Instructors Solution Manual The Science And
Engineering Of Materials 4th Edition Author:
Donald R. Askeland Latest Version
0|Page
,1
Intr ducti nt MaterialsScience and Engineering
o o o
1–5 Iron is often coated with a thin layer of zinc if it is to be used outside. What charac- teristics
do you think the zinc provides to this coated, or galvanized, steel? What precautions should
be considered in producing this product? How will the recycla- bility of the product be
affected?
Solution: The zinc provides corrosion resistance to the iron in two ways. If the iron is
completely coated with zinc, the zinc provides a barrier between the iron and
the surrounding environment, therefore protecting the underlying iron. If the
zinc coating is scratched to expose the iron, the zinc continues to protect the iron
because the zinc corrodes preferentially to the iron (see Chapter 22). To be
effective, the zinc should bond well to the iron so that it does not permit
reactions to occur at the interface with the iron and so that the zinc remains
intact during any forming of the galvanized material. When the material is
recycled, the zinc will be lost by oxidation and vaporization, often producing a
“zinc dust” that may pose an environmental hazard. Special equipment may
be required to collect and either recycle or dispose of the zinc dust.
1–6 We would like to produce a transparent canopy for an aircraft. If we were to use a ceramic
(that is, traditional window glass) canopy, rocks or birds might cause it to shatter. Design a
material that would minimize damage or at least keep the canopy from breaking into
pieces.
Solution: We might sandwich a thin sheet of a transparent polymer between two layers
of the glass. This approach, used for windshields of automobiles, will prevent
the “safety” glass from completely disintegrating when it
1
, 2 The Science and Engineering of Materials Instructor’s Solution Manual
fails, with the polymer holding the broken pieces of glass together until the
canopy can be replaced.
Another approach might be to use a transparent, “glassy” polymer material
such as polycarbonate. Some polymers have reasonably good impact
properties and may resist failure. The polymers can also be toughened to
resist impact by introducing tiny globules of a rubber,
or elastomer, into the polymer; these globules improve the energy- absorbing
ability of the composite polymer, while being too small to interfere with the
optical properties of the material.
1–7 Coiled springs ought to be very strong and stiff. Si3N4 is a strong, stiff material.
Would you select this material for a spring? Explain.
Solution: Springs are intended to resist high elastic forces, where only the atomic bonds
are stretched when the force is applied. The silicon nitride would satisfy this
requirement. However, we would like to also have good resistance to impact
and at least some ductility (in case the spring is overloaded) to assure that the
spring will not fail catastrophically. We also would like to be sure that all
springs will perform satisfactorily.
Ceramic materials such as silicon nitride have virtually no ductility, poor
impact properties, and often are difficult to manufacture without
introducing at least some small flaws that cause to fail even for relatively
low forces. The silicon nitride is NOT recommended.
1–8 Temperature indicators are sometimes produced from a coiled metal strip that uncoils a
specific amount when the temperature increases. How does this work; from what kind of
material would the indicator be made; and what are the important properties that the
material in the indicator must possess?
Solution: Bimetallic materials are produced by bonding two materials having different
coefficients of thermal expansion to one another, forming a laminar
composite. When the temperature changes, one of the materials will expand or
contract more than the other material. This difference in expansion or
contraction causes the bimetallic material to change shape; if the original shape
is that of a coil, then the device will coil or uncoil, depending on the direction of
the temperature change. In order for the material to perform well, the two
materials must have very different coefficients of thermal expansion and
should have high enough modulus of elasticity so that no permanent
deformation of the material occurs.
1–9 You would like to design an aircraft that can be flown by human power nonstop for a
distance of 30 km. What types of material properties would you recommend?
What materials might be appropriate?
Solution: Such an aircraft must possess enough strength and stiffness to resist its
own weight, the weight of the human “power source”, and any
aerodynamic forces imposed on it. On the other hand, it must be as light as
possible to assure that the human can generate enough work to operate the
aircraft. Composite materials, particularly those based on a polymer matrix,
might comprise the bulk of the aircraft. The polymers have a light weight
2|Page
, CHAPTER 1 Introduction to Materials Science and Engineering 3
(with densities of less than half that of aluminum) and can be strengthened by
introducing strong, stiff fibers made of glass, carbon, or other polymers.
