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Shear thickening fluids in cork composites for impact mitigation: the role of fumed silica concentration

Oliveira L., Serra G. F., Gürgen S., Novais R. M., de Sousa R. J. Alves, Fernandes F. A. O.

Archives of Civil and Mechanical Engineering

2024

Vol. 24, no. 2

art. no. e92, 2024

Cork composites have shown excellent potential in impact mitigating systems. Their sustainability greatly surpasses the currently used solutions. In addition, recent advances in developing cork composites with shear thickening fluids (STFs) have demonstrated exciting results for impact mitigation. This study explores different STF formulations based on polyethylene glycol (PEG), with a molecular weight of 400 g/mol, and SiO2 particles, investigating their application in layered cork composites for impact mitigation. Different STF formulations are investigated by processing suspensions with different fumed silica concentrations ranging from 10 to 60 wt.%. Using a cone-plate configuration, rheological measurements were conducted on these suspensions, which were then employed as an interfacial layer in agglomerated cork composite layered structures. These hybrid composites were then subjected to 20 J impact tests. PEG 400 exhibited fluid final states for silica concentrations up to 30 wt.% and crystallised at higher concentrations. Based on the results, STF within cork layers was positive regarding impact force reduction, drawing insights for future application of STF suspensions in cork composites for impact mitigation.

Investigation of biomechanics of skull structures damages caused by dynamic loads

Ptak M., Ratajczak M., Kwiatkowski A., Sawicki M., Wilhelm J., Fernandes F. A. O., Druszcz A.

Acta of Bioengineering and Biomechanics

2018

Vol. 20, no. 4

143--150

The aim of the study was to examine the influence of cranial sutures on the crack behaviour of a human skull after the impact. The authors focused on the assessment of skull breaking nature, based on a real-world vehicle-to-bicyclist accident. In the state of the art, there is still no consensus about sutures mechanical properties. Currently, most of the numerical head models do not have distinguished cranial sutures. Methods: The authors compared different elastic properties for cranial sutures and their influence on the nature of the skull fracture. The mathematical and numerical modelling have been applied to mimic the nature of the skull fracture. The LS-DYNA explicit code with material models featuring the erosion of finite elements was used. The models of the skull with different cranial sutures properties were impacted against a validated front-end of a vehicle. Results: Various fracture patterns were obtained for different material properties of the sutures and the results were compared to a model without the cranial sutures. Based on the results, a graph was plotted to indicate differences in sutures energy absorption capabilities. The numerical results were supported by the mathematical modelling. The developed diagram may enable better understanding of the complex mechanical phenomena on the suture interface. Conclusions: Biomechanical evidence was provided for the important role of the sutures in numerical models as well as their significant influence on the biomechanics of skull fractures caused by dynamic loads.