Rib Failure Detection Using Time-frequency Analysis: A Feasibility Study

Experimental testing is a major source of data to quantify the tolerance of the human body to impact and to develop protection strategies. In the field of vehicle safety, it has been demonstrated that chest injuries are a good predictor of an impact severity. Correlating the time of rib fractures with the kinematics of the occupant and the action of safety systems would provide valuable data for assessing safety systems and developing injury risk functions. However, there is currently no satisfying method to monitor rib fractures; time history analysis of strain gauges data is commonly used for this purpose, but this method is not very sensitive and requires instrumentation of the ribcage with more than 100 strain gauges. A new approach based on time-scale analysis of signals obtained from piezoelectric transducers (PZT) was investigated. A post-mortem human subject was instrumented with four PZT on ribs 3 and 7 on both sides and was laterallyimpacted to the shoulder and the chest. The fractures were documented after each test, and a criterion was developed to process the PZT signals. The criterion consists in detecting in the PZT signal the onset of a high frequency transient generated by the fracture of a rib using the continuous wavelet transform. Two thresholds were successfully determined to detect fractures that occurred (1) on an instrumented rib, and (2) on the rib close to it. Further development of this method should allow the detection of all rib fractures using only a few PZT.