点阵夹层结构高温蠕变强度设计理论

Lattice truss sandwich panel structure is a new type of material with periodic microstructure. It has a high strength with lightweight, and has a good application prospect at high temperature. In this paper, the creep strength at high temperature for lattice truss sandwich panel structure will be studied. Firstly, a representative volume element (RVE), which is named unit cell, is taken as the research object. A finite element model for a unit cell will be developed to analyze the creep damage, and the residual stress is taken into consideration. In particular, in-situ experiment at high temperature using neutron diffraction (ND) and small angle neutron scattering (SANS) will also be performed to verify the constitutive model. Then, by using the equivalent homogenization method, the mathematic relation between unit cell and total structure is explored, and the equivalent creep properties for the periodic lattice truss sandwich structure will be obtained. Creep tests and finite element simulation of the both unit cell and total structure are performed to identify the creep breakage mode and failure mechanism. The accelerated damage effect induced by the local node failure will be studied, and a quantitative relationship between the residual creep strength and the number of failure joints will be investigated, through which a linear cumulative damage model for life prediction will be built. The effects of topology type and the size effect on creep damage and life will be fully studied to build a quantitative relationship, which builds a creep strength design medthod for lattice truss sandwich panel structure.This method can not only study the local fracture behavior, but also can predict the creep strength of the macrostructure.

点阵夹层结构是一种新型周期性微结构材料，具有轻质、高强高韧等特点，在高温下具有较好的应用前景。本项目对点阵夹层结构的高温蠕变强度进行研究。首先以代表性单元- - 单胞为研究对象，通过蠕变、中子衍射、小角中子散射试验和计算模拟，建立考虑残余应力影响的蠕变损伤分析模型，获得单胞蠕变强度。然后，引入等效均匀化理论，探讨单胞与宏观结构之间的力学关系，获得宏观结构等效蠕变参数；将复杂点阵夹层结构等效为连续材料模型，对等效结构进行有限元分析，并与实体有限元分析和试验结果进行比较，验证等效均匀化方法的正确性。通过试验和计算，分析蠕变失效机理，探讨局部节点断裂对剩余节点的加速损伤效应，研究剩余蠕变强度与失效节点数量之间的定量关系，建立线性损伤累积的寿命预测方法。系统研究拓扑类型、尺寸效应与蠕变强度、寿命之间的定量关系,建立点阵夹层结构高温强度设计方法。采用此法，既可获得局部断裂行为，又可预测宏观结构蠕变强度。

点阵夹层结构是一种新型的多功能材料，由于其具有质轻、高强、换热效率高等优点，已逐步实现工业化应用。本项目以胞元为研究对象，对点阵夹层结构高温蠕变性能进行研究。通过蠕变试验、计算模拟、中子衍射等试验分析，阐述残余应力对蠕变损伤的影响机理，建立了扩散、相变、蠕变、热弹塑性耦合残余应力计算模型，发现钎焊工艺和尺寸的影响规律，掌握残余应力调控方法，提出降低残余应力优化工艺。构建残余应力水平与蠕变损伤之间的定量关系，提出一种新型的钎焊接头蠕变损伤本构模型，实现钎焊接头的蠕变裂纹扩展模拟，厘清了钎焊接头的蠕变断裂机理，建立了单胞结构蠕变损伤模型。提出周期性换热结构等效强度模型，建立几何尺寸相关的等效弹性模量、等效热物性参数解析模型，建立了等效均匀化理论的蠕变强度设计理论。基于等效均匀化方法，推导等效蠕变速率、破断寿命及蠕变屈曲预测公式，建立蠕变失效分析曲线，揭示了强度寿命的主控因素；建立整体结构蠕变强度与缺失分率之间的定量关系，完善点阵夹层结构高温强度设计方法。