Mode II fracture analysis of double edge cracked circular disk subjected to different diametral compression

A detailed analysis of modeⅡstress intensity factors(SIFs) for the double edge cracked Brazilian disk subjected to different diametral compression is presented using a weight function method. The mode Ⅱ SIFs at crack tips can be obtained by simply calculating an integral of the product of mode Ⅱ weight function and the shear stress on the prospective crack faces of uncracked disk loaded by a diametral compression. A semi-analytical formula for the calculation of normalized mode Ⅱ SIF, fⅡ , is derived for different crack lengths (from 0.1 to 0.7) and inclination angles (from 10^。 to 75^。) with respect to loading direction. Comparison between the obtained results and finite element method solutions shows that the weight function method is of high precision. Combined with the authors‘ previous work on modeⅠfracture analysis, the new specimen geometry can be used to study fracture through any combination of mode Ⅰ and mode Ⅱ loading by a simple alignment of the crack relative to the diameter of compression loading, and to obtain pure mode Ⅱ crack extension. Another advantage of this specimen geometry is that it is available directly from rock core and is also easy to fabricate.     

Semi-analytical weight function method for center-cracked circular disk subjected to diametral compression

Ｓｉｎｃｅｔｈｅｃｅｎｔｅｒ ｃｒａｃｋｅｄｃｉｒｃｕｌａｒｄｉｓｋｓｐｅｃｉ ｍｅｎｃａｎｂｅａｖａｉｌａｂｌｅｄｉｒｅｃｔｌｙｆｒｏｍｒｏｃｋｃｏｒｅ ,ａｎｄｍｉｘｅｄ ｍｏｄｅｆｒａｃｔｕｒｅｒａｎｇｉｎｇｆｒｏｍｐｕｒｅｍｏｄｅⅠｔｏａｎｙＫⅡ/ＫⅠ ｒａｔｉｏｃａｎｂｅｅａｓｉｌｙａｃｈｉｅｖｅｄｕｓｉｎｇｔｈｉｓｇｅｏｍｅｔｒｙ ,ｉｔｉｓｗｉｄｅｌｙｕｓｅｄｉｎｔｈｅｍｉｘｅｄ ｍｏｄｅｆｒａｃｔｕｒｅｉｎｖｅｓｔｉｇａｔｉｏｎｏｆｂｒｉｔｔｌｅｍａｔｅｒｉａｌｓ .Ｔｈｅｐｒｏｂｌｅｍｃｏ…     

Analysis of brittle fracture due to compressive loading using center-cracked Brazilian disk

Ｄｅｔｅｒｍｉｎａｔｉｏｎｏｆｆｒａｃｔｕｒｅｔｏｕｇｈｎｅｓｏｆｂｒｉｔｌｅｍａｔｅｒｉａｌｓｉｓｏｆｇｒｅａｔｉｍｐｏｒｔａｎｃｅｉｎｍｉｎｉｎｇａｎｄｇｅｏｌｏｇｉｃａｌｅｎｇｉｎｅｒｉｎｇ．Ａｖａｒｉｅｔｙｏｆｓｐｅｃｉｍｅｎｇｅｏｍｅｔ...     

Failure mode and strength anisotropic characteristic of stratified rock mass under uniaxial compressive situation

A stratified rock mass model was founded by FLAC^3D. The failure mode and anisotropic characteristic of strength for stratified rock mass were analyzed. The analysis results show that the numerical simulation can visually reflect the failure modes of rock samples under different inclination angles β of structural plane. The stiffness of rock sample before peak strength changes in the compressive procedure. With the increase of β, the compressive strength σ _c of rock sample decreases firstly and then increases; when β is in the range of 20°–30° and 80°–90°, σ _c has the largest sensitivity to β; while β falls in the range of 30°–70°, σ _c varies little. When ϕ _j <β<90° (β _j is friction angle of structure plane), the results obtained from numerical simulation and theoretical analysis are in almost the same values; while β⩽ ϕ _j or β=90°, they are in great different values. The results obtained from theoretical analysis are obvious larger than those from numerical simulation; and the results from numerical simulation can reflect the difference of compressive strength of rock samples for the two situations of β⩾ ϕ _j and β=90°, which is in more accordance with the real situation. Foundation item: Project (50099620) supported by the National Natural Science Foundation of China     

