Accession Number : ADA302024

Title :   Compression Failure Mechanisms of Composite Structures.

Descriptive Note : Final rept. 1 Aug 82-31 Jul 85,

Corporate Author : WASHINGTON UNIV ST LOUIS MO CENTER FOR COMPOSITES RESEARCH

Personal Author(s) : Hahn, H. T. ; Sohi, Mohsen ; Moon, Suresh

PDF Url : ADA302024

Report Date : JUN 1986

Pagination or Media Count : 116

Abstract : An experimental and analytical study was conducted to delineate the compression failure mechanisms of composite structures. Results on unidirectional and quasi-isotropic graphite/epoxy laminates were published previously. The present report summarizes further results on kink band formation in unidirectional composites. In order to assess the compressive strengths and failure modes of fibers themselves, a fiber bundle was embedded in epoxy casting and tested in compression. A total of six different fibers were used together with two resins of different stiffnesses. The failure of highly anisotropic fibers such as Kevlar 49 and P-75 graphite was due to kinking of fibrils. However, the remaining fibers--T3OO and T7OO graphite, E-glass, and alumina--failed by localized microbuckling. Compressive strengths of the latter group of fibers were not fully utilized in their respective composites. In addition, acoustic emission monitoring revealed that fiber-matrix debonding did not occur gradually but suddenly at final failure. The kink band formation in unidirectional composites under compression was studied analytically and through microscopy. The material combinations selected include seven graphite/epoxy composites, two graphite/thermoplastic resin composites, one Kevlar 49/epoxy composite and one S-glass/epoxy composite. The dominant mode of failure in all composites was the kink band initiation and propagation. Thus, not only microbuckling but also compressive failure of fibers could trigger kink band formation. An analytical model was developed under the assumption of plastic yielding in the matrix. (MM)

Descriptors :   *COMPOSITE STRUCTURES, *EPOXY LAMINATES, *FAILURE(MECHANICS), *GRAPHITE EPOXY COMPOSITES, COMPRESSION, STRESS STRAIN RELATIONS, FIBER OPTICS, STRESS ANALYSIS, POLYMERS, COMPOSITE MATERIALS, GLASS, FRACTURE(MECHANICS), ANISOTROPY, ISOTROPISM, COMPRESSIVE STRENGTH, EPOXY RESINS, ACOUSTIC EMISSIONS, BUNDLES.

Subject Categories : Laminates and Composite Materials

Distribution Statement : APPROVED FOR PUBLIC RELEASE