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1.
In-situ tensile testing of nano-scale specimens in SEM and TEM 总被引:1,自引:0,他引:1
We present a new experimental method for the mechanical characterization of freestanding thin films with thickness on the
order of nanometers to micrometers. The method allows, for the first time, in-situ SEM and TEM observation of materials response
under uniaxial tension, with measurements of both stresses and strains under a wide variety of environmental conditions such
as temperature and humidity. The materials that can be tested include metals, dielectrics, and multi-layer composites that
can be deposited/grown on a silicon substrate. The method involves lithography and bulk micromachining techniques to pattern
the specimen of desired geometry, release the specimen from the substrate, and co-fabricate a force sensor with the specimen.
Co-fabrication provides perfect alignment and gripping. The tensile testing fits an existing TEM straining stage, and a SEM
stage. We demonstrate the proposed methodology by fabricating a 200 nm thick, 23.5 μm wide, and 185 μm long freestanding sputter
deposited aluminum specimen. The testing was done in-situ inside an environmental SEM chamber. The stress-strain diagram of
the specimen shows a linear elastic regime up to the yield stress σ
y
MPa, with an elastic modulusE=74.6 GPa. 相似文献
2.
Measuring the Elastic Properties of Freestanding Thick Films Using a Nanoindenter-Based Bending Test
Films with thickness ranging from 10 to 100 μm are increasingly being used as the structural components of microelectromechanical
systems (MEMS). Measuring the mechanical properties of these thick films is essential for enabling the design of MEMS with
high performance and sufficient reliability. In this paper, we present a simple and convenient method for measuring the elastic
modulus of thick films by loading a clamped circular film using a spherical tip. The test is implemented using a commercial
nanoindenter so that the load and displacement can be measured with resolution of micronewtons and nanometers, respectively.
Robust protocols have been developed for implementing the test within the constraints imposed by the nanoindenter. A crucial
component of these protocols is a method for selecting loads to ensure deformation in the elastic bending regime and to minimize
the relative contribution of contact indentation. The accuracy and utility of the nanoindenter-based bending test are discussed
using measurements on thick films of aluminum and a standard epoxy. 相似文献
3.
4.
W. N. SharpeJr. J. Pulskamp D. S. Gianola C. Eberl R. G. Polcawich R. J. Thompson 《Experimental Mechanics》2007,47(5):649-658
Silicon dioxide thin film is a common component in electronic devices and in MEMS, but its mechanical properties have rarely
been studied. Techniques have been adapted and developed to conduct tensile tests on 1.0 μm thick silicon dioxide specimens
that are 100, 150, and 200 μm wide and either 1 or 2 mm long. One end of the specimen remains fastened to the substrate, and
the other is glued to a silicon carbide fiber attached to a 30 g load cell mounted on a piezoelectric translation stage. Strain
is measured by digital imaging of two gold lines applied to the gage section of the transparent specimen. Twenty-five tests
yield a Young’s modulus of 60.1 ± 3.4 GPa and a fracture strength of 364 ± 57 MPa. 相似文献
5.
H. D. Espinosa B. C. Prorok B. Peng K. H. Kim N. Moldovan O. Auciello J. A. Carlisle D. M. Gruen D. C. Mancini 《Experimental Mechanics》2003,43(3):256-268
The mechanical properties of ultrananocrystalline diamond (UNCD) thin films were measured using microcantilever deflection
and membrane deflection techniques. Bending tests on several free-standing UNCD cantilevers, 0.5 μm thick, 20 μm wide and
80 μm long, yielded elastic modulus values of 916–959 GPa. The tests showed good reproducibility by repeated testing on the
same cantilever and by testing several cantilevers of different lengths. The largest source of error in the method was accurate
measurement of film thickness. Elastic modulus measurements performed with the novel membrane deflection experiment (MDE),
developed by Espinosa and co-workers, gave results similar to those from the microcantilever-based tests. Tests were performed
on UNCD specimens grown by both micro and nano wafer-seeding techniques. The elastic modulus was measured to be between 930–970
GPa for the microseeding and between 945–963 GPa for the nanoseeding technique. The MDE test also provided the fracture strength,
which for UNCD was found to vary from 0.89 to 2.42 GPa for the microseeded samples and from 3.95 to 5.03 for the nanoseeded
samples. The narrowing of the elastic modulus variation and major increase in fracture strength is believed to result from
a reduction in surface roughness, less stress concentration, when employing the nanoseeding technique. Although both methods
yielded reliable values of elastic modulus, the MDE was found to be more versatile since it yielded additional information
about the structure and material properties, such as strength and initial stress state. 相似文献
6.
