In-plane and out-of-plane deformations in automated fiber placement employing micromechanics method

An experimental and theoretical investigation is performed on the in-plane and out-of-plane configurations of the thermoset tow prepregs in the automated fiber placement (AFP) process. Both in-plane and out-of-plane deformations, also known as waviness and wrinkle defects, respectively, are created mainly due to steering during the AFP process. This paper aims to present a viscoelastic micro-mechanics approach to capture the behavior of planar and non-planar deformations in order to predict these defects during the process and, more importantly, determine the conditions under which either in-plane or out-of-plane deformations occur. In this regard, a fiber-buckling model is employed to describe the deformation behavior of the fibers embedded in a viscoelastic uncured thermoset matrix. In this approach, fiber is considered as an elastic material embedded in an uncured viscoelastic matrix. The stickiness of the matrix in out-of-plane and in-plane directions is measured by different relaxation test methods using a rheometer equipment. On the basis of the obtained solutions, critical radii for in-plane and out-of-plane deformations are derived. The wavelength changes of out-of-plane buckling in the width direction of a steered tow are calculated and compared with the experimental results. In addition, we show the separation between the threshold of critical loading and critical radius for both in-plane and out-of-plane buckling in a steered tow. Finally, the values of the relaxation modulus that lead to a mixed mode in planar buckling are obtained, and also the effect of these values on the deformation behavior of in-plane buckling are discussed.