A gravitational analogy for defect distribution in thin laminates

acm7 Tracking Number 31

The unavoidable presence of manufacturing defects in complex fiber-placed laminates, be it gaps/overlaps, fiber angle deviation, or excessive curvature, introduces potential failure initiation sites when the defects occur at the same spatial location. The ability to alter the location of the defects within a ply is under some control of the designer through the adjustment of Automated Fiber Placement (AFP) process parameters such as ply starting points and alternate layup strategies. Development of a metric to assess the best relative distribution of the defects in each ply, and thus the laminate as a whole, provides a useful design objective for the process planner. This paper presents a methodology based on Newton’s Law of Universal Gravitation that calculates the effect of multiple defect locations within a laminate using an inverse square law. The derivation of the law for points, lines, and areas residing in overlapping thin layers is presented, highlighting the contributions of proximity and orientation for each geometric type. Several examples using basic geometries are included to demonstrate the details of the calculation. The solution is extended to the realm of composites by categorizing the expected defects due to AFP manufacture as lines and polygons, and various enhancements are introduced to form a realistic metric for defect interaction and laminate design. Demonstration of the algorithm within a process planning program illustrates the usefulness of this technique for optimal distribution of manufacturing defects.