doi:10.1016/j.compscitech.2006.02.012 
Copyright © 2006 Published by Elsevier Ltd.
Characterization of viscoelasticity and damage in high temperature polymer matrix composites
E. Ahcia and R. Talrejab, 
, 
aEurocopter Deutschland GmbH (ECD), Stress and Dynamic System Department, 81663 Muenchen, Germany
bDepartment of Aerospace Engineering, Texas A&M University, 3141 TAMU, College Station, TX 77843-3141, USA
Received 1 February 2006;
accepted 2 February 2006.
Available online 3 April 2006.
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Abstract
This paper describes a thermodynamics based model for viscoelastic composites with damage and illustrates its use in characterization of viscoelastic response of polymer matrix woven fabric composites subjected to loading at high temperatures. The characterization is conducted by an experimental method aided by finite element (FE) modeling. The experimental characterization is based on creep data obtained under constant loads of different magnitudes and at different temperatures, and on recovery data collected after unloading. A carbon fiber/polyamide resin woven composite with glass transition temperature (Tg) of around 380 °C was used in the experimental program. A FE model was developed to determine the non-linear viscoelastic response by implementing incremental constitutive relations into an ABAQUS® code. The laminate viscoelastic properties were obtained by finite element micromechanics analysis using the neat resin data as input. Comparing its results with creep-recovery test data at different temperature and stress levels validated the FE model.
There are several factors affecting the viscoelastic behavior of polymer matrix composites such as temperature, moisture and stress level. Accordingly, a large number of tests need to be performed to characterize the viscoelastic response experimentally for each fiber–matrix combination. For this purpose an efficient and systematic experimental procedure was used to understand the effects of temperature and stress level on the viscoelastic response, to clarify the damage-viscoelasticity coupling and to determine the viscoelastic properties of the material system.
Keywords: Viscoelasticity; Damage; Composite materials; High temperature
Fig. 1. Micrographs of outer edges of a virgin specimen.
Fig. 2. Field of view in micrographs related to the thickness and other dimensions of specimens.
Fig. 3. Micrographs of midsections and outer edges of specimens after creep-recovery test.
Fig. 4. Sketch of a specimen showing the details of midsections and outer edges.
Fig. 5. Micrographs of virgin specimens exposed to 700 °F at zero loads.
Fig. 6. Micrographs of specimen edges at virgin state, after pre-damage in fatigue and after 700 °F exposure for 24 h without load.
Fig. 7. A standard creep-recovery test.
Fig. 8. Creep at different temperatures under a constant stress of 13 ksi.
Fig. 9. Variation of axial strain at 700 °F with no mechanical load applied.
Fig. 10. Axial compliance versus time for different values of σ0 at T = 700 °F.
Fig. 11. Power law fit to the experimental creep data (σ0 = 13 ksi, T = 700 °F).
Fig. 12. Creep curves at two temperature and stress levels.
Fig. 13. Creep compliance curves at increasing applied stress at T = 700 °F.
Fig. 14. Stress–strain data at a constant stress rate at different temperatures.
Fig. 15. The stress history used for pre-damaging and creep-recovery test.
Fig. 16. Creep compliance curves at different stresses for T = 700 °F.
Fig. 17. Creep-recovery response at different stresses for T = 700 °F.
Fig. 18. A continuum characterization of damage.
Fig. 19. RVE for transverse cracks in a cross ply laminate.
Fig. 20. Finite element mesh used to obtain transverse/axial properties of a unidirectional lamina.
Fig. 21. Comparison of total strain determined by FE micro-mechanics model with the experimental results [18] for T300/934 [90°]8s laminate at σ0 = 1.095 ksi and T = 200 °C.
Fig. 22. Calculated transverse creep-recovery strain curves for T650-35/PMR-15 for a unidirectional lamina at T = 300 °C.
Fig. 23. Shear compliance at various stress levels determined by FE micromechanics model for T650-35/PMR-15, [90°]ns unidirectional lamina at T = 300 °C.
Fig. 24. Idealized cross-ply laminate model for 8-harness satin weave composite.
Fig. 25. Cross-ply laminate with transverse cracks and a half unit-cell.
Fig. 26. Diagram of creep and recovery for a general strain response.
Table 1.
Elastic ply properties used in cross-ply FE model obtained by micromechanics using fiber and resin data given in [20]
Table 2.
Non-linear material constants of the ISV model for T650-35/PMR-15 corresponding to C11 at T = 300 °C, [0n/90m] with (n/m = 1/2), sd = 8/in.
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