The problem that is addressed here is the measurement of the mechanical properties of very thin, transparent films using bulge
tests. All existing techniques make use of reflection from the film surface, but they can be difficult or impossible to apply
to very thin, transparent films. Consequently, a novel approach based on the formation of a lens structure and using transmitted
light is developed. In this technique, the focal length of the lens structure formed by the bulged film and the pressurizing
medium is determined by moiré deflectometry with a corrected governing equation. The resulting curvature of the bulge film
is used in the stress analysis of the bulge-test. By combining circular and rectangular configurations, the Young’s modulus
and Poisson’s ratio of a 3 μm PET film were 4.65 ± 0.11 GPa and 0.34 ± 0.01, respectively. Consistent residual stresses were
obtained from both configurations. 相似文献
7.
Ultra-lightweight spacecraft incorporating “gossamer” structures are extremely compliant, which complicates control, design,
and ground testing in full scale. One approach to model the behavior of a full-scale gossamer structure is to construct a
small-scale model test article that can be used to verify a corresponding small-scale computer model. Once the predictions
of the computer model have been verified by measurement of the physical test article, it can be scaled up to allow computation
of the full-scale structure behavior. As model verification requires accurate deflection measurements at multiple points along
the surface of the structure, a sensing system that provides full-field data without changing the dynamic response of the
structure must be developed. Hence, an optical approach is taken. Since the thin films used in gossamer space structures are
typically smooth and featureless, targets must be incorporated into the film surface to enable tracking of both in-plane and
out-of-plane displacements. A krypton fluoride excimer laser system was used to etch 35 μm wide linear features approximately
0.1 μm into the surface metallization of both 50.8 μm polyester and 127 μm polyimide films. These optically diffuse surface
features, designed mainly to investigate the precision of the laser etching method, were used as targets for ultra-close-range
photogrammetry, the method chosen for displacement tracking. A force applied to the surface of the etched mirror (test article)
produced in-plane and out-of-plane deformations that were resolved via ultra-close-range photogrammetry. To measure the in-plane
tracking resolution, 1.5 and 3.0 mm circular dots were added (using ink) to the surface of the thin film, and some of these
targets were tracked as the test article was translated on a precision linear stage. In-plane tracking resolution using ultra-close-range
photogrammetry was related to the ground sample distance of the camera, which in this case was 51.25 μm pixel−1 (equal to the ratio of sample dimension to number of pixels in the field of view). Using a manual technique to identify features
of the etched pattern for tracking, the mean tracking error was about 13 μm (σ=43 μm). Using an automated, subpixel marking
technique to identify the 1.5 mm circular targets, the mean tracking error was 22 μm (σ=13 μm). Neither of these methods achieved
the desired 10 μm tracking resolution. 相似文献
8.
In wall-bounded turbulent flows, determination of wall shear stress is an important task. The main objective of the present
work is to develop a sensor which is capable of measuring surface shear stress over an extended region applicable to wall-bounded
turbulent flows. This sensor, as a direct method for measuring wall shear stress, consists of mounting a thin flexible film
on the solid surface. The sensor is made of a homogeneous, isotropic, and incompressible material. The geometry and mechanical
properties of the film are measured, and particles with the nominal size of 11 μm in diameter are embedded on the film’s surface
to act as markers. An optical technique is used to measure the film deformation caused by the flow. The film has typically
deflection of less than 2% of the material thickness under maximum loading. The sensor sensitivity can be adjusted by changing
the thickness of the layer or the shear modulus of the film’s material. The paper reports the sensor fabrication, static and
dynamic calibration procedure, and its application to a fully developed turbulent channel flow at Reynolds numbers in the
range of 90,000–130,000 based on the bulk velocity and channel full height. The results are compared to alternative wall shear
stress measurement methods. 相似文献
9.
