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A series of tests was run to characterize the through-the-thickness tensile strength of a variety of composites that included two-dimensional (2D) braids, 2D and three-dimensional (3D) weaves, and prepreg tapes. A new test method based on a curved beam was evaluated. The through-the-thickness deformations were characterized using moire interferometry. Failures were significantly different between the 2D materials and the 3D weaves. The 2D materials delaminated between layers due to out-of-plane tensile stresses. The strength of the 2D textile composites did not increase relative to the tapes. The 3D weaves failed due to radial cracks that initiated between the surface yarns because of the circumferential stresses along the inner radius. A circumferential crack similar to the 2D materials produced the final failure. Final failure in the 3D weaves occurred at a lower bending moment than in the other materials. The early failures were caused by radial crack formation rather than a low through-the-thickness strength.
composite materials, carbon epoxy, textile composites, braids, weaves, through-the-thickness tensile strength, curved beam, delamination, moiré interferometry, testing, design
Research engineer, Army Research Laboratory Vehicle Structures Directorate, NASA Langley Research Center, Hampton, VA
Assistant professor, University of Florida, Gainesville, FL