Yap T.W*, Michael Tay Ming Kiong
International Association of Forensic Sciences, 16th Triennial Meeting
August 2002, Montpellier, France. (oral presentation)
Objectives: The fracture of a brittle or ductile material due to failure or deliberate cut has been well studied by many in the forensic science field. However, damages to ductile and brittle materials combined in a composite are not as well documented and understood. The objective of this study is to examine the cut characteristics of such a composite material using common single-bladed and double-bladed cutting tools such as penknife, scissors, pruning shears and diagonal pliers.
Materials and methods: The material used in this study was a multimode optical fibre cable commonly used for local area networks. It has 12 optical fibres surrounded by tough synthetic fibre (for increased tensile strength and compression resistance) and enclosed in a plastic outer sheath. Each optical fibre consists of a brittle inner glass core and glass cladding, a viscous gel region for buffering and a ductile colour-coded plastic jacket. Test cuts of the cable using the above-mentioned cutting tools were made. The resulting cuts were examined using stereomicroscope as well as scanning electron microscope for the characteristics of the cuts. Material analyses of the different components of the optical fibre cable were also carried out using SEM and FT-IR spectroscopy.
Results: Test cuts using a single-bladed tool such as a penknife produced relatively clean cuts with striations on the cut surfaces of the colour-coded plastic jacket. Some glass cores and claddings were cut through in a clean manner while some others presented irregular cut surfaces. On the other hand, test cuts using double-bladed tools such as pruning shears, scissors or diagonal pliers led to a mixture of effects such as significant lateral compression, necking, pinching and stretching on the colour-coded plastic jacket. Breakage of the glass cores and claddings was either uneven or occurred at different points. The proportion of the various types of effects observed with each type of double-bladed tool was also studied.
Conclusion: The optical fibre cable presents a very interesting material for the study of the different characteristics of cuts made by various tools because of the many components making up the entire cable. This study showed that cuts made by single-bladed tools displayed characteristics very different from double-bladed tools. Double-bladed tools were found to vary in their effectiveness to completely sever the multi-component cable. Differences in cut characteristics are shown to be useful for identifying the type of tool used to cut an optical cable.