Why not Designing Multidirectional Laminates with In-Plane Strength Design Sheets Applying the UD Criteria of Tsai–Wu and Cuntze? Part2: Application

Part2 of the paper outlines and demonstrates the generation of Non-first-ply-failure (Non-FPF) areas for both the Tsai–Wu and the Cuntze criteria. Since local strain envelope shapes for a single material already differ Strength Failure Criteria (SFC)-specifically, the resulting Non-FPF areas deviate as well. The question ‘How far different materials possess different envelopes?’ is answered by analyzing five differently stiff CFRPs and a single GFRP material. The computation of a Reserve Factor f_RF is in focus of the presented analyses. It is essential for designers. In this context, practical simplification is proposed. The determined Non-FPF areas are further simplified using approximate circles. The Nettles-circle (NC) has earlier been proposed for Tsai–Wu envelope. As the NC is not working for Cuntze, due to the different shapes of the resulting Non-FPF areas, a similar circle representation is presented for Cuntze’s SFC. Both circle simplifications can be efficiently used by designers to assess directly the reserve factors required for laminates. The assessment is based on comparison of the circles’ radii r and the principal strain state magnitude \(r\ge \sqrt{{\varepsilon }_{I}^{2}+{\varepsilon }_{II}^{2}}\) $r\ge \sqrt{{\epsilon }_I^2+{\epsilon }_{\mathit{II}}^2}$ of the laminate for a single examined load state or a group of loads.