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AbstractThe concept of both hierarchy and gradient are incorporated into thin-walled hexagonal tubes for a configuration with optimum crashworthiness and energy absorption. Graded hierarchical hexagonal (GHH) tubes are developed by replacing the corners of an original hexagonal tube with a series of micro hexagonal cells. The total net cross-sectional area as well as the mass are kept the same for all the GHH tubes. The axial crushing behavior of the GHH tubes is investigated in terms of deformation modes, crushing forces and energy absorption. Theoretical solutions are also derived to predict the mean crushing forces (MCFs) of the GHH tubes. Two deformation modes have been identified, a locally layer-by-layer folding deformation (Mode-L) and a globally buckling-like deformation (Mode-G). The hierarchical and graded parameters have significant but quite different influences on the crushing behavior of GHH tubes. The MCF and the specific energy absorption (SEA) can be significantly improved with reasonably hierarchical and graded arrangements, while the initial peak force (PF) remains almost constant. [ABSTRACT FROM AUTHOR]

In order to pursue better crashworthiness and higher energy absorption efficiency, a new type of multi-cell honeycomb (quadri-arc) was designed and followed by a series of numerical studies on in-plane dynamic crushing behavior and energy absorption property under different impact loading. Meanwhile, simulations of a regular circular single-cell honeycomb were also conducted as comparisons. Three distinct deformation modes were identified from the observation of deformation profiles: quasi-static, transition and dynamic, respectively. Simulations indicate that deformation modes are not only influenced by impact velocity but also sensitive to relative density of the honeycomb, based on which a deformation map was summarized. Furthermore, the plateau stress and energy absorption of the quadri-arc honeycomb as well as the circular honeycomb were explored and compared, during which effects of impact velocity and relative density of the honeycomb were discussed in detail. The results show that a much higher plateau stress and better energy absorption efficiency for the quadri-arc honeycomb are predicted compared to the circular honeycomb, especially in the quasi-static case. The investigation suggests that design of the quadri-arc multi-cell will enhance the crashworthiness and energy absorption capacity of honeycombs. [ABSTRACT FROM AUTHOR]

Indentation response and energy absorption property of honeycomb sandwich panels subjected to drop-weight impact under a spherical impactor were investigated. Experiments were conducted using a pendulum-impact system. A three-dimensional finite element model with micro-structure considered was built and validated. In conjunction with experimental and numerical methods, analytical models of indentation response and energy balance specifically aimed to solve problems of low-velocity impact of a spherical indenter on sandwich panels were deduced. Results show that a hemispherical residual dent caused by bending of top face-sheet and core crushing is left on top face-sheet after impact. It also concludes that more than 80% of impact energy is absorbed mostly by top face-sheet and honeycomb core. The main form of energy dissipation is plastic dissipation. In addition, parametric studies were carried out to explore effects of impact energy on impact behavior by altering impact velocity or impactor mass. Different effects are observed for the two approaches and some useful semi-empirical formulations based on both experimental and numerical results are overfitted to estimate the residual dent depth and energy absorbed during a drop-weight impact event on a honeycomb sandwich panel under a spherical impactor. [ABSTRACT FROM AUTHOR]

The mechanical behavior of honeycomb sandwich structures under low-velocity impact is of great significance. An experimental and numerical investigation on surface deformation and energy absorption subjected to low-velocity impact is undertaken. A high-speed camera system is employed to record the acceleration attenuation process of the impactor, a projection profile system is introduced to measure the surface profiles of the panel and the depth of the ultimate indentation is obtained. A three-dimensional finite element model is constructed and validated by the experimental results. Indentation characteristics and energy absorption are analyzed and in good agreement with experimental data. Effect of adhesive layers on energy absorption is discussed and the contribution of the facesheets and the honeycomb core to the energy absorption process is analyzed separately. Results shown that the effect of adhesive layers on energy absorption is non-ignorable and the honeycomb core plays a dominant role in energy absorption. Most of the energy absorbed by the honeycomb sandwich panel is expended as plastic dissipation, and the rest is transformed into strain energy. [ABSTRACT FROM AUTHOR]

