Ricardo J. Alves de Sousa

Head injury predictors in sports trauma--a state-of-the-art review.

Head injuries occur in a great variety of sports. Many of these have been associated with neurological injuries, affecting the central nervous system. Some examples are motorsports, cycling, skiing, horse riding, mountaineering and most contact sports such as football, ice and field hockey, soccer, lacrosse, etc. The outcome of head impacts in these sports can be very severe. The worst-case scenarios of permanent disability or even death are possibilities. Over recent decades, many In recent decades, a great number of head injury criteria and respective thresholds have been proposed. However, the available information is much dispersed and a consensus has still not been achieved regarding the best injury criteria or even their thresholds. This review paper gives a thorough overview of the work carried out by the scientific community in the field of impact biomechanics about head injuries sustained during sports activity. The main goal is to review the head injury criteria, as well as their thresholds. Several are reviewed, from the predictors based on kinematics to the ones based on human tissue thresholds. In this work, we start to briefly introduce the head injuries and their mechanisms commonly seen as a result of head trauma in sports. Then, we present and summarize the head injury criteria and their respective thresholds.

Single point incremental forming simulation with adaptive remeshing technique using solid-shell elements

Purpose – Numerical simulation of the single point incremental forming (SPIF) processes can be very demanding and time consuming due to the constantly changing contact conditions between the tool and the sheet surface, as well as the nonlinear material behaviour combined with non-monotonic strain paths. The purpose of this paper is to propose an adaptive remeshing technique implemented in the in-house implicit finite element code LAGAMINE, to reduce the simulation time. This remeshing technique automatically refines only a portion of the sheet mesh in vicinity of the tool, therefore following the tool motion. As a result, refined meshes are avoided and consequently the total CPU time can be drastically reduced. Design/methodology/approach – SPIF is a dieless manufacturing process in which a sheet is deformed by using a tool with a spherical tip. This dieless feature makes the process appropriate for rapid-prototyping and allows for an innovative possibility to reduce overall costs for small batches, since...

Assessing the effectiveness of a natural cellular material used as safety padding material in motorcycle helmets

The efficiency of cork as a material dedicated to energy absorption under impact loading is studied in the present work. The viability of the application of micro-agglomerate cork (MAC) padding on a motorcycle helmet, is studied using finite element simulations of impact tests, considering the specifications of the European Standard ECE-R.22/05. Expanded polystyrene (EPS) is a widely used material, with excellent results in energy-absorption applications. However, after a first impact, the capability of EPS for energy absorption is significantly decreased, due to the almost total absence of elastic springback. However, cork is a material characterized by having both a good energy-absorption capability and high elastic return, due to its viscoelastic behavior, meaning that its capacity to keep absorbing energy is almost unchanged after the first impact. In this work, a three-dimensional numerical model of the helmet–head system is developed, including the outer shell, safety padding and the head, together with its interactions and constitutive models suitable for the analyzed materials. Results show that the developed models can adequately reproduce the behavior of EPS and MAC, in the context of a preliminary analysis. The referred helmet–headform is then submitted to impacts at different points, as specified by the European Standard. The results from helmeted impacts with EPS padding are compared against experimental values. The application of MAC in the protective padding of the helmet is studied and the results, concerning the acceleration of the gravity center of the head, Head Injury Criterion (HIC) values and kinetic energy are presented. Results obtained with EPS and MAC are compared and discussed. Concerning cork, although the maximum acceleration values of the headform and the HIC values were not verified to be within the established limits of the regulatory standard, the results are promising, launching a sound basis for a more thorough work on the application of cork as a new material for advanced applications as an energy-absorption system.

Testing single point incremental forming molds for thermoforming operations

Low pressure polymer processing processes as thermoforming or rotational molding use much simpler molds then high pressure processes like injection. However, despite the low forces involved with the process, molds manufacturing for this operations is still a very material, energy and time consuming operation.The goal of the research is to develop and validate a method for manufacturing plastically formed sheets metal molds by single point incremental forming (SPIF) operation for thermoforming operation. Stewart platform based SPIF machines allow the forming of thick metal sheets, granting the required structural stiffness for the mold surface, and keeping the short lead time manufacture and low thermal inertia.

Computer Simulations for Head Injuries Verification After Impact

The paper describes an experimental and numerical approach to head injury verification occurring in transportation accidents. Current trends in pedestrian, cyclist and motorcyclist safety are presented and some state-of-the-art techniques are included to mitigate injuries, which occur when an external force traumatically damages the brain. Finally, a finite element analysis was conducted to assess the safety performance of a commercial motorcycle helmet.

