Seat Belt Assembly Tensile Test Procedure Development

Abstract

Federal Motor Vehicle Safety Standard (FMVSS) No. 209, Seat Belt Assemblies, specifies requirements, including performance requirements, for seat belt assemblies used in motor vehicles. The standard includes an assembly performance tensile test where seat belt assemblies must withstand a minimum tensile force and not exceed an elongation limit. NHTSA is evaluating potential changes to the test procedures, to better represent in-vehicle restraint angles. To support the tensile test procedure development, NHTSA’s Vehicle Research and Test Center collected in-vehicle measurements of seat belt assemblies with different occupant sizes and conducted tensile tests at the resulting representative angles. The seat belts were tested on fabricated fixtures using the original equipment manufacturer seat belt assemblies, including hardware and bolts. Out of 10 seat belt assemblies tested using the in-vehicle seat belt angles, four did not meet the performance criteria when tested using the procedure under evaluation. Additional testing was completed aiming to further develop the test procedure to determine if seat belt assemblies with load limiters can meet the force criterion in one test when using stroke-limited machines. All assemblies tested under the conditions of no webbing on the spool or minimal webbing on the spool reached the force criterion, although more steps were required to test with minimal webbing on the spool and the load limiters were not fully engaged. Overall, the updated test procedure was feasible and converted the in-vehicle geometry of the seat belt assembly into a more representative tensile test. The developed test procedures include a detailed method for collecting the in-vehicle angle measurements, incorporating all in-vehicle hardware, and fabricating unique fixtures to complete tensile tests with representative in-use angles.