Microscopic characteristics of different fracture modes of brittle rock

Ａｓｕｒｖｅｙｏｆｆｒａｃｔｕｒｅｍｅｃｈａｎｉｃｓｌｉｔｅｒａｔｕｒｅｒｅ ｖｅａｌｓｔｈａｔｒｅｓｅａｒｃｈｗｏｒｋｏｎｒｏｃｋｆｒａｃｔｕｒｅｍｅｃｈａｎ ｉｃｓｈａｓｍａｉｎｌｙｆｏｃｕｓｅｄｏｎＭｏｄｅⅠｆｒａｃｔｕｒｅ (ｏｐｅｎ ｉｎｇｍｏｄｅ) ,ｉｎｐａｒｔｉｃｕｌａｒ,ｏｎＭｏｄｅⅠｆｒａｃｔｕｒｅｔｏｕｇｈｎｅｓｓｔｅｓｔｉｎｇ[1 2 ] .Ｈｏｗｅｖｅｒ,ｐｒｅ ｅｘｉｓｔｉｎｇｃｒａｃｋｓｉｎｒｏｃｋｍａｔｅｒｉａｌｓｏｒｄｉｓｃｏｎｔｉｎｕｉｔｉｅｓｉｎｒｏｃｋｍａｓｓｅｓａｒｅｓｅ…     

Influence on performance and structure of spinel LiMn2O4 for lithium-ion batteries by doping rare-earth Sm

The spinel LiMn₂O₄ used as cathode materials for lithium-ion batteries was synthesized by mechano-chemistry fluid activation process, and modified by doping rare-earth Sm. Thesting of X-ray diffraction, cyclic voltammograms, charge-discharge and SEM was carried out for LiMn₂O₄ cathode materials and the modified materials. The results show that the cathode materials doped rare earth Li _x Mn_2−y Sm _z O₄ (0.95⩽x⩽1.2, 0⩽y⩽0.3, 0⩽z⩽0.2) exhibit standard spinel structure, high reversibility of electrochemistry and excellent properties of charge-discharge. In EC: DMC(1 : 1)+1 mol/L LiPF₆ electrolyte with discharge capacity more than 130 mA · h/g, and its capacity is deteriorated less than 15% after 300 cycles at room temperature and less than 20% after 200 cycles at 55°C. At the same time, Crystal Field Theory was applied to explain the function and mechanism of doped rare earth element. Foundation item: Project (02JJY2081) supported by the Natural Science Foundation of Hunan Province     

Rock fracture under anti-plane shear (Mode III) loading

Anti-plane punch-through shear test and anti-plane four-point bending test are used to study the crack initiation and propagation under anti-plane shear (Mode III) loading. The tensile and shear stresses at the crack tip are calcualted by finite element method. The results show that under Mode III loading the maximum principal stress σ₁ at crack tip is smaller or a little larger than the maximum shear stress τ_max. Since the tensile strength of brittle rock is much lower than its shear strength, σ₁ is easy to reach its critical value before τ_max reaches its critical value and thus results in Mode I fracture. The fracture trajectory is helicoid and the normal direction of tangential plane with the fractured helicoid is along the predicted direction of the maximum principal stress at the notch tip. It is further proved that Mode I instead of Mode III fracture occurs in brittle rock under Mode III loading. The fracture mode depending on the fracture mechanism must be distinguished from the loading form. Foundation item: Project (50374073) supported by the National Natural Science Foundation of China; project (2002032256) supported by the Postdoctor Science Foundation of China     

Experimental study on new method and automatic system for fast evaluating Al-Si alloy modification effect in front of furnace

A new method based on the surface tension measurement for fast evaluating modification effect of Al-Si alloy in front of furnace and an automatic system for fast measuring surface tension of molten Al-Si alloy are introduced. By theoretical analysis the relation between surface tension σe of molten Al-Si alloy and information parameters △P , N , φx and T has been established, namely, σ e = a △P b . N c . (φ x- φ0) d . T e . By ex- periments the relationship between surface tension and modification level of Al-Si alloy has been also got that σ e > 530 mN/m, 400 ≤σe ≤530 mN/m and σ e < 400 mN/m are corresponding with AFS 1-2, AFS 3-4 and AFS 5-6 of Al-Si modification effect. Depending on the conclusions, modification effect can be recognized in a few seconds, which is of practical significance for real-time evaluating modification effect of Al-Si alloy in front of furnace.     

