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Determination of Young's modulus by nanoindentation

Science China(Technological Sciences) 2004年第4期47卷 398-408页

作者： MA Dejun1, Chung Wo Ong2. LIU Jianmin1 & HE Jiawen3.1. Surface Engineering Research Institute, CMES, Beijing 100072. China 2. Department of Applied Physics and materials Research Center, The Hong Kong Polytechnic {2., Hong Kong, China {2.,{3., xian 710049, China 1. Surface Engineering Research Institute CMES 100072 Beijing China 2. Department of Applied Physics and materials Research Center The Hong Kong Polytechnic University Hong Kong China 3. state key laboratory for mechanical behavior of materials Xi’an Jiaotong University 710049 Xi’an China

A methodology for determining Youngs modulus of materials by non-ideally sharp indentation has been developed. According to the principle of the same area-to-depth ratio, a non-ideally pyramidal indenter like a Berkovich one can be approximated by a non-ideally conical indenter with a spherical cap at the tip. By applying dimensional and finite element analysis to the non-ideally conical indentation, a set of approximate one-to-one relationships between the ratio of nominal hardness/reduced Youngs modulus and the ratio of elastic work/total work, which correspond to different tip bluntness, have been revealed. The nominal hardness is defined as the maximum indentation load divided by the cross-section area of the conical indenter specified at the maximum indentation depth. As a consequence, Youngs modulus can be determined from a nanoindentation test only using the maximum indentation load and depth, and the work done during loading and unloading processes. The new method for determining Youngs modulus is referred to as pure energy method. The validity of the method was examined by performing indentation tests on five materials. The experimental results and the standard reference values are in good agreement, indicating that the proposed pure energy method is a promising substitution for the most widely used analysis models at present.

关键词： Young's modulus, nanoindentation, nominal hardness, indentation work.

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Novel strengthening methods for ultralightweight sandwich structures with periodic lattice cores

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Science China(Technological Sciences) 2010年第3期53卷 875-877页

作者： LU TianJian 1 &ZHANG QianCheng 2.1 MOE key laboratory for Strength and Vibration,School of Aerospace,Xi’an {2. {3.,Xi’an 710049,China 2.state key laboratory for mechanical behavior of materials,School of Material Science and Engineering,Xi’an {2. {3.,Xi’an 710049,China 1. MOE key laboratory for Strength and Vibration School of Aerospace Xi’an Jiaotong University Xi’an 710049 China2. State Key Laboratory for Mechanical Behavior of Materials School of Material Science and Engineering Xi’an Jiaotong University Xi’an 710049 China

Recent development of ultralightweight lattice-cored sandwiches is reviewed,with focus placed on various novel fabrication methods introduced to strengthen these structures,covering not only research results published... 详细信息

关键词： cellular metals strengthening method fabrication sandwich panels

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Effect of Annealing Ambience on the Chemical Stability of Zr-Si-N Diffusion Barrier

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材料热处理学报 2004年第5B期25卷 1225-1228页

作者： SONGZhong-xiao WANGYuan XUKe-wei LIUChun-liang keyLabforPhysicalElectronicsandDevicesMinistryofEducation Xi＇anJiaotongUniversity710049Xi＇anChina state-key{2.for{3.behaviorofmaterials Xi＇anJiaotongUniversity710049Xi＇anChina

Zr-Si-N films were deposited by RF magnetron sputtering (MS) technique. A Cu film on the top of Zr-Si-N films was prepared by DC pulsed magnetron sputtering. The Cu/Zr-Si-N systems were annealed in vacuum and N2.H2.gas mixture at 800°C, respectively. The structure of the films were characterized by X-ray diffraction (XRD), Auger electron spectroscopy (AES) and four-point probe method. The sheet resistances of the Cu/Zr-Si-N/Si contact systems annealed in N2.H2.gas mixture were lower than those of the specimens annealed in vacuum at 800°C. The residual oxygen contamination from vacuum annealing ambience influences the sheet resistances of the Cu/Zr-Si-N/Si contact systems due to residual oxygen contamination and/or voids in Cu films. Though thermal stabilities of the Cu/Zr-Si-N/Si systems were maintained up to 800°C when annealed in vacuum and N2.H2.gas mixture, the changes of thermal stability of specimens were noticeable. The vacuum can accelerate the oxidation and decomposition of Zr-Si-N barrier. On the contrary, N2.H2.gas mixture prevent from the Zr-Si-N barrier oxidation and decomposition.

