The in-plane constitutive behavior of the room temperature cure 3K70PW Carbon Fabric/INF14 material system has been characterized using standardized coupon tests. The test data was utilized to populate the LS-DYNA MAT213 orthotropic elasto-plastic material card which employs a quadratic yield criterion along with a non-associative quadratic flow rule. The material exhibited tension–compression asymmetry in addition to non-linear behavior under in-plane loading dominated by compression and shear. The test data was used to develop the flow rule parameters of the material model. The model predictions were compared with the test data for simple loading cases and were found to be in satisfactory agreement. © ASCE.