【摘要】：作為一種典型的智能材料,電流變液的力學(xué)性能在外加電場(chǎng)下能夠發(fā)生顯著的變化,而且這種變化是快速可逆的。鑒于這種特殊性質(zhì),電流變液在力電耦合裝置中具有廣闊的應(yīng)用前景。因此,電流變液力學(xué)性能變化的機(jī)理分析一直以來(lái)就是電流變液研究領(lǐng)域的重點(diǎn)和難點(diǎn)。在外加電場(chǎng)作用下,電流變顆粒在極板間形成鏈狀結(jié)構(gòu)使電流變液的剪切應(yīng)力和表觀粘度顯著增加。電流變液工作狀態(tài)下的微觀結(jié)構(gòu)與力學(xué)性能的關(guān)系是解釋電流變機(jī)理的關(guān)鍵所在。由于實(shí)驗(yàn)條件的限制,電流變顆粒的微觀結(jié)構(gòu)很難直接被觀測(cè)到,因此模擬計(jì)算成為了研究電流變液機(jī)理的重要方法。通過(guò)實(shí)驗(yàn)現(xiàn)象驗(yàn)證計(jì)算模型的正確性,用模擬計(jì)算的結(jié)果解釋實(shí)驗(yàn)中觀測(cè)的現(xiàn)象,是目前電流變液機(jī)理研究常用而有效的手段。本文采用實(shí)驗(yàn)與計(jì)算模擬相結(jié)合的方法全面研究了電流變液在壓縮和剪切時(shí)的力學(xué)性能變化,并探究了其中不同影響因素的作用機(jī)理,具體工作內(nèi)容如下:1.通過(guò)實(shí)驗(yàn)結(jié)合模擬計(jì)算的方法研究了電流變液在壓縮模式下法向應(yīng)力的變化情況。電流變液在壓縮時(shí)表現(xiàn)出較高的法向應(yīng)力,測(cè)試了壓縮速度對(duì)電流變液法向應(yīng)力的影響。同等條件下壓縮速度越小,電流變液的法向應(yīng)力越大。這是在外加電場(chǎng)作用下電流變液的顆粒與基液分離的現(xiàn)象導(dǎo)致的,壓縮速度越小,顆粒與基液分離的現(xiàn)象越顯著,電流變顆粒的鏈狀結(jié)構(gòu)更穩(wěn)固,可以承載更大的應(yīng)力。然后基于偶極子模型,提出了電流變液的壓縮模型,將模擬結(jié)果和實(shí)驗(yàn)結(jié)果進(jìn)行了比較,驗(yàn)證了壓縮計(jì)算模型的可靠性。模擬研究了外加電場(chǎng)強(qiáng)度、壓縮應(yīng)變、剪切速率對(duì)電流變液法向應(yīng)力的影響。剪切速率較小時(shí),剪切作用對(duì)電流變液法向應(yīng)力的影響很小;隨著剪切速率的增大,電流變液的法向應(yīng)力在逐漸減小。在剪切作用下電流變液的法向應(yīng)力有振蕩變化的現(xiàn)象。通過(guò)對(duì)微觀結(jié)構(gòu)的計(jì)算發(fā)現(xiàn)較大的剪切速率下電流變顆粒的微觀結(jié)構(gòu)不斷地破壞與重組是法向應(yīng)力振蕩的原因。2.通過(guò)實(shí)驗(yàn)和模擬計(jì)算研究了剪切場(chǎng)中介電損耗對(duì)電流變液力學(xué)性能的影響。采用鍶離子摻雜的方法改變二氧化鈦顆粒的介電損耗性能,測(cè)試了改性后顆粒的介電損耗頻譜圖和電流變液的剪切流變曲線,發(fā)現(xiàn)了介電損耗對(duì)電流變液流變性能的影響。鍶離子摻雜比例的提高降低了電流變顆粒的弛豫頻率,介電損耗增大,電流變液的電流變效率也在逐漸降低。當(dāng)顆粒的弛豫頻率低于100Hz時(shí),電流變液在一定的剪切速率范圍內(nèi)失去電流變效應(yīng),有效工作范圍減小。模擬研究了介電損耗過(guò)程中的弛豫時(shí)間對(duì)電流變液力學(xué)性能的影響。當(dāng)弛豫時(shí)間超過(guò)0.01 s后,臨界剪切速率降低,電流變有效工作范圍減小,與實(shí)驗(yàn)中的結(jié)論一致。給出了介電損耗對(duì)電流變液影響的機(jī)理解釋,弛豫頻率過(guò)大時(shí)顆粒偶極矩方向和顆粒鏈方向不一致,使得顆粒鏈方向顆粒間的相互作用力減弱,甚至由吸引力變?yōu)榕懦饬?顆粒鏈狀結(jié)構(gòu)的強(qiáng)度降低。3.模擬研究了剪切作用下電流變液力學(xué)性能的變化,結(jié)合實(shí)驗(yàn)研究了不同狀態(tài)下的剪切速率對(duì)電流變液剪切應(yīng)力變化的影響。利用基于偶極子極化理論的計(jì)算模型,研究了體積分?jǐn)?shù)、電場(chǎng)強(qiáng)度和剪切速率對(duì)電流變液力學(xué)性能的影響。然后進(jìn)行了穩(wěn)態(tài)剪切下的二維模擬和微觀結(jié)構(gòu)的計(jì)算,以此來(lái)解釋剪切速率對(duì)電流變液力學(xué)性能的影響。通過(guò)實(shí)驗(yàn)發(fā)現(xiàn)了剪切速率對(duì)電流變液剪切應(yīng)力影響的三種不同狀態(tài),驗(yàn)證了模擬結(jié)果。通過(guò)計(jì)算的微觀結(jié)構(gòu)演化解釋了不同狀態(tài)下的剪切速率對(duì)電流變液力學(xué)性能影響的機(jī)理:低剪切速率下,顆粒鏈結(jié)構(gòu)向剪切方向傾斜,剪切應(yīng)力隨著剪切速率的增加而增加;中等剪切速率下,顆粒鏈結(jié)構(gòu)處于破壞與重組的動(dòng)態(tài)平衡狀態(tài),剪切應(yīng)力隨時(shí)間振蕩變化;高剪切速率下,電流變液達(dá)到剪切屈服狀態(tài),鏈結(jié)構(gòu)被完全破壞,電場(chǎng)對(duì)剪切應(yīng)力的影響很弱,電流變液的剪切應(yīng)力由液體的粘性力主導(dǎo),表現(xiàn)出賓漢流體的性質(zhì)。
[Abstract]:As a typical intelligent material, the mechanical properties of the electrorheological fluid can change significantly under the applied electric field, and the change is fast and reversible. In view of this special property, the electrorheological fluid has a wide application prospect in the force-electric coupling device. Therefore, the mechanism analysis of the change of the mechanical property of the electrorheological fluid has always been the focus and difficulty in the field of current fluid-changing research. Under the effect of the applied electric field, the current-changing particles form a chain-like structure between the plates, so that the shear stress and the apparent viscosity of the electrorheological fluid are obviously increased. The relationship between the microstructure and the mechanical property in the working state of the electrorheological fluid is the key to explain the mechanism of the current transformation. Due to the limitation of the experimental conditions, the microstructure of the electrorheological particles is very difficult to be observed directly, so the simulation is an important method to study the mechanism of the rheological fluid of the current. The correctness of the calculation model is verified by the experimental phenomenon, and the phenomenon of the observation in the experiment is explained by the result of the simulation. In this paper, the mechanical properties of the electrorheological fluid at the time of compression and shearing are studied by the method of combination of experiment and calculation, and the action mechanism of the different influencing factors is explored. The specific work is as follows:1. In this paper, the variation of the normal stress in the current-changing liquid under the compression mode is studied by means of the simulation calculation of the experiment. The effect of the compression rate on the stress of the electrorheological fluid is tested by the high normal stress at the time of compression. Under the same conditions, the smaller the compression speed, the greater the normal stress of the electrorheological fluid. This is caused by the phenomenon that the particle of the electrorheological fluid