Carbon Fiber Interleaved Polyester Laminate Strength Testing with Correlation in Finite Element Simulations

Abstract

Delamination of composite structures under impact conditions has been a catastrophic and economic issue in the past and is still a problem today. Many techniques have been used to improve the toughness in composite laminates. An example of a previous dissertation was performed by Adnan Gheryani titled: “Analysis of Polyester Interleafs for Toughness Enhancement in Composite Structures.” Gheryani’s study shows that adding in polyester interleafs into composite laminates made primarily from carbon fiber fabric adds ductility and resists crack growth after delamination, which leads to improvement of the overall toughness of the laminate. However, improvements in toughness, strength, and stiffness behaviors are not parallel; improving the toughness does not mean the strength and stiffness of the laminate increases. Similarly, adding polyester interleafs into laminates could potentially degrade the overall strength of the laminate while also reducing its stiffness for load transfer. This thesis studies the strength and stiffness behavior of composite laminates interleaved with polyester. This thesis is based on performing tensile, flexure, and short beam strength tests to obtain stress-strain data and strain to failure data for carbon fiber-only laminates, polyester-only laminates, and carbon fiber interleaved with polyester laminates. Data for polyester interleaf material cast in a matrix is collected for the first time and used to determine the nonlinear response characteristics of this material. The experimental data were then used in finite element models to simulate the response of carbon fiber laminates that were interleaved with polyester using the ANSYS software. The manufacturing process of the experimental test specimens, the experimental test procedures, the experimental test results, the finite element modeling procedures, and the post processing of the finite element results are outlined and described in this thesis. The flexure experiment shows that replacing 2 structural carbon fiber plies with 1 polyester ply out of a 6 ply carbon fiber laminate improves both the effective modulus of elasticity and the effective modulus of rupture by 42% and 39%. This research shows that interleaving polyester plies into a structural laminate reduces the tensile strength of the entire laminate by 50% for a replacement of every two structural plies for one polyester ply. In addition, this research shows that interleaving polyester plies near or at the neutral axis improves the short shear beam strength of the laminate by 33%. Lastly, this research shows that using nonlinear experimental properties in ANSYS one can build finite element models that correlate with the experiment test results.