共查询到20条相似文献,搜索用时 312 毫秒
1.
Testing of ring-shaped specimens often is required for determining the hoop-direction mechanical properties of cylindrical
composite structures. A quadrant ring test method was developed in an effort to produce a relatively uniform stress distribution
in the ring specimen using a conventional tensile testing machine. Finite element analysis results indicated that the four-sector
quadrant test is capable of producing a more uniform stress distribution in the specimen than the split-disk test. However,
similar tensile strengths were obtained using the quadrant and split-disk tests, both significantly below those obtained from
tensile testing of flat specimens. The lack of improvement in tensile strength produced by the quadrant test was caused by
small rotations of the fixture quadrants during loading, producing greater peak stresses than for the ideal case of radially
displaced sectors. These results suggest that test fixturing that produces a true outward radial displacement of the fixture
sectors is required to produce accurate tensile strengths. 相似文献
2.
This paper presents a device that has been designed for tensile loading at medium impact rates (up to 10 3 s –1) and for performing either interrupted or failure tests. This machine allows us to apply prescribed pre-straining to the
specimen, and then apply subsequent loading histories such as impact fatigue. Two specimen loading systems are considered,
which make it possible to carry out tests with various ranges of force and various durations of time. A multi-CCD camera system
is triggered by a chosen threshold from the force signal. The system is dedicated to the displacement measurement and gives
both qualitative and quantitative information about the stretching mechanism leading to fracture. To illustrate the performance
of the device, experimental results concerning impact tensile tests at a strain rate of about 300 s –1 are presented, as well as consecutive impact-fatigue tests on two aluminium alloys. 相似文献
3.
使用评价纤维/基体界面力学性能的新方法纤维微滴拉伸测试,来研究M55JB碳纤维/环氧树脂基体之间的界面应力传递性能。使用自制的微加载装置对碳纤维/环氧树脂微滴试样进行对称式拉伸测试,用微拉曼光谱仪记录下不同应变下的嵌入微滴内纤维上的拉曼频移信号,经过应力/频移关系转换成纤维轴向应力。实验结果显示,微滴内纤维轴向应力随载荷而明显增加。根据界面力平衡模型得到相应的界面剪切应力呈反对称式分布,在纤维嵌入端存在剪应力集中。新测试方法能保证嵌入微滴内纤维上的应力呈对称式分布,而且能降低纤维嵌入端附近的应力奇异性。 相似文献
4.
The present paper deals with full-field strain measurement on glass/epoxy composite tensile specimens submitted to high strain
rate loading through a split Hopkinson pressure bar (SHPB) device and with the identification of their mechanical properties.
First, the adopted methodology is presented: the device, including an Ultra-High Speed camera, and the experimental procedure
to obtain relevant displacement maps are described. The different full-field results including displacement, strain and acceleration
maps for two mechanical tests are then addressed. The last part of the paper deals with an original procedure to identify
stiffnesses on this dynamic case only using the actual strain and acceleration maps (without the applied force) by using the
Virtual Fields Method. The results provide very promising values of Young’s modulus and Poisson’s ratio on a quasi-isotropic
glass-epoxy laminate. The load reconstructed from the moduli and strains compares favourably with that from the readings. 相似文献
5.
A novel micromechanical device was developed to convert the compressive force applied by a nanoindenter into pure tensile
loading at the sample stages inside a scanning electron microscope or a transmission electron microscope, in order to mechanically
deform a one-dimensional nanostructure, such as a nanotube or a nanowire. Force vs. displacement curves for samples with Young’s modulus above a threshold value can be obtained independently from readings
of a quantitative high resolution nanoindenter with considerable accuracy, using a simple conversion relationship. However,
in-depth finite element analysis revealed the existence of limitations for the device when testing samples with relatively
low Young’s modulus, where forces applied on samples derived from nanoindenter readings using a predetermined force conversion
factor will no longer be accurate. In this paper, we will demonstrate a multi-step method which can alleviate this problem
and make the device capable of testing a wide range of samples with considerable accuracy. 相似文献
6.
