Session: 03-02-03: Advanced Manufacturing

Paper Number: 137861

137861 - A Hyper-Viscoelastic Model for the Bending and Compaction Responses of Pre-Impregnated Tapes Under Processing Conditions 

Advanced fiber-reinforced polymer matrix composites have been increasingly used in the aerospace and transportation industries over the past decades owing to their noted durability, resistance to corrosion, design flexibility, and high stiffness-to-weight ratio. Thermoset and thermoplastic pre-impregnated tapes (prepreg) have been widely used in various composite manufacturing techniques including autoclave processing, stamp forming, and automated fiber placement (AFP). Defects in composite manufacturing often lead to compromised structural integrity and reduced performance of the final product, which are closely related to the bending and compaction behaviors of prepreg. Therefore, a robust constitutive modeling framework is needed to efficiently and accurately predict the bending and compaction responses of prepreg, paving the way for defect simulation.

This work proposes a novel integrated hyper-viscoelastic model based on the strain energy density function of a homogenized unit cell of unidirectional prepreg, which is decomposed into an elastic part and a viscous part. It is assumed that any complex behavior can be decomposed into six basic deformation modes: normal behaviors along three orthogonal directions and shear behaviors within three orthogonal planes. The elastic part of each deformation mode is expressed as a function of pseudo-invariants that describe the extent of tension/compression and shear. Regarding the prepreg compaction response, an additional energy term that describes the coupling between two transverse normal responses is introduced to capture the effect of squeezing flow, and a highly nonlinear transverse compression energy is proposed to predict the compaction response of prepreg with liquid and rubbery resin. The nonequilibrium transverse compaction stress caused by the viscous energy is computed using a generalized Maxwell model, whose viscoelastic parameters were characterized by a Computational Fluid Dynamics (CFD) model for liquid resin and a discrete micromechanics model for rubbery resin. The method was applied to stepwise compaction simulation at different temperatures in a commercial finite element analysis (FEA) software Abaqus using user-defined material (UMAT) subroutine and compared to experiments for validation. In the bending aspect, the effective shear modulus is expressed as a function of the second-order gradient of deformation. The nonequilibrium part of the transverse shear stress is predicted by a generalized Maxwell model. Modeling parameters were characterized by an analytical model that captures the underlying fiber and matrix deformation mechanism. Experiments will be carried out to characterize material relaxation time and validate the proposed model. The method was implemented in Abaqus using UMAT and user-defined element (UEL) subroutine to simulate three-point bending and cantilever beam bending. Parametric study was conducted to illustrate the influence of each parameter and the capability to enhance the accuracy of bending prediction. This work is innovative because macroscale prepreg behavior at elevated temperature can be predicted using FEA with consideration of microscale fiber deformation and resin flow through a CFD model and an analytical bending model.

Presenting Author: Yao Sun Purdue University

Presenting Author Biography: Yao Sun is a Graduate Research Assistant at the School of Aeronautics and Astronautics, Purdue University. He holds a Master of Science (M.S.) and Bachelor of Science (B.S.) from Purdue's Aeronautics and Astronautics Engineering program, alongside an M.S. in Motorsport Engineering from a joint program between Purdue University and Indiana University, Indianapolis (IUPUI). His current research interest is Automated Fiber Placement (AFP) in Carbon Fiber composites in reducing manufacturing related defects as well as well as exploring AFP application. Complementing this specialization, Yao also has a profound interest in experimental science. This includes meticulously designing and refining experimental procedures to enhance the accuracy and repeatability of various experiments as well as corresponding simulations.