Now showing 1 - 5 of 5
  • Publication
    Head Impact Biomechanics Simulations: A forensic tool for reconstructing head injury?
    Establishing the cause of death in forensic investigations can be facilitated by in-depth knowledge of the mechanics of skull fracture and associated lesions to intracranial tissue. Deformation of the skull arising from mechanical impact can lead directly to various soft tissue brain injuries. Advanced simulation techniques, as used in aerospace design and automotive safety, can usefully serve to quantify levels of force associated with skull fracture and with levels of strain or stress associated with brain trauma. Such simulations require physical material failure data so as to ensure predictions are accurate both in relative terms and in absolute quantitative terms. Computer simulations based on multibody dynamics and the finite element method can be used to reconstruct the mechanics of head injury in order to establish the causes of occurrences of skull fracture and TBI.
  • Publication
    Slight compressibility and sensitivity to changes in Poisson's ratio
    (Wiley Blackwell (John Wiley & Sons), 2011-12-12) ; ; ;
    Finite element simulations of rubbers and biological soft tissue usually assume that the material being deformed is slightly compressible. It is shown here that, in shearing deformations, the corresponding normal stress distribution can exhibit extreme sensitivity to changes in Poisson's ratio. These changes can even lead to a reversal of the usual Poynting effect. Therefore, the usual practice of arbitrarily choosing a value of Poisson's ratio when numerically modelling rubbers and soft tissue will, almost certainly, lead to a significant difference between the simulated and actual normal stresses in a sheared block because of the difference between the assumed and actual value of Poisson's ratio. The worrying conclusion is that simulations based on arbitrarily specifying Poisson's ratio close to 1∕2 cannot accurately predict the normal stress distribution even for the simplest of shearing deformations. It is shown analytically that this sensitivity is caused by the small volume changes, which inevitably acy all deformations of rubber-like materials. To minimise these effects, great care should be exercised to accurately determine Poisson's ratio before simulations begin.
      346Scopus© Citations 29
  • Publication
    The mechanical properties of cranial bone: The effect of loading rate and cranial sampling position
    Linear and depressed skull fractures are frequent mechanisms of head injury and are often associated with traumatic brain injury. Accurate knowledge of the fracture of cranial bone can provide insight into the prevention of skull fracture injuries and help aid the design of energy absorbing head protection systems and safety helmets. Cranial bone is a complex material comprising of a three-layered structure: external layers consist of compact, high-density cortical bone and the central layer consists of a low-density, irregularly porous bone structure. In this study, cranial bone specimens were extracted from 8 fresh-frozen cadavers (F=4, M=4; 81±11 yrs old). 63 specimens were obtained from the parietal and frontal cranial bones. Prior to testing, all specimens were scanned using a μCT scanner at a resolution of 56.9μm. The specimens were tested in a three-point bend set-up at different dynamic speeds (0.5, 1 and 2.5 m/s). The associated mechanical properties that were calculated for each specimen include the 2nd moment of inertia, the sectional elastic modulus, the maximum force at failure, the energy absorbed until failure and the maximum bending stress. Additionally, the morphological parameters of each specimen and their correlation with the resulting mechanical parameters were examined. It was found that testing speed, strain rate, cranial sampling position and intercranial variation all have a significant effect on some or all of the computed mechanical parameters. A modest correlation was also found between percent bone volume and both the elastic modulus and the maximum bending stress.
      2520Scopus© Citations 154
  • Publication
    Head impact biomechanics simulations: A forensic tool for reconstructing head injury?
    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.
      662Scopus© Citations 35