摩擦力和样品厚度对压痕法测量生物试样弹性的影响

生物试样的弹性测量可为生物体疾病的早期诊断和治疗提供依据。利用压痕法对生物试样的弹性进行了测量,并用有限元软件对压痕过程进行了模拟。研究发现,试样厚度对弹性测量存在影响,试样厚度越大,测量结果越接近试样真实的杨氏模量。当试样厚度为压痕深度的75倍时,测量误差仅为0.74%。又研究了压头速度对弹性测量结果的影响。研究发现,当压头速度较大时,由于摩擦力的作用,测量结果与试样弹性的真实值之间存在一定的差异。在模拟过程中添加摩擦力可准确反演试样的弹性,误差在5%以下。     

试样倾斜对熔融石英硅三棱锥纳米压痕测试的影响

使用三棱锥压头对不同倾斜角下的熔融石英硅进行纳米压痕实验。结果表明,试样倾斜会影响加载曲线的形状。在相同的载荷下,随着试样倾斜角的增加,压痕最大深度、残余深度及接触深度逐渐减小,但卸载曲线不受影响,彼此保持平行,卸载曲线的拟合参数m及接触刚度值保持恒定。另外,试样倾斜将导致测量的压痕接触面积偏小,从而使得测量的硬度和弹性模量偏大。     

根据压痕深度计算布氏硬度值的方法初探

指出了目前在许多关于硬度试验方法的标准和经典著作中都没有区分"压痕深度"和"装有压头的压杆位移"这两个不同的长度量。把装有压头的压杆位移当作压痕深度,对于洛氏硬度试验不会造成错误的结果;但把装有压头的压杆位移当作压痕深度计算压痕直径和布氏硬度值,则会造成明显的错误。提出了采用从压杆最大位移中扣除硬度计弹性变形得到的压痕深度计算压痕直径和布氏硬度值的方法,试验结果表明:这种方法计算得到的布氏硬度试验结果与采用光学系统测量压痕直径方法得到的结果相吻合;该方法兼具布氏硬度试验和快速布氏硬度试验的优点,可以既快速又准确地得到布氏硬度试验结果。     

基于Labview的显微维氏硬度压痕测量系统的开发

本文在显微维氏硬度计的基础上通过Labview软件设计维氏硬度测量系统,实现对压痕对角线长度的测量,进而可以直接求得维氏硬度值。其中压痕采用三种测量方法获取对角线长度,通过三种方法的比较分析寻求最优测量法。该测量系统实现了硬件结构与软件平台的完美对接,硬度计通过设计改良,确保压头在与试样接触时试样处于水平状态,有效避免压痕结果出现误差。Labview软件平台界面清晰明了,操作过程简洁,具备进一步开发的潜能。     

闭孔铝泡沫在静压痕下的力学响应

采用球形压头对闭孔铝泡沫材料进行了准静态压痕实验,研究了不同直径、铝泡沫相对密度及边界条件对铝泡沫的压痕硬度、吸能能力及能量吸收率的影响。研究表明,铝泡沫在球形压头作用下的响应曲线可采用幂函数形式进行描述,幂函数指数随相对密度的增大而线性增加。铝泡沫压痕处的断面显示铝泡沫变形被严格限制在压头之下,铝泡沫的压痕变形是局部的不均匀变形。铝泡沫的压痕硬度及吸能能力均随压头直径的增大而线性减小,但它们却均随铝泡沫相对密度的增大而线性增大;能量吸收率不随压头直径和铝泡沫相对密度而变化。在一定压痕深度范围内,刚性基础和简支条件对铝泡沫的压痕响应影响可以忽略不计。最后基于实验数据分别建立了压痕硬度和吸能能力与压头直径及铝泡沫相对密度的关系。      

金属布氏硬度试验的测量不确定度评定

金属布氏硬度试验是用较大直径球体压出较大的压痕 ,用压痕表面面积与试验力之比计算出硬度值。该方法测出的硬度值比较稳定、精度高、操作简单。试件的制备较其他力学试样和硬度试样容易。试验误差来源于试验力、压头、压痕测量装置、试样、试验力保持时间等 ,评定测量不确定度以知晓试验结果的可信度。1　试验方法1 1　原理将一定直径球体压入试样表面 ,保持一定时间后卸除试验力 ,用压痕表面面积与试验力之比计算出硬度值 ,即 :ＨＢ =ＦＳ =ＦπＤｈ=2ＦπＤ(Ｄ -Ｄ2 -ｄ2 )式中　Ｆ为试验力 ,Ｎ ;Ｓ为压痕表面积 ,ｍｍ2 ;Ｄ为球体压头…     

