An inverse analysis method was proposed for estimating nonlinear stress-strain curve with plastic deformation from load-deflection curve of three-point bending test of simply supported beam with rectangular cross section. This method was based on a small deformation theory under a few assumptions. Curvature was derived from the relation of load-deflection by applying the moment area method and geometrical relation, and bending strain was derived from the relation of strain-curvature. Then

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... g stress was derived from the relation of moment-curvature. Finite element analysis was conducted for verifying that these equations could estimate stress-strain curve. The estimated stress-strain curve showed good agreement with the actual one, verifying the usefulness of the proposed method for estimating stress-strain relation from the load-deflection curve of three-point bending test.