On the use of the Blatz-Ko constitutive model in nonlinear finite element analysis

The nearly-incompressible material model proposed by Blatz and Ko ( Trans. Soc. Rheol., 6, 223–251, 1962) is attractive for its simplicity, and is used currently in several finite element wave propagation codes. A form of the Blatz-Ko model suitable for use within static and implicit dynamic solutions is developed in this paper. Stress point equations for both stress and tangent modulus computations are given, and a typical implementation in FORTRAN is presented. The determination of material properties for the model from laboratory test data is also discussed.