IMPACT PERFORMANCE OF SYMMETRIC AND ASYMMETRIC CFRP PLY-DROP LAMINATES- A COMPARATIVE STUDY
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors​ :
Evanthia PAPPA (ITALY), Russo MARIO (ITALY), Baroni ANTONIO , Stefano G. CORVAGLIAAbstract :
Ply-drops, also known as tapering, can increase the formation of out-of-plane stresses due to the discontinuity within the laminate [1,2]. The number of the ply-drops, the lay-up and the distance (stagger distance, k) of each successive ply-drop have the strongest effect on the mechanical performance of the component. While most studies are focusing on cycling loading and static performance of ply-drops [2-6], only few are focused on the impact performance. Kairouz et al. [7] concluded that there is a drop of approximately 20% of the threshold force for a ply drop compared to a normal laminate due to stress concentration in the ply-drop region, i.e. resin-rich pocket. Abdulhamid et al. [8] drew three main conclusions: a) the resin-rich pocket is damaged only when the delamination reached the location, b) the effect of ply-drops on the extend of delamination is related to the lay-up interfaces, c) delamination is affected by the ply-drop design i.e. steep and shallow tapered ply-drops. In a recent study, scarfed ply-drop composites tested under low velocity impact and showed a decrease of 20% of the average delamination area of asymmetric ply-drops [9]. This study provides a new approach on the manufacturing of tapering composites.
Cross ply and quasi isotropic UD T800 CF pre-impregnated composites with a common aerostructure toughened epoxy grade is used for this study. The impact behavior was determined in two different energy levels. Radios was used to evaluate the experimental results for both symmetric and asymmetric cases. The total (k) in both cases was the same, Fig. 1. Shells were used to model the impact phenomenon in the ply-drop region. The materials, properties and the boundary conditions were defined respectively in the model.
Traditionally, ply-drops are considered as stress risers. A usual damage initiation point are the resin-rich pockets. Following the easiest path, the damage propagates in the form of delamination and/or fibre debonding until the next resin-rich pocket. In this study, in the asymmetric ply-drops, a new path of energy dissipation is introduced, disturbed path. This behavior is related to the change of stiffness locally on the ply-drop region. A modern ply-zone technique was adopted, which unlike the traditional zone-based modeling technique allows the creation of composite materials with different fiber orientation, thickness and geometric shape. A good agreement between the numerical analysis and the experimental results is achieved fig 2.
Cross ply and quasi isotropic UD T800 CF pre-impregnated composites with a common aerostructure toughened epoxy grade is used for this study. The impact behavior was determined in two different energy levels. Radios was used to evaluate the experimental results for both symmetric and asymmetric cases. The total (k) in both cases was the same, Fig. 1. Shells were used to model the impact phenomenon in the ply-drop region. The materials, properties and the boundary conditions were defined respectively in the model.
Traditionally, ply-drops are considered as stress risers. A usual damage initiation point are the resin-rich pockets. Following the easiest path, the damage propagates in the form of delamination and/or fibre debonding until the next resin-rich pocket. In this study, in the asymmetric ply-drops, a new path of energy dissipation is introduced, disturbed path. This behavior is related to the change of stiffness locally on the ply-drop region. A modern ply-zone technique was adopted, which unlike the traditional zone-based modeling technique allows the creation of composite materials with different fiber orientation, thickness and geometric shape. A good agreement between the numerical analysis and the experimental results is achieved fig 2.