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

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areas of the flexbeam top surface. As heat and pressure is applied to the contacted surfaces, resin flow out of the laminate reduces the height of the top surface, bringing about increasing lid contact. Height Position (m) Height Position (m) 0.090 0.085 0.080 0.075 0.070 0.065 0.060 0.055 0.050 0.090 0.085 0.080 0.075 0.070 0.065 0.060 0.055 0.050 Lid-Lam Contact 1 2 3 4 5 6 7 8 9 Lid-Lam 10 11 12 Contact 13 14 15 16 17 18 19 20 21 22 23 24 25 Position (node) 52 Laminate Tool Lid 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Position (node) Figure 4.2. Progressive Lid Contact with Laminate. 4.3 Thermal Cycle Optimization Laminate Tool Lid The first consideration for cure process optimization is control of laminate temperature, since the temperature schedule paces the entire cure process time. Pressure is applied under appropriate resin state conditions, and is completed within the temperature schedule timeframe. The laminate temperature is driven <strong>by</strong> changes in tool temperature vs. time during the cure
cycle. The ability to optimize temperature for a laminate that is 3.45” thick (at the root end) is a challenge; the highly interactive and nonlinear nature of the laminate’s thermal state with its reaction rate made finding an optimum a relative choice based on what constraints are imposed. The following groundrules were established: • A maximum laminate temperature of no more than 180°C • A maximum temperature difference within the laminate of 10°C • A dwell at 177C for 2 hours to complete cure Conventional industry practice for a cure cycle is to increase temperature from ambient via an initial ramp, of perhaps 0.1 C per minute, to an intermediate temperature within a range of 80 to 100C, followed <strong>by</strong> a dwell there of 120 minutes, then again ramping to the final cure temperature of 350F/177C. In order to optimize the cycle time, greater ramp rates are used; however, as it is increased, the temperature difference within the laminate increased. One of the constraints for an acceptable flexbeam laminate in terms of strength is limiting this difference. The purpose of the first ramp is to get the laminate to a state where pressure application can be completed while maintaining uniform cure and viscosity within the laminate. The dwell is used to allow the laminate cure and viscosity to become as homogeneous as possible, so that effects of the pressure application will be consistent throughout. For the S2/8552 flexbeam, multiple attempts were made using the model to simulate the process. The tool temperatures were manipulated through the simulation, while the temperatures of the exterior laminate surfaces in contact with the tool bottom, sides, and lid followed the tool temperatures. The first attempt using common industry practice resulted in a reasonable overall cure time of about 14.5 hours, but with excessive temperatures (unacceptable maximum temperature of approximately 216C) and exotherm. After all, this is a very thick laminate, and the energy to be released during cure is formidable. Note that the following figures, beginning with Figure 4.3, do not show the time in the cycle for cool-down following the dwell at the final temp of 177C. 53
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 and 48: 6 5 4 3 2 1 0 Figure 3.8. Model Con
Page 49 and 50: decrease for CVs that were previous
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: temperature conditions. The princip
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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