Graduate Thesis Or Dissertation
 

Experimental Classification of Intralaminar Matrix Compression Damage Propagation in Carbon Fiber Reinforced Polymers

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/g732dd292

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  • Composites often are able to carry more load after damage due to the structure of laminates. In addition, damage can be difficult to detect in composites compared to homogeneous materials. Understanding the behavior of composite material after damage is vital for composite structural design. Currently, experimental methods exist for classifying fiber tension, fiber compression, and matrix tensile damage propagation. However, little has been done on matrix compression propagation. First, several candidate specimens were identified based on fiber compression studies. These specimens were modeled using FEA and the base continuum damage mechanics models. The size of the matrix compressive damage region was compared to select the specimens. Compact compression and center notch compression specimens showed good isolation of compressive damage. Compact compression specimens were chosen, as they were less dependent on the boundary conditions to achieve the desired damage mechanisms. These specimens were then manufactured and tested along with uniform compression specimens. Shear cracks propagating through the thickness of the material were the primary failure mechanism observed, with other damage mechanisms occurring after some propagation. A contour J-integral was used to measure the strain energy release rate from DIC displacement field data. The plastic behavior of the material was classified to determine the applicability of the J-integral. It was determined that the J-integral is potentially valid for compressive damage initiation. Typical values showed a range of energy dissipation values when damage initiation between 30 kJ/m² and 40 kJ/m². These values were reflected in the areas under the uniform compression specimen stress-displacement curves for similar fracture angles. These specimens also showed correlation between energy dissipation and fracture plane angle. This is due to a greater contribution of mode I compression at lower angles. Residual stresses were observed in the past damage material due to friction, fiber bridging and crack locking. These results show the limitations of the base continuum damage mechanics models and associated assumptions.
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