- 期刊
Polarized Light Microscopic Examination of Mechanical Damage on Fabric Fibers
摘要
Fabric fibers are an important type of trace evidence that can be used to establish connections among individuals, crime scenes, and objects. In addition to the identification of fabric fibers, the examination of fabric damage also plays an important role in forensic investigation as to reconstruct an assaulting incident. Optical microscopy and scanning electron microscopy (SEM) are often used to determine the distinct morphology of fiber ends caused by different forms of mechanical damage. However, the price of SEM is not affordable to the local forensic science departments. Thus, a polarized light microscope (PLM), which is relatively inexpensive and accessible to local police laboratories, was used in this study in order to differentiate the fabric damages caused by cutting with scissors, slicing with scalpel blade, puncturing with screwdriver and discharged bullet, and ripping with hands. The results revealed that the examination procedure used in this study was able to identify the distinct characteristics in fiber ends broken by bullet, scissors, scalpel blade, Philips screwdriver, and ripping. Fabric damage caused by sharp-edged instruments produced neat fiber ends and localized interference color change under PLM. Damage created by puncturing the fabric by non-cutting means, producing irregular holes, which also resulted in rough and elongated broken fiber ends. Interference color change and bright transverse stripes were observed in these uneven fiber ends under PLM due to the change of birefringence property, stress state, and thickness. Whereas uneven fractured fiber ends without interference color change were observed when fabric yarns were pulled apart by ripping. Because characteristic features of damaged fiber ends are affected not only by varied forms of mechanical damage but also the fiber type, yarn structure, and fabric construction and orientation, it is recommended to carry out simulation experiment on the same type of fabric as that found in the forensic case to reconstruct the incident.