Creep and stress relaxation behavior of cracked CFRP cross-ply laminates

抄録

Predicting the long-term deformation behavior of CFRP laminates is important from the viewpoint of structural durability. In this paper, the behaviors of deformation and crack opening displacement (COD) of cracked CFRP laminates under creep loading or stress relaxation were investigated numerically and theoretically. Finite element analysis (FEA) was used for the numerical analysis, and the viscoelastic continuum damage mechanics (CDM) model predicting effective creep compliances was used for the theory. The maximum COD of a matrix crack in a CFRP cross-ply laminate increases with time both under creep (constant stress) and stress relaxation (constant displacement) conditions. The average longitudinal strain at the surface of the 0-degree layer increases under creep but remains constant under stress relaxation. In contrast, the average strain at the midplane of the 90-degree layer decreases under stress relaxation and increases under creep. However, the incremental creep strain in the 90-degree layer is smaller than decremental relaxation strain in the 90-degree layer and the incremental creep strain in the 0-degree layer. FEA revealed that this behavior is due to the fact that the time variation to longitudinal strain of each layer during creep or stress relaxation is different near the matrix crack and far from the matrix crack. Numerical analysis based on the CDM model supported the reasonability of this behavior.