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This paper presents a multiscale progressive fatigue damage model to predict the fatigue life of composite laminates. The multi-level damage model was employed considering the interfacial debonding effect, and effective material properties were calculated through homogenization. Damage variables and damage slopes were defined at the constituent level, and fatigue damage parameters were obtained using the residual stiffness data with the chaotic firefly algorithm. The model was implemented into ABAQUS, then validated with flat-bar and pin-loaded specimens of AS4/3501-6 composite. The numerical results corresponded well with the experimental data and showed the ability to capture the failure propagation of composite laminates. [ABSTRACT FROM AUTHOR]

This paper presents a progressive fatigue damage model to predict the damage progress and the fatigue life of composite laminates under cyclic loading. First, the maximum stress criterion was applied in the fiber direction for fiber failure (FF), and Puck's failure criteria were employed in the matrix direction in which the fracture plane is defined to determine the inter-fiber fracture (IFF). Next, material degradation rules consisting of strength and stiffness degradation were derived, and different degradation rules according to the presence of failure and failure mode were utilized for each material. The proposed model was implemented into the UMAT subroutine of ABAQUS for the finite element (FE) analysis with tension–tension cyclic loading. Finally, the progressive fatigue damage model was validated with flat-bar specimens with various lay-ups ([0]8, [90]8, [30]16, [02/902]s, [0/902]s, [0/904]s) and compared with the experimental data of static and fatigue tests. The fatigue life prediction was also conducted on the pin-loaded quasi-isotropic (QI) laminates. The simulation results showed a good agreement with the experimental data and the ability to capture the damage progress of composite laminates during their lifetime. [ABSTRACT FROM AUTHOR]

In this study, an Electromagnetic (EM) wave-absorbing composite structure design is proposed. The conventional composite EM wave absorber contains lossy fillers for dielectric characteristics, and thus the fillers affect the mechanical properties, which determine the structural performance of the composite itself. The newly proposed EM wave absorber uses a combination of the following two components: the load-bearable composite structure as the 'shell' and the EM wave-absorbing back layer as the 'absorber.' The shell type absorber does not use any additional fillers in the composite structure. However, the absorbing layer that is designed with a periodic patterned layer and low lossy foam exhibits good EM wave-absorbing performance. Design, analysis with computational simulation, and measurement of EM characteristics are performed to verify the advantages of the shell type absorber. Furthermore, the EM wave absorber is adopted in the leading edge of an aircraft to identify the contribution of Radar Cross Section reduction. This type of absorber has various applications in aerial vehicles, and the EM characteristics are widely tunable for specific purposes without changing the original shell structure. [ABSTRACT FROM AUTHOR]