Accession Number : ADA293171

Title :   Characterization of Compressive Damage Mechanisms in Ceramic and Polymeric Matrix Composite Materials.

Descriptive Note : Final rept. Oct 93-Feb 95,

Corporate Author : SOUTHWEST RESEARCH INST SAN ANTONIO TX

Personal Author(s) : Lankford, James, Jr

PDF Url : ADA293171

Report Date : FEB 1995

Pagination or Media Count : 78

Abstract : Experiments involving expansion of the dynamic strain rate capabilities of the split Hopkinson pressure bar were performed. Unusually high strain rate hardening was obtained for the compressive failure of silicon nitride, while for silicon carbide, failure followed a lower rate of hardening, crack kinetics criterion. The silicon nitride results were interpreted in terms of plastic deformation, which changed the mode of failure from that observed at low strain rates, and altered the strength-strain rate dependency, apparently through the influence of dislocation generation upon microcrack nucleation. Recent experiments involved the response of monolithic ceramics and fiber-reinforced ceramic matrix composites to dynamic loading under hydrostatic confinement. Curious results were obtained for monolithic ceramics, which appeared to derive from crack initiation/growth kinetics and the stability of confined microcrack ensembles. Composites under confinement were found to reflect both dilatational and shear aspects of damage development, which are primarily a function of the matrix phase, while the effect of the fibers was to alter the relative kinetics and, under certain circumstances, the sequence of events involved in the macroscale growth of damage through the eventual zone of failure. Considerable effort has been devoted to new approaches to capturing the critical events associated with compressive kink band nucleation and development in polymeric matrix, fiber reinforced composites. jg

Descriptors :   *DAMAGE, *POLYMERS, *COMPOSITE MATERIALS, *CERAMIC MATRIX COMPOSITES, *COMPRESSIVE PROPERTIES, PLASTIC DEFORMATION, HIGH RATE, FIBER REINFORCED COMPOSITES, FAILURE, MATRIX MATERIALS, NUCLEATION, STRAIN RATE, CERAMIC MATERIALS, CRACK PROPAGATION, DISLOCATIONS, PRESSURE, HYDROSTATICS, DYNAMIC LOADS, CONFINEMENT(GENERAL), KINETICS, SPLITTING, HARDENING, LOW RATE, SILICON CARBIDES, SILICON NITRIDES, MICROCRACKING.

Subject Categories : Laminates and Composite Materials
      Inorganic Chemistry
      Ceramics, Refractories and Glass
      Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE