess the feasibility, suitability and sensitivity of small scale probe indentation as a mechanism by which Discrete element method (DEM) may be calibrated. This meso–scale approach is chosen for investigation since it bridges the gap between the single‐particle methodologies of atomic force microscopy (AFM) and bulk measurements such as shear cell testing. Five different mono‐modal populations of glass bead and bi‐modal blends of these populations have been examined. The force‐displacement profile from a spherical probe was measured during indentation into a powder bed. Discernable differences in the resultant force‐profile are quantifiable and a mechanism has been proposed for the physical basis of these different characteristics.     

平头压痕试验确定热障涂层弹性模量的方法研究

本文模拟了典型热障涂层(TBC)结构在平头压痕作用下的力学响应,重点研究利用平头压痕法确定TBC涂层弹性模量的方法。研究发现k(单位压入应力下压头的压入位移)不仅与材料的性质有关,还与压头的半径有关。本文提出:通过两个不同尺寸的平压头可以同时确定陶瓷层和粘结层的弹性模量。     

Nanomechanical and optical studies on polymeric membranes

The nanomechanical properties of poly(ethylene terephthalate) (PET) membranes, were examined in light of nanoindentation experiments under conditions of maximum contact load in the range of 0.5-12 m?. Spectroscopic Ellipsometry (SE) from 1.5 to 6.5 ev (Vis-FUV range) was also applied to probe the dielectric function (ϵ(ω) of the industrially supplied membranes, as well as their geometrical structure. Mechanical stretching (uniaxial or biaxial) procedures are usually applied for the elongation of the polymeric membranes, their thickness reduction and enhancement of their mechanical and optical performance, causing a preferable orientation of the macromolecules close to the surface. Nanoindentation and se testing have revealed the existence of a two-layer geometrical structure of the pet membranes, consisting of a thick amorphous pet layer and a thin crystalline-like pet overlayer, with increased hardness (elastic modulus). The analyses of the experimental dataprovides quantitative information on the formed overlayer, which is ascribed to the processing history of the membrane.     

Review: Indentation size effect,indentation cracks and microhardness measurement of brittle crystalline solids – some basic concepts and trends

Indentation size effect, indentation cracks and microhardness measurement of some brittle crystals are reviewed against the background of the existing concepts of indentation deformation of crystalline solids. Several approaches reported in the literature devoted to relationships between applied indentation test load P and indentation diagonal length d are applied to analyze the experimentally observed normal and reverse indentation size effect (ISE) in brittle compounds. Using typical examples of normal and reverse ISE it is shown that the indentation induced cracking model does not give load‐independent hardness and the final expression describing the experimental data for various compounds is essentially another form of the Meyer law. Analysis of experiment data on crack lengths and indentation diagonals for different indentation loads suggests that the origin of ISE is associated with the processes of formation of indentation cracks following the general concepts of fracture mechanics. The load‐independent hardness H₀ may be determined reliably from plots of P /d against d of the proportional resistance model or of H_V against 1/d as predicted by strain gradient plasticity theories. It was found that the load‐independent hardness of depends on crystal orientation and state of the indented surface. Finally, some comments on determination of fracture toughness and brittle index of crystals are made. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Inference of Mechanical Properties from Instrumented Depth Sensing Indentation at Tiny Loads and Indentation Depths

Different hardness measures as Vickers, Brinell and Meyer hardness are discussed with respect to their physical interpretation. Meyer hardness is found to be best suited as a measure of plastic properties. The outline of a depth sensing nanoindentation experiment is described, and particular emphasis is given to the correct deduction of the contact area from indenter penetration data. Experimental complications, as phase transformations, finite machine compliance, thermal and pieco drift, and sample creep are detailed with, and their impact on the calculation of hardness and elastic modulus is shown. Furthermore the onset of yielding in dependence on critical load, indenter curvature and yield strength is discussed.