IDS Packaging - White Paper
     
Title:

Two Common Glass Container Failures

 
Author:

Dr. Thomas L. Read

 
Designation:

CEO, Read Consulting

 
Company:

Read Consulting

 
 
 
           

Introduction

Numerous people are injured annually while opening glass containers. More often than not, these failures become the subject of a law suit in which the packaging company and/or the container manufacturer are named as defendants. In this paper, two typical failures of glass containers (wine bottle and jam jar) are analyzed to show the cause of failure and to make suggestions on how to prevent these types of failures. It should be noted that in both of the incidents described below, the user was injured and thought that there was a defect in the glass. Both the failures described below are common occurrences and are worth a closer look.

Background

Glass Fractography is the most effective method for determining why a glass object, such as a bottle, failed. This technique consists of examining the fracture surfaces of the failure for artifacts such as Wallner lines and using them to trace the crack back to its origin. Once the origin has been identified, it can be examined in detail with a microscope to determine the cause of the failure.

Wine Bottle Failure

Overview: Figure #1 is a photograph of the failed bottle that was examined. It is apparent from the photographs that the bottle separated at the neck. Only two pieces of the bottle remained. There are pieces around the origin that are missing; however, one complete half of the origin is present. This is sufficient to make a determination as to the cause of failure.
Neck and Cork: Figure #’s 2 & 3 are close-ups of the cork and neck. Visible in the region of missing glass is a slit in the side of the cork. The slit is where the corkscrew exited the cork and damaged the interior wall of the bottle.
Crack Origin: The crack originated at the exit of the corkscrew (Figure #’s 4 & 5). This is indicated by the concentric Wallner lines that locate the initiation site on the interior wall of the bottle in the neck.
Corkscrew: The type of corkscrew that was used is shown in Figure # 6.

Conclusion:

The bottle failed as a result of corkscrew damage to the interior surface of the bottle. This damage occurred because the corkscrew was driven into the cork at a severe angle. This allowed the corkscrew to exit the cork on the side of the cork and drive itself into the inside wall of the bottle at the neck. The corkscrew “scored” the inner wall of the bottle and initiated the crack. The crack propagated as the cork was being pulled out. This allowed the top to separate from the remainder of the bottle. This failure was a result of improper use of the corkscrew; it was not caused by a manufacturing defect nor a defect created by the bottling process. This is strictly operator error. It is suggested that a corkscrew that aligns the screw along the axis of the cork and doesn’t use leverage to remove the cork would eliminate this type of failure

Figure #1: Photograph of the Mezza Corona wine bottle examined at Mr. Brody’s office on November 7, 2002.

Figure #2: Macro- Photograph of the bottle neck in the region of the crack initiation site. There are several important aspects of the neck that are visible in this photograph. First, there is a “slit” in the side of the cork; this is in the region of the crack. In addition, it is associated with damage at the top of the cork. The damage in the cork indicates where the corkscrew entered the top of the cork and where it exited on the side.

Figure #3: The cork and neck taken from another angle. This shows the relationship between the entry and exit of the corkscrew better. In addition, it demonstrates that the corkscrew entered the cork off center and at a severe angle.

Figure #4: Photomicrograph of the crack origin (on the left of the photograph), the cork and the side opposite the origin. This is indicated by the concentric Wallner lines emanating from the origin on the free surface. (Mag. 8X)

Figure #5: Higher magnification of the crack initiation. It is directly associated with the exit of the corkscrew from the cork. The concentric Wallner lines emanate from the initiation point (similar to waves from a rock thrown into water). Mag. 20X

Figure #6: Photograph of the type of corkscrew responsible for the damage to the interior of the bottle and the failure. The screw is driven into the cork, and then the ‘prop’ is located on the bottle top. Finally, the cork is lifted out by leveraging it off the prop. If the tip of the screw is against the bottle wall, the prying can cause the inside of the bottle neck to be scored, and this can initiate failure.

Jar Failure

Overview: Figure #7 is an overview of the failed jar. The jar separated into two pieces.
Failure Origin: Figure #’s 8 & 9 give two views of the failure origin. This fracture originated from a blow to the side of the jar. The force of this strike created a ‘star’ pattern of damage with numerous cracks leaving the center point. One of these cracks was in the proper orientation to complete the failure when an attempt was made to twist off the top. A portion of the star pattern is shown in Figure #8. Figure #9 shows the origin as it appears on the fracture surface.
Lid damage: Figure #10 is a macro-photograph of the origin that also shows the condition of the lid in the same locality. This photograph demonstrates clearly that the lid was hit in the same region as the fracture origin.

Conclusion

The jar failed as a result of a blow to its side. Damage to the lid indicates that it was being hit in order to loosen it. Jars that contain jams, jellies and other contents high in sugar often have the lids stuck after re-sealing. The liquid sugar solidifies and tends to ‘glue’ the lid in place. Hitting the lid is neither an effective way to loosen it, nor is this a safe technique. As demonstrated above one can hit the glass and initiate a crack that can cause the jar to fail when the lid is being twisted off. Often the person removing the lid can be injured by the sharp glass created by the failure. A better method is to immerse the jar in warm water to soften the ‘glue’ before trying to twist the lid off.

Figure #7: Overview of a failed jam jar. The top section came off during an attempt to remove the lid by twisting.

Figure #8: Photomicrograph of the side view of the fracture origin. This failure resulted from a blow to the side of the jar. This is demonstrated by the cracks radiating from the point where the blow struck the side of the jar. (Mag. 8X)

Figure #9: Origin of the failure as it appears on the fracture surface. This crack originated from a blow to the outside of the jar. The fracture originated on the outer surface of the jar and worked its way inward and laterally. (Mag. 40X)

Figure #10: Macro-photograph of the top of the jar. It clearly shows the failure origin. In addition, it also shows damage to the lid. The lid damage indicates that it has been hit with a hard object. Often a person will bang a stuck lid to free it so it can be removed. In this case one of the strikes missed the lid and hit the outer surface of the jar; in addition, it was severe enough to crack the glass.