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A Nonlinear Layerwise Shell Finite Element for Delamination Analysis of Laminated Composite Structures under Large Deformation

Soltani, Zahra | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 52235 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Hosseini Kordkheili, Ali
  7. Abstract:
  8. This thesis aims to develop a numerically efficient nonlinear layer-wise shell element formulation for delamination analysis of laminated composite shell structures. The element, in a mesoscale scheme, is formulated based on a zig-zag theory and features three translational degrees of freedom for each node on the mid-surface of the shell in addition with two rotational degrees of freedom for each layer. In this way, the displacement field is formulated via adapting the Mindlin-Reissner theory in each layer and an ordered second-order algorithm for finite rotations. To verify the proposed formulation, many popular benchmark problems for geometric nonlinear analysis of shell problems are analyzed with a proprietary computer program. The geometrically nonlinear layer-wise FE formulation is validated through experimental work on corrugated laminated composite shells (CLCS), as an example of compliant structures with the ability of undergoing large deformation within the elastic limit of material. The experimental work also discusses practical challenges in the manufacturing of CLCS using the prepreg-autoclave process to have a homogeneous distributions of thickness or fiber-volume content result, due to the gravity-driven resin flow during early stages of the curing process. After preparing specimens, the geometrically nonlinear behavoiur is studied under tensile test and using optical full-field surface-strain measurement with Digital Image Correlation (DIC). Adapting the Mindlin-Reissner theory in each layer, a correct distribution of out of plane shear stress through the thickness of shell structures can be achieved with increasing number of layers in the developed layer-wise shell element. The main deficiency of computational efficient shell elements for calculation of the transverse normal stress, is then eliminated by adapting the differential equation of equilibrium along the thickness direction in shell element coordinate system. The first order differential equation of equilibrium is solved using finite difference method in a curvilinear grid along the Gaussian points and by adopting the linear Lagrange interpolation to satisfy two boundary conditions at the bottom and the top surfaces. After calculating the correct distribution of interlaminar stresses, delamination onset predictions are carried out using classical strength based failure criteria. To assess the present formulation, some illustrative problems are studied. The results are in a good agreement with those available in the literature
  9. Keywords:
  10. Stress Distribution ; Laminated Composite Sheets ; Layerwise Theory ; Delamination ; Out of Plane Stress ; Compliant Structures ; Finite Element Method ; Large Deformation

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