人工水晶的压痕断裂行为及其 K_(1c)测量

藉助于声发射技术,研究了在 Vickers 钻石压头作用下人工水晶的压痕断裂行为。压头对角线与晶体试样的相对取向是,使得水晶Ⅰ和水晶Ⅱ的压痕诱发径向/中位断裂,分别沿着(10(?)0)/(1(?)10)和(11(?)0/(1(?)00)晶面对发展。压痕断裂过程中的声发射特征表明,除了随着压痕特征参数的发展所引起的准静态—声发射外,有三个相互独立的,与径向/中位裂纹的成核、径向/中位裂纹突入试样表面、以及裂纹分岔或侧向裂纹萌生等过程相关的声发射效应。以 Vickers 压痕技术测得 K_(c2)的结果与以一般力学法及 Knoop 压痕技术的测试结果作了比较。断裂韧性与晶体学取向的关系亦作了分析。实验表明,水晶Ⅰ和水晶Ⅱ具有相同的 K_(1c)值。其原因是,两种试样的径向/中位裂纹实际上沿着同样的{1100}/{1120}晶面对扩展。至于从缺口梁法或 Knoop 压痕技术得到的 K_(1c)值,由于水晶Ⅰ和水晶Ⅱ的主裂纹分别沿着(1(?)10)和(1(?)00)晶面扩展;它们的 K_(1c)值与断裂能随着晶体学取向而变有关,因而也就各不相同。     

石英玻璃纳米压痕过程有限元模拟的正交实验分析

采用有限元方法模拟纳米压痕过程的影响因素较多,依据正交实验原理提出了确定这些影响因素重要性的一种新方法．选取石英玻璃材料的屈服应力、加工硬化指数以及纳米压头的尖端半径为影响因素,由于材料与压头间的接触摩擦对仿真结果影响不大,且试样在进行纳米实验前都要进行抛光打磨处理,故不考虑摩擦系数和表面粗糙度的影响．将仿真结果与实验结果相对误差的绝对值作为正交实验的指标,利用极差分析可知压头半径是影响模拟结果最重要的因素,屈服应力和加工硬化指数只对模拟出的残余深度有一定的影响．同时通过对比模拟和实验的载荷一位移曲线,得到实际压头尖端半径为300nm,石英玻璃的屈服强度为8GPa,加工硬化指数为0.3     

磷酸二氢钾(KDP)晶体纳米压痕过程的有限元分析

为了求得KDP晶体的应力-应变曲线以及材料的屈服应力,基于圣维南定理和实验得到的材料性能参数建立了KDP晶体的压痕过程仿真模型,利用ABAQUS有限元分析软件对KDP晶体压痕过程进行了有限元仿真,得到了KDP晶体的载荷-位移曲线和加/卸载过程中的等效应力变化规律.仿真结果表明:加载过程中最大应力集中在压头尖角处,卸载后最大应力分布在压头棱边所留下的压痕处,KDP晶体材料的屈服应力为120MPa.     

平头压头下基体对压痕规律的影响研究

本文通过对软薄膜/硬基体两相材料体系的平头压痕弹塑性模拟.重点研究了平压头压入过程中,不同屈服强度比(软薄膜屈服强度与硬基体屈服强度之比)以及不同压头尺寸下硬基体对压痕规律的影响.研究发现硬基体对压痕规律的影响与屈服强度比近似满足线性关系,且这种线性关系不随压头尺寸的改变而改变,相同压头半径下,屈服强度比越大,影响就越明显;相同屈服强度比下,压头半径越大,影响就越小.研究还发现压头压入过程中,材料的堆积对压入深度没有影响.     

扫描探针显微技术测量血管内皮细胞的弹性

血管内皮细胞的功能与许多疾病间存在关联,但现在对其功能好坏的定量描述仍十分少见。该文以内皮细胞的弹性作为衡量其功能的一个标准。通过理论建立压痕测量杨氏模量的计算方法,并利用扫描探针显微镜从实验上得到了正常及过氧化氢处理过的人脐静脉内皮细胞的杨氏模量。发现过氧化氢处理后细胞的杨氏模量升高,表明通过杨氏模量来表征细胞活性是可行的。     

Measurement of mechanical properties of multilayer coatings by nanoindentation

Abstract

Multilayer protective coatings of alternate aluminium and titanium diboride TiB₂ layers have been tested by nanoindentation to measure both hardness and Young's modulus values. The initial results show that the values obtained depend upon the depth of indentation. An alternative view is presented to show that by considering the percentage of each coating in contact with the indenter a single relationship between either hardness or Young's modulus and the amount of aluminium layer penetrated can be produced. This technique allows the influence of the percentage ceramic on the results obtained to be identified. Comparison of the nanoindentation results with three point bending tests show how the coating structure influences the results obtained.     

