PAPER ENGINEERING SCIENCES; PATHOLOGY/BIOLOGY Gary Nolan, 1 B.Sc. (Hons); Sarah V. Hainsworth, 1 B.Eng. (Hons), Ph.D., C.Eng., C.Sc.; and Guy N. Rutty, 2 M.B.E., M.D. Forces Required for a Knife to Penetrate a Variety of Clothing Types ABSTRACT: In stabbing incidents, it is usual for the victim to be clothed and therefore a knife penetrates both clothes and skin. Clothes (other than leather) have been thought to make little difference to the penetration force. However, there is little quantitative data in the litera- ture. In this study, a range of clothes have been tested, either singly or in layers of, for example, T-shirt and shirt, to quantify the additional force required when clothes are present. A materials testing system has been used to test the penetration force required to stab through clothes into a foam–silicone rubber skin simulant. The results show that the force required can be significantly different, particularly when layers of clothing are penetrated. A cotton t-shirt adds c. 8 N to the penetration force, while a T-shirt and jacket can add an additional 21 N. The results allow a more quantitative assessment of forces required in stabbing. KEYWORDS: forensic science, knife, force, stabbing, clothing Stabbing is the most common method of committing homicide in the United Kingdom. Weapons that are frequently used in such attacks include kitchen knives, utility knives, sheath knives, penknives, scissors, samurai swords, bayonets, screwdrivers, and glass bottles (1,2). Following such incidents, the forensic pathol- ogist is often requested to estimate the degree of force involved (1,3). One factor to be taken into account is how much of an influence the victim’s clothing had on the resistance met to the penetration of the weapon. Some authors have made general observations that clothing can cause differences in the amount of effort [force] required to penetrate skin (4), and although a study by Kemp et al. (5) did contain force data for generic drill and knit fabrics, to the authors knowledge, there is no published quantitative data for how different clothing/fabric types influence the penetration force required for stabbing. To date, the principal area of research into the force required for a weapon/projectile to penetrate clothing has been conducted in the field of protective clothing. This work has been focused on trying to prevent penetration and minimize the severity of injuries. Through this work, fabrics that can be used for protec- tive garments have been considered in detail including their compositions, construction, weave, and also the combinations of these fabrics and the ordering of layering them (6–8). Clearly, the additional force for penetration of protective clothing such as stab vests is considerable. For example, a slash vest consisting of Kevlar and Jersey can require up to 234.4 N to penetrate (6). Despite this work, to our knowledge, no quantitative data have been published investigating the force required for penetration of normal everyday clothing. The aim of the work in this study was to quantify the varying additional amounts of force required for three types of knives to penetrate a variety of nonprotective clothing types and to consider the effect of layering of clothes on penetration. The effect of fabric weave type, number of layers, and knife tip characteristics are considered. This data will allow forensic practitioners to make a more quantitative assess- ment of the significance of clothing on altering the force required for penetration of a knife into the body. This will allow for a more scientific analysis in providing an estimation of the amount of force involved in a stabbing where a victim is wearing clothes. Materials and Methods The experimental protocol and skin simulant listed were simi- lar to that previously published in a study considering the force required for broken glass bottles to penetrate skin (2). A skin simulant was chosen as it is difficult to use human skin within the United Kingdom owing to ethical difficulties and also because it gives highly reproducible results compared with that of animal skin. For the purposes of this study, a skin simulant was more appropriate than using animal skin due to the inherent variability of skin between individuals and within varying areas of an individual’s body. The skin simulant comprised of a combination of foam and silicone rubber, which gives reproducible results that are compa- rable with those of human skin (1,2,9–16). This combination provides a realistic elastic deformation response during penetra- tion, that is, deflecting in a manner similar to that of skin. An open-cell polyether foam with a foam hardness in the region of 125–155 N and a density of 23–28 kg/m 2 was chosen for this 1 Department of Engineering, University of Leicester, University Road, Leicester LE1 7RH, U.K. 2 East Midlands Forensic Pathology Unit, University of Leicester, Robert Kilpatrick Building, Leicester Royal Infirmary, Leicester LE2 7LX, U.K. Received 21 Sept. 2011; and in revised form 17 Jan. 2012; accepted 28 Jan. 2012. 372 © 2012 American Academy of Forensic Sciences J Forensic Sci, March 2013, Vol. 58, No. 2 doi: 10.1111/1556-4029.12031 Available online at: onlinelibrary.wiley.com