Effects of Layup and Matrix Toughness on Modeling Notched Carbon Fiber Panels in Out-of-Plane Bending

摘要

Predicting the damage progression behavior of fiber composites using finite element methods is an ongoing challenge in design of high performance structures. A common application of fiber composites is out-of-plane bending of a notched composite panel. This loading occurs, for example, in an aircraft fuselage near reinforcing members such as ribs or stringers. The material parameters used by the finite element package Abaqus that dictate damage progression behavior of fiber composites include 6 strength values which control when damage is initiated, and 4 energy parameters that control how damage propagates. The values of the initiation parameters (strengths) are often accurately known, however the values of the propagation parameters (energies) are often not accurately known. The consequences of these inaccuracies are not consistent. Current research indicates that accurate FEA results for out-of-plane bending always require accurate values for the material strengths. However the effect of inaccurate material propagation energy values can vary depending on composite laminate layup. Understanding how these effects vary and which values are important can help a designer select a material and/or determine which propagation energy values need to be accurately determined. This study uses the Abaqus implicit FEA solver to model center notched carbon fiber panels to explore the effect of ply orientation on the sensitivity of maximum load to values of matrix tensile propagation energy and matrix compressive propagation energy. Preliminary studies of this loading scenario showed that these values have significant effects on maximum load only for certain layups. Five different 20 ply layups were chosen for this study with varying number of plies oriented in the 90 degree direction. The 90 degree direction is defined as perpendicular to the bending stresses and parallel to the notch. For each layup, matrix compressive and tensile propagation energies were specified at ±20% from their nominal values to create two-level factorials. Each layup was also run using nominal values as a center point to assess linearity of the effects. Furthermore, damage propagation paths were compared to understand how damage propagation was being affected. This way, nonlinear effects of matrix propagation energy values on maximum load could be separated from any regime changes in damage propagation. The results of this study lend understanding to the finite element analyst on how layup affects the need for high-accuracy values of certain material properties. Accurate FEA results for some layups do not depend on accurate matrix propagation energy values. Having this in mind can save significant resources in the fiber composite design process by eliminating unnecessary destructive tests to determine material property values accurately.