TOOLED THICK COMPOSITES by ARVEN H. SAUNDERS III ...

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3.13 Tool Geometry and Contact For the press cure process, the laminate is enclosed in a tool that constrains its dimension on the bottom and sides. The lid of the tool rests on the top of the laminate and provides the press temperature and pressure to the laminate upon contact. The lid is modeled as a separate body. Its geometry is 2D, defined in the x and y-dimensions without thickness in the z dimension. As the pressure cycle is applied the laminate is compacted and resin flows out its sides. The tool lid moves straight down in the z dimension with laminate height changes due to resulting resin flow. Contact of the lid with the laminate is detected <strong>by</strong> z position. When the gap between the positions of the laminate and lid is within a tolerance distance, then contact is defined as being made between the lid and top surface of the CV at that x-position. After contact is made, then pressure application and heat conduction to the laminate contacted CV surfaces is enabled. Laminate CVs adjacent to contacted CVs that are not in contact allow the resin to flow out of the top surface; otherwise, the path for flow is blocked. 3.14 Model Boundary Conditions Exterior nodes and CVs are located on the outside surface of the laminate and set boundary temperature and pressure conditions for the interior CVs of the laminate. Given these exterior boundary conditions, the model estimates variable values within the laminate interior. The chief boundary conditions are pressure and temperature; all nodes/CVs that are on the external edge of the laminate are assigned values. The boundary condition resin pressure for the sides of the laminate represent the interface between the laminate and the bond tool. It is assumed that resin can flow out of this interface and the resin pressure there is set to zero Pa. As the Lid makes contact with the laminate, the top CVs have pressure across their surfaces dependent on the applied force and the total laminate contacted area. The model assumes that all other CVs that are vertically aligned with the top contacted CVs share the same applied pressure. For monotonically increasing applied pressure conditions, the contact area increases, even though as additional contact area is gained, resin pressure may actually 38
decrease for CVs that were previously contacted. The applied pressure is equal within all CVs of the laminate when complete contact exist over the entire top surface. Exterior CVs possess resin and fiber volume. Their heights and resin volumes are maintained in accordance with the resin flow volume rates, updating for each timestep. Thus they are kept at the same height as the adjacent interior CVs. Contact for exterior CVs on the left or right side is not defined per se. However, contact is defined as being true there if the adjacent interior CV is contacted. All resin flow out of and heat flow into the laminate is <strong>by</strong> way of the exterior nodes, depending on permeability and contact or not (Top CVs). exterior CVs at the bottom of the laminate are assumed to be in constant contact with the tool, and therefore no resin flow out of the laminate is assumed to occur there. Temperature for the exterior nodes is set to the tool temperature upon contact. It is assumed that most all of the prepreg material fiber orientation is in the length-wise (x) direction because of design loads that the part must sustain. Longitudinal permeability is defined as that along the direction of the fibers, in contrast to transverse permeability, which is oriented across the direction of the fibers. Because longitudinal permeability is typically 2 to 3 orders of magnitude higher than transverse permeability, the predominant resin flow direction is assumed to run across its length, with resin flow out the side edges. Since the resin pressures are defined as being zero at the edges, there will be a distribution of resin pressure along the laminate length, with the maximum at the length-wise center, and declining to zero at the edges. 3.15 CV Material Properties The laminate model characterizes changes that occur during the cure process. However, CV properties are assumed to be uniform and constant during a timestep. These properties include resin pressure, permeability, resin viscosity, and degree of cure. Changes may occur based on resin flow and consolidation during the time step, and these changes are updated at the beginning of the next timestep. The height of a CV is assumed to be uniform across its width. 39
Page 1 and 2: PROCESS MODELING SYSTEM FOR PRESS C
Page 3 and 4: ACKNOWLEDGEMENTS This dissertation
Page 5 and 6: TABLE OF CONTENTS ACKNOWLEDGEMENTS
Page 7 and 8: 4. RESULTS ........................
Page 9 and 10: 4.7 Acceptable IM7/3501-6 Flexbeam
Page 11 and 12: CHAPTER 1 INTRODUCTION 1.1 Backgrou
Page 13 and 14: Inspection and evaluation technique
Page 15 and 16: Figure 1.3. Fiber/Layer Waviness in
Page 17 and 18: CHAPTER 2 REVIEW OF RELATED RESEARC
Page 19 and 20: greatly lag in temperature. As a re
Page 21 and 22: Physics-based models are often used
Page 23 and 24: equation above can be solved by wri
Page 25 and 26: keep the cure on track. Examples of
Page 27 and 28: (Chen, 2002). However, because they
Page 29 and 30: during cure and consolidation. In a
Page 31 and 32: initially in the cure process but w
Page 33 and 34: Figure 3.1. Generic Flexbeam with T
Page 35 and 36: Permeability describes the resistan
Page 37 and 38: patterns velocity and timing during
Page 39 and 40: S ii 2 f r = 4k ii ( 1− V where r
Page 41 and 42: proportion of the applied pressure
Page 43 and 44: At any timestep in the simulation,
Page 45 and 46: constant displacement ramp followed
Page 47: 6 5 4 3 2 1 0 Figure 3.8. Model Con
Page 51 and 52: total resin volume rate for the lam
Page 53 and 54: series electrical circuits—a left
Page 55 and 56: hold these values, with R(k) being
Page 57 and 58: • Resin pressure causes resin flo
Page 59 and 60: where α is cure, An is the pre-exp
Page 61 and 62: temperature conditions. The princip
Page 63 and 64: cycle. The ability to optimize temp
Page 65 and 66: Temperature (C) 200 180 160 140 120
Page 67 and 68: Temperature (C) 200 180 160 140 120
Page 69 and 70: useful; as pointed out by Cirisciol
Page 71 and 72: Flexbeam (z) Height and Tool Lid Po
Page 73 and 74: 55 minutes into the S2/8552 cycle,
Page 75 and 76: Resin Pressure (Pa) 1.2E+06 1.0E+06
Page 77 and 78: -7.138E-12 -7.138E-12 -6.517E-12 -5
Page 79 and 80: keeping the level below a certain t
Page 81 and 82: feedback to set the temperature cur
Page 83 and 84: (Chen, 2002) Chen, Y., "Modeling of
Page 85 and 86: (Mitra, 2009) Mitra, K., Majumder,
Page 87 and 88: (Walia, 2006) Walia, R., Shan, H.,

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