Investigating bloodstain dynamics at impact on the technical rear of fabric
2019
Dicken, L. | Knock, C. | Carr, D.J. | Beckett, S.
Using high speed video, the impact of blood drops falling at three velocities (1.9, 4.2 and 5.8ms−1) were filmed from both the technical face and for the first time the technical rear of three different mass per unit areas (85.1, 163.5 and 224.6g/m²) of 100% cotton calico. It was seen that there were two stages in the creation of a bloodstain on fabric; the impact dynamics, followed by wicking along the intra-yarn spaces. In the first stage, once the blood impacted the fabric, blood was visible on the technical rear of the fabrics with the medium and lightest mass per unit area within as little as 0.067ms after impact. No blood was visible on the technical rear of the fabric with the heaviest mass per unit area following impact or the medium mass per unit area from 1.7ms−1 impacts. On the technical face of the fabric, the blood drop spread laterally and then receded for 8ms following impact. The dynamics on the technical face were not affected by what was occurring on the technical rear of the fabric. The bloodstain on the technical rear initially only increased until 0.8ms following impact. The increase in technical rear bloodstain area was caused by continued movement of the blood through to the rear of the fabric as the blood drop spread on the technical face. Once the impact dynamics were concluded within 8ms of impact, there was no further change in the bloodstain for the remaining 67ms of high speed video. Following this the blood wicked into and along the yarns, resulting in a dry technical rear bloodstain on all fabrics at all velocities.
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