Accession Number : ADA320017

Title :   Deformation and Failure of Metal-Matrix Composites under Dynamic Loads.

Descriptive Note : Final technical rept. 1 Mar 92-31 Dec 95,

Corporate Author : SRI INTERNATIONAL MENLO PARK CA

Personal Author(s) : Klopp, R. W. ; Shockey, D. A. ; Crocker, J. E. ; Giovanola, J. H.

PDF Url : ADA320017

Report Date : 22 DEC 1996

Pagination or Media Count : 75

Abstract : SRI International conducted a three-year program of experiments, microstructural examinations, and analysis to determine the rate sensitivity of deformation and failure of metal-matrix composites (MMC) and to understand and model the role of interfaces and constituents on dynamic failure. Silicon-carbide fiber reinforced Timetal 21S and Ti-15-3 matrices in three heat treatment conditions were studied. The work included dynamic fiber pushout experiments to measure dynamic interface strength, notched three-point-bend experiments with acoustic emission sensors to determine the static fracture resistance, and notched one-point-bend experiments to determine dynamic fracture resistance. Microstructural examinations were performed on transverse and longitudinal cross sections. The nature of interface failure, fiber failure, and matrix failure was established. A key finding was that toughening from fiber bridging is not obtained under bending loads. In bending, fibers fail well in advance of the crack tip and are thereby prevented from bridging matrix cracks. A two-dimensional finite element model of the composite was developed in which fibers, matrix, and interfaces in the vicinity of the notch root were modeled explicitly. The model can be used in parameter studies to investigate changes in interface and constituent properties, and loading rate, and hence assist in designing MMCs having tailored combinations of strength, toughness, and, particularly, greater resistance to bend failure.

Descriptors :   *DEFORMATION, *METAL MATRIX COMPOSITES, *FAILURE(MECHANICS), STRESS STRAIN RELATIONS, MICROSTRUCTURE, STRESS ANALYSIS, FINITE ELEMENT ANALYSIS, FIBER REINFORCED COMPOSITES, FRACTURE(MECHANICS), IMPACT STRENGTH, DYNAMIC LOADS, SILICON CARBIDES, TITANIUM ALLOYS, METALLOGRAPHY, BENDING STRESS, NOTCH TOUGHNESS, MICROCRACKING.

Subject Categories : Laminates and Composite Materials
      Properties of Metals and Alloys

Distribution Statement : APPROVED FOR PUBLIC RELEASE