Micron-sized internal cracks were introduced into rounded bars of pure iron by low cycle fatigue, and the cracks had irregular
penny-shaped morphology with the critical diameter of about 30μm and the thickness of 0.5–1.5μm. The initiation and propagation
of the cracks were investigated quantitatively as well as their location and geometry. After vacuum annealing of the samples
fatigued, the morphology in a two-dimensional longitudinal section of cracks within grains had evolved from initially elliptical
one into arrays of spherical voids controlled by surface diffusion. Furthermore, a typical morphology for a broken crack with
a center spherical void surrounded by outer doughnut-like cavities was observed along a perpendicular section of the specimen.
Subsequently the spherical voids shrink and diminish gradually dominated by bulk diffusion. A physical model to heal an internal
microcrack was proposed, in particular for the various healing stages controlled by the related dominant diffusion mechanism
and their dependencies upon the morphology and geometry of an original micro-crack in materials.
The project supported by the National Outstanding Young Investigator Grant of China (59925104) and the National Natural Science
Foundation of China (59889101) 相似文献
10.
We explore the effects of fluid films of variable depths on droplets impacting into them. Corresponding to a range of fluid
“film” depths, a non-dimensional parameter—H*, defined as the ratio of the film thickness to the droplet diameter—is varied in the range 0.1≤H*≤10. In general, the effect of the fluid film imposes a dramatic difference on the dynamics of the droplet–surface interaction
when compared to a similar impact on a dry surface. This is illustrated by the size distribution and number of the splash
products. While thin fluid films (H*≈0.1) promote splashing, thicker films (1≤H*≤10) act to inhibit it. The relative roles of surface tension and viscosity are investigated by comparison of a matrix of
fluids with low and high values of these properties. Impingement conditions, as characterized by Reynolds and Weber numbers,
are varied by velocity over a range from 1.34 to 4.22 m/s, maintaining a constant droplet diameter of 2.0 mm. The dependence
of splashing dynamics, characterized by splash product size and number, on the fluid surface tension and viscosity and film
thickness are discussed. 相似文献
11.
利用纳米硬度仪研究了在Cu基底上的Cu/Cr梯度膜的机械性能。梯度膜是通过将Cu靶和Cr靶同时溅射到Cu基底材料上,但两个靶的相对溅射功率随溅射时间变化而制备。利用Oliver and Pharr方法得到了膜随其厚度变化的硬度和弹性模量。然后利用加载/卸载/再加载的方法得到了在不同深度(即膜的厚度)压头平均压力与相对压人深度之间的关系曲线,在此曲线上可以明显反映出材料的屈服特性。 相似文献
12.
Tensile and Tensile-Mode Fatigue Testing of Microscale Specimens in Constant Humidity Environment 总被引:1,自引:0,他引:1
A tensile and tensile-mode-fatigue tester has been developed for testing microscale specimens in high humidity environments
in order to investigate the fracture mechanisms of microelectromechanical materials. A humidity control system was installed
on a tensile-mode fatigue tester equipped with an electrostatic force grip. A specimen and a griping device were inserted
into a small chamber and the humidity was controlled by air flow from a temperature and humidity chamber. The humidity stability
was within ±2%RH for humidities in the range 25–90%RH for eight hours of testing. Fatigue tests were performed on single-crystal
silicon (SCS) specimens in constant humidity environments and laboratory air for up to 106 cycles. The gauge length, width, and thickness of the SCS specimens were 100 or 500 μm, 13.0 μm, and 3.3 μm, respectively.
The average tensile strength was 3.68 GPa in laboratory air; this value decreased in high humidity environments. Fatigue failure
was observed during cyclic loading at stresses lower than the average strength. A reduction in the fatigue strength was observed
at high relative humidities. Different fracture origins and fracture behaviors were observed in tensile tests and fatigue
tests, which indicates that the water vapor in air affects the fatigue properties of SCS specimens. 相似文献
13.
The methods of uniform heating and resistive (Joule) heating for microscale freestanding surface-micromachined thin metal
film specimens were evaluated by a combination of full-field strain measurements by optical microscopy/Digital Image Correlation
(DIC) and microscopic infrared (IR) imaging. The efficacy of each method was qualitatively and quantitatively evaluated with
the aid of strain fields and IR-obtained temperature distributions along 850 nm thick freestanding microscale specimens subjected
to uniaxial tension while heated by each method. The strain and temperature fields were quite uniform in experiments carried
out with uniform specimen heating except for minor end-effects at the specimen grips. However, the resistively heated specimens
showed highly uneven temperature distribution varying by 50°C along the 1,000 μm specimen gauge length. This high temperature
gradient resulted in strain localization and 40% reduction in yield and ultimate tensile strengths of resistively heated specimens
compared to the uniformly heated ones. Therefore, it is concluded that resistive heating is not a reliable method for conducting
microscale temperature experiments with metallic films. 相似文献
14.
