Finite difference modeling of phase changes and localization in elasticity. CHIMP is a finite difference dynamic relaxation program for solving plane-strain equilibrium problems in nonlinear elasticity. In addition to solving standard types of rubber elasticity problems, the method is useful for the study of localization and phase changes in elastic solids. It imploys a new algorithm called the pseudotemperature method for incompressible bodies. An antiplane shear version of the program is available. CHIMP is suitable for use on personal computers and lends itself readily to vectorization. This paper describes the theory behind the program and presents demonstration problems.