Interlaminar stress analysis of honeycomb sandwich panels based on the direct FE ² multiscale method with partitioned variable density RVE placement strategy

The structural strength and failure behavior of honeycomb sandwich panels depend strongly on the mesoscale stress state. Facesheet interlaminar stresses and core shear stresses are key stress components governing facesheet delamination and core shear failure. Equivalent single layer theory has difficulty providing these parameters, whereas fully resolved direct numerical simulation is computationally expensive. This study proposes a multiscale nonuniform computational framework based on Direct FE ² . The framework adopts a stress gradient guided, variable density RVE placement strategy. A higher RVE placement density is assigned to high gradient regions to improve the accuracy of the local stress field, while a lower RVE placement density is used in low gradient regions to control the overall model size and computational cost. To address the mesh mismatch introduced by the nonuniform discretization, an interface tying strategy based on displacement interpolation is developed to ensure continuous transfer of macroscopic deformation across the interface. Static and thermal stress analyses of honeycomb sandwich panels are carried out within this framework. The results show that the proposed method captures facesheet interlaminar stresses and core shear stresses that are difficult to obtain with conventional equivalent models, while significantly improving computational efficiency. The proposed framework provides an efficient and reliable method for refined multiscale analysis of honeycomb sandwich panels.