A complete Raman mapping of phase transitions in Si under indentation

Crystalline Si substrates are studied for pressure‐induced phase transformation under indentation at room temperature (RT) using a Berkovich tip. Raman spectroscopy, as a nondestructive tool, is used for the identification of the transformed phases. Raman lines as well as area mapping are used for locating the phases in the indented region. Calculation of pressure contours in the indented region is used for understanding the phase distribution. We report here a comprehensive study of all the phases of Si, reported so far, leading to possible understanding of material properties useful for possible electromechanical applications. As a major finding, distribution of the amorphous phase in the indented region deviates from the conventional wisdom of being in the central region alone. We present phase mapping results for both Si(100) and Si(111) substrates. Copyright © 2009 John Wiley & Sons, Ltd.     

On computations of stress intensity factors for stiffened half planes with imperfections and cracks

In this paper we consider uniform extension problems for joined two half-planes with different thickness and material behavior and one of which contains an elliptical hole, the other contains a crack. Along the boundary of these half-planes there is a stiffening stringer. Computational formulas are given in power series form by complex variable—pertubation method. Results obtained here give extension to those of Handbook of stress intensity factors. Numerical results of special cases in this paper coincide with those of refs. [1], [3].     

金属材料的强度与应力-应变关系的球压入测试方法

压入法获取材料单轴应力-应变关系和抗拉强度对服役结构完整性评价有重要的基础意义.假定材料均匀连续、各向同性、应力应变关系符合Hollomon律,基于能量等效假定,即代表性体积单元(representativevolume element, RVE)的vonMises等效和有效变形域内能量中值等效假定,本文提出了关联材料载荷、深度、球压头直径和Hollomon律的四参数半解析球压入(semi-analyticalspherical indentation,SSI)模型.通过球压入载荷-深度试验关系获得材料的应力-应变关系和抗拉强度.考虑压入过程中的损伤效应,针对金属材料提出了用于球压入测试的材料弹性模量修正模型.对11种延性金属材料完成了球压入试验,采用本文提出的球压入试验方法测到的弹性模量、应力-应变关系和抗拉强度与单轴拉伸试验结果吻合良好.      

CALCULATION OF THE YOUNG''''S MODULUS OF AN ADSORBED POLYMER LAYER

Polymer layers adsorbed to a surface or in a confined environment often change their mechanical properties. There is even the possibility of solidification of the confined layer. To judge the stiffness of such a layer, we used the Hertz model to calculate the Young's modulus of the polymer layer in the confinement of AFM experiments with silicon nitride tip with a radius of curvature of R≈50 nm and a glass sphere attached to the cantilever R = 5μm. Since there is no visible indentation of the layer in the AFM experiments, the layer is either penetrated very easily, or the indentation is too small to be seen in a force curve. The latter would be the case for a polymer layer with a Young's modulus above 4×108 Pa in case of an experiment with a silicon nitride tip and 4×105 Pa in case of a glass sphere.     

Polyimide/Diamond Nanocomposites: Microstructure and Indentation Behavior

Polyimide/diamond nanocomposites have been synthesized from 4,4′‐diaminodiphenyl ether (ODA) and 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA). All the polyimides show non‐crystalline X‐ray diffraction. The frequent occurrence of particular interatomic distances (R) denoted by the non‐crystalline X‐ray diffraction maxima are determined. An ultramicro‐indentation technique is employed to evaluate the effects of nano‐diamond particles on the indentation behavior of polyimides. Indentation size effect is observed and discussed.

     

硬质合金表面去钴和脱碳对金刚石薄膜粘结性能的影响

金刚石涂层的粘结性能是影响CVD金刚石薄膜涂层刀具使用寿命的关键因素.本文分别对硬质合金(YG6)表面进行酸蚀去钴和原位脱碳两种不同的预处理后,在热丝CVD系统中沉积金刚石薄膜,运用压痕试验评价金刚石薄膜与硬质合金基体的粘结性能.结果表明,经过原位脱碳预处理的硬质合金表面上金刚石涂层的粘结性能比酸蚀去钴法提高了近一倍;同时分析了硬质合金表面酸蚀去钴对金刚石薄膜粘结性能的影响及其剥离机制,并讨论了硬质合金表面原位脱碳的化学机制.     

Nanoscale interfibrillar adhesion in UHMWPE fibers

The goal of this research is to quantify the fibrillar adhesive energy in ultra‐high molecular weight polyethylene fibers, characteristic of nanoscale fibril interactions. Quantification of these energies is vital to the understanding of fibrillar deformation mechanisms that have been shown to play an important role in fiber performance. This is achieved through the development and implementation of a nanosplitting technique developed through the use of AFM‐enabled nanoindentation. This technique allows the quantification of nanoscale adhesive energies through careful monitoring of load and unload curves as well as examination of the residual split through high‐resolution AFM images. Results indicate that the average nanoscale fibril adhesive energy is over 3 times larger than the energy expected from van der Waals interactions alone. This indicates that a significant degree of physical interactions exist between fibrils, beyond van der Waals interactions, in the form of tie‐molecules, fibrillar network junctions, and bridging lamellar crystals. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 391–401     

Characterization of viscoelastic properties of polymeric materials through nanoindentation

Nanoindentation testing was used to determine the dynamic viscoelastic properties of eight polymer materials, which include three high-performance polymers and five densities of high-density polyethylene. It was determined that varying the harmonic frequency of nanoindentation does not have a significant effect on the measured storage and loss moduli of the polymers. Agreement was found between these nanoindentation results and data from bulk dynamic mechanical testing of the same materials. Varying the harmonic amplitude of the nanoindentation had a limited effect on the measured viscoelastic properties of the resins. However, storage and loss moduli from nanoindentation were shown to be sensitive to changes in the density of the polyethylene.     

Explicit approximations of the indentation modulus of elastically orthotropic solids for conical indenters

The elastic problem of the contact between an axisymmetric indenter and a general anisotropic (21 independent elastic constants) half space has not been solved explicitly in closed form. Implicit methods to determine the indentation modulus originate from the work of Willis [J. Mech. Phys. Solids 14 (1966) 163]; and are now available for conical, parabolic and spherical indenters [Philos. Mag. A 81 (2001) 447; J. Mech. Phys. Solids 51 (2003) 1701]. The particular case of orthotropy has also been investigated [ASME J. Tribol. 115 (1193) 650, 125 (2003) 223]. This paper proposes an explicit solution for the indentation moduli of a transversely isotropic medium and a general orthotropic medium under rigid conical indentation in the three principal material symmetry directions. The half-space Green’s functions are interpolated from their exact extreme values, then integrated and finally simplified. The proposed closed form expressions are in very good agreement with the implicit solution schemes of [Philos. Mag. A 81 (2001) 447; J. Mech. Phys. Solids 51 (2003) 1701].     

采用压痕实验获得材料性能的研究现状

本文综述了采用压痕实验获得膜基体系中薄膜弹性，塑性，蠕变性能的研究进展，并指出了目前研究中存在和需要解决的问题。