关键词：扩散势垒 Zr-Si-N 退火化学稳定性

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Ultralight X-type lattice sandwich structure (Ⅱ):Micromechanics modeling and finite element analysis

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Science China(Technological Sciences) 2009年第9期52卷 2670-2680页

作者： ZHANG QianCheng1,CHEN AiPing 2.CHEN ChangQing2.3.& LU TianJian2.1 state {2. laboratory for {3. behavior of materials,School of Material Science and Engineering,Xi’an jiaotong university,Xi’an 710049,China 2.MOE {2. laboratory for Strength and Vibration,School of Aerospace,Xi’an jiaotong university,Xi’an 710049,China 3.Department of Engineering Mechanics,AML,Tsinghua university,Beijing 100084,China state key {2. for {3. behavior of materials School of Material Science and Engineering Xi’an Jiaotong University Xi’an China MOE key laboratory for Strength and Vibration School of Aerospace Xi’an Jiaotong University Xi’an China Department of Engineering Mechanics AML Tsinghua University Beijing China

The methods of homogenization and finite elements are employed to predict the effective elastic constants and stress-strain responses of a new type of lattice structure,the X-structure proposed by the authors in a companion paper. It is shown that in most cases the predictions by the equivalent homogenization theory agree well with the experimental and 3.dimensional finite element calculated results. The theoretical and numerical study supports the argument that the X-structure is superior to the pyramid lattice structure in terms of mechanical strength.

关键词： sandwich panel lattice structure equivalent homogenization finite element model

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Preparation and Properties of Macroporous Silicon Nitride Ceramics by Gelcasting and Carbonthermal Reaction

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Journal of materials Science & Technology 2005年第6期21卷 894-898页

作者： Wen ZHANG, Hongjie WANG+ and Zhihao JIN state key {2. for {3. behavior of materials, School of materials Science and Engineering, Xi’an jiaotonguniversity, Xi’an 710049, China state key {2. for {3. behavior of materials School of Materials Science and Engineering Xi'an Jiaotong University Xi'an 710049 China

Macroporous silicon nitride （Si3.4） ceramics with high strength, uniform structure and relatively high porosity were obtained by gelcasting and carbonthermal reaction in a two-step sintering technique. Microstructure and composition were investigated by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD）. Open porosity, pore size distribution and basic mechanical performance were measured by Archimedes method, mercury intrusion porosimetry and three-point bending methods, respectively. SEM and TEM results revealed that pores were formed by elongated β-Si3.4. SADP measurement proved the formation of SiC particles. The SiC granules were beneficial for the formation of high ratio elongated β-Si3.4, and at proper amount, they also acted as reinforcement phase. Thermodynamic analysis indicated that the mechanisms of the reactions were mainly associated with liquid-solid reaction and gas-liquid reaction.

关键词： Ceramics Silicon nitride Silicon carbide X-ray diffraction

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EFFECT　OF　MICROSTRUCTURE　ON　FATIGUE　CRACK　INITIATION　OF　SHOT　PEENED　COPPER　AND　BRASS

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Acta Metallurgica Sinica(English Letters) 1996年第6期9卷 607-611页

作者： K.W.Xu N.S.Hu and J.W.He(state-key {2. for {3. behavior of materials,Xi’an jiaotong university, Xi’an 710049, ) Xi'an jiaotong Univ Xi'an China

The effect of microstructure on fatigue crack initiation was considered in the shot peened surface layer by eliminating the influence of compressive residual stress. Results indicate that the drastically deformed structure by shot peening would keep the dislocations from moving out of the surface and hold the dislocations inside the cell structure of copper or the palling structure of brass. The fatigue damage of intrusion and extrusion type could thus be depressed and the fatigue life is enhanced.

