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摘要: 周期性非均質復合材料具有微觀結構特征,需要均勻化理論進行宏觀和微觀的多尺度分析來研究其性能表現。針對其耐久強度性能,應用塑性極限安定下限定理,特別分析了其在長期交變載荷下的安定狀態。結合工程應用目標,提出一種全新的代表性單元邊界條件,結合圓錐二次優化算法進行數值計算,可以從材料微結構和組分性能出發,經過彈性應力場求解確定位移邊界載荷數值,最終由優化求解得到復合材料板材的面內塑性性能容許域。所求得的應力域以單向應力為基,可根據結構宏觀的單向應力狀態變化幅值直接進行安定狀態與否的判定。通過文中的多個算例,驗證了所編寫的軟件及計算流程的可行性及數值準確性,展示了該方法在工程模型中的應用場合和工程實踐意義。Abstract: Direct methods of plastic analysis are widely used in composites analysis to determine material strength for safety assessment or lightweight optimization design. Multi-scale processing of periodic heterogeneous composite material is needed due to its existing of microstructure. The standard method is to determine the macroscopic properties from the calculation results of microcosmic representative volume elements (RVEs) by using the homogenization theory. However, in current practice, there are some disadvantages of transforming the micro strain domain to the macro stress shakedown domain when considering multiple external loads. The domain cannot fully demonstrate the shakedown condition, and it is impossible to evaluate a known loading combination only from the knowledge of whether the load leads to the shakedown state. To overcome this disadvantage, a new comprehensive approach was proposed to enhance endurance limit strength of composites under variable loads for long term. Considering the example of in-plane strength analysis, for microcosmic RVEs, a new set of boundary condition was defined in the form of uniform strain. The boundary condition was derived from the elastic response under unit loads by using Hook’s law and stiffness matrix. The resulting elastic stress field was used later for plastic shakedown analysis. Based on the lower bound theorem of plastic mechanics, optimization programming for load factor was performed, and after proper mathematical reformulation, the conic quadratic optimization problem could be solved efficiently. Macro-stress shakedown domain can be obtained after scale-transformation of the RVE results. The bases of this stress domain are unidirectional stress in geometry space. The stress amplitude of a structure can be evaluated by this domain for determining the shakedown state in a simple and practical manner. Further, changes in the boundary condition of RVE do not affect the limit and elastic analysis. Finally, few numerical examples were presented for verification and illustration. This approach can be expanded to three dimensions and employed for more complex structures.
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表 1 由微觀位移載荷域推導宏觀應力域
Table 1. Derivation of macro-scale stress domain from micro-scale displacement boundary
點 微觀位移載荷域 宏觀應力域 x方向 y方向 x方向 y方向 P1 0 0 0 0 P2 αux 0 αk11ux/l αk21ux/l P3 αux αuy $\alpha \left( {{k_{11}}{u_x} + {k_{12}}{u_y}} \right)/l$ $\alpha \left( {{k_{21}}{u_x} + {k_{22}}{u_y}} \right)/l$ P4 0 αuy αk12uy/l αk22uy/l 表 2 由宏觀應力域推導對應的微觀位移載荷域
Table 2. Derivation of micro-scale displacement boundary from macro-scale stress domain
點 宏觀應力域 微觀位移載荷域 x方向 y方向 x方向 y方向 P1 0 0 0 0 P2 Σ1 0 s11Σ1l s21Σ1l P3 Σ1 Σ2 s11Σ1l+s12Σ2l s21Σ1l+s22Σ2l P4 0 Σ2 s12Σ2l s22Σ2l 表 3 圓孔方板模型幾何和材料參數
Table 3. Geometry and material parameters of plate with hole
長度,l/mm 孔徑,D/mm 厚度,h/mm D/l 100 20 2 0.2 材料 彈性模量,E/MPa 泊松比,υ 屈服強度,σY/MPa 鋼材 210 0.3 280 表 4 模型所用面板單層材料力學參數
Table 4. Material properties of single layer
Ex/GPa Ey/GPa Gxy/GPa μxy μyz Tx/MPa Ty/MPa Sxy/MPa 146.9 11.4 6.18 0.3 0.4 1370.6 66.5 133.8 表 5 修改后層合板RVE邊界條件
Table 5. Modified boundary condition of lamination RVE
mm 單位載荷編號 x-0-y平面 x-0-z平面 y-0-z平面 平面x=10 平面y=10 1 對稱約束 對稱約束 對稱約束 ux=0.033 uy=?0.01 2 對稱約束 對稱約束 對稱約束 ux=?0.01 uy=0.0208 表 6 多孔薄壁材料參數
Table 6. Material parameters of porous materials
材料 彈性模量,E/GPa 泊松比,υ 屈服強度,σY/MPa 鋼材 200 0.3 360 鋁合金 72 0.33 100 表 7 修改后多孔材料RVE邊界條件
