ABSTRACT
Structural preforms of solid cross-sections are braided three dimensionally using the AS4C-GP-12K graphite yarn; the preforms are matrix-consolidated with the PR-500 epoxy resin to form solid composite load-bearing members via a resin transfer molding procedure.
In this paper, results from three members of square cross-sections and one of I-section are presented. The three square sections are reinforced with varying amount of axial yarns to enhance the composite axial stiffness and strength; the I-section is also reinforced with axial yarns placed in the top and bottom flanges for the same reason. All are tested to failure under 4-point bending load. Local strains on the surfaces of the test members are measured by strain gage rosettes; global beam deflections are recorded by a linear displacement gage; local failure initiation and growth on the beam surfaces are monitored by a closed circuit television camera. All recordings are taken in real time and as a function of the applied bending moment.
Concurrent mechanics models are developed to predict the local and the global responses of the beams under pure bending. The local model takes into account the yarn structure in the local unit-cells and extracts their effective properties by homogenizing the cells as a 3D anisotropic body; the global model considers the cells as 3D finite elements, so that the local and global responses of the beam can be described in much the same manner as the conventional 3D finite element analysis for elastic homogeneous bodies.
Elastic solutions for the surface strains and the flexual moduli of the beam members tested under 4-point bending are obtained using the analysis models; a comparison is made with the recorded results from the tests. In general, the elastic responses predicted by the models agree fairly closely with that found in the tests.
Local failures and failure progression in the beams under pure bending are also analyzed with the aid of a failure model; the failure model are developed on the basis of the observed failure mechanisms. These results, however, are reported in a separate paper to be published elsewhere.
