强酸侵蚀对钠钙硅玻璃表面改性及其磨损性能研究

使用水接触角测量仪、红外光谱仪、纳米压痕仪和显微硬度计,探究了侵蚀处理时间对钠钙硅玻璃在强酸(pH=1,HCl溶液)和纯水侵蚀条件下机械化学性能的变化规律. 采用多功能往复式摩擦磨损试验机,以SiO₂球为对摩副,分析了钠钙硅玻璃在不同侵蚀条件下的磨损行为. 研究发现:经去离子水侵蚀24和50 h后,钠钙硅玻璃的机械化学性能变化不明显,而经强酸侵蚀的钠钙硅玻璃的断裂韧性显著增大,但其纳米硬度、等效弹性模量、维氏硬度和在潮湿空气(RH=50%)下的磨损性能降低. 酸性液体对钠钙硅玻璃性能的影响与Na+析出后玻璃表面形成的侵蚀层密切相关. 与纯水环境相比,钠钙硅玻璃表层Na+在强酸侵蚀时更易被析出,表面化学结构变成“富SiO₂”,同时玻璃表面变得更亲水,磨损过程产生的磨屑易于吸附在摩擦界面,从而导致界面磨损形式由摩擦化学磨损转化为黏着磨损,最终使钠钙硅玻璃的耐磨性降低.      

Influence of Surface Scratches on the Flexure Strength of Soda-Lime Silicate and Borosilicate Glass

Borosilicate (BS) and soda-lime silicate (SLS) glasses are being considered for use as the strike-face in transparent armor systems. This effort examined the effect of surface scratches generated with 1, 5, 10, and 30 N scratching loads on the equibiaxial flexure strength of both glasses including versions of each that had been thermally-tempered. At lower scratch loads there is more lateral cracking associated with the scratches in the BS while the scratches in the SLS predominantly exhibit plastic deformation. At the highest scratch load the damage is dominated by chips and lateral cracking within and along the scratch length. The tempered versions of the SLS appear to have less lateral cracking than the tempered version of the BS glass. In all instances the flexure strength decreases significantly when a 1 N scratch is introduced on the tin surface but when the scratch load increases any additional strength loss is minimal.     

Successive lag synchronization on nonlinear dynamical networks via linear feedback control

Nonlinear Dynamics - Successive lag synchronization (SLS) is defined as a new synchronization pattern, which means that lag synchronization appears between two successively numbered nodes in a...     

Process of selective laser sintering of polymer powders: Modeling,simulation, and validation

Selective laser sintering (SLS) of polymer powders involves multiphysical transient phenomena. A numerical tool for simulating such a process is developed on the basis of the reliable modeling of the corresponding thermo-physical transient phenomena and appropriate numerical methods. The present paper addresses modeling, simulation, and validation aspects that are indispensable for studying and optimizing SLS process. The coupled multiphysical models are detailed, and the numerical tool based on the finite volume method is presented, with validations in terms of numerical and physical accuracy, by considering the shrinkage involved in the process and the successive layers deposition. A parametric analysis is finally proposed in order to test the reliability of the model in terms of representing real physical phenomena and thermal history experienced by the material during the process.     

尼龙粉末在SLS预热温度下的离散元模型参数确定及其流动特性分析

尼龙粉末是增材制造中常用的粉体材料,温度对其流动性有重要影响. 探索尼龙粉末增材制造预热温度下的流动性是研究选择性激光烧结(selective laser sintering, SLS)工艺中粉体铺展成形的基础. 选取SLS技术中的尼龙粉末为原材料,采用离散元数值方法,研究尼龙粉末的流动行为,是增材制造工艺数值模拟和铺粉工艺优化的研究热点. 以Hertz-Mindlin模型为基础,基于Hamaker理论模型和库伦定律,在尼龙粉末的接触动力学模型中引入范德华力和静电力,建立预热温度下尼龙粉末流动的离散元模型(discrete element method, DEM),通过对比相应实验结果,标定了该模型的参数. 对加热旋转圆筒中尼龙粉末流动过程进行了DEM数值模拟,校核了所建模型的正确性,并研究了粉体粒径分布对尼龙粉末流动特性的影响规律. 研究表明,尼龙粉末黏附力是静电力与范德华力的共同作用结果;随着粉体粒径的增大,尼龙粉末崩塌角增大,流动性增强;相对于高斯粒径分布,粒径均匀分布的尼龙粉末颗粒流动性更强. 研究结果可指导SLS中铺粉工艺的优化.      

