Jin Tan, A' Fuentes, and K' Lozano, Department of Mechanical Engineering, University of Texas Pan Am

1
Jin Tan, A. Fuentes, and K. Lozano, Department of
Mechanical Engineering, University of Texas Pan
American
Composite Mechanical Property Enhancement through
the Use of End Shaped Short Fibers
BACKGROUND
PRELIMINARY RESULTS
RESEARCH PROCEDURE

• 1. Developed the computer models using
  Pro-Engineering Software
• Straight fiber
• Aspect ratio L/D (6,7,8,9,10, etc.)
• Volume fraction Vf/(VfVm) (5,10,15, etc.)
• Elastic modulus ratio Ef/Em (10,20,30, etc.)
• Poisson ratio (0.2, 0.38, etc.)
• Packing arrangement (Square, Hexagonal, etc.)
• Y-Branched fiber
• Angle between two branches (30, 45, 60, etc.)
• Length ratio between straight base and oblique
  branch (12,16, etc.)
• Shape of the branches end (Planar, Angular,
  Round, etc.)
• 2. Finite Element Analysis
• For example, for aspect ratio L/D20, volume
  fraction of 5 models were analyzed by Algor FEA
  software.
• Square and hexagonal packing arrangement models
  of straight fiber compositesSquare packing
  arrangement models of Y-Branched fiber
  composites
• Strength, stiffness and toughness of composite
  materials For example, to determine the
  longitudinal elastic modulus (E11)1). The
  normal displacements of the back and two
  fiber-included faces of the RVE were fixed. 2).
  The tangential displacements on all faces were
  unconstrained.3). The average stress was
  computed from the reaction force in the loading
  direction, divided by the cross-sectional area of
  the RVE. Average strains were computed from the
  initial and deformed dimensions of the RVE.

Composites reinforced by discontinuous fibers are
cheaper and more flexible than those by
continuous fibers. They can be adapted to
conventional manufacturing techniques, such as
extrusion and injection molding. Recently, a new
approach has been developed to improve strength,
stiffness and toughness of these composites. It
involves utilizing the shaped short fibers to
improve the mechanical properties of the
composites. Previously, the short fibers with
enlarged ends were used to effectively transfer
load from the matrix to the fiber via mechanical
interlocking. This research project uses finite
element analysis (FEA) method to simulate the
strength, stiffness and toughness of the
composites reinforced by fibers with different
aspect ratios and volume fractions. Fibers used
included straight fibers and Y-Branched fibers
with various lengths and angles. The objective
of this research is to determine the improvement
in mechanical properties of the composites
reinforced by these end shaped fibers.

• 1. The longitudinal elastic modulus E11
• For fiber volume fraction (vf) 5, E11 of
  composites reinforced by Y fiber are 5 more than
  those by straight fiber models, 15 more than
  Halpin-Tsai prediction and 30 more than the
  result of shear-lag models. (Diagram1 is a sample
  data. Halpin-Tsai and Shear-lag models show
  minimum expected longitudinal values for straight
  fiber.)
• For fiber volume fraction 10, E11 of composites
  reinforced by Y fiber are 10 more than those by
  straight fiber models, 25 more than Halpin-Tsai
  prediction and 45 more than the result of
  shear-lag models. (Diagram2 is a sample data)

• 2. The stress distribution
• The stresses at the interface are under study.
  One of the goals is to prevent the debonding at
  the interface between the fiber and matrix.
  (Diagram3 is a sample data of the longitudinal
  normal stress in the fiber at the interface)

RESEARCH METHOD

• Fibers straight fiber and Y-Branched fiber.
• Use modern FEA method to study the strength,
  stiffness and toughness of fiber reinforced
  composites. Representative volume element (RVE)
  of the composite materials have been studied to
  determine the properties. The studied RVE
  occupied 1/8 of the total volume of the composite.

Planar End Y Fiber
Round End Y Fiber
Straight Fiber
Angular End Y Fiber

• PRELIMINARY CONCLUSIONS
• Y fiber reinforced composites are showing
  mechanical property enhancement under some
  conditions comparing with straight fiber ones.
• The composites studied in this project can be
  extensively used in civil and military
  applications.
• Future work includes the experimental
  verification and technology transferring.
• The method and procedure developed can be
  applied to future research projects.

RVE of Square packing angular end Y fiber
RVE of Square packing planar end Y fiber
RVE of Square packing round end Y fiber
Hexagonal Packing Arrangement
The RVE's of hexagonal packing fiber
Square Packing Arrangement
The representative volume elements (RVE's) for
square packing fiber