Evaluation of Reduction of Strain Concentration around a Circular Hole in Composite Laminates by Fiber Steering Placement Technique

Abstract

Robotic Automated Fiber Placement (AFP) and Automatic Tape Lay-up (ATL) technique are well-developed and applied to practical producing process for enhancing productivity and reducing costs. The robotic process enables steering fiber or prepreg tape, which makes it possible to produce structures without fiber ends at the edge of open holes or cut-outs. It can reduce the stress concentration and prevent failure from the fiber ends located at the hole surfaces. The strength of the structure can significantly improve with the presence of cut-outs and open holes. In this study, a simplified model of a laminate comprising steered layers with a circular hole is proposed that can be produced by employing the steering technique. The thickness distribution and the elastic properties were theoretically derived on the basis of a geometrical consideration and a classical lamination theory. The stress and strain distributions of axisymmetric laminated plates were semi-analytically derived for an axisymmetric load and a uniaxial uniform load to understand the mechanism and to evaluate the degree of reduction in stress concentration.