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How sharp is sharp? Towards quantification of the sharpness and penetration ability of kitchen knives used in
S V Hainsworth1, R J Delaney, G N Rutty
1Department of Engineering, University of Leicester, Leicester, UK. svh2@leicester.ac.uk
Abstract:
Stabbing is the most common method for violent death in the UK. As part of their investigation, forensic pathologists are commonly asked to estimate or quantify the degree of force required to create a wound. The force required to penetrate the skin and body by a knife is a complex function of the sharpness of the knife, the area of the body and alignment with cleavage lines of the skin, the angle of attack and the relative movement of the person stabbing relative to the victim being stabbed. This makes it difficult for the forensic pathologist to give an objective answer to the question; hence, subjective estimations are often used. One area where some degree of quantification is more tractable is in assessing how sharp an implement (particularly a knife) is. This paper presents results of a systematic study of how the different aspects of knife geometry influence sharpness and presents a simple test for assessing knife sharpness using drop testing. The results show that the radius of the blunt edge at the tip is important for controlling the penetration ability of a kitchen knife. Using high-speed video, it also gives insight into the mechanism of knife penetration into the skin. The results of the study will aid pathologists in giving a more informed answer to the question of the degree of force used in stabbing.
Insights
Forensic pathologists can now better estimate stabbing force by quantifying knife sharpness. This study reveals how knife geometry, like edge radius, impacts penetration, aiding objective wound analysis.
Area of Science:
- Forensic science
- Biomechanics
- Materials science
Background:
- Stabbing is a leading cause of violent death in the UK.
- Forensic pathologists often estimate the force used in stabbings, but this is challenging due to multiple variables.
- Quantifying knife sharpness offers a more objective approach to assessing stabbing force.
Purpose of the Study:
- To systematically study how knife geometry influences sharpness.
- To develop a simple drop test for assessing knife sharpness.
- To provide forensic pathologists with better tools for estimating stabbing force.
Main Methods:
- Investigated the influence of various knife geometry aspects on sharpness.
- Developed and utilized a drop testing method for sharpness assessment.
- Employed high-speed video to analyze the mechanism of knife penetration into skin.
Main Results:
- The radius of the blunt edge at the knife tip is a critical factor in penetration ability.
- Knife sharpness significantly influences the force required for skin penetration.
- High-speed video provided insights into the dynamics of knife-skin interaction.
Conclusions:
- Knife sharpness can be objectively quantified, aiding force estimation in stabbing investigations.
- The study provides a practical method for assessing knife sharpness.
- Findings will help forensic pathologists provide more informed opinions on the force used in stabbing incidents.