Influence of surfactants on pool boiling of aqueous polyacrylamide solutions

The influence of a surfactant, sodium lauryl sulfate (SLS), on the pool boiling behavior of aqueous polyacrylamide solutions has been investigated. The basic test section is a heated horizontal platinum wire submerged in a saturated pool of liquid at atmospheric pressure. Results are reported for six combinations of deionized water, polyacrylamide and surfactant. Measurements of surface tension and steady shear apparent viscosity are reported for each working solution.The boiling heat transfer performance of deionized water containing concentrations of 250 and 1000 (parts per million by weight) wppm of the surfactant did not differ significantly from the values found for deionized water. For the 250 wppm aqueous polyacrylamide solution the boiling performance is poorer than that found for water alone. However, the addition of 250 wppm of SLS to the aqueous polyacrylamide solution resulted in a significant improvement in the boiling heat transfer performance compared to water. An increase in the surfactant concentration to 1000 wppm to the aqueous polymer solution revealed even greater improvement in the boiling performance. At a heat flux of 50 W/cm², increases in the heat transfer coefficient were as much as 50% for the 250 wppm AP-30 — 250 wppm SLS solution and 100% the for 250 wppm AP-30 — 1000 wppm SLS solution as compared to deionized water alone.On the basis of these results, it appears that the influence of surfactants on the boiling heat transfer performance of aqueous polymer solutions may be more significant than in the case where surfactants are added to Newtonian fluids.

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Einfluß von grenzflächenaktiven Stoffen auf das Sieden von Polyacrylamid-Lösungen

Zusammenfassung Es wurde der Einfluß des grenzflächenaktiven Stoffes Sodium-Lauryl-Sulfat (SLS) auf das Verhalten des freien Behältersiedens von Polyacrylamid-Lösungen untersucht. Die Testeinheit besteht aus einem beheizten Platindraht, der in einem mit Flüssigkeit (Umgebungsdruck) gefüllten Behälter eingetaucht ist. Ergebnisse wurden für sechs Kombinationen von vollentsalztem Wasser, Polyacrylamid-Lösungen und grenzflächenaktiven Stoffen untersucht. Messungen der Oberflächenspannung und Viskosität wurden für jedes Gemisch durchgeführt.Der Wärmetransport beim Sieden von vollentsalztem Wasser mit einem Anteil an SLS von 250 bis 1000 wppm (parts per million by weight) unterscheidet sich nicht von dem bei reinem, vollentsalztem Wasser. Bei einer Lösung mit 250 wppm Polyacryl ist das Sieden schwächer als bei reinem Wasser. Bei einer Zugabe von 250 wppm SLS zur Polyacryl-Lösung ist eine signifikante Zunahme des Wärmetransportes beim Sieden festzustellen. Ein Erhöhen der SLS-Konzentration auf 1000 wppm verstärkt nochmals diese Zunahme. Bei einem Wärmefluß von 50 W/cm² erhöht sich der Wärmetransportkoeffizient bei der AP-30 — 250 wppm SLS Lösung um 50% und bei der AP-30 — 1000 wppm SLS Lösung um 100% im Vergleich zum vollentsalzten Wasser.Mit diesen Ergebnissen wird deutlich, daß der Einfluß von grenzflächenaktiven Stoffen auf den Wärmetransport beim Sieden von polymeren Lösungen signifikanter als im Falle von Newtonschen Fluiden ist.

