It is very important industrially to estimate the degree of large deflection appearing in such members as a plate spring, plastics and so on. In this report, the problem of large deflection of a simply supported beam in a symmetrical three-point bending test was treated. It was shown that the desired specific quantities such as maximum deflection, maximum curvature, maximum bending stress and end slope, which are especially matters of great concern in the material testing, were able to be predicted easily from a conventional linear bending theory and two reduction factors derived here newly.
For the convenience of applications, the nomographs of the reduction factors were described graphically in terms of the vertical load, the large deflection at midpoint and the end slope.
An experimental investigation of large deflection of a PVC thin plate was performed to confirm the availability of the newly proposed reduction method. The experimental results obtained were in good agreement with the predicted ones by the reduction method. Therefore, the simple reduction method can be put into practical use.