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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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.

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