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Nomenclature q heat flux, (W/cm²) - T fluid temperature, (°C) - T _sat saturation temperature of the fluid, (°C) - T _w surface wall temperature, (°C) - T =T _w–T _sat, (°C) - steady shear apparent viscosity, (poise) - shear rate, (sec^–1) - surface tension, (dyne/cm) Dedicated to Prof. Dr.-Ing. U. Grigull's 80th birthday     

A comparison of the dynamic response of the ACS and SLS models for linear viscoelasticity

Using asymptotic analysis and numerical computation, we compare the behaviour of the three-parameter viscoelastic model proposed by Achenbach and Chao (ACS) with that of the Standard Linear Solid (SLS) in one-dimensional wave propagation. Our study shows that the models behave very similarly in both the near and far fields and that the much simpler form of the fundamental solution for the Achenbach-Chao model may take it preferable in many applications.     

Onset of nonlinearity and yield strain of a model soft solid

For soft solids with their low modulus, small stress already results in large strain, which may cause nonlinearity and yielding. These potentially competing effects were studied on a clay/polybutadiene (clay/sPB) composite, which is a soft physical gel. Structural changes were introduced by oscillatory shear using large amplitude (LAOS). LAOS beyond a critical limit reduced the internal connectivity. This softened the already soft solid even further, thereby moving it closer to its physical gel point. For clay/sPB, the shear-induced changes were irreversible so that they could get probed using small amplitude shear (SAOS) frequency sweeps. Sequences of SAOS-LAOS-SAOS (SLS) where repeated with increasing LAOS amplitude and increasing duration. The flow-induced structural changes in the soft solid were attributed to yielding, which began to occur at about the same stress/strain values as found for the onset of nonlinearity in traditional SAOS to LAOS (StL) stress amplitude sweeps. The onset of nonlinearity and the yielding seem to be a strain activated process since the characteristic strain amplitude is independent of frequency and temperature, but not so for the characteristic stress amplitude. The duration of LAOS in a SLS experiment beyond yielding is an important parameter since flow-induced structural changes require time to grow.     

Active control of coupled flexural-torsional vibration in a flexible rotor-bearing system using electromagnetic actuator

Rotor-shaft systems are subject to non-uniform spin speed during start-up, coast-down or any non-stationary situation changing the spin speed suddenly, e.g., load fluctuation or sudden mass-loss like loss of a blade or a part thereof. For a flexurally and torsionally compliant rotor-shaft, the dynamics under non-uniform spin-speed shows inertial coupling among transverse and torsional coordinates through mass-unbalance and gyroscopic effect. This results into coupled transverse-torsional vibration, where torsional response consists of significant harmonic components at bisynchronous spin frequency, torsional natural frequency of the shaft, and at combination frequencies corresponding to sum and difference of spin and transverse natural frequencies and twice the transverse natural frequency of the rotor-shaft. As a result of the coupling, transverse rotor motion also influences the torsional motion. The Method of Multiple Scales (MMS) is used in this work to carry out an analysis of a simplified system to get an idea about the dominant frequencies of excitation. Results of numerical simulation are presented next to show the effectiveness and influence of actively controlling the transverse rotor motion on its torsional motion, at the dominant frequencies, with the help of non-contact electromagnetic force from an actuator. Transverse vibration control is also observed to control the torsional oscillations due to coupled nature of the problem. The Stability Limit Speed (SLS) of the system is also increased as a result of application of the active control action. Constant axial torque is observed to diminish the influence of coupling, and protect the system against torsional instability, but control action is a must to stabilize the transverse vibration of the system above SLS.     

