An Estimation of Torsional Compliance (Stiffness) from Free-Free FRF Measurements: eRCF Application

  • Jeffrey Poland
  • Alexander Young
  • Hasan Pasha
  • Randall AllemangEmail author
  • Allyn Phillips
Part of the Conference Proceedings of the Society for Experimental Mechanics Series book series (CPSEMS)


The enhanced rotational compliance function (eRCF) is a useful concept for estimation of static torsional compliance/stiffness of a structure using measured frequency response functions (FRFs) from a structural system with free-free boundary conditions. The eRCF is estimated using FRF measurements from impact testing, namely a four by four (4 × 4) FRF matrix at four separate, symmetric locations on a structure. A companion paper presents the complete theoretical development and initial analytical and experimental examples. The theoretical background is summarized in this paper along with the results from extensive testing on automotive bodies, involving several tests on the same body style along with tests from different body styles. Comparisons are made to traditional, static torsion tests and a discussion of practical implementation is included.


Torsional stiffness Static torsion test eRCF 



The authors would like to thank a number of individuals who have contributed to the success of this effort. Bill Buckley at BMW-MC, Helmut Schneeweiss, Dr. Luc Cremers, and Martin Kolbe at BMW-AG, Mike Messman at Clemson-ICAR.

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Copyright information

© The Society for Experimental Mechanics, Inc. 2015

Authors and Affiliations

  • Jeffrey Poland
    • 1
  • Alexander Young
    • 2
  • Hasan Pasha
    • 2
  • Randall Allemang
    • 2
    Email author
  • Allyn Phillips
    • 2
  1. 1.Acoustic AnalystBMW Manufacturing Co., LLCGreerUSA
  2. 2.Department of Mechanical and Materials Engineering, College of Engineering and Applied ScienceUniversity of CincinnatiCincinnatiUSA

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