Evaluation of Harness Tightening Procedures for Child Restraint System (CRS) Sled Testing 2019-01-0617
Sled testing procedures should reflect a rigorous level of repeatability across trials and reproducibility across testing facilities. Currently, different testing facilities use various methods to set the harness tension for child restraint system (CRS) sled tests. The objective of this study is to identify which harness tightening procedure(s) produce tensions with the least variability within the target range and are feasible to utilize in sled room operations.
Five harness tightening procedures were selected: 1) FMVSS 213 L-shaped hook, 2) Three-prong tension gauge, 3) ECE R44/R129, 4) two-finger method, and 5) pinch test. Two CRS models were instrumented with a tension load cell in the harness system. Seven sled room operators were recruited to perform each of the five tightening procedures for ten repetitions apiece on both instrumented CRS using a Hybrid III 3-year-old ATD (100 trials per operator). The static harness tension measured by the load cell was recorded after each trial. Data were analyzed for mean, variance, repeatability, and reproducibility. Operator feedback surveys were used to determine operator preferences.
The ECE R44/R129 procedure produced harness tensions which were quite slack. The FMVSS 213 procedure produced mid-level tensions while the three-prong tension gauge, two-finger method, and pinch test produced a range of magnitudes which roughly correlated to each subject’s self-selected target tension. Poor repeatability was apparent for all five harness tightening procedures. The FMVSS 213 method ranked lowest for ease-of-use. Operators preferred using the three-prong gauge, two-finger method, and pinch test.
The load cell readings were sensitive to the order and direction in which the operators adjusted the harness components. High amounts of friction within the harness might prevent it from acting as a homogeneous, continuous system. Sequential tightening of the various sections of harness and/or monitoring the tension at multiple locations might be valuable.
Julie Mansfield, Gretchen Baker, John Bolte