Time and temperature sensitivity of the hybrid III lumbar spine

Abstract

Objective

Researchers have found a variety of uses for the Hybrid III (HIII) dummy that fall beyond the scope of its original purpose as an automotive crash test dummy. Some of these expanded roles for the HIII introduce situations that were not envisioned in the dummy’s original design parameters, such as a relatively rapid succession of tests or outdoor testing scenarios where temperature is not easily controlled. This study investigates how the axial compressive stiffness of the HIII lumbar spine component is affected by the duration of the time interval between tests. Further, it measures the effect of temperature on the compressive stiffness of the lumbar spine through a range of temperatures relevant to indoor and outdoor testing.

Methods

High-rate axial compression tests were run on a 50^th percentile male HIII lumbar component in a materials testing machine. To characterize the effects of tests recovery intervals, between-test recovery was varied from 2 hours to 1 minute. To quantify temperature effects, environmental temperature conditions of 12.5°, 25°, and 37.5 °C were tested.

Results

During repeated compressive loading, the force levels decreased consistently across long and short rest intervals. Even after 2 hours of rest between tests, full viscoelastic recovery was not observed. Temperature effects were pronounced, resulting in compressive force differences of 261% over the range of 12.5° to 37.5 °C. Compared to the stiffness of the lumbar at 25 °C, the stiffness at 37.5 °C fell by 40%; at 12.5 °C, the stiffness more than doubled, increasing by 115%.

Conclusions

A modest decrease in temperature can be sufficient to dramatically change the response and repeatability of the lumbar HIII component in compressive loading. The large magnitude of the temperature effect has severe implications in its ability to overwhelm the contributions of targeted test variables. These findings highlight the importance of controlling, monitoring and reporting temperature conditions during HIII testing, even in indoor laboratory environments.

Keywords:

• HYBRID III
• lumbar spine
• temperature
• stiffness
• compression
• repeatability

Additional information

Funding

This work was supported under contract #N00024-13-D-6400, sponsored by the U.S. Army Research Lab in support of the Warrior Injury Assessment Manikin Program. The authors gratefully acknowledge the contributions of the WIAMan Engineering Office. The views expressed are those of the authors and do not necessarily represent the official position or policy of the U. S. Government, the Department of Defense (or its branches), or the Department of the Army. The authors gratefully acknowledge the contributions made by the Zablocki VA Neuroscience Laboratory, and the Joint Department of Biomedical Engineering of Marquette University and the Medical College of Wisconsin.