Accession Number : ADA182527

Title :   Failure Modes in Composite Materials.

Descriptive Note : Final rept. 1986-1987,

Corporate Author : NAVAL ACADEMY ANNAPOLIS MD

Personal Author(s) : Robinson,David A

PDF Url : ADA182527

Report Date : 19 May 1987

Pagination or Media Count : 58

Abstract : Presently in all types of materials, mechanical stiffness is an important qualitative and quantitative measure of structural integrity. When a material is repeatedly stressed, some type of internal damage is known to occur which changes the mechanical property of the matter. Although this phenomenon has been long studied in metals, it is not well understood in composites; composites tend to fail instantly with no apparent mechanical warning. It, as is true in the case of graphite and epoxy, the fibers conduct electricity and the resin does not, then it seems likely that increases in the electrical resistance in the direction of the fibers will indicate the presence of broken fibers and thus be a measure of fatigue damage. Even if resin damage is assumed to play a role in fatigue failure, the breaking of the graphite fibers which do carry the load is an essential step in the reduction of the ultimate strength of the material. This assumption was proven in this electrical resistance was considerably greater than the percentage change in the mechanical stiffness of the material. Consequently, electrical resistance measurements prove to be a sensitive and practical method for detecting internal damage in composite materials which are made up of conducting fibers embedded in a nonconducting matrix.

Descriptors :   *COMPOSITE MATERIALS, *FAILURE(MECHANICS), ELECTRICAL MEASUREMENT, ELECTRICAL RESISTANCE, ELECTRICITY, FAILURE, CARBON FIBERS, DAMAGE, FATIGUE(MECHANICS), FIBERS, GRAPHITE, INTERNAL, MATERIALS, MECHANICAL PROPERTIES, METALS, POLYMERS, RELIABILITY, STIFFNESS, STRENGTH(GENERAL), STRUCTURAL PROPERTIES, EPOXY COMPOSITES, GLASS FIBERS, HELICOPTER ROTORS, TACTICAL AIRCRAFT, ELECTRICAL CONDUCTIVITY, IMPEDANCE BRIDGES, DAMAGE ASSESSMENT, STRUCTURAL ANALYSIS, FATIGUE TESTS(MECHANICS), AIRFRAMES

Subject Categories : Laminates and Composite Materials
      Mechanics
      Military Aircraft Operations

Distribution Statement : APPROVED FOR PUBLIC RELEASE