Effect of specimen thickness on Mode II fracture toughness of rock

Anti-symmetric four-point bending specimens with different thickness, without and with guiding grooves, were used to conduct Mode II fracture test and study the effect of specimen thickness on Mode II fracture toughness of rock. Numerical calculations show that the occurrence of Mode II fracture in the specimens without guiding grooves (when the inner and outer loading points are moved close to the notch plane) and with guiding grooves is attributed to a favorable stress condition created for Mode II fracture, i.e. tensile stress at the notch tip is depressed to be lower than the tensile strength or to be compressive stress, and the ratio of shear stress to tensile stress at notch tip is very high. The measured value of Mode II fracture toughness K _{II C} decreases with the increase of the specimen thickness or the net thickness of specimen. This is because a thick specimen promotes a plane strain state and thus results in a relatively small fracture toughness. Foundation item: The National Natural Science Foundation of China (No: 49672164) Biography of the first author: RAO Qiu-hua, doctor of engineering, born in 1965, majoring in rock fracture mechanics.     

A practical geometrical comparison between free-repelled hydraulic jumps within inclined channels

In this experimental study a practical geometrical comparison between inclined (angle φ) free and repelled hydraulic jumps (the latter in non prismatic but abruptly expanding channels) is presented, analysed and discussed. For repelled hydraulic jumps a considerable parameter is the expansion ratio r (=channels’ width ratio), which here is changing from r =0.5 to r =0.7. The comparison is made with the free jump (in prismatic channel, r =1), in the same ranges of angles φ (0° ⩽ φ ⩽8°) and Froude numbers (2⩽Fr ₁⩽8). A practical arithmetic example is presented to show the behavioral change of conjugate depths, lengths L and depths at 0.5L, in order to receive a comparison among all pertinent geometrical quantities. The present results may be useful for the hydraulic engineering when designing open channels.     

A simple method of determining stress intensity factor KI from isochromatic fringe loops

A new photoelastic method of obtaining mode I stress intensity factor (SIF) is presented. The method considers the influence of far field stress, σ _ox , on the value of SIF. The only information needed for K _I calculation is the area between isochromatic fringe loops. The method is examined by two kinds of specimen in different load cases. Experimental results show that it is quite simple and of high precision. Project supported by the National Natural Science Foundation of China Synopsis of the first author Chen Feng, associate professor, born in October 1949, worked on experimental fracture mechanics in Sweden from 1990 to 1995 as a visiting scholar. Major research fields include perturbation and weight function method and its application, experimental mechanics, rock fracture mechanmics.     

Thermal Instability and Microstructure of Strontium M-type Hexaferrite Nanoparticles Synthesized by Citrate Approach

The dried gel of SrFe12O19, prepared by citrate approach, was investigated by means of infrared spectroscopy （ IR ）, thermogravimetric analysis （ TG ）, differential scanning calorimetry （ DSC ）, X- ray diffraction（ XRD ） techniques, energy dispersive spectroscopy（ EDS ）, and transmission electron microscopy（ TEM ）. The thermal instability and the thermal decomposition of low-temperature strontium M-type hexaferrite crystallized at about 600℃ were confirmed for the first time by XRD method. The decomposition of the low-temperature strontium M-type hexaferrite took place at about 688.6℃ determined by DSC investigation. The low-temperature strontium M-type hexaferrite nanopartieles were decomposed into SrFeO2.5 with an orthorthombic cell and Fe2O3 with a tetragonal cell as well as possibl α-Fe2O3 . The agglomerated particles with sizes less than 200 nm obtained at 800℃ were plesiomorphous to strontium M-type hexaferrite. The thermally stable strontium M-type hexaferrite nanopartieles with sizes less than 100um cotdd take place at 900 ℃ . Up to 1000 ℃ , the phose transformotion to form strontium M-type hexaferrite was ended, the calcinations with the sizes more than 1μm were composed of α-Fe2O3 and strontium M-type hexaferrite. The method of distinguishing γ-Fe2O3 with a spinel structure from Fe2O3 with tetragonal cells by using powder XRD method was proposed. Fe2O3 with tetragonal cells to be crystallized before the crystallization of thermally stable strontium M-type hexaferrite was confirmed for the first time. The reason why α- Fe2O3 as an additional phase appears in the calcinations is the cationic vacancy of stroutium M-type hexaferrite , SrFe12-x□O19 （0≤x ≤0.5）.     

