Abstract

Modern composite manufacturing techniques using Automated Fiber Placement (AFP) technology incorporates process modeling simulations to predict the path of the towpreg. One of the limiting factors in process modeling for AFP is the reliance on using cured composite material properties while in practice, the properties of the uncured state is required. Variability exists in the material properties between both states, with the properties of the uncured towpreg being significantly lower due the viscous matrix. One of those properties is the tensile modulus. Through experimental uniaxial tensile testing of uncured towpreg samples, the mechanical behavior of the material is analyzed in order to propose a model to accurately predict the modulus at varying loads and temperatures. Along with this data, the effects of fiber waviness on the tensile behavior of uncured towpreg are analyzed at the microscopic level. To support the experimentation, a finite element analysis (FEA) is performed to demonstrate the correlation at the micro and mesoscale levels between fiber waviness and the tensile response curve of uncured towpreg. A mathematical model is proposed derived from free body diagram analysis and classical lamination theory and based on the assumed sinusoidal wavelength of the fibers to predict how the fiber geometry affects the system.