Evaluation of the Enhanced Assumed Strain and Assumed Natural Strain in the SSH3D and RESS3 Solid Shell Elements for Single Point Incremental Forming Simulation

Single Point Incremental Forming (SPIF) is a recent sheet forming process which can give a symmetrical or asymmetrical shape by using a small tool. Without the need of dies, the SPIF is capable to deal with rapid prototyping and small batch productions at low cost. Extensive research from both experimental and numerical sides has been carried out in the last years. Recent developments in the finite element simulations for sheet metal forming have allowed new modeling techniques, such as the Solid Shell elements, which combine the main features of shell hypothesis with a solid-brick element. In this article, two recently developed elements -SSH3D element [1, 2] and RESS3 element [3]- implemented in Lagamine (finite element code developed by the ArGEnCo department of the University of Liège) are explained and evaluated using the SPIF line test. To avoid locking problems, the well-known Enhanced Assumed Strain (EAS) and Assumed Natural Strain (ANS) techniques are used. The influence of the different EAS and ANS parameters are analized comparing the predicted tool forces and the shape of a transversal cut, at the end of the process. The results show a strong influence of the EAS in the forces prediction, proving that a correct choice is fundamental for an accurate simulation of the SPIF using Solid Shell elements.

Development of a One Point Quadrature EAS Solid‐Shell Element

A correct reproduction of thickness effect can be accurately described by the use of three‐dimensional solid elements. In addition to convenient formulation for constitutive law, solid element provides a straightforward extension to geometrically non‐linear problems, particularly in the presence of large rotations, since only translational degrees of freedom are involved. Also, compared with shell elements, it is valid to consider double‐sided contact because of real physical nodes on top and bottom surfaces without any further modification. However, for low order elements, as thickness/length ratio value tends to zero, the transverse shear‐locking phenomenon becomes more evident. Also, plasticity leads to isochoric deformation, which is the main source of the volumetric locking phenomenon. Concerning bending dominant problems, it is difficult to use a single layer of solid elements due to the limitation of integration points along thickness direction. Multi‐layered solid element increases the CPU time dr...

Development and validation of a new finite element human head model: Yet another head model (YEAHM)

Purpose Currently, there are some finite element head models developed by research groups all around the world. Nevertheless, the majority are not geometrically accurate. One of the problems is the brain geometry, which usually resembles a sphere. This may raise problems when reconstructing any event that involves brain kinematics, such as accidents, affecting the correct evaluation of resulting injuries. Thus, the purpose of this study is to develop a new finite element head model more accurate than the existing ones. Design/methodology/approach In this work, a new and geometrically detailed finite element brain model is proposed. Special attention was given to sulci and gyri modelling, making this model more geometrically accurate than currently available ones. In addition, these brain features are important to predict specific injuries such as brain contusions, which usually involve the crowns of gyri. Findings The model was validated against experimental data from impact tests on cadavers, comparing the intracranial pressure at frontal, parietal, occipital and posterior fossa regions. Originality/value As this model is validated, it can be now used in accident reconstruction and injury evaluation and even as a design tool for protective head gear.

Biomechanical investigation of impact induced rib fractures of a porcine infant surrogate model.

This study investigated the structural, biomechanical and fractographic features of rib fractures in a piglet model, to test the hypothesis that fist impact, apart from thoracic squeezing, may result in lateral costal fractures as observed in abused infants. A mechanical fist with an accelerometer was constructed and fixed to a custom jig. Twenty stillborn piglets in the supine position were impacted on the thoracic cage. The resultant force versus time curves from the accelerometer data showed a number of steps indicative of rib fracture. The correlation between impact force and number of fractures was statistically significant (Pearson׳s r=0.528). Of the fractures visualized, 15 completely pierced the parietal pleura of the thoracic wall, and 5 had butterfly fracture patterning. Scanning electron microscopy showed complete bone fractures, at the zone of impact, were normal to the axis of the ribs. Incomplete vertical fractures, with bifurcation, occurred on the periphery of the contact zone. This work suggests the mechanism of rib failure during a fist impact is typical of the transverse fracture pattern in the anterolateral region associated with cases of non-accidental rib injury. The impact events investigated have a velocity of ~2-3m/s, approximately 2×10(4) times faster than previous quasi-static axial and bending tests. While squeezing the infantile may induce buckle fractures in the anterior as well as posterior region of the highly flexible bones, a fist punch impact event may result in anterolateral transverse fractures. Hence, these findings suggest that the presence of anterolateral rib fractures may result from impact rather than manual compression.

SPIF of brass alloys: Preliminary studies

This article discusses the preliminary studies of the Single Point Incremental Forming (SPIF) process applied brass alloy Cu-35Zn, with different sheet thicknesses and formed geometries. Despite being a material widely used in industry, with excellent cold formability, there is still no relevant research on this material concerning SPIF. As a result of these preliminary studies, the necessary forces (F) during the process, the true strain (e1, e2) and maximum wall angle (ψ) supported by materials are presented and discussed.