• Two types of new classes of hierarchical circular tubes (HCTs) are constructed. • Two deformation patterns are identified, which have different crushing behavior of the HCTs. • The mean crushing force and the specific energy absorption can be significantly improved by choosing suitable hierarchical configurations. • Partial hierarch performs better than the fully compacted one in improving the crashworthiness of the tubes. In this numerical study by means of finite element modeling, the concept of hierarchy is incorporated into thin-walled circular tubes for a configuration with optimum energy absorption. Hierarchical circular tubes (HCTs) are constructed by replacing the wall of an initially single-cell circular tube (SCT) with a series of small tubes placed next to each other (Fully packed, HCT-F) or at a distance apart (partially packed, HCT-P); the total net cross-sectional area and hence the mass is kept the same. The behavior of these new classes of hierarchical tubes under axial crushing is investigated in terms of deformation modes, crushing forces and energy absorption. Two deformation modes are identified and they have different crushing behavior of the HCTs. The initial peak force (PF) remains almost constant after micro-cell tubes are hierarchically introduced, but the mean crushing force (MCF) and hence the specific energy absorption (SEA) can be significantly improved by choosing suitable configurations. It is also demonstrated that partial hierarchy performs better in enhancing the crushing performance of the tubes compared with the full hierarchy. [ABSTRACT FROM AUTHOR]

Triangular lattices were hierarchically incorporated into a regular hexagonal honeycomb to substitute each vertex of the regular honeycomb. To investigate the crushing behaviors of the newly constructed vertex-based hierarchical honeycombs, finite element (FE) analyses were carried out subsequently for both in-plane and out-of-plane crushing. Effect of the hierarchical organizational parameter on deformation mode, crushing response and energy absorption capacity were discussed respectively. The results showed that the hierarchy significantly affected the crushing behaviors of the honeycomb differently for in-plane and out-of-plane crushing. The hierarchy had a far greater influence on the deformation mode for in-plane crushing than out-of-plane crushing. Compared with that of the regular honeycomb, hierarchy not always improved the honeycomb in terms of plateau stress and specific energy absorption (SEA). The maximum plateau stress and SEA of the hierarchical honeycombs increased by up to approximately 127% and 109% respectively under crushing along L direction (in-plane ribbon direction); 122% and 108% respectively under crushing along W direction (in-plane width direction); and 30% and 34% respectively under crushing along T direction (out-of-plane direction). • A novel type of vertex-based hierarchical honeycombs with triangular substructures was introduced. • Hierarchy significantly affected the crushing behaviors for in-plane and out-of-plane crushing differently. • Hierarchy not always improved the honeycombs in terms of plateau stress and energy absorption capacity. • The maximum improvement of crashworthiness performed much better for in-plane crushing than out-of-plane crushing. [ABSTRACT FROM AUTHOR]

• The performances of FML pin joints under in-plane high-speed dynamic loads are analyzed. • The effects of ply stacking sequences on energy absorption efficiency and damage evolution of FML pin joints are revealed. • The dynamic ultimate strength of FML pin joint incorporates contributions from inertia effects. • The design guide about fiber direction in FML pin joint is constructed for an excellent energy absorption efficiency. With fiber reinforced composites widely applied in aerospace, the crashworthiness aspects for aircraft have been an important part of the design. Fiber metal laminate (FML) is a kind of hybrid composite fabricated by fiber reinforced plastic composites and metal layers, showing a potential application on energy absorption. In this work, the damage evolution and energy absorption of FML pin joints are investigated comprehensively. The configurations of FML pin joints with constant geometric parameters are designed to avoid net-tension damage failure in the experiments. The damage evolution processes of specimens are captured by a high-speed camera, and the surface strain is calculated by Digital Image Correlation (DIC) method. Abaqus/Explicit solver is adopted to simulate the mechanical responses of FML pin joint considering ductile damage of metal, damage evolution of composites, and delamination of the interface. The results indicate that the initial dynamic ultimate bearing strength of FML incorporate notable contribution from inertia effects. The average bearing strength associated with energy absorption efficiency is related to the ply stacking sequence of composites. The fiber direction of laminates should be perpendicular to the movement direction of pin as much as possible under the premise that the initial ultimate bearing strength satisfies the design requirement. The results obtained in this work provide comprehensive design guidance for the improvement of crashworthiness in the composite fuselage. [ABSTRACT FROM AUTHOR]