Institute of Forensic Medicine, University of Bern, Bern, Switzerland.
Institute of Applied Physics, University of Bern, Bern, Switzerland.
Int J Legal Med. 2020 Mar;134(2):553-563. doi: 10.1007/s00414-019-02023-2. Epub 2019 Mar 19.
The formation of skull fractures is an important topic in legal medicine. In particular, the influence of boundary conditions is controversially discussed in the literature. A study focusing solely on this aspect was missing. This study aimed to investigate the influence of boundary conditions on the energy threshold for head fractures. Because of the great variability of biological tissue of real skulls, we opted for a head model made from a polyurethane sphere filled with gelatin. Furthermore, we decided to investigate two opposite situations: A fixed configuration where a model was placed on a rigid surface and a (quasi) free boundary configuration where the head model was held at a force of 5 N compensating for gravity. For both configurations, we determined the acceleration signal of the impactor, the force, and the energy threshold for head fracture. It turned out that the fracture forces for both configurations were the same whereas the energy threshold was 11.0 J for the fixed and 13.6 J for the free boundary. The difference seems to be negligible if compared to the effect of varying structural mechanical properties of real human heads. This means that in a forensic case, the two situations most probably cannot be distinguished. To investigate the influence of the impactor mass, we developed a mathematical model and fitted the experimental data. As a result, we found that in the free configuration, a larger mass increases the energy threshold for head fracture. So that in principle, the two configurations are distinguishable.
颅骨骨折的形成是法医学中的一个重要课题。特别是，边界条件的影响在文献中存在争议。缺少专门针对这一方面的研究。本研究旨在调查边界条件对头部骨折能量阈值的影响。由于真实颅骨的生物组织具有很大的可变性，我们选择了一个由充满明胶的聚氨酯球体制成的头部模型。此外，我们决定研究两种相反的情况：一种是模型放置在刚性表面上的固定配置，另一种是头部模型在 5N 的力下保持平衡以补偿重力的（准）自由边界配置。对于这两种配置，我们确定了撞击器的加速度信号、力和头部骨折的能量阈值。结果表明，两种配置的骨折力相同，而固定边界的能量阈值为 11.0J，自由边界的能量阈值为 13.6J。与真实人类头部结构力学性能的变化相比，这种差异似乎可以忽略不计。这意味着在法医学案例中，这两种情况很可能无法区分。为了研究撞击器质量的影响，我们开发了一个数学模型并拟合了实验数据。结果发现，在自由配置中，较大的质量会增加头部骨折的能量阈值。因此，原则上这两种配置是可区分的。
