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Design of Testing System and Study of Mechanical Properties of Small-scale Materials

Author: XuWenLiang
Tutor: ZhangBin
School: Northeastern University
Course: Materials Science
Keywords: Microforce testing system small-scale material tensile test fatigue three-point-bending test
CLC: TB301
Type: Master's thesis
Year: 2008
Downloads: 61
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Abstract

With the initiation and development of microelectromechanical system (MEMS) technology, MEMS devices have been extensively applied in the fields, such as information technology, energy, transportation as well as military, etc. Materials in MEMS devices are unavoidably subjected to monotonic and/or cyclic loading, and even fail during the preparation, fabrication and actual service of the materials. Thus, how to evaluate and measure mechanical properties of the small-scale materials in MEMS devices becomes quite important. The applied load and deformation displacement are quite small due to the decrease in the material dimension. That gives rise to big difficulties in the experimental measurement. Although there are a few of studies on the measurement of mechanical properties of small scale materials, quite few investigations on the setup of the mechanical testing system have been conducted.In this work the principle of electromagnetics was utilized to produce a novel microforce testing system with multifunction. All kinds of specimen holders suitable for different kind of testing methods were also designed. By using the testing system, monotonic and cyclic loading, three-point bending tests were performed for micron-scale polycrystalline Cu wires, single crystal Cu foils and GaAs films, respectively. The mechanical properties of the materials were measured and characterized experimentally.The experimental results show that the operation process of the testing system is relatively simple. The loading can be applied to the samples manually and electromagnetically-driven. The load resolution is 5 mN, and the displacement resolution can be controlled by the voltage output of the electrical power system. The load range of the testing system is 0.01-3 N. The different types of the loading modes can be obtained by outputting different kinds of waveforms of the power system. The multifunctional testing system was successfully setup. The tensile test of the polycrystalline Cu wires demonstrates that the measurement of the tensile strength of the small scale materials can be performed by using the testing system. The relationship between the tensile strength of the Cu wires and the wire diameter was obtained. Fatigue test of the single crystal Cu foils reveals that the fatigue life of the metal foil can be determined by using this testing system, and that facilitates the further investigation of fatigue damage behavior. The fatigue damage behavior of the 50μm thick Cu foils was observed. The fracture strength of the GaAs films with different thickness was measured through three-point-bending test. A comparison of the fracture strength of the GaAs films with that of Si reported in the literature further demonstrates that the experimental results are reliable and the three-point-bending test under the testing system is feasible.

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