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Progressive Flexural Fatigue Failure Analysis of Composites Through Layer Failure Determination

Zabihpoor, Mahmood | 2008

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 39447 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Adibnazari, Saeed
  7. Abstract:
  8. Non-uniform damage growth of the composites under flexural fatigue loading condition makes it difficult to predict the fatigue behavior. In this thesis, A new modeling procedure is developed to introduce a progressive damage model. By using this model, it will be possible to define layer failure through its damage growth and layers constituents’ properties. On the other hand, an efficient micromechanics model must be utilized to relate the external loading to the constituents’ properties. Indeed the micromechanics model must be capable of including both constituent's properties and also fiber/matrix interface efficiency. For representing a complete description of the constituents’ properties and their interactions, the effect of fiber/matrix interface efficiency is introduced into the bridging micromechanics model. The relations have been derived based on the constituents' properties, primary damage mode in unidirectional composites and boundary conditions defined for elements of the micromechanics model. The proposed model introduces a new coupled stiffness/strength technique by relating lamina stiffness to the stress field in its constituents. Therefore, the stress field and strength considerations in the constituents could be studied when the lamina stiffness is determined by a non-destructive process. Conformation of model stiffness predictions with the best described residual stiffness model indicates the way to find the remaining constants in the simulated relation. Finally through this relation, the values of cyclic corrected stress components in the constituents could be determined. A number of experiments are conducted to verify the simulated relations in extended micromechanics model. The results are more realistic than those obtained from a basic bridging model with perfect bonding and yet the method is easier to apply. A number of tests were performed both to determine the constants in the extended micromechanics and also compare the results from the progressive damage model predictions and experiments. The comparison of theoretical and experimental predictions shows that the results are satisfactorily in good agreement. The proposed progressive damage model predicted the final failure instant through a local dropping in load value
  9. Keywords:
  10. Bending Fatigue ; Continuum Damage Mechanics ; Micromechanical Model ; Progressive Failure Analysis ; Unidirectional Composites ; Layer Failure ; Damge Model ; Fiber/Matrix Interface

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