SYMPOSIA PAPER Published: 01 January 1993

The Effect of Mixed-Mode Loading on Delamination Fracture Toughness


Interlaminar fracture (delamination) is the dominant failure mechanism in most advanced composite materials. The resistance of a material system to delamination failure is generally quantified in terms of the interlaminar fracture toughness, Gc. The recently developed Mixed-Mode Bending (MMB) test is unique in that it facilitates measurement of the fracture toughness Gc under any combination of mixed-mode loading from pure Mode I to pure Mode II. This makes it a very attractive technique for developing interlaminar fracture failure criteria. This paper reports on an application of the MMB test to fatigue loading for the generation of Gc versus-curves and identification of the threshold value, Gth. Fatigue results from unidirectional IM7/5260 graphite/bismaleimide and IM7/8320 graphite/thermoplastic specimens are presented for a GI/GII ratio of 0.25. Static test results are also presented for both materials with the mode mix varying from pure Mode I to pure Mode II. The static results indicate different mixed mode failure laws for the two materials. All tests were conducted using displacement controlled loading under room temperature, dry conditions.

Author Information

Sriram, P
Wichita State University, Wichita, KS
Khourchid, Y
Wichita State University, Wichita, KS
Hooper, SJ
Wichita State University, Wichita, KS
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Developed by Committee: D30
Pages: 291–302
DOI: 10.1520/STP12635S
ISBN-EB: 978-0-8031-5252-6
ISBN-13: 978-0-8031-1879-9