L‐shaped stiffened composite panels inevitably produce delamination defects during manufacturing and service, which seriously affect the load‐bearing performance of the structure. In the present work, a combination of experimental and numerical simulations was used to investigate the effect of initial delamination defects with three different shapes (lossless, elliptical, and circular) in the skin on the axial compression properties of carbon fiber L‐shaped stiffened composite panels. Furthermore, to predict the damage initiation and evolution process of carbon fiber‐reinforced polymer (CFRP) L‐stiffened plates under compression loading, a progressive damage model (PDM) that combines the Hashin failure criterion and the cohesive zone model (CZM) is proposed. Also, a user‐defined field variable (USDFLD) subroutine based on the Hashin failure criteria is developed in Abaqus software to study the initiation and progression of intra‐laminar damages L‐stiffened panels. Damage initiation and evolution process of skin delamination defects are predicted based on CZM. Finally, the finite element simulation results are in good agreement with the experimental measurements, which confirms the reliability of the finite element models (FEMs).

Composite stiffened panels have become one of the most usual components in the design process of the aircraft's structure due to their splendid mechanical properties in the last decades. The main purpose of this work is investigating and presenting a more precise method to forecast the residual compressive mechanical behavior of the composite stiffened panel. First of all, an axial compression after impact (CAI) test is performed to understand the failure mechanism of different type of L‐shaped stiffened carbon fiber reinforced polymer panels with barely visible impact damage, which is introduced by the low velocity impact test. Subsequently, a finite element model, which contains a quantification damage model, is established in ABAQUS software based on the CAI test results to predict the mechanical behavior of these composite stiffened panels during the CAI test process. Both of the experimental and predicted results demonstrate that the propagation of the delamination caused by LVI is going to exert a destructive influence on the total failure of the composite stiffened panel, and the prediction results of the residual compressive strength of these composite stiffened panels are well consistent to that measured in the CAI test.

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