Chapter 9
what reinforcing fibers are generally used to make composites? which type of fiber is the strongest? which type is the weakest?
reinforce fibers can be made from a number of materials. the most common in industrial application is glass, graphite, boron, aramids using more than one of these materials to form a composite is called a hybrid. The strongest of these reinforcing fibers are aramids, while glass is the weakest.
why are fibers capable of supporting a major portion of the load in composite?
the fibers in composites are stiffer than the matrix in which they reside.when subjected to the same load, the matrix yields leaving the non yielding fibers to carry most of the load.
do metal matrix composites have advantages over reinforced plastics
the main advantage that metal- matrix have over reinforced plastics is that they can withstand a much higher range of temperature without losing strength or degrading.
List the important factors that determine the properties of reinforced plastics.
the mechanical and physical properties of reinforced plastics depend on the fibers. the kind, shape, orientation, and length. also the percentage of reinforced materials. Silane can be added to improve the bond between fiber and matrix.
is there a difference between a carbon fiber and a graphite fiber
the principal difference between carbon and graphite is their composition carbon contains 80 to 90% carbon while graphite contains 99% carbon.
what are the most commonly used matrix materials?
there are four main matrix materials Polyester polyimides epoxy silicon
Identify metals and alloys that have strengths comparable to those of reinforced plastics? how can you tell?
Many reinforced plastics are comparable in strength to aluminum, ABS,Nylon, Polyester. Reinforced Nylon and Polyester can be compared to magnesium in strength.
what is a whisker? whats the difference between a whisker and a fiber?
Whiskers are small single crystalline structures between 1 and 10 micrometers in length. their small size accounts for is minimal amount of imperfections. Fibers are much longer than whiskers, this makes any imperfections more likely to affect the mechanical properties.
what is the purpose of the matrix material?
matrix materials are necessary protect the fibers from physical damage. also to support and transfer stresses to them.to reduce propagation of cracks in the composites, by virtue of greater ductility and toughness of the plastic matrix. the purpose of the matrix material is to transfer the stresses to the fibers. the second purpose is to prevent the formation of cracks in the composite.
Distinguish between composites and metal alloys
A composite material is a combination of two or more chemically distinct and insoluble materials; its properties and structural performance are superior to each acting individually. Metal alloys are composed of two or more metallic elements. By combining different elements the alloy changes.
what factors contribute to the cost of reinforcing fibers?
A fibers value is based on three specific properties: tensile strength, density, and its Modulus of elasticity.
a hybrid composite is defined as one containing two or more. different types of reinforcing fibers, what advantages would such a composite have over others.
A hybrid composite has advanced properties over those of normal composites due to the addition of fibers into the matrix. for example higher strength and stiffness
what material properties are improved by the addition of reinforcing fibers?
Addition of reinforced fibers account for a higher strength in bonds, improved strength in materials, as well as higher stiffness.
how would you go about trying to determine the strength of a fiber?
Because of its size discovering the strength of a fiber through a test would be difficult. the only plausible way would be to apply a tensile test.
what do boron fibers consist of? why are they heavy?
Boron fibers consist of boron deposited onto tungsten or carbon. the tungsten in the fibers give it the significant weight due to its high density.
give reasons for the develop of ceramic matrix composites name some possible applications?
Ceramics- matrix composites were created to defeat the impurities and defects in pure ceramics. one main improvement is its toughness.they have high thermal conductivity, low thermal expansion, and good corrosive resistance. Ceramic Matrix composites have the advantages of high strength to weight and stiffness to weight ratios associated with composite materials, but a much higher allowable operating temperature. further, the reinforcements tends to make the material tougher than typical ceramics. applications are mainly aerospace and turbine engine components
what is the range in length and diameter of reinforcing fibers?
Fibers can be categorized by length, short or continuous fibers can range from 20 to 50 mm. long or discontinuous fibers will range between 200 and 500 mm.
compare the advantage and limitations of metal matrix composites, reinforced plastics, and ceramic-matrix composites
Metal- matrix composites usually have high density and toughness compared to other composites. this contributes to greater difficulty in processing parts made from these materials Reinforced plastics are susceptible to flaws, making inspection and quality control a necessity. this causes the price of processing to increase. Ceramic Matrix composites are strong and unmalleable. they also lack toughness
what is a hybrid composite
a hybrid composites have more than one fiber material in the matrix
Describe the function of the matrix and of the reinforcing fibers. what fundamental differences are there in the characteristics of the two materials?
a matrix is a continuous phase while fibers are in the discontinuous phase.Metals and ceramics are materials that can be improved by embedding them with reinforcements that improve their properties. when these two are combined they create a composite matrix. the purpose of the matrix is to support the fibers in place and transfer the stresses to them, protect the fibers, reduced propagation and cracks.
