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.

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A ball drop test is amongst the tests used to assess the response of an LCD device under impact conditions. Two different glass thicknesses − 0.5 mm and 0.7 mm ‐ were submitted to this test in consideration for this paper. The result of the testing demonstrated that when a ball is dropped onto the outside surface of color‐filter glass, the peak stress occurs on the bottom of color‐filter glass, and not on the bottom of the TFT glass. In addition to this, we studied an extreme case where the back plate is rigid, since most LCD displays have a diffuser plate or back plate behind the panel. The rigid plate restricts the panel deflection when impacted by a ball. The findings from this study can be used as guidelines to go for thinner panels by balancing panel thickness, diffuser / back plate stiffness and the distance between the panel and the back plate. When appropriately implemented, panels made with 0.5 mm glass substrates may experience lower stress when compared to those made with 0.7 mm glass.

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The four-point bend test is used extensively to measure the edge (and surface) strength of AMLCD displays both in panel form and single substrate. The subtleties of four-point bend test for AMLCD panel applications and how one might use additional techniques, such as strain gage, finite element modeling and failure mode analysis, to better understand the data generated are investigated. This paper attempts to show the following: i) the standard fourpoint bend equation (figure 1) is not applicable to thin AMLCD panels, ii) the edges and surface experience different stress, iii) stresses can be quantified by knowing break location and the appropriate strain level, and iv) failure mode analysis can support the strain analysis and provide valuable information to the experimenter.