Y. H. Huh D. I. Kim D. J. Kim H. M. Lee S. G. Hong J. H. Park 《Experimental Mechanics》2011,51(7):1033-1038
Tensile and fatigue behaviors of the copper film coated by tin (Sn) were investigated considering S-N relationships and scanning
electron microscope (SEM) observation of fracture surfaces. The fatigue behavior was investigated considering the effect of
load ratio, R. The specimen of 2000 μm width, 8000 μm length and 15.26 μm thickness was fabricated by etching process. Tensile
properties were measured using the micro-tensile testing system and in-plane electronic speckle pattern interferometric (ESPI)
system for measuring the tensile strain during the test. The fatigue tests of the film were carried out in load-control mode
with 40 Hz at three different stress ratios of 0.05, 0.3 and 0.5. The S-N curves, including the slope of the curve and fatigue
limit, at the respective stress ratios were obtained. These curves were dependent on the load ratio. Empirical relationships
indicating the dependency of the fatigue limit and S-N curve on the load ratio were suggested in this study. SEM observation
of the tensile fracture surface showed that the cross-sectional area of the testing section was necked in the direction of
the film thickness (i.e. parallel to the substrate surface normal) and some ductile dimples in the fracture surface were present.
The fracture of the copper film under cyclic loading was progressed in the transgranular fracture mode. 相似文献
15.
A new method for measuring the strain around the high-temperature creep-crack tip is proposed in the present paper. A grid
pattern was described in a space of about 30 μm with a diamond stylus in the area ahead of the precrack of the specimen. Then,
the distortion of the grids and the change in specimen thickness which were induced by the creep deformation were measured
by means of a photo-microscope and a roughness-measuring system, respectively. The three-dimensional components of the strain
were calculated using the Lagrangian equation, into which the above measurement was introduced. The route of the creep-crack
extension was examined in association with the local strain measured by the proposed method. 相似文献
16.
Structure-property relationships in polymer composites with micrometer and submicrometer graphite platelets 总被引:1,自引:0,他引:1
The objectives of this work were (a) to investigate the influence of micrometer and submicrometer scale graphite platelets
of different aspect ratios and volume fractions on the effective and local quasi-static and dynamic properties of composites
with micrometer and submicrometer scale reinforcement, and (b) to compare and evaluate mechanical property measurements of
inhomogeneous materials via local (microscale) and bulk (macroscale) experimental methods. Small platelet volume fractions
(0.5%) provided proportionally larger increase of the elastic and storage moduli compared to large volume fractions (3.0%).
Randomly distributed 15 μm platelets provided marginally higher composite stiffness compared to 1 μm platelets while small
volume fractions (0.5%) of 15 μm platelets had a pronounced effect on the effective Poisson's ratio. It was found that local
property measurements of inhomogeneous materials conducted by nanoindentation are not representative of the bulk behavior
even when the characteristic length of the inhomogeneity is an order of magnitude smaller than the indentation contact area.
In this case, statistical averaging of data from a large number of indentations does not result in agreement with bulk measurements.
On the other hand, for small aspect ratio platelets with dimensions two orders of magnitude smaller than the nanoindentation
contact area, the nanoindenter-obtained properties agreed well with the effective material behavior. It was found that platelets
residing at the specimen surface contribute the most to nanoindentation data, which implies that this technique is only valid
for well-distributed nanoparticulate and microparticulate systems, and that nanoindentation cannot be used for depth profiling
of microstructured composites. 相似文献
17.
In this paper a micro tensile test which allows the determination and observation of the crack growth behaviour in thin polymer
layers is presented. The setup consists of micromanipulators and piezo actuators for straining the sample while an atomic
force microscope (AFM) is used for scanning the crack tip area with high lateral resolution. The stress in the specimen is
determined by an optical microscope for observation of the deflection of a force sensing beam. The material under investigation
is an amorphous and strongly entangled thermoplastic polyimide which can be patterned photolithographically and is spin cast
to form layers of 3 μm thickness. The results show the potential of the setup to measure crack length, crack tip opening and
nominal stress. The stress-crack length-diagram then allows to determine different stages during crack growth. 相似文献
18.
