Mechanism of brittle-ductile transition of a glass-ceramic rigid substrate

The hardness, elastic modulus, and scratch resistance of a glass-ceramic rigid substrate were measured by nanoindentation and nanoscratch, and the fracture toughness was measured by indentation using a Vickers indenter. The results show that the hardness and elastic modulus at a peak indentation depth of 200 nm are 9.04 and 94.70 GPa, respectively. These values reflect the properties of the glass-ceramic rigid substrate. The fracture toughness value of the glass-ceramic rigid substrate is 2.63 MPa？m1/2. The material removal mechanisms are seen to be directly related to normal force on the tip. The critical load and scratch depth estimated from the scratch depth profile after scratching and the friction profile are 268.60 mN and 335.10 nm, respectively. If the load and scratch depth are under the critical values, the glass-ceramic rigid substrate will undergo plastic flow rather than fracture. The formula of critical depth of cut described by Bifnao et al. is modified based on the difference of critical scratch depth

Anisotropic brittle-ductile transition of monocrystalline sapphire during orthogonal cutting and nanoindentation experiments

Single-crystal sapphire is utilized as a high-performance engineering material,especially in extreme and harsh environments.However,due to its extreme hardness and brittleness,the machinability of sapphire is still a challenge.By means of nanoindentation and plunge-cut experiments,the anisotropic brittle-ductile transition of the prismatic M-plane and rhombohedral R-plane is examined by analyzing crack morphologies and the critical depth-of-cut(CDC).The experimental results of the nanoindentation tests are correlated to the plunge-cut experiment.Both the prism plane and the rhombohedral crystal plane exhibit a two-fold symmetry of ductility with various crack patterns along the machined grooves.The direction-dependent plasticity of the hexagonal sapphire crystal is mainly connected to a twinning process accompanied by slip dislocation.

BRITTLE-DUCTILE TRANSITION OF PP/EPDM/ELASTOMERIC NANO-PARTICLE TERNARY BLENDS

The brittle-ductile transition is a very important phenomenon for polymer toughening. Polypropylene （PP） is often toughened by using rubbers, e.g., ethylene-propylene diene monomer （EPDM） has often been used as a modifier. In this article, the toughening of PP by using a new kind of rubber, known as elastomeric nano-particle （ENP）, and the brittleductile transition of PP/EPDM/ENP was studied. Compared to PP/EPDM binary blends, the brittle-ductile transition of PP/EPDM/ENP ternary blends occurred at lower EPDM contents. SEM experiment was carried out to investigate the etched and impact-fractured surfaces. ENP alone had no effect on the impact strength of PP, however, with the same EPDM content, PP/EPDM/ENP ternary blends had smaller particle size, better dispersion and smaller interparticle distance in contrary to PP/EPDM binary blends, which promoted the brittle-ductile transition to occur earlier.

BRITTLE-DUCTILE TRANSITION OF POLYMERS AND ITS PERCOLATION MODEL

The brittle-ductile transition (BDT) of particlc toughened polymers was extensively studied in terms ofmorphology, strain rate, and temperature. The calculation results showed that both the critical interparticle distance (ID_c) andthe brittle-ductile transition temperature (T_(BD)) of polymers were a function of strain rate. The ID_c reduced nonlinearly withincreasing strain rate, whereas T_(BD) increased considerably with increasing strain rate. The effects of temperature andplasticizer concentration on BDT were discussed using a percolation model. The results were in agreement with theexperiments.

A Fractal Study on Brittle-Ductile Transition forTi-24Al-11Nb Alloy

The mechanical behaviours of Ti-24Al-11Nb alloy in the brittle-ductile transition (BOT) have been investigated by using three-point bending tests. The temperature dependence of the fractal dimensions and fractal characterization of fracture surfaces are presented. The probable mechanism controlling BDT of intermetallic alloys are proposed according to fractal geometry.Additionally. it is found that there is a positive relationship between the fractal dimension and fracture toughness in BDT for Ti-24Al-11Nb

Critical transition Reynolds number for plane channel flow

The determination of the critical transition Reynolds number is of practical importance for some engineering problems. However, it is not available with the current theoretical method, and has to rely on experiments. For supersonic/hypersonic boundary layer flows, the experimental method for determination is not feasible either. Therefore, in this paper, a numerical method for the determination of the critical transition Reynolds number for an incompressible plane channel flow is proposed. It is basically aimed to test the feasibility of the method. The proposed method is extended to determine the critical Reynolds number of the supersonic/hypersonic boundary layer flow in the subsequent papers.

