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Head

This section of the documentation is under development

This section is being updated

Bones

The skull, mandible and teeth were modelled as 1 mm shells, originally with material model MAT_RIGID and properties according to data for cortical bone 1, density 2.e-6, Young's modulus 17.1 GPa, and poisson ratio 0.3. However, ist was identified that this has led to too high HIC values when impacting rigid surfaces. Therefore, the material was changed to a deformable material, which was calibrated using the drop tests published by Loyd et al., 2014 2. As a preliminary fix, the nodes that were originally connected to the full skull (accelerometer and added mass), are now connected to the mandible. This should be updated in the future.

Soft tissues

Skin

The head skin is modelled using 1mm membrane elements (ELFORM=9), with material model MAT_FABRIC with stress-strain curves based on 3 (across the tibial direction). Further, Young's modulus for the skin was set to 1 MPa (roughly the slope of the initial part of the non-linear curve) for both material directions and poisson's ratio to 0.49 (assumed close to incompressible). Shear modulus was set to 0.33MPa (based on isotropic assumption). Compressive stresses were eliminated CSE=1. The stiffness of the "liner" were set to 1E-6 GPa (to not contribute to the overall stiffness). A rayleigh damping coefficient of 0.05 (recommended according to the LS-DYNA manual) was used. For the density a value of 1E-6 was assumed for the skin.

The eyelids were modelled using 1 mm thick, fully integrated shells, using material model MAT_ELASTIC with parameters; density 1e-6, Young's modulus 2MPa and poisson ratio 0.3.

Scalp

The scalp was modelled using solid elements with material model MAT_OGDEN_RUBBER based on Wood et al., 2010 4

Oral cavity

The oral cavity was modelled using solid elements with material model MAT_OGDEN_RUBBER, with material parameters according to 5

Adjustment of mass and inertia

Six discrete mass elements, aligned along the principal axes (crossing at the head CoG), were used to adjust the total mass and principal inertias of the head. Using the sex parameter different masses were assigned for 50F and 50M. The mass and inertia properties were taken from 6, with original data from 7.

Sex Mass [kg] Ixx [kgmm^2] Iyy [kgmm^2] Izz [kgmm^2] CGx* [mm] CGz* [mm]
Female 3.82 16955 18392 12226 0.2 29.1
Male 4.42 21491 23323 15489 1.3 26.4

* Relative to tragion

References

  1. Donald T. Reilly and Albert H. Burstein. The elastic and ultimate properties of compact bone tissue. Journal of Biomechanics, 86:393–405, jan 1975. doi:10.1016/0021-92907590075-5. ↩

  2. Andre Matthew Loyd, Roger W. Nightingale, Yin Song, Jason F. Luck, Hattie Cutcliffe, Barry S. Myers, and Cameron ‘Dale’ Bass. The response of the adult and atd heads to impacts onto a rigid surface. Accident Analysis & Prevention, 72:219–229, 2014. URL: https://www.sciencedirect.com/science/article/pii/S000145751400195X, doi:https://doi.org/10.1016/j.aap.2014.06.022. ↩

  3. J.F.M. Manschot and A.J.M. Brakkee. The measurement and modelling of the mechanical properties of human skin in vivo—II. the model. Journal of Biomechanics, 197:517–521, jan 1986. doi:10.1016/0021-92908690125-9. ↩

  4. Garrett W Wood, Matthew B Panzer, Cameron R Bass, and Barry S Myers. Viscoelastic properties of hybrid iii head skin. SAE International Journal of Materials and Manufacturing, 31:186–193, apr 2010. URL: https://doi.org/10.4271/2010-01-0383, doi:https://doi.org/10.4271/2010-01-0383. ↩

  5. Kristofer Engelbrektsson. Evaluation of material models in ls-dyna for impact simulation of white adipose tissue. Master's thesis, Chalmers University of Technology, 2011. ↩

  6. Narayan Yoganandan, Frank A. Pintar, Jiangyue Zhang, and Jamie L. Baisden. Physical properties of the human head: mass, center of gravity and moment of inertia. Journal of Biomechanics, 429:1177–1192, jun 2009. doi:10.1016/j.jbiomech.2009.03.029. ↩

  7. John A Plaga, Chris Albery, Mark Boehmer, Chuck Goodyear, and Glenn Thomas. Design and development of anthropometrically correct head forms for joint strike fighter ejection seat testing. Technical Report, AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH HUMAN EFFECTIVENESS DIRECTORATE, 2005. ↩