A new test set-up for skull fracture characterisation (original) (raw)
Related papers
2014
With the mortality, disability and socioeconomic costs associated with head injury, head impact biomechanics is important to developing injury criterions and safety tolerances. However, the current state of knowledge is contradictory and vague. This thesis will contribute to research done on the vibrational response of the head to impact by discussing two studies. The first will describe the design, implementation and validation of a head impactor setup specific for the study of the frequency response of the skull. An impactor capable of producing sub-5ms duration, sub-fracture impacts was successfully designed. The apparatus was validated by comparing the results of a protocol to the results published in established literature and a repeatability study was done to prove the repeatability and reproducibility of the impactor. The second part discusses the effects of various factors on the frequency response of the head. Strain gauge data were transformed to the frequency domain and frequency peaks were extracted. Resonant frequencies were then identified by a cluster analysis. ANOVA tests were used to determine the significance of factors on changes to the frequency response. Individual specimen differences were found to have a significant effect on the vibrational response observed, whereas the impact location was found to effect the frequency power ratios only, and not the resonant frequency values. The presence of fracture was also found to have an effect on the overall vibrational response, however the impact energy was not found to have a significant effect.
Biomechanics of Frontal Skull Fracture
Journal of Neurotrauma, 2007
The purpose of the present study was to investigate whether an energy failure level applies to the skull fracture mechanics in unembalmed post-mortem human heads under dynamic frontal loading conditions. A double-pendulum model was used to conduct frontal impact tests on specimens from 18 unembalmed post-mortem human subjects. The specimens were isolated at the occipital condyle level, and pre-test computed tomography images were obtained. The specimens were rigidly attached to an aluminum pendulum in an upside down position and obtained a single degree of freedom, allowing motion in the plane of impact. A steel pendulum delivered the impact and was fitted with a flat-surfaced, cylindrical aluminum impactor, which distributed the load to a force sensor. The relative displacement between the two pendulums was used as a measure for the deformation of the specimen in the plane of impact. Three impact velocity conditions were created: low (3.60+/-0.23 m/sec), intermediate (5.21+/-0.04 m/sec), and high (6.95+/-0.04 m/sec) velocity. Computed tomography and dissection techniques were used to detect pathology. If no fracture was detected, repeated tests on the same specimen were performed with higher impact energy until fracture occurred. Peak force, displacement and energy variables were used to describe the biomechanics. Our data suggests the existence of an energy failure level in the range of 22-24 J for dynamic frontal loading of an intact unembalmed head, allowed to move with one degree of freedom. Further experiments, however, are necessary to confirm that this is a definitive energy criterion for skull fracture following impact.
The objective of this study was to determine the responses of 5th-percentile female, and 50th- and 95thpercentile male human heads during lateral impacts at different velocities and determine the role of the stiffness and shape of the impacting surface on peak forces and derived skull fracture metrics. A state-of-the-art validated finite element (FE) head model was used to study the influence of different population human heads on skull fracture for lateral impacts. The mass of the FE head model was altered to match the adult size dummies. Numerical simulations of lateral head impacts for 45 cases (15 experiments X3 different population human heads) were performed at velocities ranging from 2.4 to 6.5 m/s and three impacting conditions (flat and cylindrical 90D; and flat 40D padding). The entire forcetime signals from simulations were compared with experimental mean and upper/lower corridors at each velocity, stiffness (40 and 90 durometer) and shapes (flat and cylindrical) of the impacting surfaces. Average deviation of peak force from the 50th male to 95th male and 5th female were 6.4% and 10.6% considering impacts on the three impactors. These results indicate hierarchy of variables which can be used in injury mitigation efforts.
