Axial impact tests conducted at the Medical College of Wisconsin on isolated cadaver lower limbs and the original version of the 50th percentile Hybrid III dummy lower limb were examined to characterize their dynamic response. Unlike the more recent version of the Hybrid III dummy lower limb, the original Hybrid III dummy lower limb allows only 30 degrees of foot rotation in dorsiflexion and lacks biofidelic heel pad compression characteristics. This original version of the Hybrid III dummy lower limb will henceforth be referred to as HIII-o dummy lower limb. Results of the test suggested that the axial force measured in the HIII-o lower limb was higher than that measured in the cadaver lower limb for similar impacts applied to the plantar surface of the foot. The dynamic properties of the cadaver and HIII-o dummy lower limb were characterized by representing the lower limb in the axial impact tests as a single degree of freedom system with a Kelvin element having linear stiffness and damping properties. The stiffness and damping coefficients of the cadaver and HIII-o dummy lower limbs were obtained from linear regression using the measured accelerations on the pendulum and the leg as input and output of the system, respectively. The average stiffness and damping coefficients were estimated to be 963 kN/m and 0.21 for the cadaver and 3256 kN/m and 0.25 for the HIII-o dummy lower limbs, respectively. The axial force response ratio between the HIII-o dummy and cadaver lower limbs under similar impact conditions was obtained using Runge-Kutta simulations of the equation of motion for the single degree of freedom system. The axial force response ratio was represented as a funciton of the rise time of the axial force (the time to maximum force) in the HIII-o dummy lower limb. The greater than one for HIII-o dummy axial force rise times below 55 msec (short duration tibia force pulse). The axial force in the HIII-o dummy and cadaver are approximately the same for long duration HIII-o dummy axial force pulse. (A)
Abstract