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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 university, Hong Kong, china 3. state key laboratory for mechanical behavior of materials, xian jiaotong university, xian 71.049, 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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DISLOCATION ARRAY AT VARIOUS DEFORMING AND HARDENING STAGES OF STEEL 103.

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Acta Metallurgica Sinica(English Letters) 1995年第3期8卷 195-198页

作者： LUO Jingxi TAN Yuxu (state key laboratory for {3. Behaviour of materials,Xi’an jiaotong. university, china Xi'an jiaotong Univ Xi'an China

The alteration of dislocation arrays in the process of strain hardening for normalized carbon steel 103. was investigated by transmission electron microscopy. At primary stage the separated dislocation lines tend to form tangles and networks, dislocation cells appear at the secondary stage, the amount of the cells increases significantly, its average dimension does not change and the cell walls become clear. The third stage of strain hardening was observed in the process from necking to fracture and shows a straight line segment on the lg σ -lg ε curve, at this time the dislocation cells become smaller and tend to form band structure.

关键词： strain hardening dislocation array cell structure steel 103.

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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 jiaotong {3.,Xi’an 71.049,china 2 state key laboratory for mechanical behavior of materials,School of Material Science and Engineering,Xi’an jiaotong {3.,Xi’an 71.049,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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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 laboratory for {3. behavior of materials, School of materials Science and Engineering, Xi’an jiaotonguniversity, Xi’an 71.049, china state key laboratory 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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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 laboratory for {3. behavior of materials, School of materials Science and Engineering, Xi an jiaotong university, Xi’an 71.049, china [a] state key laboratory for {3. behavior of materials School of materials Science and Engineering Xi'an jiaotong university Xi'an 71.049 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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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 key laboratory for {3. behavior of materials,School of Material Science and Engineering,Xi’an jiaotong university,Xi’an 71.049,china 2 MOE key laboratory for Strength and Vibration,School of Aerospace,Xi’an jiaotong university,Xi’an 71.049,china 3.Department of Engineering Mechanics,AML,Tsinghua university,Beijing 100084,china state key laboratory 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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Microstructural characterization of the Al/Cu/steel diffusion bonded joint

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Rare Metals 2009年第5期28卷 478-481页

作者： BAI Bingzhe GAO Yimin FENG Chun laboratory of Advanced materials Department of Materials Science and Engineering Tsinghua University Beijing 100084 China state key laboratory for {3. behavior of materials School of Materials Science and Engineering Xi＇an Jiaotong University Xi＇an 710049 China

A vacuum hot-pressed diffusion method was used to prepare an Al/Cu/steel composite with a gradient structure. The Al/Cu interface was investigated layer by layer by means of scanning electron microscopy, energy dispersive X-ray spectrometry, electron probe microanalysis, and Vickers microhardness. The results show that two kinds of intermetallic compounds, Cu9Al4 adjacent to the Cu side and CuAl2 adjacent to the Al side, are formed in the interface of Al/Cu. The conductivity is 0.3.9 mS/cm in the intermetallic compound with a thickness of 3.5 μm, higher than that of the intermetallic compound with a thickness of 23.μm, in which the conductivity is 0.242 mS/cm.

关键词： metal composites diffusion bonding intermetallic compounds microhardness interface

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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 laboratory for {3. behavior of materials, Xi’an jiaotong university, Xi’an 71.049, 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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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 mechanical {3. of materials, Xi’an jiaotong university, Xi’an 71.049, 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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EFFECTS　OF　PRESTRAIN　ON　FATIGUE　THRESHOLD　AND　INITIAL　YIELD　STRESS　OF　NORMALIZED　103.　STEEL

引用

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 mechanical {3. of materials Xi′an jiaotong university, Xi’an 71.049, 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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