•Road accidents are one of the major causes of death in the world.•Motorcyclists are less protected when compared to users of some other vehicles, such as car occupants.•Rotational acceleration is a ...mechanism of severe head injuries.•Currently, motorcycle helmet standards do not access rotational acceleration.•Finite Element Method is useful to reconstruct real accidents and predict head injuries.
This paper tries to make an overview of the work carried out by scientific community in the area of road helmets safety. In an area that is constantly being pushed forward by market competition, self-awareness of danger and tighter standards, several research groups around the world have contributed to safety gear improvement.
In this work concepts related to head impact protection and energy absorption are explained. It also makes reference to the theories related to the development of helmets, as well as to the different existing types nowadays. The materials that are typically used in impact situations and new design concepts are also approached. In addition, it is presented a literature review of current – and most commonly used – helmet test standards, along with new tests and helmet concepts to assess the effects of rotational motion.
In a non-restrictive, and never up-to-date report, a state-of-art review on road helmets safety is done, with a special insight into brain injury, helmet design and standards.
•The assessment of crashworthiness properties for impact energy of 500 J for extreme environmental conditions was done.•Five different types of cork material with distinct grain sizes were ...evaluated.•It was proven that cork agglomerates performance is affected by the temperature – the factor, which is especially important for high-energy impacts.•A mathematical Cork Agglomerates Model for Energy Absorption (CAMEA) was introduced.
Agglomerated cork, made from the scraps of wine stoppers, has been finding a wide set of applications due to its excellent thermal and acoustic insulation properties. The random orientation of grains makes the material nearly isotropic, while its dominant viscoelastic behaviour and nearly zero Poisson's ratio make the material also very interesting in applications where dimensional stability is highly demanded. With proven properties, agglomerated cork has been widely used for manufacturing of architectural facades, in civil construction, aerospace engineering and even home appliances production. For outdoor applications, the performance of cork material under different working temperatures is a vital point to be considered. This paper assesses the capability of five different types of cork agglomerates to withstand 500 J impact energy under different temperature conditions. Keeping 11.2 kg impact mass and velocity of 9.2 m/s, impact tests were performed for a wide range of temperatures starting from sub-zero temperature (−30 °C) up to 100 °C in order to cover a full span of working circumstances. Results show significant variations of amount of absorbed energy depending on testing temperature, calling the attention of designers and product developers for important aspects to be considered upon the application of this material under extreme weather conditions.
Shear thickening fluids (STFs) are a unique type of fluids that can quickly transform into a solid-like state when subjected to forces (rate dependent). These fluids are created by dispersing micro ...and nanoparticles within a medium. When the force is removed, they return to their original liquid state. Shear thickening fluids can absorb a significant amount of impact energy, making them useful for reducing vibrations and serving as a damper. This study provides a comprehensive and brief overview of existing literature on shear thickening fluids, including their properties, classification, and the rheological mechanisms behind the shear thickening behaviour. It also examines the use of these fluids in various applications, such as improving resistance to stabs and spikes, protecting against low- and high-velocity impacts, and as a new medium for energy dissipation in industries such as battery safety, vibration control and adaptive structures. Lastly, this work reviews the promising combination of STFs with cork. Given the sustainability of cork and its energy absorption capacity, cork-STF composites are a promising solution for various impact-absorbing applications. Overall, the paper underscores the versatility and potential of STFs, and advocates for further research and exploration.
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•Shear thickening fluids enhance composites energy absorption•Shear thickening colloidal suspensions perform well as sandwich structure interface•Cork composites are highly sustainable•Promising combination of shear thickening fluids with cork composites
In isogeometric analysis (IGA), the functions used to describe the CAD geometry (such as NURBS) are also employed, in an isoparametric fashion, for the approximation of the unknown fields, leading to ...an exact geometry representation. Since the introduction of IGA, it has been shown that the high regularity properties of the employed functions lead in many cases to superior accuracy per degree of freedom with respect to standard FEM. However, as in Lagrangian elements, NURBS-based formulations can be negatively affected by the appearance of non-physical phenomena that “lock” the solution when constrained problems are considered. In order to alleviate such locking behaviors, the Assumed Natural Strain (ANS) method proposed for Lagrangian formulations is extended to NURBS-based elements in the present work, within the context of solid-shell formulations. The performance of the proposed methodology is assessed by means of a set of numerical examples. The results allow to conclude that the employment of the ANS method to quadratic NURBS-based elements successfully alleviates non-physical phenomena such as shear and membrane locking, significantly improving the element performance.
•Assessment of crashworthiness properties for impact energies from 120J to 850J allows expanding the application of the material to a wider range of safety applications.•Three different type of ...agglomerate cork evaluated with 3 distinct grain sizes.•Assessment of temperature influence on agglomerated cork crashworthiness properties.
