Glass Expert performs a Failure Analysis of a Wine Glass

 California glass expert performed a failure analysis on a failed wine glass. Glass failure analysis requires locating the fracture origin. The origin is then analyzed microscopically to determine the cause of failure. In this case the failure origin was on the rim of the glass. At the failure origin is a very small mirror fracture surrounded by mist hackle. This demonstrates that the glass was impacted on the inner rim and propagated from that point to failure. The failure analysis labs at Read Consulting have the capability to analyze all sorts of glass failures.

Glass Bottle Failure Analysis

Larger Point Impact (1/8" Dia.)

Fracture Surface at Origin
of 1/8" at 40X

Small Point Impact (1/32" Dia.)

Fracture Surface at Origin
of 1/32" at 40X

Often bottles and other glass objects fail as a result of "point impact". Given here are two examples of point impact failure origins discovered as a result of glass failure analysis performed at the Read Consulting Failure Analysis Lab. The origin is found by tracing the crack backwards on the fracture surface. Often there is a crushed glass region at the point of impact. This blog demonstrates two impact failures. Shown are the are both the impact point on the free surface and the origin as observed on the fracture surface as viewed at 40X using an optical microscope.  

Failure Analysis Lab Analyzes Shower Door Failure

Installed Shower Door

Top Roller  at Stop

Disassembled Roller

Fracture Surface at Origin

Tempered glass shower doors have been modernized. Recent designs have the doors suspended by rollers that ride on a pipe. In certain cases the door stop is on the top. In this case, the roller is stopped by a rubber bumper. Several of these doors had failed during use, and the glass experts at Read Consulting were asked to perform a failure analysis and suggest solutions to the glass fracture problem.

The two top photographs illustrate how these types of doors are installed. Basically they are hung on two rollers that are bolted to the tempered glass doors using holes cut into the glass. At the end of travel, these doors are stopped when one roller hits a rubber bumper. There is some cushion from the rubber bumper; however, this is not enough.

Glass failure analysis was performed on a representative failed door. In this case, the failure origin was clamped in one of the two rollers. The failure initiated on the interior wall of one of the through holes in the glass. It is believed that the failure forces are created by torsional moments generated because the top of the door is stopped, but the bottom of the door is not. When the door is stopped at the top, the unrestrained bottom creates a large rotation moment. This moment puts high forces on the walls holes in the glass. These forces act on the ground hole walls to cause failure.

The two lower photographs document the glass failure analysis. It is believed that the stopping mechanism must not generate twisting moments. One solution is to put the rubber stopper in the center of the door, not at the top. Another solution is to slowly reduce the door speed (i.e. create drag) before it hits the stop at the top.

Failure Analysis Lab performs Electronic Failure Analysis

Array of Pogo Pins

Top of Pogo Pin at Mag. 30 X

Cross sectioned Pogo Pins at Mag. 5 X

Read Consulting Failure Analysis Labs often perform electronic failure analysis for various manufacturers. The objective is to determine the root cause of the failure and help the manufacturer correct the problem.In this case, a company that assembles an array of Pogo connector pins into an instrument for multiple contacts. Some of the Pogo pin arrays are hand soldered into the equipment; other arrays are assembled using a wave solder machine. The wave soldered arrays had poor contact. Initially we were told that there were two shipment lots of Pogo pin arrays, and it was thought that  one was bad. Read Consulting tested a representative sample from both lots and could find no difference:
1. Through the optical microscope the pins from both lots were found to have good gold plating. On the upper left is a  photomicrograph of the surface of a "bad" pin.
2. In both cases testing the Pogo pins with a needle showed good contact all through the instrument.
3. Samples were cross sectioned and both lots showed good plating on the interior of the Pogo pins. Center photomicrograph.

The client was advised that there was no bad lot. It was suggested that the Pogo pins be wiped with isopropyl alcohol and retested. This test was successful; therefore one must conclude that a contaminant film settled on the contact surfaces during the wave solder operation. The alcohol wipe was added to the procedure.

Shot Glass Failure Analysis

The glass expert at Read Consulting failure analysis lab was asked to perform a failure analysis on a glass sliver removed from a woman's stomach. The woman had been out drinking the night before, and the following morning had stomach pains. The cause of the pain was found to be a glass sliver logged in her stomach. Part of the analysis was to determine how the glass sliver was created and from what type of glass. The glass piece was determined to come from the rim of either a shot glass or a "rocks" glass. The glass failure indicated that the sliver was created by side impact at the top of the glass. In addition, impact tests on representative glasses indicated that to form this piece the impact forces would have been high. Most likely the chipping of the glass occurred during toasting. Cheers!    

California Glass Expert Examines an Aircraft Windshield Failure

Read Consulting failure analysis lab performed a glass failure analysis on a failed aircraft windshield. The  windshield of a turbo-prop aircraft suddenly cracked during descent through clouds. Initially it was thought that static electricity had caused the glass failure. Initially it was proposed that the static electricity sought the aircraft "ground" through heating wires in the windshield. The failure analysis determined that the failure was caused by impact to the outer layer of the windshield. This is demonstrated by the crushed glass at the origin and the subsurface conchoidal fracture around the origin. The flight was in icy conditions; it is possible that a piece of ice came off the propeller and impacted the windshield. 

Failure Analysis of Glass Encapsulated Zener Diodes

Failure Analysis Lab examines performs a failure analysis on surface mount glass encapsulated Zener diodes. These diodes were in an appliance control board, and they are surface mounted to the underside a printed circuit board. The entire board is encapsulated in rigid polyurethane. There was a significant yield loss due to cracking of the glass encapsulation around the active assembly. Glass failure analysis determined that the failure origin was at the end of the diode where the glass is in contact with the metal end contact. Examination of  new diodes by glass experts found that the glass was cracked in the same location on new diodes. Thus, the failures were initiated before these diodes were assembled onto the printed circuit board.

Glass Expert Discusses Bend Test Fracture Surface

 California Failure Analysis lab performed a compound bend test to determine if the failure surface can be at an angle to the surface. One curious result was a curved fracture surface. This occurs when the clamp on the topside (i.e. tensile side) was behind the support underneath. If the two clamped sides are aligned, the crack is perpendicular to the sample face This information is useful when analyzing failures of other brittle materials such as ceramics (i.e. ceramic failure analysis).

Glass Expert Performs Glass Bottle Failure Analysis

Read Consulting failure analysis lab was asked to determine the cause of failure of a small glass cosmetic bottle that had failed in on the filling line as the cap was being tightened. A glass failure analysis was performed using a low power microscope. The root cause of the failure was a chill check on the bottle neck. This damage  occurred during bottle manufacturing. The bottling company will work with the bottle manufacturer to eliminate this manufacturing defect.

Tempered Glass Expert Discusses Glass Edge Finish

California glass expert discusses the importance of edge finish on tempered glass. Tempered soda lime glass has replaced low expansion borosilicate glass for small oven doors and glass tops for cookware. This reduces costs, but can reduce reliability. One important aspect of these tempered glass pieces is the edge quality. Poor edge finishing can introduce defects that can cause eventual failure. There are three common edge defects. These are chipping, missed seaming and "dry" seaming. Normally these pieces are scribed and broken, seamed with a wet belt sander and tempered. These three edge defects are illustrated by the figures. Read Consulting failure analysis lab has looked at numerous tempered glass failures that have originated at the edge; thus, edge finish is extremely important for any glass piece that can be preferentially heated in the center.