Accession Number : ADA299718

Title :   Mechanics of Multi-Layered Materials and Composites.

Descriptive Note : Final rept.,

Corporate Author : BROWN UNIV PROVIDENCE RI DIV OF ENGINEERING

Personal Author(s) : Shih, C. F.

PDF Url : ADA299718

Report Date : 1995

Pagination or Media Count : 5

Abstract : Using a video microscope equipped with microscope lens, we have recorded various stages of kink band formation and band width broadening in unidirectional fiber composites. These deformation modes are different from the commonly assumed kinematics employed by many investigators. The in-situ video pictures show that the early stage of kink band formation involves progressive, cooperative fiber bending/rotation and plastic shearing of the matrix within a shallow narrow band of about 10 fiber diameters wide. This deformation mode causes geometric softening of the material within the band. At some point in this process, fiber rotation within the kink band is halted. The termination of fiber rotation, referred to as fiber lock-up, is believed to be brought about by the stiffening of the composite shearing response at large shear strains. This forces the kink band to spread into the unkinked material (which is soft in shear) by band width broadening to accommodate the continuous overall end-shortening of the specimen. In the band broadening stage, the bends in the fiber (at the edges of the kink band) propagate into the unkinked material much like a pair of dislocations moving away from one another. Band widths of 30 to 50 fiber diameters with a steeper inclination than the initial band orientation have been observed. The final width of the kink band is set when the fibers snap. The mechanism of band broadening bears some similarity to neck propagation in certain polymers often termed cold drawing.

Descriptors :   *COMPOSITE MATERIALS, *FIBER REINFORCED COMPOSITES, FIBERS, POLYMERS, DEFORMATION, STRAIN(MECHANICS), BENDING, STRENGTH(MECHANICS), DISLOCATIONS, SHEAR STRESSES, PLASTIC PROPERTIES, HARDNESS, COLD DRAWING.

Subject Categories : Laminates and Composite Materials

Distribution Statement : APPROVED FOR PUBLIC RELEASE