Development of an Apparatus to Produce Fractures From Short-Duration High-Impulse Loading With an Application in the Lower Leg

Abstract

Axial loading of the lower leg during impact events can cause significant fractures of the tibia. The magnitude of lower leg axial loading that occurs during short-duration high-impulse events, such as antivehicular landmine blasts, can lead to life-altering injuries. These events achieve higher forces over shorter durations than car crashes, the current standard used for protective measures. In order to determine appropriate injury limits for the lower limb, a testing apparatus has been designed that can simulate these types of events for testing of anthropomorphic test device (ATD) lower legs as well as cadaveric specimens. Moreover, the design allows for the velocity at which the specimen is struck to be varied independently of the force applied, thus allowing independent investigation into the effect of momentum or energy on fracture strength. Test specimens are supported on a low-friction bearing system, and receive the controlled impulse from a projectile of variable mass that is accelerated using pneumatics. The apparatus includes velocity sensors, a six-degree-of-freedom load cell, and an accelerometer to completely quantify the loading event. The apparatus’ performance was validated against an ATD lower leg. It was able to create impulse events with forces from 0.5 kN to 17.0 kN, and projectile speeds of 2.3–13.9 m/s. Various momenta could be achieved at a constant force level by varying the mass of the projectile, with a maximum difference of 65%, whereas kinetic energy was inherently linked to the impact force. This apparatus will be useful in future studies for determining the appropriateness of currently used injury limits for the lower limb to high-impulse events, as well as for quantifying the relationship between cadaveric fracture response and ATD measurements. This device can also be readily applied to other bones of the body, to create realistic fracture patterns for known injury mechanisms.