Four-point flexure beam test configuration

2 Four-point flexure beam test configuration 

A topic of particular concern in fracture studies of such multilayer 

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Assuming that deformation can be adequately described by means of elementary beam theory, derive the expression for energy release rate for the four-point flexure beam test configuration given in (4.54). 

The flexural testing of polyethylene can be performed in a two-, three-, or four-point bending mode, the configurations of which are illustrated schematically in Figure 29. Three-point bending produces a line of maximum stress directly beneath the central beam, whereas the four-point mode results in maximum stress in the region between the two central beams. The three- and four-point modes, described in ASTM Method D 790, are typically used for stiffer samples, while the two-point (cantilever beam) method, described in ASTM Method D 747, is used for more flexible ones. 

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