Calculation of Electronic Structure of Anatase TiO_2 Doped with Transition Metal V,Cr,Fe and Cu Atoms by the Linearized Augmented Plane Wave Method

The electronic density of states and band structures of doped and un-doped anatase TiO2 were studied by the Linearized Augmented Plane Wave method based on the density functional theory. The calculation shows that the band structures of TiO2 crystals doped with transition metal atoms become narrower. Interesting, an excursion towards high energy level with increasing atomic number in the same element period could be observed after doping with transition metal atoms.

Micro-and submicrostructural evidence for high-temperature brittle-ductile transition deformation of hornblende: Case study of high-grade mylonites from Diancangshan, western Yunnan

OM (optical microscope)/TEM (transmission electron microscope) micro- and submicrostructural analysis of hornblende rocks sheared at high temperatures from the Diancangshan area, western Yunnan reveals evidence for deformation in the brittle-ductile transition of hornblende at middle crustal level (about 637℃ and 0.653 GPa) and mechanisms of deformation in the transitional regime are further discussed. Sheared hornblende rocks at middle crustal level have typical mylonitic microstructures, shown by coarse porphyroclasts and fine matrix grains. Different mineral phases in the rocks show distinct deformation characteristics. Hornblende and feldspar grains are intensely deformed with ob- vious grainsize reduction, but quartz grains are recrystallized dominantly by grain growth. Hornblende grains show typical brittle-ductile transition nature. Initial crystallographic orientations of porphyro- clasts have strong effects on the behavior of grains during deformation. There are mainly two types of porphyroclasts, type I "hard" porphyroclasts and type II "soft" porphyroclasts, with [001] perpendicular and parallel to external shear stresses respectively. "Hard" porphyroclasts generally occur as compe- tent grains that are rarely deformed or sometimes deformed by fracturing and dislocation tangling. "Soft" porphyroclasts are highly deformed primarily by dislocation tangling (as shown in the cores of the porphyroclasts), but twinning, dislocation glide and climb probably due to hydrolytic weakening also contribute to dynamic recrystallization of the porphyroclasts into fine grains in the matrix. The micro- and submicrostructures of the two types of porphyroclasts and fine-grained matrix provide powerful evidence for the behavior of brittle-ductile transition of hornblende grains. It is concluded that twinning nucleation is one of the most important processes that operate during dynamic recrystalliza- tion of hornblende crystals at the brittle-ductile transition. (100) [001] twin gliding and dislocation creep (dislocation glide and climb) are mutually enhanced during twinning nucleation. As a newly discovered mechanism of dynamic recrystallization, it may have played more important roles than ever recognized during dynamic recrystallization of crystals with twins in the brittle-ductile transition.

Threshold and decay properties of transient isolated turbulent band in plane Couette flow

By direct numerical simulations of the plane Couette flow (PCF) in a large computational domain, it is shown that an isolated turbulent band decays monotonically at low Reynolds numbers but experiences transient growth before the eventual relaminarization at moderate Reynolds numbers. The lower bound Reynolds number of the transient-growth regime is determined as 286. The width, length, and tilt angle of the iso- lated band structure are defined based on the disturbance kinetic energy in the mid-plane, and the geometric characteristics of the band can be described with a tilted rectangle. It is illustrated that before its eventual fragmentation, the isolated turbulent band decays in a style of longitudinal contraction, where the center, width, and tilt angle of the band keep almost constant but the band length contracts with a statistically constant velocity.

Crystal plane induced in-situ electrochemical activation of manganese-based cathode enable long-term aqueous zinc-ion batteries

Rapid capacity decay and sluggish reaction kinetics are major barriers hindering the applications of manganese-based cathode materials for aqueous zinc-ion batteries.Herein,the effects of crystal plane on the in-situ transformation behavior and electrochemical performance of manganese-based cathode is discussed.A comprehensive discussion manifests that the exposed(100)crystal plane is beneficial to the phase transformation from tunnel-structured MnO_(2) to layer-structured ZnMn_(3)O_(7)·3H_(2)O,which plays a critical role for the high reactivity,high capacity,fast diffusion kinetics and long cycling stability.Additionally,a two-stage zinc storage mechanism can be demonstrated,involving continuous activation reaction and phase transition reaction.As expected,it exhibits a high capacity of 275 mAh g^(-1)at 100 mA g^(-1),a superior durability over 1000 cycles and good rate capability.This study may open new windows toward developing advanced cathodes for ZIBs,and facilitate the applications of ZIBs in large-scale energy storage system.