Preparation and Properties of Sensing Membrane for Fiber Optic Oxygen Sensor

Four sensing membranes based on fluorescence quenching were prepared by sol-gel method and CA membrane method, and the Ru( Ⅱ ) complexes, Ru( bpy )3 Cl2 and Ru(phen)3 Cl2, were used as the indicators. The results indicate that the volume fraction of oxygen Ψo2 have a linear relationship in large scale with tanΨ0/ tanΨfor all of the sensing membranes. They have super properties such as excellent limit of detection ,fast re-sponse time and good reproducibility. The stability of the sensing membranes made by sol-gel method is better than those by CA membranes, but the uniformity of the latter is better than that of the former.     

Preparation of ITO nano-powders by hydrothermal-calcining process

1 INTRODUCTIONSn-doped In2O3(ITO) is one kind of n-typesemiconductor material[1].It has excellent electro-optical properties , such as electrical conductivityand high transparency under visible light[2],andiswidely used in electronic , transparent electrode ,solar cells and electro-irradiance , especially inscreen display[3 ,4].Recently nearly half of the met-al indium has been used to prepare ITO materialsin the developed countries[5], such as Japan, A-merica ,France and so on.So the…     

The effect of alumina content on fracture property of all-ceramics zirconia

The purpose of the present study was to evaluate the effect of Al2O3 content on the fracture property of all-ceramics ZrO2. To improve the all-ceramics ZrO2 restoration mechanics properity ,96 samples containing 0,5,10 and 15 wt% of Al2O3 particles were prepared by cold isostatic pressing (200 MPa) and 1 550 ℃ sintered .The phase was analyzed by X-ray diffraction analysis and the bulk densities of the samples were made using Archimedes principle. Samples were randomly divided into four groups. In each group, 24 specimens were prepared so that the angle between notch and specimen’s long axis is 90o and 60o. Notch depths were 1 mm for all samples. Samples were loaded with three-point bending method. 90° cut samples were used to measure fracture toughness while 60°cut samples were used to observe fracture curve by taking points on the fracture extension path under microscope, plotting points on coordinates, generating fitting curve by software "Origin", and analyzing the microstructure of the specimen fracture surfaces by scanning electron microscopy (SEM).The results show that the increment of Al2O3 has insignificant effect on the densification of all-ceramic ZrO2.XRD analysis shows that the specimen is comprised of t-ZrO2 and α- Al2O3 before fracture while fracture surface is m-ZrO2, t-ZrO2 and a-Al2O3. ZrO2 containing 10% Al2O3 has the optimum mechanical properties and unconspicuous crack propagation and distribution. The observations may provide a reference for the materials selection, shape design , and production process of all-ceramic crown and bridge.     

DZ125合金超高周疲劳微观裂纹萌生机制

DZ125合金具有优良的综合性能表现,已被广泛应用于燃气涡轮高温部件的铸造。关于DZ125合金的疲劳问题研究已有较多文献报道,但从微观断口分析的角度系统阐述该合金超高周疲劳裂纹萌生及失效机制的研究则相对较少。通过研究发现,随着疲劳强度的降低,疲劳数据离散性有增大的趋势;较小的疲劳应力（小于220 MPa）所对应的疲劳寿命并未有明显增加,上述特征与疲劳微观裂纹萌生机制的改变直接相关。在高应力作用下,疲劳裂纹倾向于从材料的表面或次表面萌生,巨型二次裂纹成为其断口形貌的主要特征;在低应力状态下,材料内部的孔洞缺陷是疲劳裂纹萌生的主要区域,并严重影响材料的疲劳寿命。驻留滑移带（PSB）可导致表面粗糙区的形成,成为裂纹尖端的主要特征。主裂纹与其他二次裂纹存在竞争关系,并最终引起疲劳断裂的发生。基于Murakami公式,DZ125合金在裂纹萌生阶段的平均应力强度因子为3.15 MPa·m^1/2,裂纹快速扩展阶段的平均应力强度因子和材料的断裂韧性（K_IC）分别为7.72和15.70 MPa·m^1/2。     

Physical simulation of hot deformation of TiAI based alloy

In order to establish a model between the grain size and the process parameters, the hot deformation behaviors of Ti-49.5Al alloy was investigated by isothermal compressive tests at temperatures ranging from 800 to 1 100 ℃ with strain rates of 10^-3-10^-1 s^-1. Within this range, the deformation behavior obeys the power law relationship, which can be described using the kinetic rate equation. The stress exponent, n, has a value of about 5.0, and the apparent activation energy is about 320 J/mol, which fits well with the value estimated in previous investigations. The results show that, the dependence of flow stress on the recrystallized grain size can be expressed by the equation: σ = K1 drex^-0.56. The relationship between the deformed microstructure and the process control parameter can be expressed by the formula: lgdrex= -0.281 1gZ 3.908 1.     