Military Medicine
Military combat helmets protect the wearer from a variety of battlefield threats, including projectiles. Helmet back-face deformation (BFD) is the result of the helmet defeating a projectile and deforming inward. Back-face deformation can result in localized blunt impacts to the head. A method was developed to investigate skull injury due to BFD behind-armor blunt trauma. A representative impactor was designed from the BFD profiles of modern combat helmets subjected to ballistic impacts. Three post-mortem human subject head specimens were each impacted using the representative impactor at three anatomical regions (frontal bone, right/left temporo-parietal regions) using a pneumatic projectile launcher. Thirty-six impacts were conducted at energy levels between 5 J and 25 J. Fractures were detected in two specimens. Two of the specimens experienced temporo-parietal fractures while the third specimen experienced no fractures. Biomechanical metrics, including impactor acceleration, were obtained for all tests. The work presented herein describes initial research utilizing a test method enabling the collection of dynamic exposure and biomechanical response data for the skull at the BFD-head interface.
Journal of the Mechanical Behavior of Biomedical Materials, 2016
The objective of this study was to enhance an existing finite element (FE) head model with composite modeling and a new constitutive law for the skull. The response of the state-ofthe-art FE head model was validated in the time domain using data from 15 temporoparietal impact experiments, conducted with postmortem human surrogates. The new model predicted skull fractures observed in these tests. Further, 70 well-documented head trauma cases were reconstructed. The 15 experiments and 70 real-world head trauma cases were combined to derive skull fracture injury risk curves. The skull internal energy was found to be the best candidate to predict skull failure based on an in depth statistical analysis of different mechanical parameters (force, skull internal energy), head kinematicbased parameter, the head injury criterion (HIC), and skull fracture correlate (SFC). The proposed tolerance limit for 50% risk of skull fracture was associated with 453 mJ of internal energy. Statistical analyses were extended for individual impact locations (frontal, occipital and temporo-parietal) and separate injury risk curves were obtained. The 50% risk of skull fracture for each location: frontal: 481 mJ, occipital: 457 mJ, temporo-parietal: 456 mJ of skull internal energy.
A study of the response of the human cadaver head to impact
2007
High-speed biplane x-ray and neutral density targets were used to examine brain displacement and deformation during impact. Relative motion, maximum principal strain, maximum shear strain, and intracranial pressure were measured in thirty-five impacts using eight human cadaver head and neck specimens. The effect of a helmet was evaluated. During impact, local brain tissue tends to keep its position and shape with respect to the inertial frame, resulting in relative motion between the brain and skull and deformation of the brain. The local brain motions tend to follow looping patterns. Similar patterns are observed for impact in different planes, with some degree of posterior-anterior and right-left symmetry. Peak coup pressure and pressure rate increase with increasing linear acceleration, but coup pressure pulse duration decreases. Peak average maximum principal strain and maximum shear are on the order of 0.09 for CFC 60 Hz data for these tests. Peak average maximum principal strain and maximum shear increase with increasing linear acceleration, coup pressure, and coup pressure rate. Linear and angular acceleration of the head are reduced with use of a helmet, but strain increases. These results can be used for the validation of finite element models of the human head.
Biomechanical Aspects of Blunt and Penentrating Head Injuries
Solid Mechanics and Its Applications, 2005
The objective of this presentation is to discuss certain biomechanical aspects of head injuries due to blunt and penetrating impacts. Emphasis is given to fundamental data leading to injury criteria used in the United States (US) regulations for motor vehicle safety. Full-scale and component tests done under US Federal Motor Vehicle Safety Standards (FMVSS) are described. In addition, results providing occupant safety and vehicle crashworthiness information to the consumer from frontal and lateral impact crash tests are discussed with an emphasis on head injury assessment and mitigation. Recent advancements are presented in angular acceleration thresholds for quantifying brain trauma. In the area of penetrating impact, newer experimental techniques are described for a better understanding of head injury secondary to penetrating impacts, with specific reference to the civilian population.
Head impact biomechanics simulations: A forensic tool for reconstructing head injury?
Legal Medicine, 2009
This paper describes a computer simulation method, which is used widely in engineering design and accident investigation reconstructions, which could constitute a valuable forensic tool for investigating cases of head impact injury and skull fracture. This method, the finite element method, relies on knowing the physical properties and strength of biological materials, including cranial bone and neural tissue, and on having evidence of the extent of head injuries in order to deduce causative forces. This method could help forensic pathologists to infer causes of skull fracture and to determine whether probable causes of fracture were accidental or intentional.