SEDL / STP / STP1230-EB / STP14005S

Experimental Development of a Mixed-Mode Fatigue Delamination Criterion

Sriram, P
Wichita State University, Wichita, KS

Khourchid, Y
Wichita State University, Wichita, KS

Hooper, SJ
Wichita State University, Wichita, KS

Martin, RH
Analytical Services and Materials, Inc., Hampton, VA

Pages: 16    Published: Jan 1995

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Abstract

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, G^c. The recently developed mixed-mode bending (MMB) test is unique in that it facilitates measurement of the fracture toughness G^c 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 G versus N curves and identification of applicable mixed-mode fatigue failure laws. Fatigue results from unidirectional IM7/5260 carbon/bismaleimide and IM7/8320 carbon/thermoplastic specimens are presented for mode mixes varying from pure Mode I to pure Mode II. Static test results are also presented for both materials. The static and fatigue results indicate different mixed-mode failure laws for the two materials. Further, the effect of fatigue is shown to be both material and mode-mix dependent. All tests were conducted using displacement-controlled loading under room temperature dry conditions.