Spatio-temporal development of the endothelial glycocalyx layer and its mechanical property in vitro

The endothelial glycocalyx is a thin layer of polysaccharide matrix on the luminal surface of endothelial cells (ECs), which contains sulphated proteoglycans and glycoproteins. It is a mechanotransducer and functions as an amplifier of the shear stress on ECs. It controls the vessel permeability and mediates the blood–endothelium interaction. This study investigates the spatial distribution and temporal development of the glycocalyx on cultured ECs, and evaluates mechanical properties of the glycocalyx using atomic force microscopy (AFM) nano-indentation. The glycocalyx on human umbilical vein endothelial cells (HUVECs) is observed under a confocal microscope. Manipulation of the glycocalyx is achieved using heparanase or neuraminidase. The Young''s modulus of the cell membrane is calculated from the force–distance curve during AFM indentation. Results show that the glycocalyx appears predominantly on the edge of cells in the early days in culture, e.g. up to day 5 after seeding. On day 7, the glycocalyx is also seen in the apical area of the cell membrane. The thickness of the glycocalyx is approximately 300 nm–1 μm. AFM indentation reveals the Young''s modulus of the cell membrane decreases from day 3 (2.93 ± 1.16 kPa) to day 14 (0.35 ± 0.15 kPa) and remains unchanged to day 21 (0.33 ± 0.19 kPa). Significant difference in the Young''s modulus is also seen between the apical (1.54 ± 0.58 kPa) and the edge (0.69 ± 0.55 kPa) of cells at day 7. By contrast, neuraminidase-treated cells (i.e. without the glycocalyx) have similar values between day 3 (3.18 ± 0.88 kPa), day 14 (2.12 ± 0.78 kPa) and day 21 (2.15 ± 0.48 kPa). The endothelial glycocalyx in vitro shows temporal development in the early days in culture. It covers predominantly the edge of cells initially and appears on the apical membrane of cells as time progresses. The Young''s modulus of the glycocalyx is deduced from Young''s moduli of cell membranes with and without the glycocalyx layer. Our results show the glycocalyx on cultured HUVECs has a Young''s modulus of approximately 0.39 kPa.     

Adhesive Backing Foil Interactions Affecting the Elasticity,Adhesion Strength of Laminates,and How to Interpret These Properties of Branded Transdermal Patches

ABSTRACT

Standard tensile strength and peel adhesion tests were carried out to investigate interactions of pressure-sensitive adhesives (PSAs) with several backing foils used for transdermal patches. Seven branded transdermal patches (Alora®, Cutanum®, Estraderm MX® 50, Estraderm TTS® 50, Fem7®-50 μg, Menorest®, Oesclim®) were included in the investigation. Their skin adhesion measured in several clinical trials was compared with the results of the laboratory measurements according to PSTC-1 (Peel Adhesion for Single Coated Tapes 180° Angle, Pressure Sensitive Tape Council, Illinois, 1996), such as Young's modulus at 3% elongation and peel adhesion to stainless steel. Data obtained for the PSA-coated backings (laminates) show increasing elasticity with increasing PSA thickness. Interactions of PSAs with backing foil became evident in significant changes in Young's modulus by low PSA thickness, as seen for the silicone adhesive. The Young's moduli of the laminates were found to be influenced not only by the elasticity of the backing foil but also by the chemical structure of the PSA. There was no correlation between the elasticity and peel adhesion of both the laminates and the branded patches. Likewise, for the branded patches the peel adhesion to stainless steel does not correlate with skin adhesion values obtained from clinical trials.

The Young's modulus of the branded patches was between 4 N/mm² (Oesclim®) and 501 N/mm² (Fem7®). For the branded transdermal patches no correlation was found between Young's modulus and both the peel force on stainless steel and the skin adhesion reported in studies.     