Percolation Model of Brittle-Ductile Transition in PP/EPDM Blends

1 Introduction S. Wu reported the brittle-ductile transition master curve for the relation between the notched izod impact strength of Nylon-6/EPDM blends and rubber fractions. It was interpreted by the strong interaction between polar Nylon-6 matrix and modified EPDM dispersed phase. However, similar brittle-ductile transition master curve in non-polar PP/EPDM blends was also observed in this laboratory (Fig. 1).

A New Criterion for Brittle-Ductile Transition of Polymer Blends

The T_c criterion was first used by S. Wu for characterizing the brittleductile (B-D) transition of N6/EPDM blends. But in this paper, a new criterion which is based on the stress analysis of blends is proposed to characterize the B-D transitions of blends, namely, A criterionV_(fc) and d_c are the critical volume fractions and particle size of dispersed particles in blends, respectively. For given blends, A is independent of the morphology of dispersed phase and is only the characteristic parameter of matrix. The B-D transitions of different blends, including polar N6/EPDM blends, nonpolar PP/EPDM blends and PE/CaCO_3 composites, were manipulated with A criterion and satisfactory results were obtained. In addition, a new master curve for the impact strength of PP/EPDM blends versus V_f^2/d was obtained. The results showed that A criterion is more suitable than T_c criterion for characterizing the B-D transition of blends.

The electronic structure and grain boundary segregation by boron addition——A binding energy shifting criterion for the brittle-ductile fracture transition in Ni_3Al

The electronic structure and grain boundary segregation caused by boron addition to Ni3Al have been studied by X-ray photoelectron spectroscopy and Auger electron spectroscopy, respectively. The obtained results show that the Ni2p3/2 electron binding energy rises gradually in the sequence of pure Ni< Ni76Al24< Ni74Al26 < Ni25Al25, while it reduces monotonously with an increase in boron addition to Ni3Al. Besides, it is found that the gram boundary segregation of boron occurring in Ni3Al is a combined equilibrium and non-equilibrium type in nature. Based on the concept of the bonding environmental inhomogeneity, measured by the shift in Ni2p3/2 electron binding energy from the nickel atoms in the simple substance nickel to those in the intermetallic compound Ni3Al (ΔEB), being responsible for the brittle behavior of the alloy, a binding energy shifting criterion for the brittle-ductile fracture transition in Ni3Al is presented: when ΔEB>0, the brittle failure occurs in Ni3Al; when ΔEB<0, the ductile one appears. Combined with the above experimental rules, the criterion predicts that pure Ni3Al is brittle, and there exist the stoichiometric effect and concentration effect in the ductilization process for Ni3Al by boron addition. Hence the criterion can be taken as a theoretical guide to alloy design in developing ductile intermetallics.

Development of VTOL Drone for Stable Transit Flight

Fixed wing unmanned aerial vehicles typically have longer running (flight) time than multicopers, but runways are needed. Because it is difficult to expect a wide runway in the city area, the great need is there to develop a vertical takeoff and landing (VTOL) type fixed-wing UAV that does not require any runway. In addition, our goal was to develop a VTOL plane that contains a stable transit flight characteristic. To achieve this goal, we have designed and developed a test plane and the flight parameters have been extensively tested. For the airframe design, the carbon-bar method was selected for vertical takeoff and landing, and the 11-way method was adopted through dynamics analysis. We assembled the airframe and made a prototype using the Pixhawk flight computer. The developed VTOL plane shows a very smooth transition flight. It is expected that the VOTL UAV will be widely used in the city area in the future for various purposes, such as cargo delivery and emergency medical supply delivery.

Damage Studies of Brittle-Ductile Transition in PP EPDM Blends

Damage zones of brittle-ductile (B-D) transition in PP/EPDM blends are studied in this paper. The contribution of crazing and shear yielding zones in damage zones to energy dissipation of blends was measured with computer image analysis (CIA) and the transition of shear yielding zone (A_(sh)) with rubber volume fraction (V_f) was also manipulated. Results showed that the B-D transition of impact strength of blends corresponded to the fracture mechanism in PP/EPDM blends, from matrix crazing to matrix shear yielding. In addition, two new parameters, density of energy dissipation for crazing zone (F_(cz)) and for shear yielding zone (F_(sh)), are first obtained in this paper. The value of F_(sh) is about four times larger than that of F_(cz) for PP/EPDM blends, which confirmed that the matrix shear yielding is a more effective way of energy dissipation in blends.

