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Experimental observations and finite element analysis of the initiation of fiber microbuckling in notched composite laminatesAn understanding was developed of the factors that determine the semi-circular edge-notched compressive strength and the associated failure mode(s) were identified of thermoplastic composite laminates with multidirectional stacking sequences. The experimental observations and the detailed literature review suggest at least four factors that affected the determination of the strain levels at which fiber microbuckling initiates and thus, partially control the composite's compression strength. The dependent variables studied are the compressive strength of a reduced gage section compression specimen and the compression strength of a compression specimen with two semi-circular edge notches (no opposite free edges) centered along the gage section. In this research, specimens containing two semi-circular edge notches (no opposite free edges) were loaded in compression at a relatively slow rate to provide more stable development of fiber microbuckling damage. The results indicate that the local constraints (free surfaces, supporting ply orientation, and resin-rich regions) significantly affect the strain level for the initiation of in-plane fiber microbuckling. Preliminary results at an elevated temperature, 77 C, showed the shear stress yield strength of the resin was reduced and consequently, the resistance to fiber microbuckling was also reduced. The finite element analysis of the perfectly straight fiber problem indicates that the free surface effect causes a 10 percent reduction in the critical buckling strain. However, the experimentally measured reduction for fibers with an initial fiber curvature, was 35 percent.
Document ID
19900016043
Acquisition Source
Legacy CDMS
Document Type
Contractor Report (CR)
Authors
Guynn, E. Gail (Texas A&M Univ. College Station, TX, United States)
Bradley, Walter L. (Texas A&M Univ. College Station, TX, United States)
Date Acquired
September 6, 2013
Publication Date
December 20, 1989
Subject Category
Structural Mechanics
Report/Patent Number
NAS 1.26:186207
NASA-CR-186207
Accession Number
90N25359
Funding Number(s)
CONTRACT_GRANT: NAG1-659
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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