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.