On Transposed Translation Planes

This paper is devoted to the study of a translation plane π(C) associated with a t-spread set C and its transposed t-spread set C t. In this paper, an explicit matrix form of the inverse of an isomorphism from a translation plane into another translation plane associated with t-spread sets is derived and proved that two translation planes associated with t-spread sets are isomorphic if and only if their corresponding transposed translation planes are isomorphic. Further, it is shown that the transpose of a flag-transitive plane is flag-transitive and derived a necessary and sufficient condition for a translation plane π(C) to be isomorphic to its transposed translation plane.

齿轨铁路线路平面关键设计参数研究

线路平面设计参数的确定对齿轨铁路试验线及运营线建设具有重要作用。以标准轨距铁路线路计算原理为基础,结合米轨车辆与线路之间的匹配关系,基于行驶动力学理论对齿轨铁路线路平面关键设计参数取值进行初步研究。通过类比标准轨距铁路和总结国内外规范相关参数取值,得出齿轨铁路曲线半径和缓和曲线长度的计算公式和控制指标取值。结果表明:对于黏着路段最高设计速度120 km/h和齿轨路段最高设计速度40 km/h的齿轨铁路,黏着路段的最小曲线半径一般和困难条件下分别可取900,750 m,齿轨路段的最小曲线半径一般和困难条件下分别可取350,300 m;黏着路段的缓和曲线长度应结合曲线半径相应选择,齿轨路段的最小缓和曲线长度均取为20 m。

Inherent mechanism of breakdown in laminar-turbulent transition of plane channel flows

Laminar-turbulent transition is an old yet unsolved problem. Notwithstanding the great effort made, there is an important question that seems not to have been addressed yet, that is, what is the inherent mechanism of breakdown that eventually leads to transition? The conventional idea is that the transition starts from the amplification of disturbances, and when the disturbances become larger, higher harmonics will be generated due to nonlinear effect, making the flow more and more complicated, and finally turbulent. Though the scenario seems clear, yet there is a missing link, that is, what happens in the breakdown process. Here we show by analyzing the results from direct numerical simulations that the change of stability characteristics of the mean flow profile plays a key role in the breakdown process.

全功率型逆变电源侧工频变化量距离保护性能下降机理分析

受逆变型分布式电源(IIDG)系统内阻抗不稳定的影响,工频变化量距离保护在全功率型逆变电源侧存在拒动风险,但现有理论未能从机理方面明确指出造成内阻抗不稳定的具体因素,难以提出针对性的保护改进方案。为了深入探究IIDG侧工频变化量距离保护性能急剧下降的机理,基于阻抗平面法分析指出,在全功率型逆变电源控制策略的作用下,IIDG侧正序电流增量表现为相位、幅值受控的独立变量,其与过渡电阻共同构成的附加阻抗大小随故障工况变化且矢量方向发生不确定性偏转,导致保护正确动作可行域不明晰,在传统阻抗继电器整定判据下保护可靠性严重劣化。在此基础上,进一步研究了主流的PQ控制及低电压穿越控制策略对该保护动作安全性和耐受过渡电阻能力的影响。基于PSCAD/EMTDC的仿真结果验证了理论分析的正确性,为工频变化量距离保护在IIDG并网工况下故障响应能力的恢复提供了有益的理论参考。

Compressive performance of innovative reinforced pillars in closed/abandoned mines

Pillar is closely related to the stability and reliability of underground spaces in closed/abandoned mines.The present research introduced a new technique to strengthen square cement mortar columns via fiber-reinforced polymer(FRP)strips to verify the strengthening effect of FRP on pillars.Compared to a fully wrapped FRP jacket,the advantages of FRP strip are cost-effective and easy-to-construct.A series of compression tests as well as theoretical analysis were carried out to explore the mechanical behavior of square cement mortar specimens partially strengthened with FRP strips.The results verified the effectiveness of FRP strips in enhancing the stress and strain of cement mortar.Different from unconfined cement mortar specimens,these FRP-strengthened cement mortar specimens are featured with the double-peaked behaviors,mainly attributed to the stress state transformation from a one-dimensional to a three-dimensional stress state.It also indicated that the enhancement of stress increased with the FRP strip width.Moreover,the brittle-ductile transition ductile failure characteristics were also observed in FRP-confined cement mortar specimens.The ultimate ductility of the cement mortar specimen decreases gradually with the growth of the FRP strip width.The main contribution of this research is to enrich the strengthening techniques for residual pillars.