Design optimization of consolidated granular-solid polymer prismatic beam using metamorphic development

Topologically optimized granular-solid structures from additive manufacturing processes have impending applications as lightweight load bearing structures. To facilitate application, a procedure for characterizing optimal structural performance is devised for the design optimization of ‘end-use’ functional structures. An approach capable of realizing this objective is presented and demonstrated for horizontal prismatic beams produced from Nylon-12 granular-solid polymer, by Selective Laser Sintering (SLS). It combines topology (or layout) optimization, calibration of material parameters, and finite element (FE) modelling. The metamorphic development (MD) method forms the basis of an adaptive growth and degeneration optimization by material distribution approach. Experimental measurements are used to calibrate a bimodulus constitutive Drucker–Prager (D–P) model. Simply-supported three-point bending (3PB) tests are used to assess the fidelity of optimized beams on the basis of numerically predicted performance.     

Modeling compaction in agricultural soils

Research was conducted to quantify the effect of tire variables (section width, diameter, inflation pressure); soil variables (soil moisture content, initial cone index, initial bulk density); and external variables (travel speed, axle load, number of tire passes) on soil compaction and to develop models to assess compaction in agricultural soils. Experiments were conducted in a laboratory soil bin at the Asian Institute of Technology in three soils, namely: clay soil (CS), silty clay loam soil (SCLS), and silty loam soil (SLS). A dimensional analysis technique was used to develop the compaction models. The axle load and the number of tire passes proved to be the most dominant factors which influenced compaction. Up to 13% increase in bulk density and cone index were observed when working at 3 kN axle load in a single pass using a 8.0–16 tire. Most of the compaction occurred during the first three passes of the tire. It was also found that the aspect ratio, tire inflation pressure and soil moisture content have significant effect on soil compaction. The initial cone index did not show significant effect. The compaction models provided good predictions even when tested with actual field data from previous studies. Thus, using the models, a decision support system could be developed which may be able to provide useful recommendations for appropriate soil management practices and solutions to site-specific compaction problems.     

The site model theory and the standard linear solid

Summary The site model theory (SMT) is shown to lead to the same deformation behaviour as that displayed by the standard linear solid (SLS), group I, for all loading conditions. If a second deformation mechanism (inter-molecular slip) is introduced the result is the same as that obtained with the standard linear solid, group II, and models the behaviour of a polymer melt near to the solidification temperature.

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Zusammenfassung Es wird gezeigt, daß ein einfaches Platzwechsel-Modell (site model theory) bei allen Belastungsbedingungen das gleiche Deformationsverhalten voraussagt wie der lineare Drei-Parameter-Festkörper (standard linear solid, group I). Wenn ein weiterer Deformationsmechanismus (zwischenmolekulare Gleitung) eingeführt wird, entspricht das Verhalten dagegen demjenigen einer linearen Drei-Parameter-Flüssigkeit (standard linear solid, group II), welche das Verhalten einer Polymerschmelze in der Nähe der Schmelztemperatur beschreibt.

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a = ₁₂ ⁰ + ₂₁ ⁰ , see eq. [1] - b =N ₁ ⁰ ₁₂ ⁰ (V ₁₂ +V ₂₁), see eq. [1] - c = 2N _s ⁰ V _s see eq. [6] - k Boltzmann constant - t time - E,E ₁,E ₂ spring constants, see figures 1 and 3 - E _u unrelaxed modulus - N ₁ ⁰ site 1 equilibrium population in the unstressed state - N _s number of units available for slip - N(t) decrease in site 1 population - N _s (t) net number of slip jumps in the stressaided direction - T temperature (K) - V _i,j activation volume for jumps in directioni j - V _s activation volume for the slip process - strain - strain rate - incremental change in strain per unit change in site population - µ,µ ₁,µ ₂ dashpot constants, see figures 1 and 3 - applied stress - ₀ initial applied stress, (stress relaxation) =(t) (creep) - incremental change in stress per unit change in site population - ⁰ jump rate for slip in the unstressed state - _i,j ⁰ jump rate in the directioni j in the unstressed state With 3 figures and 3 tables