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• A micromechanics-based multiscale damage model for 3D woven composites (3DWCs) is proposed. • Interface properties exhibit different effects on tensile and compressive damage mechanisms of 3DWCs. • The interaction of different damage modes controls the overall trend of the tensile strength of 3DWCs. • In contrast, the better the interface properties, the higher the compressive strength of 3DWCs. A multiscale damage model is proposed based on a micro-mesoscale bridging model and a multiscale kinking model, which can predict the damage development processes of 3D woven composites (3DWCs) under different loading conditions using only few material parameters. At the microscale, the various mesoscopic damage modes of yarns, including tensile fiber breakage, compressive fiber kinking and transverse inter-fiber crack, can be simply divided into matrix- and fiber-dominated damage. Using this multiscale damage model, a numerical comparative study is conducted to investigate the effect of interfacial properties on the mechanical performances and damage mechanism of 3DWCs. The numerical results indicate that the interfacial properties exhibit different effects on the tensile and compressive strengths and damage mechanisms of 3DWCs. The interaction of different damage modes controls the overall trend of the tensile strength of 3DWCs. There is an optimum point for the tensile strength of 3DWCs at different interfacial fracture toughness. Beyond the optimum point, the tensile strength of 3DWCs is negatively correlated with interfacial properties. Unlike the tensile loading case, the better the interfacial properties, the later fiber kinking occurs, resulting in higher compressive strength of 3DWCs. [ABSTRACT FROM AUTHOR]

An important element of the process of aircraft certification is the demonstration of the crashworthiness of the structure in the event of an emergency landing on water, also referred to as ditching. Novel numerical simulation methods, that incorporate the interaction between fluid and structure, open up a promising way to model ditching in full scale. This study focuses on two main issues of high-fidelity ditching simulations: the development of a suitable fluid-structure coupling framework and the generation of the structural model of the aircraft. The first issue is addressed by implementing a partitioned coupling approach, which combines a finite volume hydrodynamic fluid solver as well as a finite element structural solver. The developed framework is validated by means of two ditching-like experiments, which consider the drop test of a rigid cylinder and a deformable cylindrical shell. The results of the validation studies indicate that an alternative to the standard Dirichlet-Neumann partitioning approach is needed if a strong added-mass effect is present. For the full-scale simulation of aircraft ditching, structural models become more complex and have to account for damage. Due to its high localization, the damage creates large differences in model scale and usually entails severe non-linearities in the model. To address the issue of increasing computational effort for such models, the process of developing a multi-scale model for the simulation of the failure of fuselage frames is presented.

• The load-bearing capacity of CP, QI and HC laminate structures was tested by indentation test and bulging test. • A multi-scale damage model for SCA method was proposed and the mesh dependency was effectively reduced. • A series of concurrent simulation for the damage process of different laminate structures were conducted with SCA method. • The detailed failure process and enhancement mechanism of HC structure were explained at both macro-scale and micro-scale. The bio-inspired helicoidal structure has been proved to exhibit excellent load-bearing capacity and damage resistance performance. However, there are few relevant researches to analyze its failure process from micro-scale. In this study, three types of carbon fiber reinforced plastics (CFRP) laminate structures were prepared—cross-ply, quasi-isotropic, and helicoidal. The mechanical performance of the laminates was tested using an indentation test. The experiment results verified the excellent mechanical performance of the helicoidal structure. In order to analyze its intrinsic enhancement mechanism, a multi-scale damage model for self-consistent clustering analysis method was proposed, and the damage evolution process of the laminates was simulated at both macro and micro scales. The results indicated that owing to the small rotation angle between adjacent layers in the helicoidal structure, the stress distribution along the thickness direction was more uniform. Moreover, the laminate was more likely to be divided into several sub-laminates by primary delamination. The fibers of each sub-laminate would be cracked in sequence from top to bottom, accompanied by the subprime delamination, resulting in the failure of the laminate. Besides, a twisted crack path could be generated, making the helicoidal structure exhibit excellent load-bearing capacity and damage resistance. [ABSTRACT FROM AUTHOR]

An important element of the process of aircraft certification is the demonstration of the crashworthiness of the structure in the event of an emergency landing on water, also referred to as ditching. Novel numerical simulation methods, that incorporate the interaction between fluid and structure, open up a promising way to model ditching in full scale. This study focuses on two main issues of high-fidelity ditching simulations: the development of a suitable fluid-structure coupling framework and the generation of the structural model of the aircraft. The first issue is addressed by implementing a partitioned coupling approach, which combines a finite volume hydrodynamic fluid solver as well as a finite element structural solver. The developed framework is validated by means of two ditching-like experiments, which consider the drop test of a rigid cylinder and a deformable cylindrical shell. The results of the validation studies indicate that an alternative to the standard Dirichlet-Neumann partitioning approach is needed if a strong added-mass effect is present. For the full-scale simulation of aircraft ditching, structural models become more complex and have to account for damage. Due to its high localization, the damage creates large differences in model scale and usually entails severe non-linearities in the model. To address the issue of increasing computational effort for such models, the process of developing a multi-scale model for the simulation of the failure of fuselage frames is presented. [ABSTRACT FROM AUTHOR]