Considerations for a Femur Injury Criterion

A femur fracture injury criterion is presented that assesses the dependence of the permissible human knee load on the duration of the primary force exposure. Currently a constant allowable femur load limit of 7.6 kN (1700 lb) is specified in FMVSS 208, but recently the Federal Government proposed elevating the allowable limit to 10.0 kN (2250 lb), which is in excess of the limited experimental average static femur fracture force of 8.90 kN (2000 lb). A general analysis of all of the available biomechanics data and mathematical models on femoral impact response and fracture indicates a significant load time dependence for primary pulse durations below 20 ms that can elevate the permissible femur load above the Federally proposed allowable limit of 10.0 kN (2250 lb). A femur injury criterion was therefore formulated that is consistent with the available experimental data, incorporates the temporal characteristics of the femur fracture force, and provides a technically feasible and improved protective test standard for car occupant safety evaluations. Dynamic differences between the femoral response of the human cadaver and the Part 572 dummy were subsequently quantified to substantiate the efficacy of applying the Femur Injury Criterion to the measured response of the Part 572 dummy.