Low-Velocity Impacts on a Polymeric Foam for the Passive Safety Improvement of Sports Fields: Meshless Approach and Experimental Validation

Over the past few years, foam materials have been increasingly used in the passive safety of sport fields, to mitigate the risk of crash injury. Currently, the passive safety certification process of these materials represents an expensive and time-consuming task, since a considerable number of impact tests on material samples have to be carried out by an ad hoc testing apparatus. To overcome this difficulty and speed up the design process of new protective devices, a virtual model for the low-velocity impact behaviour of foam protective mats is needed. In this study a modelling approach based on the mesh-free Element Galerkin method was developed to investigate the impact behaviour of ethylene-vinyl acetate (EVA) foam protective mats. The main advantage of this novel technique is that the difficulties related to the computational mesh distortion and caused by the large deformation of the foam material are avoided and a good accuracy is achieved at a relatively low computational cost. The numerical model was validated statistically by comparing numerical and experimental acceleration data acquired during a series of impact events on EVA foam mats of various thicknesses. The findings of this study are useful for the design and improvement of foam protective devices and allow for optimizing sports fields’ facilities by reducing head injury risk by a reliable computational method

Computational simulation of skull fracture patterns in pediatric subjects using a porcine model

In cases of suspected child abuse with skeletal trauma, it is often the role of the injury biomechanist, forensic pathologist, clinical radiologist, and forensic anthropologist to determine the mechanism of injury when the child victims cannot speak for themselves. This is a challenging task, especially for the head, as comprehensive biomechanical data on skull fracture in infants and children do not currently exist, and frequently the determination regarding cause of injury is based on anecdotal evidence from the medical literature and unsubstantiated eyewitness accounts. The current process may result in unreliable autopsy interpretation and miscarriages of justice due to a lack of scientific verification in expert witness testimony. A method to examine the mechanisms of skeletal trauma, specifically skull fracture, in children would be beneficial in providing a solid biomechanical foundation to the forensic investigators in these child abuse cases. Finite element (FE) computational modeling techniques can be used to simulate failure of materials, including biological materials such as bone. However the efficacy of these methods has not been thoroughly tested against a well-defined experimental dataset, particularly for the pediatric population. The specific aims of this study were: (1)To determine appropriate constitutive laws and material properties for the piglet skull and suture, (2) To predict skull fracture patterns in a piglet model using FE methods, and (3) To analyze the sensitivity and robustness of these FE techniques for reliable biomechanical and forensic analysis. Results highlight the ability of macro-scale blunt impact computational models to predict fracture initiation sites and the role of computational models in guiding future experimental work

Development of a 50th Percentile Female Femur Model

This study illustrates the development of a generic femur model representative of a 50th percentile female in terms of geometry, material data, and injury risk curve. A female femur model consisting of 14,520 hexahedral elements was developed, calibrated, and validated. The outer shape and cortical thickness of the femur shaft were adjusted to meet a regression model reported in literature for an average 50 year old female. For the proximal femur, five computed tomography scans were morphed to the target geometry and the mean thickness of the cortical bone was calculated. Material properties for the cortical bone were calculated from experimental data for both tension and compression loading. To validate the proximal femur mode and calibrate an injury risk curve, 15 dynamic drop-tower tests were reproduced. For the validation of the femur shaft, 16 bending tests were simulated. The characteristics of the experimental curves were generally well captured for experiments with normal bone density. Maximum principal strains and 99th percentile strains of the cortical bone at the time of fracture were used to develop risk curves for fractures of the proximal femur and the femur shaft, which were identified as the most relevant femoral injuries in an accident analysis. The model as well as the post-processing scripts are openly available and can be applied or further enhanced by other researchers

Investigation of high rate mechanical properties and damage evolution in porcine liver tissue

Each year, 6.4 million automobile accidents account for approximately 40,000 deaths in the United States. With increasing requirements for automobile safety, computational models capable of simulating organ deformation/ injury during high impact scenarios would be extremely valuable for optimizing safety measures. Accurate experimental data is essential for the accuracy of the models; however, there has been a sparse investigation into high-strain biomechanics which is necessary to address organ/tissue response in high impact scenarios. Damage threshold criterion and damage evolution are other areas that have not been well studied. In vehicular accidents, damage to the liver is the most common cause of death after abdominal injury. High fidelity computational modeling with damage predictor is thus capable of describing liver tissue that is subjected to blunt impact. In this study, we address high strain biomechanics and damage evolution of liver tissue in an effort to generate valuable meaningful FE models

Investigation of high rate mechanical properties and damage evolution in porcine liver tissue

Each year, 6.4 million automobile accidents account for approximately 40,000 deaths in the United States. With increasing requirements for automobile safety, computational models capable of simulating organ deformation/ injury during high impact scenarios would be extremely valuable for optimizing safety measures. Accurate experimental data is essential for the accuracy of the models; however, there has been a sparse investigation into high-strain biomechanics which is necessary to address organ/tissue response in high impact scenarios. Damage threshold criterion and damage evolution are other areas that have not been well studied. In vehicular accidents, damage to the liver is the most common cause of death after abdominal injury. High fidelity computational modeling with damage predictor is thus capable of describing liver tissue that is subjected to blunt impact. In this study, we address high strain biomechanics and damage evolution of liver tissue in an effort to generate valuable meaningful FE models