Yi Wu Hangfeng Wang Zhaohui Liu Jing Li Liqi Zhang Chuguang Zheng 《Acta Mechanica Sinica》2006,22(2):99-108
Particle-laden flows in a horizontal channel were investigated by means of a two-phase particle image velocimetry (PIV) technique.
Experiments were performed at a Reynolds number of 6 826 and the flow is seeded with polythene beads of two sizes, 60 μm and 110 μm. One was slightly smaller than and the other was larger than the Kolmogorov length scale. The particle loadings were relatively
low, with mass loading ratio ranging from 5×10−4 to 4×10−2 and volume fractions from 6×10−7 to 4.8×10−5, respectively. The results show that the presence of particles can dramatically modify the turbulence even under the lowest
mass loading ratio of 5×10−4. The mean flow is attenuated and decreased with increasing particle size and mass loading. The turbulence intensities are
enhanced in all the cases concerned. With the increase of the mass loading, the intensities vary in a complicated manner in
the case of small particles, indicating complicated particle-turbulence interactions; whereas they increase monotonously in
the case of large particles. The particle velocities and concentrations are also given. The particles lag behind the fluid
in the center region but lead in the wall region, and this trend is more prominent for the large particles. The streamwise
particle fluctuations are larger than the gas fluctuations for both sizes of particles, however their varying trend with the
mass loadings is not so clear. The wall-normal fluctuations increase with increasing mass loadings. They are smaller in the
60 μm particle case but larger in the 110 μm particle case than those of the gas phase. It seems that the small particles follow the fluid motion to certain extent while
the larger particles are more likely dominated by their own inertia. Finally, remarkable non-uniform distributions of particle
concentration are observed, especially for the large particles. The inertia of particles is proved to be very important for
the turbulence modification and particles behaviors and thus should be considered in horizontal channels.
The project supported by the National Natural Science Foundation of China (50276021), and Program for New Century Excellent
Talents in University, Ministry of Education (NCET-04-0708) The English text was polished by Yunming Chen. 相似文献
19.
利用多靶磁控溅射法制备MoS_2基系列复合薄膜,通过扫描电子显微镜、X-ray衍射、拉曼光谱对薄膜微观形貌及晶体结构进行表征,利用纳米压入表征薄膜硬度及弹性模量,通过微动摩擦磨损试验对比分析了该系列薄膜在大气环境下的润滑性能.研究结果表明:MoS_2薄膜中复合C、Ti元素可有效抑制薄膜生长过程中柱状结构的形成,薄膜更为致密;复合薄膜的摩擦系数及磨损率显著降低.其中,MoS_2+C+Ti三元复合薄膜硬度为7.43 GPa,其弹性模量及弹性恢复量分别为98.1 GPa和61.7%.在大气环境(RH 35%~50%)下,法向载荷10 N时MoS_2+C+Ti薄膜具有最低的磨损率4.67×10–17 m~3/(N·m),该薄膜在不同载荷的微动摩擦试验中均具有最好的承载力. 相似文献
20.
Submicron deformation field measurements: Part 1. Developing a digital scanning tunneling microscope 总被引:4,自引:0,他引:4
A new experimental method has been developed for studying deformations of micromechanical material systems at the submicron
scale. To that end, a special digital scanning tunneling microscope (STM) was designed to be coupled to a mechanically deforming
specimen. Operating in constant current mode, this digitally controlled STM records detailed topographies of specimen surfaces
with a resolution of 10 nm in-plane and 7 nm out-of-plane over a 10 μ × 10 μ area. Three-dimensional displacement field information
is extracted by comparing topographies of the same specimen area before and after deformation by way of a modified digital
image correlation algorithm. The resolution of this (combined) displacement measuring method was assessed on translation and
uniaxial tensile tests to be 5 nm for in-plane displacement components and 1.5 nm for out-of-plane motion over the same area.
This is the first paper in a series of three in which the authors delineate the main features of this specially designed microscope
and describe how it is constituted, calibrated and used with the improved version of the digital image correlation method
to determine deformations in a test specimen at the nanoscale. 相似文献