Impact tests used to certify safety devices are becoming more severe with higher impact energies. Currently, there is a need of liner materials to withstand significant amounts of impact energy without complete deterioration. In addition, these liner materials should have the capacity to keep low accelerations to protect their user. Due to this increasing tendency of having higher impact energies, by using the same liner materials, liners are becoming thicker. Thus, there is also a need for new liner materials that can maintain an adequate thickness in order to permit sophisticated designs. This paper assesses the capacity of three different types of agglomerated cork to withstand large quantities of impact energy. Impact tests with a 9kg impact mass travelling at velocities up to 13.7m/s were performed. These are much higher than the ones required by EU and US safety devices certification standards. Finally, the material performance is evaluated under different temperatures to simulate work in diverse environmental conditions. Results attest the robustness of this natural cellular material in the range of studied conditions. Finally, numerical simulations are performed using finite element analysis in order to check the validity of the developed material model for high impact energies.
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One of the most severe traumatic brain injuries, the subdural haematoma, is related to damage and rupture of the bridging veins, generating an abnormal collection of blood between the dura mater and ...arachnoid mater. Current numerical models of these vessels rely on very simple geometries and material laws, limiting its accuracy and bio-fidelity.
In this work, departing from an existing human head numerical model, a realistic geometry for the bridging veins was developed, devoting special attention to the finite elements type employed. A novel and adequate constitutive model including damage behavior was also successfully implemented.
Results attest that vessel tearing onset was correctly captured, after comparison against experiments on cadavers.
Doing so, the model allow to precisely predict the individual influence of kinematic parameters such as the pulse duration, linear and rotational accelerations in promoting vessel tearing.
•Detailed numerical modeling of the superior sagittal sinus and 9 pairs of bridging veins•Constitutive modeling including elasto-plasticity and ductile damage•Integration into a finite element head model and validation against experiments on cadavers
In this work, a recently proposed quadratic NURBS-based solid-shell element based on the Assumed Natural Strain (ANS) method is applied in the analysis of shell-like structures in the geometrical ...nonlinear regime, together with small strain plasticity. The proposed formulation is based on the additive split of the Green–Lagrange strain tensor, leading to a straightforward implementation of the nonlinear kinematics and to the introduction of a corotational coordinate system, used to integrate the constitutive law, ensuring incremental objectivity. Since the proposed approach is based on Updated Lagrangian formulation combined with a corotational coordinate system, the extension of the ANS methodology is straightforward. Well-known benchmark tests are employed to assess the performance of the proposed formulation and to establish a detailed comparison with the formulations available in the literature. The results indicate that the proposed solid-shell approach based on the NURBS ANS methodology presents good predictability characteristics in the analysis of elasto-plastic thin-shell structures subjected to large deformations.
•The Assumed Natural Strain method for Isogeometric Analysis is proposed.•The formulation proves effective in alleviating locking in shell structures.•The extension to nonlinear problems is straightforward and detailed in the paper.
This paper presents three optimal low-order fully integrated geometrically nonlinear solid-shell elements based on the enhanced assumed strain (EAS) method and the assumed natural strain method for ...different types of structural analyses, e.g. analysis of thin homogeneous isotropic and multilayer anisotropic composite shell-like structures and the analysis of (near) incompressible materials. The proposed solid-shell elements possess eight nodes with only displacement degrees of freedom and a few internal EAS parameters. Due to the 3D geometric description of the proposed elements, 3D constitutive laws can directly be employed in these formulations. The present formulations are based on the well-known Fraeijs de Veubeke–Hu–Washizu multifield variational principle. In terms of accuracy as well as efficiency point of view, the choice of the optimal EAS parameters plays a very critical role in the EAS method, therefore a systematic numerical study has been carried out to find out the optimal EAS parameters to alleviate different locking phenomena for the proposed solid-shell formulations. To assess the accuracy of the proposed solid-shell elements, a variety of popular numerical benchmark examples related to element convergence, mesh distortions, element aspect ratios and different locking phenomena are investigated and the results are compared with the well-known solid-shell formulations available in the literature. The results of our numerical assessment show that the proposed solid-shell formulations provide very accurate results, without showing any numerical problems, for a variety of geometrically linear and nonlinear structural problems.
•Study of distinct cork agglomerates, with different densities and granule sizes.•Static and dynamic (impact) tests compare and fully characterize the materials.•The capacity of the different ...compounds to withstand multiple impacts is studied.•Allow proper material choices using this fully sustainable and recyclable material.
Cork is a natural cellular material capable of withstanding considerable amounts of energy and exhibiting a viscoelastic return to its original shape. This feature is particularly interesting to resist to successive impacts. In this study, the behavior of different types of agglomerated cork (AC) and expanded cork (EC) is investigated under static and dynamic loadings. Double impact was carried out on the samples using a hemispheric actuator. The peak acceleration data for all compounds were further analyzed. Static compression tests gave an interesting insight into the stress–strain curve of agglomerates and Poisson’s ratio variation during deformation. Results demonstrate a clear influence of agglomerated density and grain size on the resulting mechanical properties and point out a tremendous potential for this sustainable material to be tailored to fit diverse crashworthiness applications.
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