Biomechanical Response of the Human Pelvis: a High-Rate Vertical Loading Pilot Study

The proliferation of improvised explosive devices (IEDs) in recent military conflicts have caused injuries which present new challenges to the biomechanics community. Vehicle-mounted U.S. and coalition warfighters are being exposed to extreme loading conditions from under-body blasts (UBB), and are suffering devastating injuries. One region of the body that is injured in these UBB events is the pelvis. For UBB events, the primary load vector is applied verticaly through the seat, thus loading the pelvis in a direction and at a rate never before researched. This study aims to quantify the mechanical response of the component pelvis from a high-rate vertical load, so as to improve understanding of the pelvic response and to provide data for anthropomorphic test device (ATD) development.

In ten post-mortem human surrogate (PMHS) pelves, the superior surface of the sacrum was rigidly secured to a 6-axis load cell, which was then rigidly mounted to an effective mass, equivalent to that of a 50th percentile male torso. This assembly was resting against a seat platen, which was impacted by a linear impactor, providing a single high-rate loading condition into the specimen. Accelerometers were used to quantify the boundary conditions. Additionally, accelerometers, an angular rate sensor, and strain gauges were used to capture the response of the pelvis.

The average input seat velocity for this study was 5.9 ± 0.3 m/s with a time to peak of 6.6 ± 0.2 ms. This input condtion yielded a calculated axial stiffness of 995 ± 159 kN/m before there was a failure at the rigid potting boundary. The average failure time was 4 ± 0.6 ms, and the peak axial force was -6 ± 1.8 kN. The primary rotation was positive about the y-axis, and the moment at time of failure was 311± 16 Nm.

This study offers detailed biomechanical response data of the component pelvis from a single high-rate impulse, including force and moment response corridors, as well as strain response and sacrum acceleration . This data is necessary for the development of a biofidelic pelvis for UBB applications, both for finite element analysis, and ATD development.