Failure Modeling of Thermoplastic Butt-Joint Stiffened Panels by Quasi-Static Loading

In this work the quasi-static response of thermoplastic butt-joint stiffened beam in bending conditions is modeled. In these panels, the stiffener is connected to the skin by a short- fiber reinforced filler. Although this type of connection performs very well in a pull-off loading (fracture loading is 10 times higher than welded connection), optimization is required regarding its impact performance. The main issue concerning this loading type is the extreme resistance to impact until a certain threshold, upon which the stiffener-skin connection fails in an instable manner, however leaving only barely visible damage on the skin side. Impact tests have been performed on a typical butt joint panel and the main conclusion was that the impact resistance of the butt joint and understanding the impact and post impact behavior is of prime importance. Control of the impact induced damage is therefore crucial for the applicability of such production and connection techniques. This asks for thorough understanding of the mechanism playing a role in deformation, failure initiation and propagation for the combination of materials and production process used. Numerical simulations and experiments for quasi-static and dynamic behavior of structure are presented. This study is performed in the framework of a collaborative research project on behavior of butt- joint stiffened panels under low velocity impact. The particularity of the studied stiffened panel is that skin and stiffeners are co-consolidated in one production step with the use of thermoplastic composites. The objective of this project is to understand the processes of damage of a panel under the impact by means of experiments and numerical modeling of these processes, and optimization of geometrical and physical parameters of the structure. It has become clear that optimization of the design without a correct numerical simulation is difficult. The numerical simulation is planned in several stages. The first step is the simulation of a structural failure in two-dimensional formulation for the quasi-static and impact loading (three-point bending test) in a view to calibrate the physical properties necessary for the simulation of a full panel. This will be followed by the simulation in three-dimensional formulation of a full panel. This article describes the experiment and numerical simulation of structural failure in two-dimensional formulation for the three-point bending test.