Composites having the strength and stiffness
Engineering Of Materials 4th Edition Author:
Donald R. Askeland Latest Version
0|Page
,1
Intr ducti nt MaterialsScience and Engineering
o o o
1–5 Iron is often coated with a thin layer of zinc if it is to be used outside. What charac- teristics
do you think the zinc provides to this coated, or galvanized, steel? What precautions should
be considered in producing this product? How will the recycla- bility of the product be
affected?
Solution: The zinc provides corrosion resistance to the iron in two ways. If the iron is
completely coated with zinc, the zinc provides a barrier between the iron and
the surrounding environment, therefore protecting the underlying iron. If the
zinc coating is scratched to expose the iron, the zinc continues to protect the iron
because the zinc corrodes preferentially to the iron (see Chapter 22). To be
effective, the zinc should bond well to the iron so that it does not permit
reactions to occur at the interface with the iron and so that the zinc remains
intact during any forming of the galvanized material. When the material is
recycled, the zinc will be lost by oxidation and vaporization, often producing a
“zinc dust” that may pose an environmental hazard. Special equipment may
be required to collect and either recycle or dispose of the zinc dust.
1–6 We would like to produce a transparent canopy for an aircraft. If we were to use a ceramic
(that is, traditional window glass) canopy, rocks or birds might cause it to shatter. Design a
material that would minimize damage or at least keep the canopy from breaking into
pieces.
Solution: We might sandwich a thin sheet of a transparent polymer between two layers
of the glass. This approach, used for windshields of automobiles, will prevent
the “safety” glass from completely disintegrating when it
1
, 2 The Science and Engineering of Materials Instructor’s Solution Manual
fails, with the polymer holding the broken pieces of glass together until the
canopy can be replaced.
Another approach might be to use a transparent, “glassy” polymer material
such as polycarbonate. Some polymers have reasonably good impact
properties and may resist failure. The polymers can also be toughened to
resist impact by introducing tiny globules of a rubber,
or elastomer, into the polymer; these globules improve the energy- absorbing
ability of the composite polymer, while being too small to interfere with the
optical properties of the material.
1–7 Coiled springs ought to be very strong and stiff. Si3N4 is a strong, stiff material.
Would you select this material for a spring? Explain.
Solution: Springs are intended to resist high elastic forces, where only the atomic bonds
are stretched when the force is applied. The silicon nitride would satisfy this
requirement. However, we would like to also have good resistance to impact
and at least some ductility (in case the spring is overloaded) to assure that the
spring will not fail catastrophically. We also would like to be sure that all
springs will perform satisfactorily.
Ceramic materials such as silicon nitride have virtually no ductility, poor
impact properties, and often are difficult to manufacture without
introducing at least some small flaws that cause to fail even for relatively
low forces. The silicon nitride is NOT recommended.
1–8 Temperature indicators are sometimes produced from a coiled metal strip that uncoils a
specific amount when the temperature increases. How does this work; from what kind of
material would the indicator be made; and what are the important properties that the
material in the indicator must possess?
Solution: Bimetallic materials are produced by bonding two materials having different
coefficients of thermal expansion to one another, forming a laminar
composite. When the temperature changes, one of the materials will expand or
contract more than the other material. This difference in expansion or
contraction causes the bimetallic material to change shape; if the original shape
is that of a coil, then the device will coil or uncoil, depending on the direction of
the temperature change. In order for the material to perform well, the two
materials must have very different coefficients of thermal expansion and
should have high enough modulus of elasticity so that no permanent
deformation of the material occurs.
1–9 You would like to design an aircraft that can be flown by human power nonstop for a
distance of 30 km. What types of material properties would you recommend?
What materials might be appropriate?
Solution: Such an aircraft must possess enough strength and stiffness to resist its
own weight, the weight of the human “power source”, and any
aerodynamic forces imposed on it. On the other hand, it must be as light as
possible to assure that the human can generate enough work to operate the
aircraft. Composite materials, particularly those based on a polymer matrix,
might comprise the bulk of the aircraft. The polymers have a light weight
2|Page
, CHAPTER 1 Introduction to Materials Science and Engineering 3
(with densities of less than half that of aluminum) and can be strengthened by
introducing strong, stiff fibers made of glass, carbon, or other polymers.
Composites having the strength and stiffness
