Effects of Temperature and Humidity on Dynamic Test Components

Principal Investigator: John H. Bolte, IV, PhD, The Ohio State University

WHAT WAS THE PURPOSE OF THIS PROJECT?

This project examined the foam cushion used on the federal compliance test bench, in FMVSS 213, used by all CRS manufacturers to crash test their products. NHTSA is in the process of replacing the polyurethane foam cushion with a new formulation that better represents the modern vehicle fleet. However, there are little data currently available to understand the mechanical properties of this new foam and how it might vary with respect to temperature and humidity in testing facilities. The goal of this study was to better understand how the ambient environment might influence stiffness properties of the test bench foam and, therefore, crash test outcomes.

HOW WAS THE RESEARCH CONDUCTED?

We obtained 25 samples of the newly formulated foam and placed them for at least 24 hours in a climate chamber set to a specific temperature (ranging from 32.9 to 86.0°F) and humidity (ranging from 46.0 to 86.2% relative humidity). We then conducted quasistatic indentation force deflection tests in a universal testing machine by compressing each sample by 25%, 50%, and 65% of its original height, recording the corresponding force at each of those indentations to quantify the stiffness of the foam.

WHAT WERE THE FINDINGS AND WAS ANYTHING SURPRISING?

We found that the stiffness of the foam was sensitive to both temperature and humidity over the ranges tested. Something that surprised us was how large of a role the humidity played. Under current FMVSS 213 standards, NHTSA specifies that crash testing should be conducted at relative humidity between 10% and 70%. We found that there was quite a range in stiffness within that 10% to 70% range. Based on these results, we would recommend that the humidity range be tightened, which may ultimately produce more repeatable results.

HOW ARE THESE RESULTS APPLICABLE TO INDUSTRY MEMBERS?

Our results complement testing that NHTSA is currently conducting and can help CRS manufacturers better understand how their crash test results might vary with respect to ambient conditions, especially across different test facilities in different geographic climates.

FMVSS Chart — The indentation forces of the newly proposed FMVSS 213 test bench foam varied considerably with respect to humidity for all three indentation levels. The solid lines model the data over the humidity range tested in this study, and the dashed lines show the extrapolation of the results over the current FMVSS 213 humidity range of 10 to 70% relative humidity.

Co-Investigator

Julie Mansfield, PhD, The Ohio State University

Student

Rosalie Connell, BSE, The Ohio State University

IAB Mentors

Mark LaPlante, Graco Children’s Products Inc.; Jerry Wang,Humanetics Innovative Solutions Inc.; Curt Hartenstein, Iron Mountains; Erin Hutter, National Highway Traffic Safety Administration; Uwe Meissner, Technical Advisor