Improved Fiber Orientation Predictions for Injection Molded Composites

1. Improved Fiber Orientation Predictions for Injection Molded Composites Charles L. Tucker III and Jin Wang Department of Mechanical and Industrial Engineering University of Illinois at Urbana-Champaign John F. O’Gara and Gabriel DeBarr Delphi Research Labs NSF/DOE/APC Workshop: The Future of Modeling in Composites Molding Processes June 9-10, 2004

2. L z y x 2h Fiber Orientation Prediction: State of the Art • Describe orientation using A = pp • Orientation evolves according to Jeffery’s eqn. + interaction term • Hele-Shaw or 3-D mold filling simulation gives velocity distribution, D, W p

3. E11 E22 W L 2h The Problem: Orientation at Short Flow Lengths • Edge-gated strips, PBT 30% glass fiber • Measure elastic modulus in flow (E11) and crossflow (E22) directions • Predict modulus using measured or predicted fiber orientation

4. z z x x Orientation Structure: End-Gated Plaque top 2h shell: flow-aligned shell shell midplane core core: random or cross-flow (depending on inlet) bottom bottom midplane top

5. 1.5, 2.0, 3.0, 6.0 mm A C B 80 mm 90 mm Predicted vs. Measured Orientation, Standard Model • In short plaques, predicted core is too narrow • Leads to over-prediction of E11,under-prediction of E22 • 2 mm, slow fill

6. Progress Toward a Better Model • Hypothesis: fibers experience local strain that is lower than average • resin-rich “slip layers” absorb most of the strain • fibers follow Jeffery-type motion based on local strain rate • Strain Reduction Factor (SRF) = (fiber strain rate / total strain rate)

7. Experiment vs. SRF Theory • New theory with SRF=20 does a good job for short plaquesover a range of thicknesses and filling speeds • 80902 mm • slow fill speed

8. Further Steps for an Improved Model • Our simple SRF theory is not objective • does not behave sensibly in rigid-body rotation;need an objective version of the model • Can only get SRF value by fitting experimental data • need a micromechanics theory to predict SRF if SRF = 20, fiber rotates at 5 RPM! flow rotates at 100 RPM

9. plate measur. measr. measur. simul. simul. simul. Long-Fiber/Thermoplastic Composites :Predicted vs. Measured Orientation Data from Reinhard Hafellner, Advanced Polymer Engineering Leoben, Austria specimen “plate”

10. Gaps: Processing of Injection Molded Composites • Fiber orientation modeling • capture the transient behavior at short flow lengths • models for long-fiber thermoplastics (include migration, fiber breakage, bundle dispersion) • predict orientation model parameters (CI, SRF) as function of fiber volume fraction, l/d, . . . • models tested in a variety of flow geometries • Fiber orientation measurement methods • non-destructive • capture full 3-D orientation • use online • . . .

11. Gaps, continued • Models for warp/shrink/residual stress • state of the art: predict warp within factor of 2 • reach quantitative accuracy (fiber orientation, matrix PVT, . . . ) • incorporate flow-induced crystallization of matrix