SYMPOSIA PAPER Published: 01 January 1991

Effects of T-Tabs and Large Deflections in Double Cantilever Beam Specimen Tests


A simple strength of materials analysis was developed for a double cantilever beam (DCB) specimen to account for geometric nonlinearity effects due to large deflections and T-tabs. A new DCB data analysis procedure was developed to include the effects of these nonlinearities. The results of the analysis were evaluated by performing DCB tests on materials having a wide range of fracture toughnesses. The composite materials used in the present study were T300/5208, IM7/8551-7, and AS4/PEEK.

Based on the present analysis, for a typical load-point deflection/crack length ratio of 0.3 (for AS4/PEEK), T-tabs and large deflections lead to a 19 and 6% effect, respectively, in the computed Mode I strain energy release rate. Design guidelines for DCB specimen thickness and T-tab height were also developed in order to keep effects due to these nonlinearities within 2%.

Based on the test results, for both hinged and tabbed specimens, the effects of large deflection (compared to linear DCB results) on the Mode I fracture toughness (GIc) were almost negligible (less than 1%) in the case of T300/5208 and IM7/8551-7; however, for AS4/PEEK, the effect was from 2 to 3%. The effects of T-tabs (compared to a linear DCB with tabs) on GIc were more significant, with T300/5208, IM7/8551-7, and, AS4/PEEK showing a 5, 15, and 20% effect, in that order.

Author Information

Naik, RA
Analytical Services & Materials, Inc., Hampton, VA
Crews, JH
NASA Langley Research Center, Hampton, VA
Shivakumar, KN
Analytical Services & Materials, Inc., Hampton, VA
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Developed by Committee: D30
Pages: 169–186
DOI: 10.1520/STP17718S
ISBN-EB: 978-0-8031-5169-7
ISBN-13: 978-0-8031-1419-7