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

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Typical short-answer questions from lectures:Interfaces are important in Composites for load transfer from Matrix(weak) toReinforcement(strong). Definition: An interface between any two phases (e.g., between areinforcement and a matrix) is a surface across which there is a discontinuity in one or morematerial and properties.Interactions between the matrix and the fiber take place across this internal interface andits properties will be important inload transfer, and fiber pullout during fracture. Becausethe thermal expansion of the matrix and the fiber will generally be different, the interfacemay be in a state of shear even under zero external load conditions if the composite isfabricated 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 interfaceMechanical bonds (e) between the matrix and a rough fiber are also important and mayenhance the toughness of brittle matrix compositessuch as high temperature ceramicmatrix 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 area2.a)1.Hand lay-up is suitable for making composites products from very small to very large. Handlay-up is the simplest method.1.First, using a spray gun apply the Gel coat to the mold. (Gel is normally made by resin , canImprove 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 thickness6.Finally wait for curing and de-moulding.b)1.Lightweight and Durable2.Fatigue and Corrosion Resistantc)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, whichfurther increases cost.Damage inspection - Delamination and cracks in composites are mostly internal and hencerequire complicated inspection techniques for detection.Composite to metal joining - Metals expand and contract more on variations in temperature ascompared to composites. This may cause an imbalance at joinery and may lead to failure.3.In materials science, a general rule of mixtures isa weighted meanused topredict variouspropertiesof a composite material made up of continuous and unidirectional fibers.[1][2][3] Itprovides a theoretical upper- and lower-bound on properties such as the elastic modulus, massdensity, ultimate tensile strength, thermal conductivity, and electrical conductivity. In generalthere are two models, one for axial loading (Voigt model), and one for transverse loading.

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Term
Fall
Professor
Robin Drew
Tags
carbon fiber, Composite material, PMCs, Metal matrix composite

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