A screw-driven new biaxial testing machine for the realization of experimental investigations on anisotropic sheet materials,
such as composite plates or rolled sheet metals, is presented. The described mechanical concept and servocontrol system allow
cruciform specimens to be subjected to large strain biaxial tensile and compressive tests without kinematic incompatibilities.
Moreover, for the proper implementation of biaxial tensile tests, the specific problems linked to the anisotropic properties
of the investigated materials are taken into account; therefore, for the first time, the biaxial machine is supplied with
the original ‘off-axes testing device,’ consisting of hinged fixtures with knife-edges at each arm of the cruciform specimen.
A recently developed optimization method for the optimal design of flat tensile cruciform specimens is shortly reviewed. Numerical
simulations illustrate the decisive superiority of the optimized specimen compared with specimen designs proposed in the literature,
as well as the necessity to use the ‘off-axes’ testing technique in biaxial tests on anisotropic materials. 相似文献
7.
Mechanical characterization of sub-micron thin films or similar small scale structures have been a continuous challenge to the mechanics community due to the difficulty in accurately quantizing the applied load and the resulted deformation. In this paper, a new force-domain analog-to-digital converter (F-D ADC) created from the concept of Flash ADC in electronics is developed to perform thin film tensile tests. The key component of the F-D ADC is a quantizer-array of microfabricated buckling beams of varying lengths. During testing, the tensile force applied in the test specimen is converted to the compressive force in the quantizer beam array and digitized by using the critical buckling load of the beams as they progressively buckle with increasing force amplitude. The deformation of the specimen is controlled by the piezoelectric actuator. Successful testing of (110) single crystal silicon and titanium/nickel (Ti/Ni) multilayer thin film specimens demonstrated the feasibility of this novel F-D ADC concept. 相似文献
8.
An experimental methodology has been developed to characterize local strain heterogeneities in alloys via in-situ scanning electron microscope (SEM) based mechanical testing. Quantitative measurements of local strains as a function of
grain orientation, morphology and neighborhood are crucial for mechanistic understanding and validation of crystal plasticity
models. This study focuses on the technical challenges associated with performing creep tests at elevated temperatures ≤700°C
in an SEM. Samples of nickel-based superalloy Rene 104 were used for this study, but the technique is applicable to testing
of any metal samples at elevated temperature. Electron beam lithography was employed to produce a suitable surface speckle
pattern of hafnium oxide to facilitate full field displacement measurements using a commercial software package. The speckle
pattern proved to have good thermal stability and provided excellent contrast for image acquisition using secondary electron
imaging at elevated temperature. The speckle pattern and microscope magnification were optimized to obtain the resolution
necessary to discern strain localizations within grain interiors and along grain boundaries. Minimum strain resolution due
to SEM image distortions was determined prior to tensile testing, and image integration methods were utilized to minimize
imaging artifacts. Limitations due to the present specimen heating method and potential solutions to these limitations are
also addressed. 相似文献
9.
材料动力学试验技术远比准静态力学中的复杂,为了模拟各种速率的冲击加载过程,试验装置设计就成为关键问题之一.特别是针对材料动态拉伸性能的测试,目前的冲击拉伸装置还没有统一标准,因此本文基于一维弹性应力波原理设计了一套双气室间接杆-杆型冲击拉伸试验装置.该装置采用了双气室对称布置的方式,通过气体转换器实现气路的转换,克服了现有气动式冲击拉伸设备结构复杂、密封要求严格的缺点.本文利用该装置对2A12T4铝合金试件的冲击拉伸性能进行了测试,并数值分析了应力波在杆系和试件中的传播效应.通过试验测试和数值分析论证了该冲击拉伸装置实验的可靠性和设计的合理性. 相似文献
10.