Pedestrian Head Protection During Car To Pedestrian Accidents: In The Event Of Primary Impact With Vehicle And Secondary Impact With Ground

Current regulations for assessing pedestrian safety use a simplified test setup that ignores many real-world factors. In particular, the level of protection is assessed using a free-motion headform impacting the vehicle\u27s hood at a fixed angle. As such, this test setup does not capture the effect due to the vehicle front-end profile, nor does it comprehend injury due to a possible secondary impact of the pedestrian\u27s head with ground. This thesis aims to numerically simulate vehicle to pedestrian crashes to develop knowledge that may suggest ways to improve safety above and beyond the regulatory tests. Inputs to the simulations include the vehicle front-end profile, impact speed, and pedestrian size. Outputs include the angle of primary head impact to the hood, the extent of head injury (HIC), and whether or not there is a secondary head impact with the ground. One key finding is that head impact angles, and hence head injury measures, vary greatly due to changes in vehicle front-end profile. This suggests that the current test setup for assessing pedestrian head impact, which assumes a fixed head-impact angle, could be improved to better capture the kinematics of real-world pedestrian crash events. One improvement could be the use of a full scale pedestrian dummy or human body model rather than a free motion headform. A second finding is that severity of head injury is much greater in a secondary head impact with ground than in the primary impact with the hood. Moreover, it is possible to avoid the secondary head impact with ground by careful designing of vehicle front-end profile. More research needs to be carried out to prove that concepts developed through numerical simulations also works in physical tests

Desenvolvimento de um modelo computacional do crânio humano

The leading cause of mortality for both children and adults, between the ages of 5 and 29 years old, is road traffic accidents. To better understand the mechanisms that cause them or to develop prevention and detection mechanisms, several finite element models of the human head have been developed, with the YEAHM developed by members of the university of Aveiro. For this reason, the purpose of this dissertation is to improve the YEAHM, in particular the skull, with differentiation between different types of bone tissues, based on the original external geometry, but segmenting it with sutures, diploë and cortical bone, and validating it as a tool to predict cranial fractures. Several validations are performed, comparing the results of the simulation with the experimental results available in the literature at three levels: i) local validation of the material; ii) Isolated skull blunt trauma; iii) Coupled cranio-intracranial structures subjected to three impacts at different speeds, simulating falls. Accelerations, impact forces and fracture patterns are used to validate the skull model.A principal causa de mortalidade de crianças e adultos, entre 5 e 29 anos, são os acidentes de trânsito. Para melhor compreender os mecanismos que os causam ou desenvolver mecanismos de prevenção e deteção, foram desenvolvidos vários modelos de elementos finitos da cabeça humana, como o YEAHM desenvolvido por membros da Universidade de Aveiro. Por esse motivo, o objetivo desta dissertação é a melhoria do YEAHM, em particular o crânio, com diferenciação entre diferentes tipos de tecidos ósseos, com base na geometria externa original, mas segmentando-a com suturas, diploë e osso cortical, e validá-lo como ferramenta para prever fraturas cranianas. Diversas validações são realizadas, comparando os resultados da simulação com os resultados experimentais disponíveis na literatura em três níveis: i) validação local do material; ii) Lesão contusa isolada do crânio; iii) Estruturas crânio-intracranianas acopladas submetidas a três impactos em diferentes velocidades, simulando quedas. Acelerações, forças de impacto e padrões de fratura são usados para validar o modelo do crânio.Mestrado em Engenharia Mecânic

Biomechanics and injury assessment of household falls in children : clinical, anthropomorphic surrogate, and computer simulation studies.

Pediatric short-distance falls, especially from beds or other furniture, are common false histories given by caretakers to cover up abusive trauma. However, short-distance falls are also a common occurrence in young children. Knowledge of the types and severity of injuries that can result from these short falls can aid clinicians in distinguishing between inflicted and non-inflicted injuries. Early detection of abuse may lead to prevention of further escalating injuries and, in some cases, prevent the death of the child. The purpose of this study was to describe relationships between biomechanical measures and injury potential in short-distance household falls. This study involved three components: case-based biomechanical fall assessments, fall simulations using an anthropomorphic test device (ATD), and development/validation of a computer simulation model used to investigate sensitivity of injury outcome measures to fall environment and child surrogate parameters. Overall, the risk of severe or life-threatening injury in short-distance household falls is low. Fractures of the skull and extremities commonly result from these falls (21.5% of falls resulting in Emergency Department visits). 2 of 79 fall cases involved small, contact-type subdural hematomas. These subjects both had unique fall dynamics that contributed to their injuries. Results of ATD experiments supported those from the clinical portion of the study with the exception of neck injury potential. Future studies are needed to both improve ATD neck biofidelity and determine more accurate pediatric neck injury thresholds. Fall environment parameters (fall height and impact surface type) have been shown previously to influence injury potential, but this is the first study to investigate the influence of child or surrogate parameters (body mass index, overall mass, head stiffness, and neck properties) on injury potential. Additionally, through a parametric sensitivity analysis, it was found that fall environment and surrogate parameters that altered fall dynamics had the greatest influence on injury potential. These results highlight the need for obtaining detailed case histories when making injury assessments that include not only environment and child factors, but descriptions of the fall dynamics and orientation of the child upon impact with the ground