本文關鍵詞： 相場 數值模擬 定向核 串晶 流場 枝晶　出處：《太原科技大學》2017年碩士論文　論文類型：學位論文

【摘要】：在凝固過程中,流動對晶體成核和晶體生長產生很大的影響。在晶體成核階段,流動會影響成核形狀;晶體生長階段,流動影響結晶形態(tài),晶體又影響流動。把流動考慮到微觀組織模擬中,可以進一步了解材料的各種特性。在微觀組織模擬方面,相場模型是一種有效的材料模擬方法,能夠獲取微觀組織在空間和時間上的瞬時狀態(tài)。論文運用相場方法模擬了聚合物串晶晶體和流動下的聚合物動態(tài)結晶過程中的晶粒生長形貌。論文主要研究的內容為:首先,建立耦合流場的相場模型。在已有的相場模型上,考慮流體流動對結晶過程的影響,重新構造溫度場方程。根據能量守恒,將流動添加到溫度控制方程中,從而得到耦合流場的溫度方程。并在該方程中引入一個耦合系數,使得熔體為固相時,流體流速為零;熔體為液相時,流體流速不為零。通過一組實驗獲得的材料物理參數計算相場模型參數,計算出的模型參數能夠呈現許多種晶體相貌。其次,離散相場模型。用有限差分方法對無量綱流動下的聚合物動態(tài)結晶模型進行求解,模型中出現的時間和空間導數分別用向前差分格式、中心差分格式,拉普拉斯算子用九點格式離散。通過FORTRAN計算機語言進行編程,利用可視化軟件進行后處理,得到相應的結晶圖像,并進行比較。再次,用相場方法分別模擬以棒狀和螺紋狀為初始核的串晶形貌。通過改變前者與方向軸的角度,發(fā)現界面的不連續(xù)是串晶形成的主要原因;形成的串晶的橫向薄片相互平行,并等距離分布;隨著定向核的角度不同,模擬出不同的串晶形貌,橫向薄片的稠密程度也不相同。而模擬出的螺紋狀串晶上的薄片分布不規(guī)律,定向角對薄片的密度影響不大。最后,通過改變流速、各性異性系數、溫度、無量綱擴散率、驅動力參數的數值,研究了在流場下各因素對聚合物(ips)結晶形態(tài)的影響。通過實驗比對,結果顯示:在流場下,聚合物結晶形貌不對稱;各項異性系數、過冷度、無量綱驅動力的增加,能夠促進晶體上分枝的增加,晶體長的比較密;擴散系數的增加反而抑制了枝晶二次分枝的形成。而流動促進順流方向枝晶的生長,抑制逆流方向枝晶的生長。
[Abstract]:In the solidification process, the flow has a great influence on the nucleation and growth of the crystal. In the nucleation stage, the flow will affect the nucleation shape, while in the crystal growth stage, the flow will affect the morphology of the crystal. When the flow is considered in the microstructure simulation, the properties of the material can be further understood. In the field of microstructure simulation, the phase field model is an effective material simulation method. The transient state of microstructure in space and time can be obtained. In this paper, the morphology of grain growth in the process of dynamic crystallization of polymer is simulated by using phase field method. The main contents of this paper are as follows: first of all, The phase field model of coupled flow field is established. In the existing phase field model, considering the effect of fluid flow on crystallization process, the temperature field equation is re-constructed. According to the conservation of energy, the flow is added to the temperature control equation. The temperature equation of the coupled flow field is obtained, and a coupling coefficient is introduced into the equation so that the flow velocity is zero when the melt is a solid phase, and the melt is a liquid phase. The flow velocity of the fluid is not zero. The parameters of the phase field model can be calculated by the physical parameters of the material obtained from a group of experiments, and the calculated model parameters can present many kinds of crystal features. Discrete phase field model. The dynamic crystallization model of polymer under dimensionless flow is solved by finite difference method. The time and space derivatives in the model are obtained by the forward difference scheme and the central difference scheme, respectively. Laplacian operator is discretized in nine-point format. It is programmed by FORTRAN computer language and processed by visualization software. The corresponding crystalline images are obtained and compared. The phase field method is used to simulate the morphology of strands and threaded nuclei respectively. By changing the angle between the former and the directional axis, it is found that the discontinuity of the interface is the main cause of the formation of the crystals, and the transverse slices of the formed crystals are parallel to each other. And isometric distribution; with the different angle of the directional nucleus, different crystal morphology is simulated, and the density of the transverse slice is not the same, while the distribution of the thin slice on the threaded string is not regular, and the thickness of the transverse slice is not the same. The orientation angle has little effect on the density of the sheet. Finally, by changing the velocity of flow, coefficient of heterogeneity, temperature, dimensionless diffusivity, driving force parameters, The effects of various factors under the flow field on the crystalline morphology of the polymer were studied. The experimental results show that the morphology of the polymer is asymmetric, the heterogeneity coefficient, the undercooling degree and the dimensionless driving force increase in the flow field. The increase of diffusion coefficient inhibited the formation of secondary branching of dendrite, while the flow promoted the growth of dendrite in downstream direction and inhibited the growth of dendrite in countercurrent direction.
【學位授予單位】：太原科技大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：O631.1

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