Table 7. Modified boundary condition of porous material RVE
mm 單位載荷編號 x-0-y平面 x-0-z平面 y-0-z平面 x=4平面 y=3平面 1 對稱約束 對稱約束 對稱約束 ux=0.01 uy=?0.001998 2 對稱約束 對稱約束 對稱約束 ux=?0.003732 uy=0.01 www.77susu.com -
參考文獻
[1] Zheng X X, Zheng X T, Gou L H. The research progress on multiscale method for the mechanical analysis of composites. Adv Mech, 2010, 40(1): 41 doi: 10.6052/1000-0992-2010-1-J2008-104鄭曉霞, 鄭錫濤, 緱林虎. 多尺度方法在復合材料力學分析中的研究進展. 力學進展, 2010, 40(1):41 doi: 10.6052/1000-0992-2010-1-J2008-104 [2] Suquet P M. Discontinuities and plasticity//Nonsmooth Mechanics and Applications. Vienna: Springer, 1988: 279 [3] Weichert D, Hachemi A, Schwabe F. Application of shakedown analysis to the plastic design of composites. Arch Appl Mech, 1999, 69(9-10): 623 doi: 10.1007/s004190050247 [4] Weichert D, Hachemi A, Schwabe F. Shakedown analysis of composites. Mech Res Commun, 1999, 26(3): 309 doi: 10.1016/S0093-6413(99)00029-4 [5] Ponter A R S, Leckie F A. On the behaviour of metal matrix composites subjected to cyclic thermal loading. J Mech Phys Solids, 1998, 46(11): 2183 doi: 10.1016/S0022-5096(98)00074-X [6] Hachemi A, Chen M, Chen G, et al. Limit state of structures made of heterogeneous materials. Int J Plast, 2014, 63: 124 doi: 10.1016/j.ijplas.2014.03.019 [7] Chen G, Bezold A, Broeckmann C, et al. On the size of the representative volume element used for the strength prediction: A statistical survey applied to the particulate reinforce metal matrix composites (PRMMCs)//Advances in Direct Methods for Materials and Structures. Cham: Springer, 2018: 51 [8] Chen G, Bezold A, Broeckmann C, et al. On the statistical determination of strength of random heterogeneous materials. Compos Struct, 2016, 149: 220 doi: 10.1016/j.compstruct.2016.04.023 [9] Zhang J, Oueslati A, Shen W Q, et al. Shakedown of porous material with Drucker-Prager dilatant matrix under general cyclic loadings. Composite Structures, 2019, 220: 566 doi: 10.1016/j.compstruct.2019.03.029 [10] Li H X, Liu Y H, Feng X Q, et al. Plastic limit analysis of ductile composites based on homogenization theory. Acta Mech Sin, 2002, 34(4): 550 doi: 10.3321/j.issn:0459-1879.2002.04.009李華祥, 劉應華, 馮西橋, 等. 基于均勻化理論韌性復合材料塑性極限分析. 力學學報, 2002, 34(4):550 doi: 10.3321/j.issn:0459-1879.2002.04.009 [11] Zhang H T, Liu Y H, Xu B Y. Lower bound shakedown analysis of periodic ductile composites. J Tsinghua Univ Sci Technol, 2005, 45(2): 267張宏濤, 劉應華, 徐秉業. 周期性韌性復合材料的安定下限分析. 清華大學學報: 自然科學版, 2005, 45(2):267 [12] Qin F, Zhang L L, Chen M, et al. Lower bound analysis of plastic limit and shakedown state of orthotropic materials. J Tsinghua Univ Sci Technol, 2018, 58(11): 966秦方, 張樂樂, 陳敏, 等. 正交各向異性材料塑性極限與安定的下限分析. 清華大學學報: 自然科學版, 2018, 58(11):966 [13] Chen S S, Liu Y H, Cen Z Z. Lower bound shakedown analysis by using the element free Galerkin method and non-linear programming. Comput Methods Appl Mech Eng, 2008, 197(45-48): 3911 doi: 10.1016/j.cma.2008.03.009 [14] Simon J W, Weichert D. Numerical lower bound shakedown analysis of engineering structures. Comput Methods Appl Mech Eng, 2011, 200(41-44): 2828 doi: 10.1016/j.cma.2011.05.006 [15] Carvelli V, Cen Z Z, Liu Y, et al. Shakedown analysis of defective pressure vessels by a kinematic approach. Arch Appl Mech, 1999, 69(9-10): 751 doi: 10.1007/s004190050254 [16] Huang C F, Xiao J Y, Huang Z H, et al. Buckling of composite cylindrical shells fabricated using thin-ply under axial compression. Chin J Eng, 2018, 40(07): 857黃春芳, 肖加余, 黃展鴻, 等. 薄鋪層復合材料薄壁管軸壓屈曲行為研究. 工程科學學報, 2018, 40(07):857 [17] Wang Y Q, Tong M B, Zhu S H. 3D nonlinear progressive damage analysis model for composite laminates. Acta Mater Compos Sin, 2009, 26(5): 159 doi: 10.3321/j.issn:1000-3851.2009.05.026王躍全, 童明波, 朱書華. 三維復合材料層合板漸進損傷非線性分析模型. 復合材料學報, 2009, 26(5):159 doi: 10.3321/j.issn:1000-3851.2009.05.026 -