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In this study, additively manufactured aluminum thin-walled tubes with different slit dimensions are proposed to improve energy absorption efficiency. A total of 18 samples, which varied in the number of slits, slit length, slit width, and slit ends, were tested under quasi-static axial compression at a rate of 20 mm/min. The deformation and failure modes, load-displacement curves, and a number of crashworthiness factors were investigated. The factors considered included, but were not limited to, the specific energy absorption, crushing force efficiency, and energy absorbed per stroke. The results indicated that all the considered physical parameters, except for the slit ends, had an influence on the crashworthiness of the structures. The initial peak load decreases significantly as the number, width, and length of the slits increase. The bulk of the tested tubes exhibited a crushing force efficiency greater than 0.8. Overall, the presence of slits with length 15 mm and width 5 mm resulted in lower and smoother crushing forces than the straight tubes and, therefore, greater crushing force efficiency, validating them as crashworthy structures. The authors are grateful to the Department of Mechanical and Industrial Engineering at Qatar University for the financial support provided to this research project. Scopus

This paper investigates the influence of multiple surface treatment, including chemical etching and plasma treatments, on the mode I inter-laminar fracture toughness () of aluminum/fiberglass fiber-metal laminates. Laser technology was employed to further enhance aluminum substrate surface morphology to promote micro-mechanical interlocks (MMI) with non-crimp [0°/−45°/90°/+45°] fiberglass/epoxy resin. A vacuum assisted resin transfer molding technique was used to produce the hybrid laminates. Five surface pre-treatments were compared; N2 plasma, O2 plasma, alkaline etch, laser, and laser+N2 plasma. Alkaline etched specimens absorbed the highest energy (237.8%) whereas laser+N2 plasma treated specimens exhibited the highest (73.2%). In addition, when MMI is promoted, the mechanical locks acted as localized obstacles resisting the propagating crack and caused transition of failure mode from adhesive to adhesive-cohesive mixed mode. The authors would like to acknowledge the financial support of the Qatar National Research Fund (a member of Qatar Foundation) through the National Priorities Research Program NPRP # 6 - 292 - 2- 127 . Scopus

Recent polymer and metal additive manufacturing technologies were proven capable of building complex structures with high accuracy. Although their final products differ significantly in terms of mechanical properties and building cost, many structural optimization studies were performed with either one without systematic justification. Therefore, this study investigated whether the Direct Metal Laser Sintering (DMLS) and Fused Deposition Modelling (FDM) methodologies can provide similar conclusions when performing geometrical manipulations for optimizing structural crashworthiness. Two identical sets of four shapes of stiffened hexagonal cells were built and crushed under quasi-static loading. The results were compared in terms of collapsing behavior, load-carrying performance, and energy-absorption capability. Although the observed failure modes were different since the base-materials differ, similar improvement trends in performance were observed between both fabrication approaches. Therefore, FDM was recommended as a fabrication method to optimize thin-walled cellular hexagonal parameters since it was 80% more time-efficient and 53.6% cheaper than the DMLS technique.

Fiber reinforced plastic composites are promising candidates for building the next generation of automotive and aircraft structures. However, these materials are sensitive to any potential impact, which may cause matrix micro-cracking or internal inter-laminar delamination damages. This study provides insights into the sensitivity of braided Carbon/Kevlar round tubes to external damages and neural network-based models that can predict the consequences of damages on the crush-behavior (load-bearing capability). This was investigated by subjecting the tube to transverse low-velocity impacts at different energy levels and locations. Then, these pre-damaged tubes were crushed using a quasi-static compression test. The results indicate that the pre-impact energy levels have a significant effect on the deterioration of both the structure strength and the crush behavior. The locations of the damages are mainly responsible for altering the collapse behavior of the structure rather than its performance. The crush force efficiency is not significantly affected by the pre-impact energy levels, but it is highly affected by the pre-impact/damage locations. The undamaged tubes were collapsed in a progressive manner, whereas splitting and crack propagation were the dominant failure modes in the tubes with residual damages. The path of those cracks was governed by the damage location. Artificial neural network-based models were developed, compared and improved with the objective to model the highly non-linear behavior of the load carrying capacity of the pre-impacted tubes. The developed model successfully provides a quick and accurate assessment at all compression strokes with an MSE of 0.000191 KN.

Thin-walled structures are used for crashworthiness energy absorption applications such as automobile vehciles and aircraft. Structures of sinusoidally corrugated profiles were of great interest because of their ability to reduce the peak crushing forces and provide stable energy-absorbing patterns. Studies on structures of sinusoidally corrugated profiles are limited to numerical studies due to manufacturing limitations. Advancement in additive manufacturing enables the fabrication of structures of complex profiles such as corrugated tubes. This could solve the issue of mass productions of such structures for energy absorption applications. This paper aims to additively manufacture and test sinusoidally corrugated tubes experimentally. A sample of 8 sinusoidally corrugated tubes was additively manufactured and tested under a quasi-static displacement rate of 20 mm/min. The results showed that corrugated tubes exhibit lower and stable crushing forces compared to conventional straight tubes. It was found that increasing the wavelength from 10 to 20 mm results in changing deformation mode from ring to diamond, while increasing the amplitude from 1 to 2 mm has no effect when the thickness is 1 mm. Corrugated tubes achieved a maximum peak force reduction of 75%, and a maximum crushing force efficiency increase of 63%. However, they also resulted in a reduction of 46 and 55% in energy absorption and specific energy absorption, respectively. - 2019 Elsevier Ltd Scopus