Experimental Study of Modal Characteristics for Heated Composite Structures

Abstract

Aircrafts with high Mach speeds are exposed to severe thermal load, which affect the performance of aircraft components. Although several experimental studies have been performed on the mechanical behavior of aircraft structures subjected to high temperatures, the experimental research on dynamic characteristics of structures under thermal load is limited. In this work, a series of laboratory modal tests have been carried out on carbon fiber reinforced silicon carbide matrix (C/SiC) composite plates under various radiant-heating conditions. High temperatures are achieved using quartz lamps, and their dynamic responses are measured using a scanning laser vibrometer. The modal parameters are evaluated by PolyMAX at several static temperature distributions. The temperatures are acquired by both full-field noncontacting infrared thermography and contacting thermocouples. The flat plates are with both free and constrained boundary conditions and the high temperature modal survey are performed for two kinds of thickness. The stiffened plate with free boundary condition is further studied as a more practical structure. Both the changes of the modal frequency and modal shape as temperature rises are presented. The effects of the thermal loads on the modal characteristics are investigated by test. The results show that the thermal stresses have a much greater effect on the modal characteristics than the change of the material properties due to heating. The test results could provide technical material for the limited database of high-temperature modal testing results.