Analysis of glass fracture patterns on glass panes

摘要

Glass is one of the most common and important evidence submitted to forensic laboratories for analysis. It is frequently encountered at crime scenes, particularly those involving motor vehicle accidents or burglaries. This study emphasized on the examination of the fracture patterns performed on different types of glass panes after broken by different type of impact objects, analysis of fracture features to determine direction of force and identifying of refractive index of glass as further analysis. Three types of glass panes (float, tempered and laminated) and four levels of breaking devices (hammer, bat, golf ball and stone either by throwing or using catapult) were used in the experiment. The results show that almost the whole float glass panes were shatters into sharp glass pieces after broken by all type of breaking devices. Then, tempered glass pane was broken with the whole glass panes shatters into small pieces of blunt granules when only hammer exerted on the glass, meanwhile, for other breaking devices were caused a scratch marks on glass surface. For laminated glass when broken by bat, throwing a stone and using catapult, almost the whole of glass panes were remains intact on its interlayer film and got some splinters from point of impact were flying out. Meanwhile, fracture patterns on laminated glass pane when broken by hammer produced a cone or crater after striking. However, impact objects used to break those types of glass panes are not really reliable to be distinguished. This is because the fracture patterns on glass panes obviously differ by its types of glass only. When a pane of glass is broken by an impact, majority of the broken fragments will fall in the direction of the force, which is on the side of the glass panes opposite direction of the application of force. A determination of the direction of force in breaking a glass pane can be determined by the direction of the rib marks. As the impact occurs, concentric fractures form around the impact and interconnect with radial cracks to form triangular pieces. The edge of each triangular piece has visible stress lines that describe the direction of the blow. The refractive index of each type of glass was determined by GRIM 3 equipment which produce results of refractive index for float glass panes are about 1.5200; tempered glass panes are about 1.5181 and, laminated glass panes are about 1.5188.