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Quasi-static axial compression experiments were conducted on the composite thin-walled C-channels with different flange widths. The axial compression failure modes and failure mechanisms were analyzed through CT scanning，and the effects of different flange widths on the axial compression energy-absorption characteristics of C-channels were evaluated by using the energy-absorption indexes. The single-layer shell model and multi-layer shell model of composite C-channel were established，and the finite element models were verified by comparing the failure modes，load-displacement curves and energy-absorption indexes. The results show that the flange width has a significant effect on the axial compression failure modes and energy-absorption characteristics of C-channels. The C-channels with flange widths of 25 mm and 30 mm are failed in the stable and asymptotic manner under the axial compression loads and have good energy-absorption characteristics. The deviation of mean crushing force，energy absorption and specific energy absorption obtained by the multi-layer shell model is within 5%，while that obtained by the single-layer shell model is within 8%，which indicating that the multi-layer shell model of C-channel has the higher simulation accuracy.

For three groups of composite T700/MTM28 C-channels with different ply orientation, the load-displacement curves were obtained by axial crushing test. Based on initial peak load, mean crush load, specific energy absorption and crushing efficiency, the effect of ply orientation on crush deformation mode and energy-absorbing characteristics were investigated. The results show that the stable progressive crushing processes are observed during experiments, and various macroscopic failure modes are also presented, such as interlayer cracking, bending fracture, local buckling and shear failure. The [0/90]3 s specimens absorb the largest energy, the [45/90/-45/0]3 specimens absorb the middle energy, while the [45/-45]3 s specimens absorb the smallest energy. The energy-absorbing characteristics can be improved by reasonable design, such as adding 0° plies and 90° plies to ±45° plies.

To study the crushing energy-absorbing characteristics and failure mode, the multi-shells finite element model of composite thin-walled C-channel specimen was established based on the quasi-static crushing test results. The simulation results show that the delamination failure, local buckling and beam bending failure of C-channel specimen can be simulated with the multi-shells finite element model. The load-displacement curve well fits the test results, and the deviation of initial peak load (Fmax), specific energy absorption (Es) and crushing mean load (Fmean) is small compared with the test results. The initial peak load of C-channel specimen is larger and the load efficiency is lower, so it is necessary to further reduce the initial peak load by the design optimization.

For the demand of crashworthiness verification and certification of composite aircraft structures,a finite element model of fuselage section with waved-plates under cargo floor was suggested,and rigid simplified model of cargo was also developed. The crashworthiness performance was researched under 7 m / s vertical impact velocity. A comparative analysis of failure modes,acceleration response and energy-absorbing characteristics were given for composite fuselage section with and without cargo loading and the analysis were helpful to design and analysis of civil aircrafts. The results show that the energy absorbed by waved-plates is increased because of cargo loading,the acceleration of junction between outside seats and floor for fuselage section with cargo loading are lower than that of fuselage section without cargo loading,and there is no cascading crash scenario.

Polymer composite materials are increasingly used in civil aircraft structures. The failure mode and energy-absorption characteristics of polymer composite structures have garnered significant attention from academia and industry. For thin-walled polymer composite C-channels with layups of [0/90]3s, [45/-45]3s, and [45/90/-45/0]3, low-speed axial compression tests were performed to investigate the failure modes, failure mechanisms, and energy-absorbing characteristics. After parametric studies using [0] and [90] single-element models, stacked shell models of thin-walled composite C-channels were established using the Lavadèze single-layer damage constitutive model, Puck 2000, and Yamada Sun failure criteria. The results show that these thin-walled composite C-channels exhibit a stable progressive crushing process with a local buckling failure mode, encompassing local buckling, fiber break-age, matrix cracks, delamination, and corner cracking. The stacked shell model demonstrates reasonable agreement with the progressive crushing process of thin-walled composites, accurately capturing interlayer matrix failure and interface delamination cracking behavior. A comparison of the specific energy absorption (SEA) and mean crushing force (Fmean) between the simulation and test results yields a difference of less than 6%, indicating a strong correlation between the simulation results and the experimental energy-absorbing characteristics. It also shows that a deep understanding of the parameters is helpful for accurate numerical modeling. [ABSTRACT FROM AUTHOR]

This article discusses important improvements in the sensitivity-based coordination method (SCM) for the optimization of product family or quasi-separable problems. In this method, first presented by Zou et al. [Engineering Optimization 48(7), 2016], the system level coordinates each subsystem based on sensitivity information. Test results suggest that the SCM is robust and efficient; however, for complex engineering problems the computing cost is significant. In this article, the SCM is improved by adopting the optimum sensitivity derivatives as the sensitivity information for global objective F in the system level. The performance of the improved SCM is demonstrated by a numerical test example, and the results show that the solutions and computational efficiency are both improved. The potential of the improved SCM is then demonstrated by structural optimization of the wings of an unmanned aerial vehicle family. The difference between the individual design and family design of wing structures is further investigated. [ABSTRACT FROM AUTHOR]

The single lap joints with different overlap lengths were fabricated by titanium alloy/aramid fiber composites, and their tensile strains and ultimate loads were characterized by DIC and universal testing machine. The effect of overlap length on the bonding properties and failure modes of the single lap joints of dissimilar materials was investigated. The results indicated that the ultimate load of single lap joints increased with an increase of overlap length, but their bonding strength decreased. The joints of high overlap length were damaged progressively. The joints rotation caused by the eccentric bending moment decreased, and the proportion of longitudinal strain area in overlap region was also reduced. Moreover, the fiber-tear failure of the composites increased, but the adhesive failure between the titanium alloy and adhesive layer decreased. In addition, the layer number of the stripped composites increased. [ABSTRACT FROM AUTHOR]