The ring-on-ring test is one of the most popular surface strength testing methods used to test LCD panels. This paper uses finite element analysis to show that a panel behaves like two independent pieces of glass during a ring-on-ring test. The epoxy region where the color filter and thin-film transistor (TFT) glasses are glued together does not affect the stress at the center. As LCD panels get thinner, the contribution of membrane stress increases significantly. Because the color filter and TFT glasses act independently, they experience maximum principal stresses within 15% of each other. For deflections greater than one-half (sometimes one-fourth) the glass thickness, the stresses are not uniform inside the load ring, requiring finite element analysis to obtain an accurate stress distribution.
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