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The Challenge of Dynamic Similarity Assessment

  • Adam C. MoyaEmail author
  • Julie M. Harvie
  • Mike J. Starr
Conference paper
Part of the Conference Proceedings of the Society for Experimental Mechanics Series book series (CPSEMS)

Abstract

Throughout the development cycle of structural components or assemblies that require new and unproven manufacturing techniques, the issue of unit to unit variability inevitably arises. The challenge of defining dynamic similarity between units is a problem that is often overlooked or forgotten, but can be very important depending on the functional criteria of the final product. This work aims to provide some guidance on the approach to such a problem, utilizing different methodologies from the modal and vibration testing community. Expanding on previous efforts, a non-intrusive dynamic characterization test is defined to assess similarity on an assembly that is currently being developed. As the assembly is qualified through various test units, the same data sets are taken to build a database of “similarity” data. The work presented here will describe the challenges observed with defining similarity metrics on a multi-body structure with a limited quantity of test units. Also, two statistical characterizations of dynamic FRFs are presented from which one may choose criterion based on some judgment to establish whether units are in or out of family. The methods may be used when the “intended purpose” or “functional criteria” are unknown.

Keywords

Modal testing Correlation Frequency response functions Similarity 

Nomenclature

GT(ω)

Complex average of all FRF’s in data set

i

Degree of freedom

n

Total number of DOF’s

T

Individual test run

Hi(ω)

FRF for individual DOF

N

Total number of variability tests

L

Individual test unit

PL(ω)

Complex average of all FRF’s for individual test unit L

\( \overline{X}\left(\omega \right) \)

Mean of all average FRF’s, P L (ω)

Nt

Total number if test units available

α

Bounding scale factor

\( \overline{\sigma}\left(\omega \right) \)

Average standard deviation from all test units

ECSAC

Experimental Cross Signature Scale Factor

ECSF

Experimental Cross Signature Assurance Criterion

ECSC

Experimental Cross Signature Correlation value

H

Hermitian transpose

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Copyright information

© The Society for Experimental Mechanics, Inc. 2016

Authors and Affiliations

  • Adam C. Moya
    • 1
    Email author
  • Julie M. Harvie
    • 2
  • Mike J. Starr
    • 2
  1. 1.Experimental Mechanics, NDE, and Model Validation DepartmentSandia National LaboratoriesAlbuquerqueUSA
  2. 2.Program and Test Integration DepartmentSandia National LaboratoriesAlbuquerqueUSA

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