The present application relates to a method for determining the bending deformation of plate glass. In the method, the
radius of curvature of the plate glass corresponding to the bending deformation of the plate glass is determined on the basis of a Stoney relational expression and / or an elastic-plastic strain relational expression that reflects a configuration for width changes, wherein a first layer and a second layer included in the Stoney relational expression can be set such that, on the basis of a value, obtained by integrating a concentration distribution up to an
ion exchange depth layer after
ion exchange of glass comprising alkali, and an effective
diffusion length, which is the depth calculated to have the same area under the assumption that the
surface concentration remains the same according to depth, the thickness corresponding to the effective
diffusion length in the thickness of the plate glass is considered as the first layer, and the thickness excluding the effective
diffusion length from the thickness of the plate glass is considered as the second layer, and the plastic strain included in the elastic-plastic strain relational expression can be set such that, on the basis of width changes occurring after the
ion exchange in the plate glass through a
shape change caused by a structural
relaxation effect due to a α-relaxation, width changes gradually occurring according to concentration at the
ion exchange depth layer are averaged to obtain a single value, the width changes are assumed to occur from the half depth of the
ion exchange depth layer to the half depth of a non-
ion exchange depth layer through a simple
geometric method, and plastic curvature occurs according to the width changes.