Accession Number : ADA185855

Title :   Interlaminar Shear Fracture Toughness and Fatigue Thresholds for Composite Materials.

Descriptive Note : Technical memo.,

Corporate Author : NATIONAL AERONAUTICS AND SPACE ADMINISTRATION HAMPTON VA LANGLEY RESEARCH CEN TER

Personal Author(s) : O'Brien, T K ; Murri, Gretchen B ; Salpekar, Satish A

PDF Url : ADA185855

Report Date : Aug 1987

Pagination or Media Count : 68

Abstract : Static and cyclic end notched flexure (ENF) tests were conducted on a T300/BP907 graphite epoxy, and S2/SP250 glass epoxy, and an AS4/PEEK graphite thermoplastic to determine their interlaminar shear fracture toughness and fatigue thresholds for delamination in terms of limiting values of the mode II strain energy release rate, GII, for delamination growth. The influence of precracking and data reduction schemes are discussed. Finite-element analysis indicated that the beam theory calculation for GII with the transverse shear contribution included was reasonably accurate over the entire range of crack lengths. Cyclic loading significantly reduced the critical Gii for delamination. A threshold value of the maximum cyclic GII below which no delamination occurred after one million cycles was identified for each material. In addition, residual static toughness tests were conducted on glass epoxy specimens that had undergone one million cycles without delamination. A linear mixed-mode delamination criteria was used to characterize the static toughness of several composite materials; however, a total G threshold criterion appears to characterize the fatigue delamination durability of composite materials with a wide range of static toughnesses. Keywords: Fatigue, Delamination, Interlaminar, Shear, Composite materials.

Descriptors :   *COMPOSITE MATERIALS, *TOUGHNESS, *FATIGUE(MECHANICS), *FRACTURE(MECHANICS), CRACKS, CYCLES, DATA REDUCTION, EPOXY COMPOUNDS, FATIGUE, FINITE ELEMENT ANALYSIS, GLASS, GRAPHITE, GROWTH(GENERAL), LAMINATES, LENGTH, LOADS(FORCES), SEPARATION, SHEAR PROPERTIES, STATIC TESTS, STATICS, THERMOPLASTIC RESINS, THRESHOLD EFFECTS, STATIC TESTS, NOTCH SENSITIVITY

Subject Categories : Ceramics, Refractories and Glass

Distribution Statement : APPROVED FOR PUBLIC RELEASE