Faulds Laboratories, Department of Chemical and Forensic Sciences, Keele University, Keele, Staffordshire, UK.
Forensic Sci Int. 2012 Jun 10;219(1-3):76-87. doi: 10.1016/j.forsciint.2011.12.002. Epub 2012 Jan 5.
A detailed understanding of blood droplet impact dynamics and stain formation is an essential prerequisite to the interpretation of both individual bloodstains and spatter patterns. The current literature on theoretical models for the spreading and splashing of liquid drops on surfaces relevant to the forensic context of bloodstain formation has been reviewed. These models have been evaluated for a paper substrate using experimental data obtained as function of droplet size, impact velocity and angle. It is shown that for perpendicular impact there are fairly simple mathematical models for the spreading diameter and the number of scallops or spines formed around the stain though these have quite limited ranges of validity in their basic form. In particular, predictions for the diameter are best for small droplets impacting at high velocity and the number of spines saturates for higher impact velocities. In the case of spreading, a modification to the energy conservation model is found to provide excellent agreement with experimental stain diameters across a wide range of impact velocities. For non-perpendicular impact, the width of stains is found to depend principally on the normal component of impact velocity and may be predicted by an appropriate modification to the expression for the perpendicular case. Limitations in the calculation of impact angle from the stain aspect ratio are identified and a theoretical basis for the prediction of spines around an elliptical stain is proposed. Some key issues for future research are identified which include a systematic, quantitative study of the effect of surface properties on bloodstain formation.
详细了解血滴冲击动力学和血斑形成是解释单个血斑和喷溅模式的必要前提。本文回顾了与法医血斑形成背景相关的表面液滴扩展和飞溅的理论模型的现有文献。使用作为液滴大小、冲击速度和角度函数获得的实验数据对这些模型进行了纸基评估。结果表明，对于垂直冲击，尽管在基本形式下其有效性相当有限，但存在用于扩展直径和围绕斑点形成的脊或刺数量的相当简单的数学模型。特别是，对于高速撞击的小液滴，直径的预测最佳，而对于更高的撞击速度，脊的数量会饱和。在扩展的情况下，发现对能量守恒模型的修改可以在很宽的冲击速度范围内与实验斑点直径提供极好的一致性。对于非垂直冲击，发现斑点的宽度主要取决于冲击速度的法向分量，并且可以通过对垂直情况的表达式进行适当修改来预测。确定了从斑点纵横比计算冲击角度的局限性，并提出了预测椭圆形斑点周围脊的理论基础。确定了一些未来研究的关键问题，包括对表面特性对血斑形成影响的系统、定量研究。
