Accession Number : ADA303093

Title :   An Assessment of Buffer Strips for Improving Damage Tolerance of Composite Laminates at Elevated Temperature,

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

Personal Author(s) : Bigelow, C. A.

PDF Url : ADA303093

Report Date : DEC 1981

Pagination or Media Count : 14

Abstract : Fibrous composite materials like graphite/polyimide are light, stiff, and strong. They have great potential for reducing weight in aircraft structures. However, fibrous composites are usually notch sensitive and lose much of their strength when damaged. In the reference, buffer strips have been shown to greatly improve the damage tolerance of graphite/epoxy laminates loaded in tension. The purpose of the present investigation was to test the buffer strip configuration at elevated temperature. Accordingly, graphite/polyimide buffer strip panels were made and tested to determine their residual strength at ambient and elevated (l77 deg C) temperature. Each panel was cut in the center to represent damage. Panels were radiographed and crack-opening displacements were recorded to indicate fracture, fracture arrest, and the extent of damage in the buffer strip after arrest. One layup was used: 45/0/-45/90sub 2s. All panels had the same buffer strip spacing and width. The buffer strip material was O deg s-glass/PMR-l5. The buffer strips were made by replacing narrow strips of the 0 deg graphite plies with strips of the 0 deg S-glass on either a one-for-one or a two-for-one basis. Half of the panels were heated to l77+ or - 3 deg C before and during the testing. Elevated temperature did not alter the fracture behavior of the buffer configuration. (MM)

Descriptors :   *LAMINATES, BUFFERS, AIRCRAFT, COMPOSITE MATERIALS, DAMAGE ASSESSMENT, DISPLACEMENT, STRENGTH(MECHANICS), FRACTURE(MECHANICS), EPOXY LAMINATES, AIRFRAMES, TOLERANCES(MECHANICS), FAILURE(MECHANICS), GRAPHITE EPOXY COMPOSITES, POLYIMIDE PLASTICS.

Subject Categories : Laminates and Composite Materials

Distribution Statement : APPROVED FOR PUBLIC RELEASE