GLASS BOTTLE FAILURE FROM INTERNAL PRESSURE


by
Charles C. Roberts, Jr.


Glass fails in a brittle manner at nominal ambient temperatures with little stretching or elongation prior to failure. Crack propagation is influenced by many factors, including stress distribution and structural shape. The following is a study in failure analysis of an ordinary milk bottle. Figure 1 is a view of the initial condition of the artifact.


Figure 1
A first step is to attempt to delicately reassemble the bottle to observe distinguishing fracture patterns. Clear tape is a useful tool in holding the bottle in position. Start with major pieces and carefully tape together the fragments. The result is shown in Figures 2 and 3. A piece of white paper is placed inside the bottle as it is reconstructed so that the fracture can be analyzed without optical interference from the other side. Figure 2 is a view of one side of the bottle



Figure 2 Figure 3

showing far less fragmentation of the glass than that shown in Figure 3. Typically, the fracture origin is at an area of high stress and high energy release. This results in branching of the fracture in many directions. Figure 4 is a view of


Figure 4


the fracture origin near the middle of the long side of the bottle. This fracture pattern is typical of pressure inside the bottle. The pressure induces bending stresses near the middle of one of the large sides of the bottle. Once the fracture initiates, it branches quickly into the double Y pattern shown in Figure 4. When the pressure is relieved, there is usually less damage to the opposite large side of the bottle, as was evident in Figure 2. The fracture of the bottle in Figures 1 through 4 was a result of a test where a glass bottle, full of water, was placed in a freezer. After the water froze, expansion caused the internal pressure related fracture pattern. Fractures of milk bottles are often blamed on manufacturing defects. However, investigation of the means of storage of full milk bottles may yield information showing the bottle to have been improperly stored in a freezing environment. The classical double Y fracture shown in Figure 4 is a significant indicator of such misuse.


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