扭转是一种常用的冷作硬化方法。本文通过实心圆轴扭转实验和预扭试件的单向拉伸实验,研究了扭转塑性变形程度对6063铝合金拉伸力学性能的影响。通过理论研究和硬度分析探究了造成这一影响的内在机理。结果表明,试件扭转后其内部形成的以屈服强度为特征参数的梯度结构,是造成预扭试件力学性能得到改善的根本原因。并且,扭转不同的角度,材料内部产生的梯度结构也是不同的。而不同的梯度结构对试件力学性能的影响则表现为后继拉伸屈服强度随预扭角度的增大而增大。为了预测预扭试件的后继拉伸力学行为,验证前述结论的正确性,建立了由内到外屈服强度逐渐变化的有限元模型。此模型代表了预扭转变形试件,对其施加位移载荷,模拟后继单向拉伸加载过程。模拟所得材料力学性能随扭转角的变化趋势与实验结果基本吻合,从而验证了扭转冷作硬化后,圆轴试件内部产生了以屈服强度为特征参数的梯度结构这一结论。同时,也提供了一种有效的预测材料扭转后拉伸力学性能的数值模拟方法。 相似文献
11.
Microelectromechanical system (MEMS) devices based on electro-thermal actuation have been used over the past few years to perform tensile tests on nanomaterials. However, previous MEMS designs only allowed small ( e. g., <100 nm) total displacement range without a significant increase in temperature near the nanospecimens (<20°C), thereby limiting the design of the load sensor or the range of nanomaterials to test. Here we characterize the thermo-mechanical behavior of three MEMS devices, using optical displacement measurements, micro-Raman temperature measurements, and finite element modeling. We observe the increase in temperature near the nanospecimen gap per displacement of thermal actuator to linearly decrease with the distance between nanospecimen gap and thermal actuator. We also present a MEMS device that can provide up to 1.6 μm of total displacement with less than 10°C increase in temperature near the nanospecimens, more than one order of magnitude improvement with respect to previously published MEMS material testing setups. This MEMS device can be used for accurate, temperature-controlled tensile testing of nanocrystalline metallic nanobeams. 相似文献
12.
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 modulus E=74.6 GPa. 相似文献
13.
For both single-phase and multiphase metallic materials, it is necessary to understand the mechanical behavior on the grain-size scale in detail to get information that is not obtainable from macro-scale mechanical characterizations. This paper presents a methodology for uniaxial tensile testing of micro-specimens isolated from a bulk material. The proposed concept of multiple parallel micro-tensile specimens at the tip of a macro-sized wedge reduces the alignment work and offers an easy way for specimen handling. The selection of site-specific specimens is based on detailed microstructural and crystallographic characterization. Three kinds of representative specimens are presented to illustrate the wide range of application of the methodology for a variety of materials. Accurate, reproducible measurement of force (2.5 μN resolution) and displacement (~10 nm resolution) is demonstrated, while accurate alignment (in-plane rotational and out-of-plane tilt misalignment of <0.2°) limits the stress due to bending to <0.2% of the imposed uni-axial stress. Combined with detailed material characterization on both sides of the micro-specimens, this method yields detailed insights into the micro-mechanics of bulk materials which is hard to obtain from traditional macro-mechanical tests. 相似文献
14.
基于液压伺服高速加载系统,发展了一种材料双轴拉伸力学性能测试技术。利用锥面接触导向驱动方法,把加载锤竖直方向的驱动力转化为水平方向的双轴驱动力,从而实现对十字形试样平面双轴加载。借助有限元数值模拟手段优化了锥面接触角和十字形试样尺寸。当接触锥角为45°时,既有较好的水平驱动转化效率,同时又保持较小的接触力,确保水平驱动加载各组件在弹性变形范围内,可多次重复使用。确定了加载臂狭缝个数、狭缝与减薄区边缘长度和标距段厚度等试样设计关键参数,在十字形试样测试标距段内实现了均匀变形。设计了测力夹持一体化导杆和非接触光学全场应变测试系统,准确获得了试样的应力和应变。利用此平面双轴拉伸加载装置,开展2024-T351铝合金板单轴拉伸实验和激光探测同步性验证实验,验证装置设计的可行性;开展铝合金板材在不同加载速率下的双轴拉伸实验,得到在双轴加载下铝合金板材应力应变曲线,并与单轴加载下实验结果进行了对比分析。 相似文献
15.
