Typical questions.docx - Typical short-answer questions...

Typical short-answer questions from lectures:
Interfaces are important in Composites for load transfer from Matrix(weak) to
Reinforcement(strong). Definition: An interface between any two phases (e.g., between a
reinforcement and a matrix) is a surface across which there is a discontinuity in one or more
material and properties.
Interactions between the matrix and the fiber take place across this internal interface and
its properties will be important in load transfer, and fiber pullout during fracture . Because
the thermal expansion of the matrix and the fiber will generally be different, the interface
may be in a state of shear even under zero external load conditions if the composite is
fabricated at elevated temperatures and used at room temperature.
Types of Interfaces in Composites
•Mechanical interlocking
•Chemical due to reaction between reinforcement and matrix
•Other factors:
–Wetting of reinforcement by the matrix material
–Important in both types of interface
Mechanical bonds (e) between the matrix and a rough fiber are also important and may
enhance the toughness of brittle matrix composites such as high temperature ceramic
matrix materials.
Cylindrical fiber (diameter, d) in a matrix
•Interfacial area = surface area of the fiber
•Surface area per unit of a fiber (ignoring the ends)
– 𝑆/? = 2/ ? = 4/ ?
–Fine fiber (diameter ≈ a few μm) can lead to very large interfacial area
2.
a)
1.Hand lay-up is suitable for making composites products from very small to very large. Hand
lay-up is the simplest method.
1.First, using a spray gun apply the Gel coat to the mold. (Gel is normally made by resin , can
Improve surface quality and increase mold use life,).
2.When the gel coat has cured ,Then placed fiberglass reinforcement on the mold

3.using the hand roller wet the reinforcement and removing entrapped air.
4.Add resin to build laminate thickness,
5.Repeat the process until reach desired thickness
6.Finally wait for curing and de-moulding.
b)
1. Lightweight and Durable
2. Fatigue and Corrosion Resistant
c)
High Cost - They are a relatively new material, and as such have a high cost.
Complex Fabrication - The fabrication process is usually labor intensive and complex, which
further increases cost.
Damage inspection - Delamination and cracks in composites are mostly internal and hence
require complicated inspection techniques for detection.
Composite to metal joining - Metals expand and contract more on variations in temperature as
compared to composites. This may cause an imbalance at joinery and may lead to failure.
3.
In materials science, a general rule of mixtures is a weighted mean used to predict various
properties of a composite material made up of continuous and unidirectional fibers.[1][2][3] It
provides a theoretical upper- and lower-bound on properties such as the elastic modulus, mass
density, ultimate tensile strength, thermal conductivity, and electrical conductivity. In general
there are two models, one for axial loading (Voigt model), and one for transverse loading.