Commercially available lattices contain various kinds of morphological imperfections which result in great degradation in lattices' mechanical properties, therefore, to obtain imperfection insensitive lattice structure is obviously a practical research subject. Hierarchical structure materials were found to be a class of promising anti-defect materials. This paper builds hierarchical lattice by adding soft adhesion to lattice's cell edges and numerical results show that its imperfection sensitivity to missing bars is minor compared with the classic lattice. Soft adhesion with appropriate properties reinforce cell edge's bending stiffness and thus reduce the bending deformation in lattice caused by missing bars defect, which is confirmed by statistical analysis of normalized node displacements of imperfect lattices under hydrostatic compression and shear loads.
According to previous studies,stiffened shells with convex hyperbolic generatrix shape are less sensitive to imperfections.In this study,the effects of generatrix shape on the performances of elastic and plastic buckling in stiffened shells are investigated.Then,a more general description of generatrix shape is proposed,which can simply be expressed as a convex B-spline curve(controlled by four key points).An optimization framework of stiffened shells with a convex B-spline generatrix is established,with optimization objective being measured in terms of nominal collapse load,which can be expressed as a weighted sum of geometrically imperfect shells.The effectiveness of the proposed framework is demonstrated by a detailed comparison of the optimum designs for the B-spline and hyperbolic generatrix shapes.The decrease of imperfection sensitivity allows for a significant weight saving,which is particularly important in the development of future heavy-lift launch vehicles.
WANG BoHAO PengLI GangWANG XiaoJunTANG XiaoHanLUAN Yu
A concept of hierarchical stiffened shell is proposed in this study,aiming at reducing the imperfection sensitivity without adding additional weight.Hierarchical stiffened shell is composed of major stiffeners and minor stiffeners,and the minor stiffeners are generally distributed between adjacent major stiffeners.For various types of geometric imperfections,e.g.,eigenmode-shape imperfections,hierarchical stiffened shell shows significantly low imperfection sensitivity compared to traditional stiffened shell.Furthermore,a surrogate-based optimization framework is proposed to search for the hierarchical optimum design.Then,two optimum designs based on two different optimization objectives(including the critical buckling load and the weighted sum of collapse loads of geometrically imperfect shells with small-and large-amplitude imperfections)are compared and discussed in detail.The illustrative example demonstrates the inherent superiority of hierarchical stiffened shells in resisting imperfections and the effectiveness of the proposed framework.Moreover,the decrease of imperfection sensitivity can finally be converted into a decrease of structural weight,which is particularly important in the development of large-diameter launch vehicles.
Bo WangPeng HaoGang LiJia-Xin ZhangKai-Fan DuKuo TianXiao-Jun WangXiao-Han Tang
