https://popups.uliege.be/esaform21/index.php?id=511 Publications of Auteurs Kari D. White fr 0 https://popups.uliege.be/esaform21/index.php?id=759 Thermoforming is an attractive process for the low-cost high-volume manufacture of textile-reinforced composite structures with complicated geometries. Tool/ply and ply/ply frictions play critical roles during forming. The friction between the binder ring and the blank induce an in-plane tensile stress that mitigates wrinkling. Unwanted wrinkling can develop across the part if the in-plane stresses are too low but tearing of the material can occur if the applied stresses are too high. Understanding the role that friction plays during thermoforming can give insight on how to mitigate these manufacturing-induced defects in the part. In the current work, the coefficients of friction for two unidirectional cross-ply ultra-high molecular weight polyethylene (UHMWPE) materials are characterized as a function of pressure, fiber orientation, side of material, and pulling rate for [0/90/0/90] cross-ply sheets. The materials are tested at multiple fiber orientations to understand the influence that fiber direction has with respect to the coefficients of friction and on each respective side of the material to understand how surface topology influences the coefficients of friction. The results of the testing are found to correlate with modified Hersey numbers. Sun, 21 Mar 2021 13:07:11 +0100 Mon, 12 Apr 2021 09:10:09 +0200 https://popups.uliege.be/esaform21/index.php?id=759 https://popups.uliege.be/esaform21/index.php?id=506 In composite sheet preforming, the combination of binder-ring force and friction induce in-plane tension that mitigates the onset of wrinkling, but too much force can induce tearing. Thus, the processing conditions must be designed to strike a balance between these competing manufacturing-induced defects. Compounding the challenge to prescribe the appropriate processing conditions is the potential change in thickness of the sheets as a function of in-plane shear. The variation in the thickness from point to point in the ply stack will result in a nonuniform pressure under the binder ring. In the current research, the preforming step is simulated using a discrete mesoscopic modeling approach in LS-DYNA. Thickness-stretch shell elements are used to capture the evolution in the sheet thickness and the in-plane shear stiffness of the deformed sheet. Finite element simulations and preforming experiments are completed for the same processing conditions. The preliminary results for the punch force as a function of displacement, the state of shear over the part surface, and the distribution and magnitude of the wrinkles showed excellent correlation between the model and the experiment. The simulation results show that the shape of the punch force vs. tool depth curve gives insight into the onset of wrinkles. The simulation is then used to predict a binder-ring force that would mitigate wrinkle formation in a four-layer preform. Sat, 20 Mar 2021 00:19:42 +0100 Fri, 02 Apr 2021 17:09:08 +0200 https://popups.uliege.be/esaform21/index.php?id=506