Investigations of Generalized Joint Stiffness Model in LSTC Hybrid III Rigid-FE Dummies

The joint restraint model *CONSTRAINED_JOINT_STIFFNESS_GENERALIZED in LS-DYNA® provides users a way to define stiffness characteristics for joints defined by *CONSTRAINED_JOINT_OPTION. Based on the relative angles between two coordinate systems, moments are generated according to user-defined curves. It has been defined in LSTC Rigid-FE dummy models to describe the joint behaviors at limb joints such as hip, elbow and knee joints. There are two approaches in LS-DYNA® to calculate the relative angles, incremental update (default) and total formulation (option defined in *CONTROL_RIGID). In this paper, differences of the angular calculation of the two methods were investigated. In LSTC Rigid-FE dummy models, the default (incremental update) is used for the joint stiffness model. It demonstrates the shortcoming of the incremental update method for the joint that rotates about more than one axis. Consequently, joints at elbows and wrists in the Rigid-FE dummy models are limited to a single axis rotation, which are capable to rotate along two axes in a physical hybrid III dummy. Alternatively, a modified Rigid-FE dummy model with the total formulation method defined for the joint stiffness was then suggested.