Design and Development of a New Model for Predicting the Mechanical Properties of Three-Dimensional Braided Composite Materials

• Author / Creator

  Aldrich, Daniel R.

• Three-dimensional (3D) braided composite materials have been used in the transportation, aviation, and military applications because of their many beneficial attributes. Included in these attributes is their increased through thickness properties that make them an idea replacement for composites where structural integrity is required. This increase to the through thickness properties arises from the additional interlocking yarns in the through thickness direction. However, due the complexities introduced by the additional yarns and undulations in the through thickness direction, modelling, predicting the properties, and tailoring the properties becomes quite difficult.

  The goal of this thesis is to present an investigation on three-dimensional braids produced from a rotary three-dimensional braider. Additionally, to develop a geometric and finite element models using sub-modelling. And to create a model for predicting the axial and transverse tensile elastic moduli of the 3D braids.

  The development of an in-house rotary three-dimensional braiding machine is presented. The machine is commissioned, and braids are produced to demonstrate the geometric similarities between the geometric models produced with the same braiding parameters.

  Two geometric models are developed, a mathematical model as well as a computer aided design model. These models provide a visual representation of the braided structure and allow further development of a FEA analysis to determine the braid properties. A finite element model is developed, as well as a global-local model. The models are used to predict the axial and transverse modulus for the braid, and the axial and transverse stiffness for the sub-unit cells, respectively. Finally, a method of combining the individual sub-unit cell stiffnesses is developed to predict the axial and transverse moduli. This method provides a rapid way of calculating the moduli of the braided structure, as well as a method for predicting the properties of braids with a larger cross-sectional area.

  To analyse the data collected during this study, a design of experiments (DoE) is used. Further, the DoE allowed for the determination of the significance of the factors on the axial and transverse moduli. It is found that the cross-section braided structure has a significant effect on the each of these moduli. Further, these properties are attributed to the number of each of the sub-unit cells present in the braided structure. It is then shown that the as the braided structure increases in size, the moduli approached the stiffness value of the middle sub-unit cell due the larger rate at which the number of middle sub-unit cells grow compared to the others.

  Finally, the study compares the results of the new method for determining 3D braided properties to the well established FGM model. It is shown that the new method's values for predicting the elastic properties are more accurate when compared to the FGM model.

• Subjects / Keywords

  • 3D Braided
  • Composites
  • Modelling

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3BC3TC8M

• License

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