SYMPOSIA PAPER Published: 01 January 1992

Efficient Use of Film Adhesive Interlayers to Suppress Delamination


An experimental and analytical study was conducted to assess the effectiveness of the efficient use of film adhesive interlayers in suppressing delamination in composite laminates. Efficiency was achieved by two means: (1) the adhesive interlayer was placed only at delamination critical interfaces, identified by calculating the interlaminar stresses and applying the Quadratic Delamination Criterion, in comparison to all ply interfaces as in previous investigations and (2) finite-width strips were used rather than full-width film adhesive layers. Graphite/epoxy [± 157/07]s laminates, with FM300 Interleaf material placed at the + 15/-15 interface, were tested in uniaxial tension. For all specimens with film adhesive interlayers, the load at which delaminations initiated was about 50% higher than in the case of the specimens without film adhesive. The final failure stresses of the specimens with film adhesive also averaged 40% higher than those without the interlayers. These results were not discernably affected by the use of a reduced number of interlayers and, furthermore, did not depend upon the width of the strip. This indicates that, within practical manufacturing limitations, any strip which is as large as the interlaminar stress boundary layer would be successful in inhibiting delamination initiation. However, in tests which Teflon® strips were inserted to simulate preinitiated delamination, the results were similar to those in which no film adhesive interlayers were present. This indicates that the interlayers are not successful in suppressing the growth of delamination which is already present. Experimental results also suggest the possible existence of a “critical” delamination initiation size.

Author Information

Lagace, PA
Massachusetts Institute of Technology, Cambridge, MA
Bhat, NV
Massachusetts Institute of Technology, Cambridge, MA
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Developed by Committee: D30
Pages: 384–396
DOI: 10.1520/STP20171S
ISBN-EB: 978-0-8031-5184-0
ISBN-13: 978-0-8031-1426-5