Fracture Patterns in Glass

Fracture Patterns Glass has some flexibility, so when hit, there is subtle stretching As force increases, fracture lines first appear which may be followed by the glass breaking. The fracture patterns on broken glass can provide clues about the direction and rate of impact. This is more qualitative data than quantitative (numeric) Shattered Glass When force is applied to glass it will breaks in a specific manner Glass begins to break OPPOSITE the applied force Forms 2 types of fractures Radial Concentric Primary Radial Fractures When glass breaks, fracture patterns form on the surface. Breaks, called primary radial fractures, are produced. These fractures start at the point of impact and radiate (like spokes on a wheel) outward from there. Radial fractures form on the side opposite the point of impact. Concentric (Secondary) Fractures Secondary fractures may also form. These fractures take the form of concentric circles around the point of impact. Concentric circles are circles that have the same center. Concentric circles form on the same side of the glass as the point of impact. 4R Rule- Determining Side of Impact Ridge lines on Radial fractures are at Right angles to the Rear (side opposite the impact) Bullet Holes in Glass When the projectile hits a glass surface the glass bends and energy dissipating from the point of impact causes ‘radial’ fractures to occur on the side of the glass opposite the point of impact. Stress marks on the edges of the radial fractures conform in a specific way which will show the direction of impact. Stress marks are curved. One end of the curve runs parallel to the glass surface. The other end of the curve runs perpendicular to the glass. Breakage of Glass from a Fire During a fire, glass may break as a result of heat fracturing which produces a different pattern than an impact. Wavy fracture lines develop in glass that has been exposed to high heat. Glass will tend to break toward the region of higher temperature. If the glass was not broken before the fire, there will be no radial or concentric circle fracture patterns in glass that is broken by high heat. Link to Lecture Slides: *Due to the description character limit the full work cited for “Fracture Patterns in Glass“ can be viewed at...