Sébastien Roth

Finite element analysis of impact and shaking inflicted to a child.

This study compares a vigorous shaking and an inflicted impact, defined as the terminal portion of a vigorous shaking, using a finite element model of a 6-month-old child head. Whereas the calculated values in terms of shearing stress and brain pressure remain different and corroborate the previous studies based on angular and linear velocity and acceleration, the calculated relative brain and skull motions that can be considered at the origin of a subdural haematoma show similar results for the two simulated events. Finite element methods appear as an emerging tool in the study of the biomechanics of head injuries in children.

Biofidelic child head FE model to simulate real world trauma

Biomechanics of human head has been widely studied since several decades. At a mechanical level, the use of engineering allowed investigating injury mechanisms developing numerical models of adult head. For children, the problem is more difficult and evaluating child injury mechanisms using data obtained from scaling adult injury criteria does not account for differences in morphology and structure between adults and children. During growth, child head undergoes different modifications in morphology and structure. The present paper compares the anthropometry and numerical simulations of a child head model based on medical CT scans to a child head model developed by scaling an adult head model using the method proposed by Mertz [H.J. Mertz, A procedure for normalizing impact response data, SAE paper 840884, 1984]. These analysis point out significant differences showing that scaling down an adult head to obtain a child head does not appear relevant. Biofidelic and specific child geometry is needed to investigate child injury mechanisms.

Finite element modelling of paediatric head impact: Global validation against experimental data

Biomechanics of the human head has been widely studied for several decades. At a mechanical level, the use of engineering and finite element (FE) methods has allowed injury mechanisms to be investigated using biofidelic FE models. These models are generally validated using experimental data then used to simulate real-world head trauma in order to derive numerical tolerance limits, leading to efficient injury predicting tools. Due to ethical issues, experimental tests on the paediatric population remain prohibitive so direct validations of numerical models cannot be performed. However injury biomechanics on paediatric population is emerging with experimental tests on the paediatric cadavers or tests on biological tissue and the development of finite element models. The present paper proposes a new finite element model of a newborn head, simulating its main features, with material properties from the literature. Global validation of the model against experimental data in terms of skull deflection is performed and the model is used to simulate paediatric skull fracture coming from real-world head trauma.

Towards child versus adult brain mechanical properties.

The characterization of brain tissue mechanical properties is of crucial importance in the development of realistic numerical models of the human head. While the mechanical behavior of the adult brain has been extensively investigated in several studies, there is a considerable paucity of data concerning the influence of age on mechanical properties of the brain. Therefore, the implementation of child and infant head models often involves restrictive assumptions like properties scaling from adult or animal data. The present study presents a step towards the investigation of the effects of age on viscoelastic properties of human brain tissue from a first set of dynamic oscillatory shear experiments. Tests were also performed on three different locations of brain (corona radiata, thalamus and brainstem) in order to investigate regional differences. Despite the limited number of child brain samples a significant increase in both storage and loss moduli occurring between the age of 5 months and the age of 22 months was found, confirmed by statistical Students t-tests (p=0.104,0.038 and 0.054 for respectively corona radiata, thalamus and brain stem samples locations respectively). The adult brain appears to be 3-4 times stiffer than the young child one. Moreover, the brainstem was found to be approximately 2-3 times stiffer than both gray and white matter from corona radiata and thalamus. As a tentative conclusion, this study provides the first rheological data on the human brain at different ages and brain regions. This data could be implemented in numerical models of the human head, especially in models concerning pediatric population.

Influence of the benign enlargement of the subarachnoid space on the bridging veins strain during a shaking event: a finite element study

There is controversy regarding the influence of the benign enlargement of the subarachnoid space on intracranial injuries in the field of the shaken baby syndrome. In the literature, several terminologies exists to define this entity illustrating the lack of unicity on this theme, and often what is “benign” enlargement is mistaken with an old subdural bleeding or with abnormal enlargement due to brain pathology. This certainly led to mistaken conclusions. To investigate the influence of the benign enlargement of the subarachnoid space on child head injury and especially its influence on the bridging veins, we used a finite element model of a 6-month-old child head on which the size of the subarachnoid space was modified. Regarding the bridging veins strain, which is at the origin of the subdural bleeding when shaking an infant, our results show that the enlargement of the subarachnoid space has a damping effect which reduces the relative brain/skull displacement. Our numerical simulations suggest that the benign enlargement of the subarachnoid space may not be considered as a risk factor for subdural bleeding.

Limitation of scaling methods in child head finite element modelling

During growth, a childs head undergoes different modifications in morphology and structure. This paper presents an anthropometric study in terms of dimension compared to the scaling method developed by Mertz which consists of reducing the adult head model with a scaling coefficient to obtain a child head. A detailed sizes and shape analysis of brain contour in sagittal and frontal plans is then proposed, for child head versus a scaled adult head. The superimposition of those contours allowed pointing to main differences. Numerical simulations performed with the detailed three year old child head model developed in this present study, and a scaled adult head finite element model, showed that reducing an adult finite element model to obtain a child head by scaling method does not seem to be realistic. Then, the creation of specific finite element models of child head seems necessary to understand paediatric injuries.

Child neck FE model development and validation

Despite recent progresses in occupant safety, the protection of children is not still optimal. To offer a better understanding of child injury mechanisms, the present study proposes a human-like finite element model of a three-years-old childs neck. Based on child neck scanner slices, an original and realistic meshing was developed. For validation purposes, the FEM response was superimposed with time corridors available in the literature for different impact cases, which have been scaled down using adapted scale factors from Irwin and Mertz (1997).

Investigations of impact biomechanics for penetrating ballistic cases

This study aims to investigate the penetration of a projectile into a surrogate human tissue numerically, using Finite Element (FE) simulation. 20% Balistic Gelatin material (BG) is simulated with an elasto-plastic hydrodynamic constitutive law, and then impacted by steel spheres at different velocities. The results from the FE simulations are compared with existing experimental data and other analytical equations from the literature. To our knowledge, this is the first study to investigate a projectile penetration by numerical simulation, and then compare the results with analytical and experimental data from previous studies. This developed model gives encouraging results for further investigations of penetrating impact of projectile in the human body.

A first step in finite-element simulation of a grasping task

Abstract This paper investigates a biomechanical aspect of human hand during grasping, using the finite-element method. A realistic three-dimensional finite–element (FE) model of a human hand is developed, including wrist bones, phalanges, soft tissues and skin, reconstructed from medical computed tomography (CT) scan images. Material laws of the literature have been implemented in the model, in order to be able to simulate a simple activity of grasping. In a human design context, this model allows an interesting biomechanical study, which simulates the grasping task in a biofidelic manner. This model is a first step in the modeling of the human hand that can lead to future studies dealing with the interaction of the hand with its environment for the improvement of safety requirements of future products development.

Axis-symmetrical Riemann problem solved with standard SPH method. Development of a polar formulation with artificial viscosity

Abstract This paper presents the development of a cylindrical SPH formulation based on previous study of the literature (Petschek et al) with an explicit formulation for the artificial viscosity. The entire development is explained to propose a formulation adapted to solve Euler equations in the case of a Riemann problem with axis-symmetric conditions. Thus, the artificial viscosity is constructed to find smooth solutions of well-known Riemann problems such as Sod, Noh and Sedov problems. Numerical results are compared to exact solutions and observations are made on numerical parameters influence. This study contributes to validate the axis-symmetrical formulation for pure hydrodynamics tests.