Mechanical performance of through thickness reinforcement for damage tolerant aircraft structurse

Abstract

This thesis is focused on investigating the mechanical performance of Z-pin reinforced laminate under different loading conditions and the development of automatic Z-pin insertion machines. A versatile surface-based finite element modeling strategy is developed for the analysing of cohesive contact analysis. The modeling approach is developed based on bridging law and modified Coulomb friction law. This modeling method has been validated via comparing against the benchmark work, including the Double cantilever beam test, 4-point End-Notched Flexure test, Mixed-mode Bending test. The tensile fibre failure, modeled using the Weibull Failure criterion, verified through comparing the modeling results to an experimental tensile test result of unidirectional laminate coupon. The modeling approach carried forward to the analysis of the Z-pin reinforced laminate. A three-dimensional modeling approach was used in order to address the microstructural features of Z-pinned laminates. These features, including the presence of resin pockets surrounding Z-pin, stacking sequence, Internal splitting. The interface between Z-pin and laminate, as well as internal splitting, were described by customised surface-based cohesive contact. There are a few factors that significantly affect the modeling results, including Frictional coefficient, internal splitting, mode mixities, and each of them was discussed in the parametric study section. The modeling approach was used to justify the performance of Z-pins in resisting dynamic mode I and mode II delamination has been investigated at a high loading rate. It was found that the Z-pin efficiency in resisting mode I delamination decreased with increasing loading rate compared to the quasi-static loading case, and the loading rate in the mode II test did not significantly influence the maximum bridging force. Moreover, the FE result tends to delay the shift of the failure mode from pull-out to pin rupture. An automatic Z-pin insertion machine is proposed in the last chapter. Building based on a 3D-printer, the insertion machines able to move, heat, and insert Z-pins by the control of Commerical software LabView. Keywords: Bridging law, Surface-based, Benchmark work. Three-Dimensional FE model, Dynamic bridging, LabView