Jamie T. Westbrook

45.2: Two Point Bending of Thin Glass Substrate

The two-point bend test has been used extensively for optical fiber strength and fatigue measurements. This paper extends the theory of 2-point bending to thin glass substrates. The key advantages of the 2-point bend test are 1) the simplicity of a test fixture and its operation, 2) the uniformity of a bend stress along the width of a substrate, 3) the inverse relationship between a bend stress and parallel plate spacing, and 4) the non-contact bending.

Finite Element Analysis of Four-Point Bending of LCD Panels

The four-point bend test is one of the most popular strength testing methods used to test LCD panels. Traditionally, a panel is assumed to be either a monolithic piece of glass or two independent pieces of glass sliding against each other. This paper uses finite element analysis to show that a panel behaves like a monolithic piece of glass in the epoxy region (near the edges) but behaves like two pieces of glass at the center. Assuming a panel to be a monolithic piece of glass may overpredict the stresses by a factor of two at the center. Similarly, assuming a panel to be two pieces of glass may underpredict the stresses by a factor of two at the edges. During four-point testing of a panel, the stresses are not uniform in the load-span region and so finite element analysis is required to obtain an accurate stress distribution.

Finite Element Analysis of Ring-on-Ring Test on LCD Panels

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.

72.2: Strength Measurements of Thin AMLCD Panels

The biaxial strength using ring-on-ring (ROR) test and uniaxial strength using 4-point bend test (4PB) were measured for 13.3″ panels with substrate thicknesses ranging from 0.25 mm to 0.5 mm. The effect of thinning process was quantified by these data along with identifying break sources using fractography. Strain gages were used to convert failure load to strength.