Development of a laboratory test for knicker tearing re-creation studies

https://doi.org/10.1016/j.forsciint.2016.02.038Get rights and content

Highlights

  • A laboratory test method has been developed for recreating knicker ripping.

  • Laundering affected the appearance of the garments.

  • Laundering did not affect mechanical properties of the garments.

  • Faster test speeds resulted in higher forces and typically more damage.

Abstract

False sexual assault and rape claims result in wasted forensic and police resources and stigma for the alleged offender. In this work a laboratory method was developed to (i) recreate the ripping of knickers and (ii) measure the force required to rip the garments. The effect of laundering was considered as a means to mimic age of garment, and the effect of speed of ripping was used as a measure of forcible removal of garments. Whilst laundering resulted in visual damage to the thongs, it did not affect the mechanical properties. Faster test speeds resulted in higher measured forces and increased levels of damage. This may allow comment to be made regarding the level of force used during an attack.

Introduction

Sexual assault is the most rapidly growing violent crime [1]. The legal definition of sexual assault in the UK is “A person (A) commits an offence if (a) he intentionally touches another person (B), (b) the touching is sexual, (c) B does not consent to the touching, and (d) A does not reasonably believe that B consents.” [2]. Rape is defined as “A person (A) commits an offence if (a) he intentionally penetrates the vagina, anus or mouth of another person (B) with his penis, (b) B does not consent to the penetration, and (c) A does not reasonably believe that B consents.” [2]. During an alleged sexual assault or rape of a female, knickers are often damaged. Knickers are “a woman's or girl's undergarments covering the body from the waist or hips to the top of the thighs and having leg-holes or separate legs” [3].

In 2013–2014 there were 67,805 sexual offences against children and adults in England and Wales, a reported 21% increase compared to 2012–2013 [4]. Current offences (as opposed to historic offences) accounted for 73% of these instances [4]. Instances of rape increased by 29% (n = 22,116) and other sexual offences by 18% compared to the previous year [4]. In the UK during 2008–2009 nearly 8,000 claims were made for compensation in relation to sexual offences, and involved a total of over £40 million [5]. Internationally, rape is reportedly one of the most under-reported crimes; it has been estimated that only approximately 15% of women who are raped report the attack to the police [4], [6]. Reportedly, 44% of sexual assaults/rapes involve the use of significant force with general body trauma occurring in approximately 70% of cases [7], [8], [9]. Thus sexual assaults/rapes are generally associated with a high level of violence.

A false allegation of sexual assault or rape can be defined as “the intentional reporting of a forcible rape or assault by an alleged victim when none has occurred” [10]. It has been suggested that the frequency of false reports of sexual assault/rape is higher than for any other criminal act e.g. [6], [11].

Females are more commonly subjected to sexual assaults/rape (86%–99% of all reported cases) although male rape is known to be severely under reported [4], [5], [8], [9]. Highest rates occur in the 16 year–25 year age group [8], [9]. The most likely piece of clothing to be presented to textile damage examiners during a sexual assault/rape investigation is the victim's underwear [12], [13]. In the UK, the majority of underwear submitted to LGC's laboratories with respect to sexual assault/rape casework is from females and of the thong (g-string) style [13]. Information on victims’ ages is important as it informs the likely size of knickers worn by victims; therefore national anthropometric data sets are useful. Anthropometric data for 16 year–25 year old women living in the UK are not easily accessible, but a 2009 study cited the mean circumference of a British woman's waist as approximately 870 mm, making the average dress size a UK 16 [14]. However, the same study also stated that the rate of obesity is lower in the 16 years–25 years age range. Therefore, it seems reasonable to assume that a UK female aged 16 years–25 years is likely to wear knickers that are smaller than UK 16.

Ripping of knicker fabrics with reference to alleged sexual assaults has been investigated [15]. Fibre content and age of fabric (described by the number of laundering cycles undergone) affected tearing behaviour. Torn fibre ends appeared similar to those previously observed when examining textile damage caused by sharp-weapon impacts, suggesting investigating fibre end morphology could lead to conflicting information. That fabric properties (including strength) and textile damage to fabrics are affected by laundering is well recognised e.g. [16], [17], [18]. Seam properties are also affected by laundering e.g. [19], [20]. Thus understanding how laundering affects tearing of knickers is critical.

The aim of the work summarised in this paper was to develop a laboratory test to recreate the forcible ripping of knickers.

Section snippets

Materials

White 100% cotton size 12–14 women's thongs1 were used in this work (n = 5 per pack; n = 120 garments). A fibre content/care instruction label was sewn into the left side seam of each garment. The thongs typically measured waist = 650 mm, leg holes = 590 mm and length from the waist band to crotch-seam = 120 mm (Fig. 1). Garments were randomly assigned to one of three different batches for laundering (0, 6, 60 cycles).

Laundering

Garments were laundered using a domestic washing

Physical properties

The effect of laundering on the physical properties of the thongs is summarised in Table 1. Garment mass was not affected by laundering (F2, 117 = 2.23, p = NS). Mean garment mass was 12.52 g (s.d. = 0.51 g). Fabric thickness was affected by laundering (F2, 117 = 136.56, p  0.001). Mean fabric thickness for as-new garments was thinner (0.41 mm, s.d. = 0.02 mm) compared to garments that had been laundered (6 cycles = 0.49 mm, s.d. = 0.03 mm; 60 cycles = 0.49 mm, s.d. = 0.02 mm). This change in thickness was associated

Discussion

There are two points that warrant further discussion (i) the effect of laundering and (ii) the effect of test speed.

Laundering that was representative of thongs being laundered once a week for a year did not affect the force or energy required to initiate tearing, or the maximum force at failure. This was somewhat surprising given the visible degradation of the fabric and seams that was observed using scanning electron microscopy and the loss in mass for garments laundered for 60 cycles

Conclusions

A laboratory test method has been developed to recreate knicker ripping. Whilst laundering resulted in visual damage to the thongs, it did not affect the mechanical properties. This was surprising as previous studies have suggested that laundering affects physical and mechanical properties of fabrics and garment. It may be that the level of fabric degradation due to laundering had not reached a critical level. The method allowed the force required to rip the thongs at different test speeds to

Acknowledgements

The following funding is acknowledged: (i) the receipt of a Winston Churchill Memorial Trust Traveling Fellowship (DJC), (ii) a Cranfield Defence and Security Intern Award (JLM) and (iii) internal funding from the Impact and Armour Group at Cranfield University and The Otago Centre for Electron Microscopy at the University of Otago. The scanning electron microscopy reported in this paper was conducted while DJC was a Winston Churchill Visiting Fellow in the Sir John Walsh Research Institute at

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