This paper proposes a novel material testing method, gripless nanotension technique (GNT), to assess the basic mechanical properties of nano-scale structures in top-down processes. The GNT exhibits prominent advantages over conventional methods, i.e., use of a nanoindenter as a reliable and simple testing device, high-quality nano-scale metallic specimen with negligible residual stress, and tensile testing possible in the through-thickness direction. Using the proposed method, nano-scale polycrystalline specimens obtained from a nickel film were tested. Through the experiment, well-defined values of material properties with extraordinary phenomenal findings, i.e., strikingly reduced elastic modulus, yield strength and tensile strength of much higher values could be reliably observed and determined at the nano-scale. 相似文献
16.
In situ tensile tests in a scanning electron microscope (SEM) have been conducted on a 8-layer 5-harness satin carbon fibre and epoxy matrix composite to observe the first stages of damage at the scale of fibres and matrix. A speckle pattern based on a suspension of alumina particles was applied onto the surface of the specimen to facilitate the use of digital image correlation (DIC). Local and finite element (FE) DIC are compared on pictures acquired during the tensile tests, with and without a speckle pattern. FE DIC with mechanical regularization was found to be the only approach able to measure displacement fields at a fine enough resolution in both cases. This method, initially created for homogeneous materials, was then adapted to heterogeneous materials. First, a microstructure consistent mesh was created and used for correlation purposes. Second, the difference between the mechanical properties of the constituents is taken into account in the mechanical regularization. Last, the accuracy of the method is analysed. The adaptation presented herein was proved to be able to measure displacement fields in the matrix between fibres with an error of 10 nm (a fifth of a pixel) and to detect the initiation of the first damage mechanisms by means of the mechanical residuals. 相似文献
17.
A new micro-system for the on-chip mechanical characterization of thin polysilicon films was designed, fabricated and tested.
The device contains a micro electro-thermo mechanical actuator which is able to load a specimen until rupture in purely tensile
conditions. The elongation of the specimen is measured during the test through the capacitance variation of a set of parallel
plate capacitors, while the force in the specimen can be computed starting from the applied voltage. Through a unique loading
cycle in which the voltage is first increased until specimen rupture and then decreased, the new device allows for the determination
of the specimen elastic stiffness and nominal tensile strength. The obtained experimental results were compared with values
previously obtained by means of different on-chip test devices. Multi-physics FE simulations were performed for additional
comparison with analytical formulae used in the data reduction procedure and with the obtained experimental results. 相似文献
18.
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 10 6 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
19.
Thin films at the micrometer and submicrometer scales exhibit mechanical properties that are different than those of bulk
polycrystals. Industrial application of these materials requires accurate mechanical characterization. Also, a fundamental
understanding of the deformation processes at smaller length scales is required to exploit the size and interface effects
to develop new and technologically attractive materials. Specimen fabrication, small-scale force and displacement generation,
and high resolution in the measurements are generic challenges in microscale and nanoscale mechanical testing. In this paper,
we review small-scale materials testing techniques with special focus on the application of microelectromechanical systems
(MEMS). Small size and high force and displacement resolution make MEMS suitable for small-scale mechanical testing. We discuss
the development of tensile and bending testing techniques using MEMS, along with the experimental results on nanoscale aluminum
specimens. 相似文献
20.
Hydrogel actuators in microfluidic devices must endure the forces of aqueous flow, the constraint of device walls, and the
restoring force of elastic membranes. In order to assess the capabilities of hydrogels, three experimental techniques for
determining the uniaxial tensile properties and functional swelling properties of microscale hydrogel structures have been
developed. Tensile tests were conducted to determine Young's modulus and Poisson's ratio at varying degrees of swelling equilibrium.
Force response tests were performed to determine the force exerted by cylindrical hydrogel structures on compression platens
held at fixed displacement. Particle image velocimetry, a method originally developed to measure velocity fields in fluid
flows, was adapted to investigate the deformation rates at various times within hydrogel structures during volumetric swelling.
The techniques and sample fabrication methods outlined are applicable to a variety of hydrogel chemistries. 相似文献
|