Atomic force microscopy of 3T3 and SW-13 cell lines: An investigation of cell elasticity changes due to fixation

Mechanical properties of single cells are of increasing interest both from a fundamental cell biological perspective and in the context of disease diagnostics. In this respect, atomic force microscopy (AFM) has become a powerful tool for imaging and assessing mechanical properties of biological samples. However, while these tests are typically carried out on chemically fixed cells, the most important data is that on living cells. The present study applies AFM technique to assess the Young's modulus of two cell lines: mouse embryonic fibroblasts (NIH/3T3) and human epithelial cancer cells (SW-13). Both living cells and those fixed with paraformaldehyde were investigated. This analysis quantifies the difference between Young's modulus for these two conditions and provides a coefficient to relate them. Knowing the relation between Young's modulus of living and fixed cells, allows carrying out and comparing data obtained during steady-state measurements on fixed cells that are more frequently available in the clinical and research settings and simpler to maintain and probe.     

Effect of surface roughness on nanoindentation test of thin films

By using the two-dimensional quasicontinuum method, the nanoindentation process on a single crystal copper thin film with surface roughness is simulated to study the effect of surface morphology on the measurements of mechanical parameters. The nanohardness and elastic modulus are calculated according to Oliver-Pharr’s method. The obtained results show a good agreement with relevant theoretical and experimental results. It is found that surface roughness has a significant influence on both the nanohardness and elastic modulus of thin films determined from nanoindentation tests. The effect of such factors as the indenter size, indentation depth and surface morphology are also examined. To rule out the influence of surface morphology, the indentation depth should be much greater than the characteristic size of surface roughness and a reasonable indenter size should be chosen. This study is helpful for identifying the mechanical parameters of rough thin films by nanoindentation test and designing nanoindentation experiments.     

Finite-element modelling reveals force modulation of jaw adductors in stag beetles

Male stag beetles carry large and heavy mandibles that arose through sexual selection over mating rights. Although the mandibles of Cyclommatus metallifer males are used in pugnacious fights, they are surprisingly slender. Our bite force measurements show a muscle force reduction of 18% for tip biting when compared with bites with the teeth located halfway along the mandibles. This suggests a behavioural adaptation to prevent failure. We confirmed this by constructing finite-element (FE) models that mimic both natural bite situations as well as the hypothetical situation of tip biting without muscle force modulation. These models, based on micro-CT images, investigate the material stresses in the mandibles for different combinations of bite location and muscle force. Young''s modulus of the cuticle was experimentally determined to be 5.1 GPa with the double indentation method, and the model was validated by digital image correlation on living beetles. FE analysis proves to be a valuable tool in the investigation of the trade-offs of (animal) weapon morphology and usage. Furthermore, the demonstrated bite force modulation in male stag beetles suggests the presence of mechanosensors inside the armature.     

Estimating Young's modulus of zona pellucida by micropipette aspiration in combination with theoretical models of ovum

The zona pellucida (ZP) is the spherical layer that surrounds the mammalian oocyte. The physical hardness of this layer plays a crucial role in fertilization and is largely unknown because of the lack of appropriate measuring and modelling methods. The aim of this study is to measure the biomechanical properties of the ZP of human/mouse ovum and to test the hypothesis that Young''s modulus of the ZP varies with fertilization. Young''s moduli of ZP are determined before and after fertilization by using the micropipette aspiration technique, coupled with theoretical models of the oocyte as an elastic incompressible half-space (half-space model), an elastic compressible bilayer (layered model) or an elastic compressible shell (shell model). Comparison of the models shows that incorporation of the layered geometry of the ovum and the compressibility of the ZP in the layered and shell models may provide a means of more accurately characterizing ZP elasticity. Evaluation of results shows that although the results of the models are different, all confirm that the hardening of ZP will increase following fertilization. As can be seen, different choices of models and experimental parameters can affect the interpretation of experimental data and lead to differing mechanical properties.     

Mechanical characterization of free-standing polypyrrole film

Free-standing polypyrrole films, neutral or doped with ClO₄⁻, have been mechanically characterized. Their elasticity of both dry and wet states was characterized by mean of the Young's modulus. In addition, the Young's modulus was calculated as a function of the film oxidation deep by “in situ” polarization at different potentials ranging from − 0.6 up to 0.8 V. The samples also were characterized under oxidation and reduction by reverse constant currents. When the films were submitted to a constant stretching force the length variations were obtained. At a constant length of the sample the electro-chemo-mechanical force developed by the redox processes was obtained. As predicted by the ESCR model lineal variations of both, length and force, as a function of the consumed charge were obtained.