1.Key Laboratory of Liaoning Province for Composite Structural Analysis of Aerocraft and Simulation,Shenyang Aerospace University,Shenyang 110136,China
2a.a. Light Alloy Research Institute,Central South University,Changsha 410083,China
2b.b. State Key Laboratory of Precision Manufacturing for Extreme Service Performance,Central South University,Changsha 410083,China
Using the carbon fiber-reinforced composite tank can remarkably reduce the weight of the launch vehicle.However,the analysis method for cryogenic tanks subjected to mechanical-thermal loads remains to be studied,especially to accurately consider the microthermal stress produced between fiber and matrix in the cryogenic environment.A representative volume model containing multiple fibers was adopted,combined with the matrix and fiber failure criteria,to establish a microscopic stress field and failure prediction model.The k-means clustering method was used for dimensionality reduction calculation,and an efficient and high-fidelity trans-scale analysis method for composite tanks was proposed.The results of illustrative examples show that the proposed method can accurately predict the elastic constants and failure strength of the composite single-layer plate according to the thermal and mechanical constants of fiber and matrix.The leakage failure process of a composite tank subjected to mechanical-thermal loads was simulated,and the critical load and failure state were given.
式中,T为温度变化量。首先,将1.2节中的周期性边界条件施加于多纤维RVE,确保RVE上节点力的平衡与位移连续。其次,不考虑温度的影响,在线弹性阶段对RVE分别施加6组单位应变载荷,可得到RVE细观应力场。此时,对1组细观应力场中单元应力进行体平均得到等效应力,由等效应力除以施加的单位应变载荷可得到等效刚度矩阵 C 的1列。最后,对其余细观应力场进行计算得到完整的刚度矩阵。由刚度矩阵求逆得到柔度矩阵,根据工程弹性常数与柔度系数的关系[23]可求得材料的等效参数。体平均公式如式(3)所示[6]。
式中:、分别为第k个单元中第i个应力分量与单元体积;N为RVE中总单元数;V为所有单元总体积。若不考虑应变载荷,对RVE施加单位温度载荷,由等效刚度矩阵 C 与式(4)可获得热膨胀系数。
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