The effect of matrix cracking on hysteresis behavior of cross-ply ceramic matrix composites is investigated in the present analysis. The cracking of cross-ply ceramic composites was classified into five modes, where cracking mode 3 and mode 5 involve matrix cracking and fiber/matrix interface debonding in 0° ply. The matrix crack space and interface debonded length are obtained by matrix statistical cracking model and fracture mechanics interface debonding criterion. Based on the damage mechanisms of fiber sliding relative to matrix in the interface debonded region, the unloading interface reverse slip length and reloading interface new slip length of cracking mode 3 and mode 5 are determined by the fracture mechanics approach. The hysteresis loops of four different cases for cracking mode 3 and mode 5 are derived respectively. The hysteresis loss energy as a function of interface shear stress of mode 3 and mode 5 are analyzed. The theoretical results have been compared with experimental data of two different cross-ply ceramic composites.

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To obtain some basic laws for bird-strike resistance of composite materials in aeronautical application, the high-velocity impact behaviors of composite laminates with different materials were studied by numerical methods. The smoothed particle hydrodynamics (SPH) and finite element method (FEM) coupling models were validated from various perspectives, and the numerical results were comparatively investigated. Results show that the different composite materials have relatively little effect on projectile deformations during the bird impact. However, the impact-damage distributions can be significantly different for different composite materials. The strength parameters and fracture energy parameters play different roles in different damage modes. Lastly, modal frequency was tentatively used to explain the damage behavior of the composite laminates, for it can manifest the mass and stiffness characteristics of a dynamic structure. The dynamic properties and strength properties jointly determine the impact-damage resistance of composite laminates under bird strike. Future optimization study can be considered from these two aspects.

Competing failures are time domain contention situations between the propagated failures (PFs) that originate from dependent components and the failure isolation caused by the trigger component. The methods based on combinatorial analysis commonly used in the analysis of competing failures require a complicated formula derivation and model reduction process. This paper proposes an integrated model based on generalized stochastic Petri nets (GSPNs) for analyzing the competing failures in the system, and further considers the effect of common cause failures (CCFs). The proposed modeling method inherits the advantages of GSPNs and provides a simplified method to compute the reliability of systems, which affect by competing failures and CCFs. Finally, the proposed method is applied in the flight control system (FCS) and demonstrated by the efficient decomposition and aggregation (EDA) method and combinatorial analysis method.

Compared with federated avionic architecture, the integrated modular avionic (IMA) system architecture in the aircraft can provide more sophisticated and powerful avionic functionality, and meanwhile, it becomes structurally dynamic, variably interconnected, and highly complex. The traditional approach such as fault tree analysis (FTA) becomes neither convenient nor sufficient in making safety analysis of the IMA system. In order to overcome the limitations, the approach that FTA combines with generalized stochastic petri net (GSPN) is proposed. First, FTA is used to establish the static model for the top level of the IMA system, while GSPN is used to build a dynamic model for each cell system. Finally, the combination model is generated, which is called the FTGPN model. Moreover, the FTGPN model is made safety analysis with the PIPE2 tool. According to the simulation result, corresponding measures are taken to meet the safety requirements of the IMA system.

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Bird-strike failure of fan blades is one of the basic challenges for the safety of aircraft engines. Simplified slender blade-like plates are always used to evaluate the impact-induced damage mechanism at design stage. One undesirable issue is the failure at the root of clamped slender plates, which cannot recover the real case of twisted blades. For this purpose, three different strategies were exploited to obtain desirable deformation and stress responses, namely the impact location, additional weight, and the boundary condition. Numerical models of the simplified slender blade and the bird projectile were constructed by using finite element method (FEM) and smoothed particle hydrodynamics (SPH) approaches. The impact deformations and stress distributions were comparatively investigated in detail. The numerical results show that changing the boundary condition is the most effective way to obtain preferable impact responses for further failure analysis of real fan blades. Present results will be useful to future experimental design of simplified bird-strike testing.

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