本文關鍵詞： 實體殼單元 自適應網格加密 板料沖壓全工序仿真 閉鎖現象 穩(wěn)定化　出處：《華中科技大學》2016年博士論文　論文類型：學位論文

【摘要】：近年來,有限單元法已經成為一種重要的數值模擬手段,基于有限單元法的數值模擬軟件已經在板料沖壓領域得到了廣泛應用。現有的商業(yè)有限元數值模擬軟件主要采用薄膜單元和殼單元進行板料沖壓過程模擬。但是,對于以汽車結構件為代表的厚板件,薄膜單元和殼單元并不能準確模擬板料變形。這是因為薄膜單元和殼單元都忽略了沿板料厚度方向的正應力,且無法體現板料的雙面接觸效果。為了彌補薄膜單元和殼單元存在的不足,本文提出了一種新的實體殼單元模型,建立了基于該單元的動力顯式算法,并成功開發(fā)出了一套實體殼單元板料沖壓全工序仿真算法。該算法既能有效反映成形過程中模具對板料的擠壓效果,又能準確描述沿板料厚度方向的應力分布,顯著改善了現有板料沖壓有限元數值模擬軟件在非平面應力成形問題中表現失真的問題,大大提高了板料沖壓成形仿真和回彈預測的準確性。本文提出了一種無閉鎖現象和沙漏模式的新型實體殼單元。通過引入1個EAS(Enhanced Assumed Strain,改善擬應變)內部變量,消除了單元的體積閉鎖和厚向閉鎖。采用ANS (Assumed Nature Strain,假設自然應變)四點插值方法,克服了單元的梯形閉鎖和橫向剪切閉鎖。為了有效抑制面內單點積分引起的沙漏模式,提出了對應變轉換矩陣和協(xié)變應變-位移矩陣Taylor展開,并對二者乘積進行投影和重構的方法,構建了不產生過剛現象的物理穩(wěn)定化方法。采用若干經典線性算例驗證了該實體殼單元的計算精度和收斂速度。建立了動力顯式求解格式的實體殼單元成形仿真算法,解決了板料拉深、彎曲、翻邊整形等大變形動態(tài)接觸問題仿真中的收斂性難題。提出了內部變量的顯式凝聚方法,有效減少了數據存儲量。為了提高成形仿真的計算效率,提出了實體殼單元的自適應網格加密技術,并采用沙漏應力的繼承保證了單元的穩(wěn)定性。推導了服從Yld91和Y1d2004-18p屈服準則的彈塑性本構模型,為準確描述各向異性板材的變形行為提供了前提條件�；诮⒌膶嶓w殼單元模型,開發(fā)了一套完整的板料沖壓全工序仿真算法,并將該算法成功地應用于汽車鋁合金結構件等厚板零件的成形、切邊沖孔及回彈模擬。為了提高沖裁邊界的尺寸精度,切邊沖孔算法采用了網格加密的方法,并通過向前推進網格調整法和網格優(yōu)化等措施,避免了畸形單元的產生�；跓o模具的靜力隱式回彈仿真算法,推導了隱式格式的單元穩(wěn)定化方法,消除了剛度矩陣的秩缺陷,保證了回彈預測的準確性。多個算例表明,開發(fā)的實體殼單元板料沖壓全工序仿真算法能獲得較高的計算精度,基本達到了實用化水平。
[Abstract]:In recent years, the finite element method has become an important means of numerical simulation. The numerical simulation software based on finite element method has been widely used in the field of sheet metal stamping. The commercial finite element numerical simulation software mainly uses thin film element and shell element to simulate sheet metal stamping process. The film element and the shell element can not accurately simulate the deformation of the sheet metal for the thick plate represented by the automobile structure. This is because both the film element and the shell element ignore the normal stress along the direction of the thickness of the sheet metal. In order to make up for the shortage of thin film element and shell element, a new solid shell element model is proposed, and a dynamic explicit algorithm based on this element is established. A set of simulation algorithm for the whole process of solid shell unit sheet stamping is developed, which can not only effectively reflect the extrusion effect of the die on the sheet metal in the forming process, but also accurately describe the stress distribution along the direction of the thickness of the sheet metal. The problem that the finite element numerical simulation software of sheet metal stamping in the non-plane stress forming problem is obviously improved is improved. The accuracy of sheet metal stamping simulation and springback prediction is greatly improved. In this paper, a new type of solid shell element without locking phenomenon and hourglass mode is proposed. By introducing a EAS(Enhanced Assumed training, the internal variable is improved. The volume and thick latchup of the element are eliminated. The trapezoidal locking and transverse shear latchup are overcome by using ANS sumed Nature training (assuming natural strain) four-point interpolation method. In order to effectively suppress the hourglass mode caused by in-plane single point integration, the trapezoidal latchup and transverse shear latchup of the element are overcome. The Taylor expansion of strain transformation matrix and covariant strain-displacement matrix is proposed, and the method of projecting and reconstructing the product of the two matrices is presented. In this paper, a physical stabilization method without overstiffness is constructed, and some classical linear examples are used to verify the accuracy and convergence speed of the solid shell element. A dynamic explicit solution scheme is established to simulate the forming of the solid shell element. The convergence problem in the simulation of large deformation dynamic contact problems such as drawing, bending and flanging of sheet metal is solved. The explicit condensation method of internal variables is proposed, which effectively reduces the data storage. In order to improve the computational efficiency of forming simulation, An adaptive mesh encryption technique for solid shell elements is proposed, and the stability of the element is guaranteed by inheriting the hourglass stress. An elastoplastic constitutive model is derived, which is based on the yield criteria of Yld91 and Y1d2004-18p. In order to accurately describe the deformation behavior of anisotropic sheet metal, a complete simulation algorithm for sheet metal stamping process is developed based on the established solid shell element model. The algorithm is successfully applied to the forming, edge-punching and springback simulation of automotive aluminum alloy parts with equal thickness plate. In order to improve the dimension accuracy of blanking boundary, the edge-cutting punching algorithm adopts the method of mesh encryption. By advancing forward mesh adjustment method and mesh optimization, the generation of deformable element is avoided. Based on the static implicit springback simulation algorithm without mould, the element stabilization method of implicit scheme is derived, which eliminates the rank defect of stiffness matrix. The accuracy of springback prediction is ensured. Several examples show that the developed simulation algorithm for the whole stamping process of solid shell plate can obtain high calculation accuracy and reach the practical level.
【學位授予單位】：華中科技大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TG386;TP391.9

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