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Title: Modes of deformation and failure of Kevlar 49 fibers and composites

Fracture-topography and stress-optical-microscopy are utilized to study the deformation and failure modes of Kevlar 49 fibers and their epoxy composites. Fracture topographies of bare yarns, composite strands, and pressure vessels reveal Kevlar 49 fibers fail in tension by axially splitting 20 to 50 times their diameter D (20 to 50D) along their lengths. This type of fiber failure involves shear-induced microvoid growth throughout the fiber which occurs principally along the fiber axis, followed by macroscopic crack propagation through such microscopic crack propagation through such microvoids. Fiber splitting in the fracture of single filaments is < 5D because of the absence of external shear stresses. The topographies observed in fractured single filaments are described in terms of longitudinal and transverse fiber crack propagation paths in the fiber skin and core. Hydrolytically-degraded Kevlar 49 fibers exhibit lower fiber split lengths in composites. There is a correlation between the percentage of fibers that exhibit transverse failure without splitting and the composite strength. Stress-optical-microscopy studies of the deformation and failure processes of simple composite laminates are reported as a function of laminate geometry, temperature, and fiber surface treatment.
Authors:
; ; ; ; ;
Publication Date:
OSTI Identifier:
5277375
Report Number(s):
UCRL-89626; CONF-840459-3
ON: DE84004162
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: 29. national SAMPE symposium, Reno, NV, USA, 3 Apr 1984
Research Org:
Lawrence Livermore National Lab., CA (USA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ARAMIDS; FAILURES; COMPOSITE MATERIALS; DEFORMATION; EPOXIDES; FIBERS; FILAMENTS; FRACTURES; OPTICAL MICROSCOPY; SCANNING ELECTRON MICROSCOPY; TOPOGRAPHY; ELECTRON MICROSCOPY; MATERIALS; MICROSCOPY; ORGANIC COMPOUNDS; ORGANIC OXYGEN COMPOUNDS; PETROCHEMICALS; PETROLEUM PRODUCTS; PLASTICS; SYNTHETIC MATERIALS 360303* -- Composite Materials-- Mechanical Properties-- (-1987); 360403 -- Materials-- Polymers & Plastics-- Mechanical Properties-- (-1987)