ILLUSTRATION OF THE USE OF MODAL ASSURANCE CRITERION TO DETECT STRUCTURAL CHANGES IN AN ORBITER TEST SPECIMEN

摘要

The modal assurance criterion provides a numerical basis for identifying changes in dynamic characteristics. The scalar constant is normally used to indicate consistency between modal vector estimates obtained from an empirically-based model and modal vector estimates obtained from a finite element model. Application of the Modal Assurance Criterion to vector estimates, obtained at successive intervals in the operational life of a structure/provides a basis for determining that significant structural change has occurred. The basis for isolating the change, or damage, to a particular locale is also determined. This paper illustrates that application of numerical processes to modal test data, obtained at successive intervals in an environmental test of an Orbiter aft bulkhead (AFA-12), provided an indication of change in dynamic characteristics caused by local fatigue damage and wear on friction-producing seal surfaces. The process reported herein illustrates that Modal Assurance Criteria comparisons were most inconsistent in areas where damage was found by conventional inspection methods. This indicates that such comparisons provide a practical basis for detecting and locating specific areas of structural damage in a complex structure.