Gilchrist M D, Keenan S, Curtis M, Cassidy M, Byrne G, Destrade M
Centre for Materials & Manufacturing, School of Electrical, Electronic & Mechanical Engineering, University College Dublin, Belfield, Dublin 4, Ireland.
Forensic Sci Int. 2008 May 2;177(1):52-65. doi: 10.1016/j.forsciint.2007.10.010. Epub 2008 Feb 21.
This paper describes the development and use of a biaxial measurement device to analyse the mechanics of knife stabbings. In medicolegal situations it is typical to describe the consequences of a stabbing incident in relative terms that are qualitative and descriptive without being numerically quantitative. Here, the mechanical variables involved in the possible range of knife-tissue penetration events are considered so as to determine the necessary parameters that would need to be controlled in a measurement device. These include knife geometry, in-plane mechanical stress state of skin, angle and speed of knife penetration, and underlying fascia such as muscle or cartilage. Four commonly available household knives with different geometries were used: the blade tips in all cases were single-edged, double-sided and without serrations. Appropriate synthetic materials were used to simulate the response of skin, fat and cartilage, namely polyurethane, compliant foam and ballistic soap, respectively. The force and energy applied by the blade of the knife and the out of plane displacement of the skin were all used successfully to identify the occurrence of skin penetration. The skin tension is shown to have a direct effect on both the force and energy for knife penetration and the depth of out of plane displacement of the skin simulant prior to penetration: larger levels of in-plane tension in the skin are associated with lower penetration forces, energies and displacements. Less force and energy are also required to puncture the skin when the plane of the blade is parallel to a direction of greater skin tension than when perpendicular. This is consistent with the observed behaviour when cutting biological skin: less force is required to cut parallel to the Langer lines than perpendicularly and less force is required to cut when the skin is under a greater level of tension. Finally, and perhaps somewhat surprisingly, evidence is shown to suggest that the quality control processes used to manufacture knives fail to produce consistently uniform blade points in knives that are nominally identical. The consequences of this are that the penetration forces associated with nominally identical knives can vary by as much as 100%.
本文描述了一种用于分析刀刺力学的双轴测量装置的开发与应用。在法医学情况下，通常以定性和描述性的相对术语来描述刺伤事件的后果，而不是进行数值量化。在此，考虑了刀与组织穿透事件可能范围内涉及的力学变量，以确定测量装置中需要控制的必要参数。这些参数包括刀具几何形状、皮肤的平面内机械应力状态、刀具穿透的角度和速度，以及诸如肌肉或软骨等下层筋膜。使用了四种具有不同几何形状的常见家用刀具：所有情况下的刀尖均为单刃、双面且无锯齿。分别使用合适的合成材料来模拟皮肤、脂肪和软骨的反应，即聚氨酯、柔性泡沫和防弹肥皂。刀具刀片施加的力和能量以及皮肤的平面外位移都成功地用于识别皮肤穿透的发生。结果表明，皮肤张力对刀具穿透的力和能量以及穿透前皮肤模拟物的平面外位移深度都有直接影响：皮肤中平面内张力水平越高，穿透力、能量和位移越低。当刀片平面与皮肤张力较大的方向平行时，刺破皮肤所需的力和能量也比垂直时少。这与切割生物皮肤时观察到的行为一致：与垂直切割相比，平行于朗格线切割所需的力更小，并且当皮肤处于更大张力水平时切割所需的力更小。最后，也许有点令人惊讶的是，有证据表明，用于制造刀具的质量控制过程未能在名义上相同的刀具中生产出始终一致的均匀刀尖。其结果是，名义上相同的刀具的穿透力可能相差高达100%。