关键词： shot peening fatigue,microstructure

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Microstructure and mechanical Properties of Nanocrystalline Tungsten Thin Films

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Journal of materials Science & Technology 2010年第1期26卷 87-92页

作者： H.L. Sun, Z.X. Song, D.G. Guo, F. Ma and K.W. Xu state key {2. for {3. behavior of materials, School of materials Science and Engineering, Xi an jiaotong university, Xi’an 710049, China [a] state key {2. for {3. behavior of materials School of materials Science and Engineering Xi'an jiaotong university Xi'an 710049 China

Tungsten （W） thin films were prepared by magnetron sputtering onto Si （100） substrates. Their microstructures were characterized by X-ray diffraction （XRD）, field emission scanning electron microscopy （FE-SEM） and transmission electron microscopy （TEM）. The hardness and modulus were evaluated by nanoindentation. It is found that a 3. nm Cr sticking layer induces structure changes of deposited W film from β-W to α-W structure. In addition, remarkable hardness enhancement both for the deposited and annealed W films, were compared with that of bulk coarse-grained W, although their nanoindentation modulus is very close to that of corresponding bulk W. The intrinsic reasons that lead to structure changes and super hardness are discussed.

关键词： Tungsten film Microstructure Nanoindentation Hardness Modulus

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A NEW NON-UNIFORM YIELD PHENOMENON AND ITS MECHANISM

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Acta Metallurgica Sinica(English Letters) 2000年第3期13卷 862-866页

作者： W.F. Zhang Y.M. Chen and J.H. Zhu(state key {2. for {3. behavior of materials, Xi’an jiaotong university, Xi’an 710049, China) Xi'an jiaotong Univ Xi'an China

A new non-uniform yield phenomenon is found during tension of austenite stainless steel at -190℃, which consists of elasto-plastic instability ξph and stress plateau ξL resulting from strain-induced martensite transformation. It is essentially different from non-uniform yield that is related to dislocation obstacles. The experimental results show that ξph and ξL increase with increaslng strain rate, and ξph, increases but ξL decreases with increasing *** enengy of strain-induced martensite keeps a constant, 3.85×106J/m3. with increasing strain at the stages of both elasto-plastic instability and stress plateau.

关键词： non-uniform yield elasto-plastic instability stress plateau,strain-induced martensite transformation

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EFFECTS　OF　PRESTRAIN　ON　FATIGUE　THRESHOLD　AND　INITIAL　YIELD　STRESS　OF　NORMALIZED　103.　STEEL

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Acta Metallurgica Sinica(English Letters) 1996年第4期9卷 247-250页

作者： J.X Luo and Y.X. Tan (state key Lab. for {2. {3. of materials Xi′an jiaotong university, Xi’an 710049, China )

The relationships between fatigue threshold △Kth and the initial yield .strength σ0 of normalized 103. steel after various prestrain (at fist, second and third hardening stages respectively) were investigated through the analysis of theσ-εcurves and transmission electron microscope (TEM). After prestraining at first or second hardening stage, there is a marked drop in the values of △Kth and σ0. This is in correspondence with the depinning of the solute atoms from the dislocation lines in the Cottrell *** the third hardening stage of prestrain the fatigue threshold increases rapidly and △Kth is even 1.6 times as large as the original value. This is because at this stage no dislocation-cell free areas can be found and the refinement of the dislocation cells occurs with the increase in the prestrain level.

关键词： deformation hardening fatigue threshold initial yield strength,dislocation array,103. steel

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EFFECT OF SPECIMEN SIZE ON J_R RESISTANCE CURVE

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Acta Metallurgica Sinica(English Letters) 1996年第5期9卷 350-354页

作者： H.P. Chen and Z.J. Deng (state key Lab. for {2. {3. of materials, Xi’an jiaotong university, Xi’an 710049, China)

The effect of specimen thinkness on JR resistance curve has been investigated using low and middle strength steels. As the J dominance regime is reached, the initial J-integral values, J(i), are definite even if the elastic component Ji(e) and plastic component Ji(p)vary with the thinkness of specimen. The wider the specimen width, the larger the Ji(e)/Ji and the smaller the Ji(p)/Ji. The crack propagation resistance, dJR/da and dJp/da, decreases, while dJe/da increases linearly with increasing specimen *** on the above experimental results, an empirical formula dJ/da = α+β. B is given, which can be used to evaluate the safety of practical structural components.A modified J-integral is presented, upon which a new view is Put forward that the increase in crack growth resistance is induced mainly by the increase in the plastic J-integral component with the crack propagation,

关键词： fracture mechanics J-R curve modified J elastic-plastic fracture

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