A 3D modeling of the effect of layup orientation on the thickness uniformity of cured composite L-shaped laminates

This paper presents a three-dimensional modeling approach for the curing process of polymer-matrix composites (PMCs). The presented model could fully characterize the heat transfer, exothermic reactions in resin crosslinking, material time-varying properties, resin flow, and fiber compaction during the curing process. The predicted non-uniform distribution of thickness of the L-shaped composite laminate samples coincides well with experimental results. It is observed that the three-dimensional model, compared to the two-dimensional model, better captures the solidification in complex structural regions, such as the R-corner and the thickness variation region. By comparing the residual stress, fiber volume fraction, and non-uniform thickness of the laminate samples with different layup orientations, the experimental and computational results both show that the corner region of [90]₂₀ laminate is thinner than other regions, with a higher fiber volume fraction. This is attributed to the mismatch of reactive stresses between the tool side and bag side, primarily compressive radial stress. In contrast, the corner region of the [0]₂₀ laminate is thicker than other regions, with a lower fiber volume fraction. This difference is mainly due to the mismatch of radial stresses, hindrance caused by compressive hoop stresses in the compaction process, and potential wrinkling of hoop fibers due to interlaminar shear constraints.