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The four-point bend test is widely used for testing the edge strength of glass specimens. Vertical four-point bend (V4PB) setup involves orienting the specimen in a vertical fashion. However, thin specimens tend to buckle when using V4PB setup. In this study, a finite element model was built to simulate the buckling that occurs during V4PB testing. To validate this model, experiments were conducted on the existing setup. Upon validation, the finite element model was used to propose an improved setup. Then, experiments were carried out on the improved setup to verify that it worked as intended. The primary advantage of the proposed setup is that the standard ASTM [ASTM (2007), C158–02] four-point bending formula can continue to be used to calculate the stress from the applied force.

This paper provides general guidelines and watch outs while conducting strength testing on LCD glass. Importance of failure modes, large deflections, membrane stresses, failure locations, device design, fatigue, fractography and strain gauging are discussed in this paper. It also gives an example on why panels cannot be treated as monolithic glass when calculating the strength.

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.

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.

As glass samples get thinner they tend to buckle during vertical four-point bend testing resulting in erroneous strength measurements. This paper suggests design modifications to the existing setup to overcome this issue. The standard four-point bending formula can still be used for calculating the applied stress.

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 four-point 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.

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.