三维连续体结构仿生拓扑优化新方法

A NEW METHOD FOR TOPOLOGY OPTIMIZATION OF THREE-DIMENSIONAL CONTINUUM STRUCTURES BASED ON BIONICS

  • 摘要: Wolff法则是指骨骼通过重建/生长,保证骨小梁方向趋于与主应力方向一致以不断地适应它的力学环境。根据Wolff法则,建立了一种新的拓扑优化的准则法。该方法的基本思想是:(1) 将待优化的结构看作是一块遵从Wolff法则生长的骨骼,骨骼的重建过程作为三维连续体结构寻找最优拓扑的过程;(2) 用构造张量描述正交各向异性材料的弹性本构;(3) 重建规律为结构中材料的更新规律。通过引入参考应变区间,材料更新规律可解释为:设计域内一点处主应变的绝对值不在该区间时,该点处构造张量出现变化;否则,构造张量不变化,该点处于生长平衡状态。(4) 当设计域内所有点都处于生长平衡状态时,结构拓扑优化结束。采用各向同性本构模型,即令二阶构造张量与二阶单位张量成比例,分析三维结构拓扑优化。实例进一步验证基于Wolf法则的连续体结构优化方法的正确性和可行性。

     

    Abstract: Wolff’s law in biomechanics states that the microstructure of bone adapts gradually to the environment as a result of remodeling process. A new method for topology optimization of three-dimensional (3D) continuum structure based on Wolff’s law is proposed. The continuum structure is optimized as a piece of bone which obeys Wolff’s law, and the process of locating the optimum topology of structure is assumed to be equivalent to the “bone” remodeling process. Secondly, a second order positive definite fabric tensor is introduced to express the material anisotropy. If the fabric tensor is proportional to the second order identity tensor, the material is isotropic. Thirdly, an interval of reference strain is adopted and the remodeling rule can be established. During the growing process, at any material point, if the absolute value of its principal strain is out of the interval, then the increment of the corresponding eigenvalue of fabric tensor, i.e. the growth speed is non-zero; but if all the absolute values locate in the interval, the growth speeds are equal to zero and the material point is in a state of remodeling equilibrium. Finally, the global optimum of structure requires all material points being in the state of remodeling equilibrium under the loading conditions. Degenerated method, in which all fabric tensors of all the material points are restricted to be proportional to the second order identity tensor, is proposed to solve the topology optimization problem of the 3D continuum structures. Numerical results are given to demonstrate the validity and capability of the theories and algorithm developed.

     

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