is separated from the base liquid under the action of the applied electric field, the smaller the compression speed, the more obvious the phenomenon of the separation of the particles from the base liquid, and the chain structure of the current-changing particles is more stable and can bear more stress. Then, based on the dipole model, the compression model of the electrorheological fluid is put forward, and the simulation results and the experimental results are compared, and the reliability of the compression calculation model is verified. The effects of the applied electric field strength, compressive strain and shear rate on the stress of the electrorheological fluid are simulated. The shear rate is small, and the effect of shear on the stress of the electrorheological fluid is very small; with the increase of the shear rate, the normal stress of the electrorheological fluid is gradually reduced. The normal stress of the electrorheological fluid under the shearing action is the phenomenon of the oscillation change. Through the calculation of the micro-structure, it is found that the micro-structure of the current-variable particles is destroyed and the recombination is the reason of the normal stress oscillation. The effect of the dielectric loss on the mechanical properties of the rheological fluid in the shear field is studied by means of experiment and simulation. The dielectric loss performance of the titanium dioxide particles was changed by the method of ion doping. The dielectric loss spectrum of modified particles and the shear rheological curve of the electrorheological fluid were tested, and the effect of the dielectric loss on the rheological property of the rheological fluid was found. The increase of the ion doping ratio reduces the relaxation frequency and the dielectric loss of the current-variable particles, and the current-changing efficiency of the current-changing liquid is also gradually reduced. When the relaxation frequency of the particles is lower than 100 Hz, the current transformer loses the current variable effect in a certain shear rate range, and the effective working range is reduced. The effect of relaxation time in the dielectric loss on the mechanical properties of the electrorheological fluid is simulated. When the relaxation time is more than 0.01 s, the critical shear rate is reduced, and the effective working range of the current transformer is reduced, which is consistent with the conclusion in the experiment. The mechanism of the effect of the dielectric loss on the electrorheological fluid is given. The direction of the particle dipole moment and the direction of the particle chain are not uniform when the relaxation frequency is too large, so that the interaction force between the particles in the particle chain direction is weakened, and the strength of the particle chain structure is reduced even by the attractive force becoming a repulsive force. The changes of the mechanical properties of the rheological fluid under shear are simulated, and the effect of shear rate on the shear stress of the rheological fluid under different conditions is studied in combination with the experiment. The effect of volume fraction, electric field strength and shear rate on the mechanical properties of the electrorheological fluid is studied by using the calculation model based on the dipole-polarization theory. The effect of the shear rate on the mechanical properties of the electrorheological fluid is explained by the calculation of the two-dimensional simulation and the microstructure under the steady-state shear. In this paper, three different states of shear rate on the shear stress of current-varying fluid are found, and the simulation results are verified. The mechanism of the effect of shear rate on the mechanical properties of the electrorheological fluid under different conditions is explained by the calculated microstructure evolution: under the low shear rate, the particle chain structure is inclined to the shearing direction, and the shear stress is increased with the increase of the shear rate; at the moderate shear rate, the structure of the particle chain is in a dynamic equilibrium state of destruction and recombination, and the shear stress changes with time; under the high shear rate, the current variable reaches the shear yield state, the chain structure is completely destroyed, the influence of the electric field on the shear stress is weak, The shear stress of the electrorheological fluid is dominated by the force of the liquid, showing the properties of the Bingham fluid.
【學(xué)位授予單位】：中國(guó)科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：TB381

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