Global Symmetry, Sphericity, and Roundness in Hemisphere Forming of Fabric Reinforcements: Associations With Local Fiber Distortions and a Black‐Box Quality Prediction

ABSTRACT An experimental analysis is conducted to identify the effect of design variables on a set of global geometrical quality metrics, including sphericity, roundness, and symmetry, in hemisphere draping of woven fabrics, next to the commonly employed primary (local) quality metrics concerning the fiber distortions. These secondary global metrics may be deemed important in practice, for example, during post‐forming processes and assembly of draped parts. Thirty punch‐forming configurations were designed and tested by varying process control factors, including (1) the fabric orientation, (2) the number of layers, (3) the number of clamps on the blank holder, and (4) the pressure distribution on the clamps. It was found that most samples with a fully uniform distribution of clamping pressure and sufficiently high mean pressure, result in a roundness value of 90% and above. Next to these control factors, a higher number of clamps (with equally‐spaced positions) generated a higher symmetry in the draped parts—identified via the center of mass displacement of samples. The sphericity for all tested configurations was similar ( ±4%; out of the maximum of 84% for a perfect hemisphere). The study also showed how a basic primary “quality score” as well as “forming quality classes” may be defined and predicted for design. Among the secondary metrics studied, the symmetry was most highly correlated with the primary fiber distortion factors, followed by the roundness.