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This work aims to explore crashworthiness of square aluminum/CFRP tubes with different hybrid schemes under quasi-static axial loading condition, and maximize their crashworthiness by performing multi-objective discrete robust optimization design. In the present study, metal/CFRP hybrid tubes with two hybrid schemes and their corresponding individual tubes are manufactured. The crushing process and crashworthiness indictors of all specimens are experimentally investigated under quasi-static axial crushing load. According to the experimental results, the AC hybrid tubes, made of outer aluminum square tube and internally adhered CFRP layers, show excellent energy-absorbing characteristics. Subsequently, numerical simulations are performed for the AC hybrid tubes to further investigate the effects of aluminum wall thickness, CFRP layer number and ply orientation on the energy-absorbing characteristics. It is found that the total energy absorption increases with the increasing tubal wall thickness of aluminum and CFRP layer, and ply orientation makes great contribution to the overall deformation modes and energy-absorbing characteristics of AC hybrid structures. Finally, a multi-objective discrete robust optimization has been conducted to optimize AC hybrid structures for the optimal crashworthy performance. [ABSTRACT FROM AUTHOR]

Metal/composite hybrid thin-walled structures exhibit tremendous merits on the balance design among material costs, weight reduction and mechanical performances. In spite of these advantages, their underlying energy dissipating mechanisms and the influence law of key factors (such as mechanical properties, hybrid ratio, loading angle, etc.) on crushing behavior are still not well illustrated. This study aims to comprehensively explore the crushing deformation characteristics and underlying energy dissipating mechanisms of various square aluminum/CFRP hybrid structures (i.e., aluminum tube internally strengthened with CFRP namely CFRP/AL; aluminum tube externally strengthened with CFRP namely AL/CFRP tubes). Specifically, several axial quasi-static compression tests are performed to compare crushing behavior and performances of between hybrid tubes together with the corresponding net aluminum and CFRP tubes. Experimental results indicate that the total energy absorption of the CFRP/AL hybrid tubes is considerably higher than that of the summation of corresponding individual tubes. Subsequently, finite element models are developed for CFRP/AL hybrid columns to explore the underlying energy-absorbing mechanisms (the contribution of each constituent part on total energy absorption) and the influence law of key factors (mechanical properties, hybrid ratio, loading angle), which cannot be observed from experimental results. Numerical results indicate that the main reasons for the improvement in total energy absorption of CFRP/AL hybrid tubes are the altered deformation pattern of the outer aluminum tube and the significantly increased friction energy. Further, their outer aluminum tube seems to be more likely to generate plastic folding deformation rather than splaying progressive failure mode with increasing initial yield stress. The hybrid ratio and CFRP layer thickness jointly determine the deformation pattern of the CFRP/AL hybrid columns. Finally, it is also found that the load carrying capacity and energy-absorbing characteristics of CFRP/AL hybrid columns gradually reduce with increasing loading angle. The present study is expected to illustrate the potential of such hybrid structure as a crashworthy device and offer some design guidance for application and dissemination. • Crushing behavior of square aluminum/WF-CFRP hybrid structures under axial and oblique loading are investigated. • The underlying energy dissipating mechanisms of square aluminum/WF-CFRP hybrid columns are explored. • The influence mechanisms on crushing behavior of aluminum/WF-CFRP hybrid structures are illustrated. [ABSTRACT FROM AUTHOR]

[Display omitted] • Impacting performances of both single aluminum stringers and aluminum/CFRP hybrid stringers were experimentally and numerically explored. • The energy-absorbing mechanisms of aluminum/CFRP hybrid stringers under impact loads were experimentally, numerically and analytically revealed. • The crashworthiness and lightweight performances of aluminum/CFRP hybrid stringers were optimized through a multi-objectives discrete optimization method accounting for multiple impact angles. Metal/composite hybrid structures exhibit advantages in crashworthiness and lightweightness and have been extended to many fields, including automobile, aerospace, and civil engineering. However, to date, studies on energy-absorbing mechanisms and the design methods of metal/hybrid structures are still insufficient. This study aims to develop an efficient and reliable optimization approach for structural lightweight design of aluminum/CFRP hybrid stringers. Both physical and virtual impact tests of single aluminum stringers and aluminum/CFRP hybrid stringers were carried out. The results show that the total energy absorption of the hybrid stringer are higher than the sum of the single aluminum stringer and the CFRP core. The energy absorption enhancement of the aluminum mainly contributed to the load-carrying improvement of the hybrid stringer because of the reinforcement effects caused by the internal CFRP core. Parametric studies indicate that the crashworthiness performances of the hybrid stringer can be improved by increasing the aluminum thickness, CFRP layer, and foam filling density, but the weight and the cost of the hybrid stringer also increase. The multi-objective discrete optimisation design can provide a cost-efficient approach to better balance the relationships among impact performance and material cost and structure weight for aluminum/CFRP hybrid stringers. [ABSTRACT FROM AUTHOR]

In the present study, thin-walled tubes filled with aluminum foam and CFRP skeleton (FCFTs) are developed and manufactured based on a multiple material system. The structural crashworthiness of the proposed design is investigated under quasi-static lateral loading. Further, the aluminum tube, the foam-filled tube and the tubes filled with CFRP skeleton are also designed and tested to perform a comparative study. It is found that the FCFT-1 (the tube filled with foam and CFRP skeleton with square cells) exhibits superior SEA (specific energy absorption), which is almost five times that of the individual aluminum tube, and almost 10% higher than that of the foam-filled tube. However, FCFT-2 (the tube filled with foam and CFRP skeleton with triangular cells) provides relatively lower energy-absorbing capacity, as its aluminum tube generates several axial cracks during crushing process leading to low deformation level of the foams. Furthermore, crush simulations are conducted to better understand the energy-absorbing mechanisms of the FCFT-1. The numerical results demonstrate that the plastic deformation of the separated foams makes up the major part of the total energy absorption. Besides, the performance improvement of FCFT-1 can be partly attributed to the fact that the separated foams generate larger plastic deformation during crushing process. Apart from this, the increased interaction effects between the separated foams and the CFRP skeleton lead to a higher FE (frictional energy), which also makes a slight contribution to the performance improvement of FCFT-1. Finally, parametric studies are performed to explore the influences of design parameters on the crashworthiness characteristics of FCFT-1. It is indicated that the energy-absorbing capacity can be slightly improved by raising cell number, proportion of 45° layer or foam density. The present work is expected to provide some insights for researchers and engineers to design such structures for energy absorption applications. • Lateral crushing of thin-walled tubes filled with aluminum foam and CFRP skeleton (FCFTs) is investigated. • Energy-absorbing mechanisms of FCFTs are explored. • A parametric study is further conducted to explore the influences of design parameters. [ABSTRACT FROM AUTHOR]