Accession Number : ADA290261

Title :   Origins of Imperfections in Composite Materials.

Descriptive Note : Final rept. 30 Sep 91-29 Sep 94,

Corporate Author : JOHNS HOPKINS UNIV BALTIMORE MD CENTER FOR NONDESTRUCTIVE EVALUATION

Personal Author(s) : Green, Robert E., Jr

PDF Url : ADA290261

Report Date : 29 NOV 1994

Pagination or Media Count : 55

Abstract : This research applied advanced ultrasonic techniques for detection of the origin of imperfections in composite materials used in aircraft and aerospace structures. Previous work supported by the U.S. Air Force Office of Scientific Research showed that ultrasonic attenuation monitoring proved to be superior to other nondestructive evaluation techniques for detection of early fatigue damage in aluminum alloys used in aircraft construction. In addition ultrasonics is the only technique which affords the possibility of detecting defects from one side of the material. In order to detect microscopic defects, an additional aspect of this work was to optimize acoustic microscopy techniques for detection of the origin of very small imperfections. Included in the techniques used were air-coupled ultrasound to detect the quality of composite prepregs. Because ultrasonic techniques are not capable of measuring residual stress in composite materials a novel micro-photoelastic system was developed for measurement of residual stress in optically translucent ceramic matrix composites. However, ultrasonics could detect manufacturing flaws and micro-porosity in ceramic composites. The overall goal was to identify the origin of imperfections in composite materials used in aircraft and aerospace structures and to optimize ultrasonic nondestructive evaluation techniques for detecting these imperfections. (MM)

Descriptors :   *COMPOSITE MATERIALS, *DEFECTS(MATERIALS), AIRCRAFT, NONDESTRUCTIVE TESTING, ALUMINUM ALLOYS, LAMINATES, CERAMIC MATRIX COMPOSITES, FIBER REINFORCED COMPOSITES, ACOUSTIC DETECTION, METAL MATRIX COMPOSITES, GLASS, CRACK PROPAGATION, CARBON CARBON COMPOSITES, RESIDUAL STRESS, AEROSPACE CRAFT, PREPREGS, FAILURE(MECHANICS), FATIGUE TESTS(MECHANICS), ULTRASONIC TESTS, PHOTOELASTICITY, ELASTIC WAVES, GRAPHITE EPOXY COMPOSITES, THERMOSETTING PLASTICS.

Subject Categories : Laminates and Composite Materials
      Aircraft
      Test Facilities, Equipment and Methods

Distribution Statement : APPROVED FOR PUBLIC RELEASE