EVIDENCE OF BLUNT FORCE IMPACT ON FABRICS

I've been reading some fascinating and extremely well-written journal articles regarding the forensic evidence of violent crime left on clothing. The following is excerpted from Daroux, et al. [1]

ABSTRACT:
Blunt force assault is a growing issue worldwide. In New Zealand, recorded cases of grievous blunt force assault increased steadily from 1011 in 1999 to 2139 in 2008 [2]. In many cases of blunt force assault victims are struck on parts of their body covered by clothing, yet the use of damage to apparel as forensic evidence largely appears to have been overlooked. The current research investigated blunt force impact
(BFI) damage in common apparel fabrics and the effects prior and post-laundering had on this damage. Two 100% cotton fabrics (single jersey knit, bull drill) were impacted as single and double layers using an impactor representative of a hammer face, the force transmitted through specimens was measured and impulse calculated. Impacting and laundering were completed cumulatively to establish the effects of impact damage on new, dimensionally stable (laundered 6 times) and aged fabrics (laundered up to 30 times), and the effects of laundering on impacted specimens. BFI left recognisable patterns of damage in specimens, although the extent of this damage varied. Laundering after the impact event altered the visible and microscopic damage. Laundering previously impacted fabrics produced holes in some specimens and some fibres exhibited failure characteristic of blunt force impact.

Fig. 5. Typical examples of fibre failure: (a) impacted, not laundered; b–d impacted then laundered fibres (b = example of fibre retaining flattened appearance, little fibrillar separation after laundering, c and d = fibres regained more three-dimensional appearance; c = short, uneven break, perpendicular to fibre axis, d = examples of messy, bulbous and collapsed fibre ends after laundering).

5. Conclusions
BFI can cause recognisable damage in apparel fabrics. Laundering apparel fabrics prior to impacting did not significantly alter the visible damage. Laundering apparel fabrics after impacting did not generally destroy evidence of BFI damage, but rather altered the damage. BFI damage to fabrics varied considerably due to other variables investigated, i.e. fabric structure, number of layers. Further research is required to develop comprehensive knowledge regarding BFI damage in apparel fabrics. Of particular importance would be consideration of incorporating an underlying human
tissue simulant, as fabric damage due to BFI is likely to be significantly affected by the underlying substrate. Different methods can be used to compare BFI damage. The most effective method investigated in this work, but one which needs to be
interpreted with care was SEM.

SOURCES:

1. Daroux, F.Y., Carr, D.J., Kieser, J., Niven, B.E., Taylor, M.C. (2010). Effect of laundering on blunt force impact damage in fabrics. Forensic Science International Vol. 197 (21-29).

2. Statistics New Zealand, New Zealand recorded crime tables, available online at
http://www.stats.govt.nz (14.02.08). [This is a direct reference from the journal article.]

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