Synthesis of γ-Al2O3 nanoparticles by chemical precipitation method

Highly pure active γ-Al₂O₃ nanoparticles were synthesized from aluminum nitrate and ammonium carbonate with a little surfactant by chemical precipitation method. The factors affecting the synthesis process were studied. The properties of γ-Al₂O₃ nanoparticles were characterized by DTA, XRD, BET, TEM, laser granularity analysis and impurity content analysis. The results show that the amorphous precursor Al(OH)₃ sols are produced by using 0.1 mol/L Al(NO₃)₃ · 9H₂O and 0.16 mol/L (NH₄)₂CO₃ · H₂O reaction solutions, according to the volume ratio 1.33, adding 0.024% (volume fraction) surfactant PEG600, and reacting at 40 °C, 1 000 r/min stirring rate for 15 min. Then, after stabilizing for 24 h, the precursors were extracted and filtrated by vacuum, washed thoroughly with deionized water and dehydrated ethanol, dried in vacuum at 80°C for 8 h, final calcined at 800 °C for 1 h in the air, and high purity active γ-Al₂O₃ nanoparticles can be prepared with cubic in crystal system, O _H ⁷ -FD3M in space group, about 9 nm in crystal grain size, about 20 nm in particle size and uniform size distribution, 131. 35 m²/g in BET specific surface area, 7 – 11 nm in pore diameter, and not lower than 99.93% in purity. Foundation item: Project(03JJY3015) supported by the Natural Science Foundation of Hunan Province     

Flow stress behavior of Cu13Zn alloy deformed at elevated temperature

Ｃｏｎｓｔｉｔｕｔｉｖｅｍｏｄｅｌｉｓａｍａｔｈｅｍａｔｉｃａｌｒｅｐｒｅｓｅｎｔａｔｉｏｎｏｆｔｈｅｄｅｆｏｒｍａｔｉｏｎｒｅｓｐｏｎｓｅｏｆａｍａｔｅｒｉａｌｔｏｅｘｔｅｒｎａｌｌｙａｐ ｐｌｉｅｄｌｏａｄｉｎｇ ,ｉｎｃｌｕｄｉｎｇｅｎｖｉｒｏｎｍｅｎｔａｌｆａｃｔｏｒｓ .Ｔｈｅｐｒｅ ｃｉｓｅｋｎｏｗｌｅｄｇｅｏｆｔｈｅｃｏｎｓｔｉｔｕｔｉｖｅｂｅｈａｖｉｏｒｏｆｔｈｅｍａｔｅｒｉａｌｉｓｔｈｅｆｏｕｎｄａｔｉｏｎｏｆｎｕｍｅｒｉｃａｌｓｉｍｕｌａｔｉｏｎｔｅｃｈｎｏｌｏｇｙｏｆｍａｔｅｒｉ…     

Effect of tin on the reaction synthesis of ternary carbide Ti3AlC2

The effect of tin on synthesis of Ti₃AlC₂ by spark plasma sintering (SPS) from TiC/Ti/Al powders was investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used for phase identification and microstructure evaluation. The experimental results show that addition of tin can considerably accelerate the synthesis reaction of Ti₃AlC₂ and fully dense, essentially single-phase polycrystalline Ti₃AlC₂ could be successfully obtained by sintering 2TiC/1Ti/1Al/0.2Sn powders at 1200–1250 °C under a pressure of 30 MPa. SEM images show that Ti₃AlC₂ samples in about 2–5 μm thick and 10–25 μm long platelets can be obtained. The fracture toughness and flexural strength of Ti₃AlC₂ were 6.5±0.2 MPa·m^1/2 and 560±10 MPa, respectively. Funded by the National Natural Science Foundation of China (No.20771088, No.50572080) and Doctoral Foundation of Wuhan University of Technology (No.471-38650142)