The load-bearing capacity of the stiffener runout structure is significantly reduced by interface debonding due to load eccentricity and stiffness discontinuity. This study investigates that failure behavior of the stiffener runout with crack stop bolts under tension load considering the influence of debonding at the skin/stiffener interface. Finite element models of pre-disbonding between stiffener and skin interface of stiffener runout with bolts were established using the ABAQUS platform. The bolt reinforcement area was modeled using the Global Bolted Joint Model (GBJM). The effect of the prefabricated debonding area on the damage initiation and structural load carrying capacity was analyzed, and the bolt transfer loads of the structure with different prefabricated debonding areas were compared. The results demonstrate that the damage initiation load increases with the expansion of the interface debonding area, and the damage load of the structure is almost independent of the interface debonding area. Additionally, the larger the intact area of the stiffener-skin bonding interface, the smaller the total load transferred through the crack stop bolt.
According to the two failure mechanisms of fatigue fracture of fasteners, the fatigue damage evolution equation of microcrack initiation and propagation of fasteners is proposed, and the crack initiation life and crack propagation life models are deduced. After superposition, the fatigue model of fastener fracture failure is obtained. Based on the fatigue test results, two widely used fatigue life models (exponential and power functions) are compared. The results show that the exponential type and power function type only fit the test data without considering the different failure modes of the structure. Based on the failure mechanism, the fitting results of the model are in good agreement with the experimental results, and have great reference value in the design of fatigue structure.
Liquid Composite Molding (LCM) processes are more cost-effective compared to autoclave-cured prepreg, but an independent preforming step is typically required to convert 2D fabric blanks into complex 3D shapes prior to molding. Numerical models are therefore important to predict the formation of defects during the design phase, in order to ensure the quality of final composite components. A macroscopic finite element model was employed to predict the forming behavior of multi-layered biaxial Non-Crimp Fabrics (NCF) during the press tool forming using a hemispherical punch. The forming behavior of the NCF was predicted by simulations considering the bending stiffness of the NCF, enabling fabric wrinkling to be simulated. Simulation results indicate a correlation between fabric wrinkling and the in-plane shear deformation of fabrics. The severity of wrinkles was also influenced by the layup sequence. Compared with the single orientation layups, more wrinkles were predicted for the layup comprising plies stacked at different orientations due to the dissimilar shear deformation between these plies.
Based on digital image correlation method (DIC), the shear stability of two configurations of composite stiffened plates was experimentally studied. The test results show that the buckling load and failure load of I-stiffened panels are 158.2 kN and 282.1 kN respectively, and the main failure models are the debonding of the truss skin interface and skin folding; the buckling load and failure load of M-stiffened panels are 181.9 kN and 292.3 kN respectively, and the main failure modes are consistent with that of T-stiffened panels. Then, a progressive damage failure model of stiffened panels was established to simulate the buckling and post-buckling behaviour. The results show that the buckling mode, buckling load, failure load and failure mode are consistent with the experimental results.
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