GMW GMW16598 [ Active ]

Introduction

Note: Nothing in this standard supercedes applicable laws and regulations.

Note: In the event of conflict between the English and domestic language, the English language shall take precedence.

Purpose. This test will simulate scratches (damage sites/flaws) on the windshield, which will result in breakage if excessive residual stresses exist in the glass sample. By simulating these scratches/defects in the glass, an evaluation of the residual manufacturing stresses (thus, susceptibility for breakage) is possible. Performing this evaluation will help ensure the final product will not exhibit these concerns.

Applicability. All GM windshields worldwide.

Remarks. Due to varying residual stresses developed within the glass during the forming process, windshield breakage can result if the stresses are excessive or not counterbalanced by inherent compressive stresses. These excessive or unbalanced stresses are due to insufficient heating or cooling of localized regions within the glass during the bending process (improper annealing). The design and geometry of bending rings or oven parameters are often the root cause for these residual stresses. Breakage can occur after delivery of the vehicle to the customer, typically when a small or minor scratch occurs, (e.g., stone chip). Glass breakage results in undesirable warranty costs and customer dissatisfaction. A method has been developed that can identify susceptible parts and then help pinpoint the root cause so resolution can be sought. This methodology is described and should be followed by all GM windshield suppliers.

Note that another common cause or contributor to windshield breakage is installation or applied stresses, but the effect of these stresses cannot be evaluated using this test procedure. Also note that a combination of installation and residual manufacturing stresses may lead to windshield breakage, further confounding and obscuring the root-cause for a glass breakage concern as installed in a vehicle.