13-13) Assume that the energy transferred in the collision between the shell and the
armor plate in the previous Exercise affects only the shaded area of the armor plate
beneath contact with the flat tip of the shell (a circle of diameter 0.010 m) and does not
spread out to affect the rest of the plate. What is the energy density delivered within that
shaded volume by the shell?
Need: Energy density in armor ____ J/m3.
Know: Energy delivered by shell = 4.5 104 J and volume of “armories”
affected = diameter of 0.010 m to depth of 0.10 m.
13-14) Which of the following will happen as a result of the collision in Exercise 13?
Support your answer with numbers.
a) The shell will bounce off without denting the armor plate.
b) The armor plate will be damaged, but will protect the region beyond it from the
collision.
c) The shell will destroy the armor plate and retain sufficient kinetic energy with
which to harm the region beyond the plate.
Need: Predict whether armor will survive, ____ Yes/no? What margin?
Know: Energy deposited = 5.7 109 J/m3 and , diagram for the armor.
13-15) In Exercise 14 what is the highest speed the artillery shell can have, yet still
bounce off the armor plate without damaging it?
Need: Max speed of shell, v, = ___ m/s allowing the armor (and tank
crew) to survive.
Know: Mass of shell = 1.00 kg. Elastic energy absorption capability of
armor from the previous Exercise, is 1.0 1010 J/m3. Volume V of armor
engaged = 7.85 10-6 m3.
Problems 16 –19 involve the situation depicted below. Consider a “micrometeorite” to be
13-16) Using the stress-strain diagram for steel in Figure 13.11, determine the minimum
thickness a steel micrometeorite shield would have to be to protect the spacecraft from
destruction (even though the shield itself might be dented, cracked or even destroyed in
the process).
Need: Thickness of shield, T = ____ mm.
Know: KE of micrometeorite and volume of steel affected; also the steel
with properties shown in Figure 11 is symmetric with respect to tension
and compression. Its compressive yield is -2.0 102 MPa at = -0.15%
and its fracture occurs at = -1.0%. Micrometeorite density 2.00 103
kg/m3 and relative speed = 5.0 103 m/s.
How: Compare the shield’s toughness with the KE/volume material. If
contact area is A, 1/2 mv2/AT = toughness gives T, where toughness is area
to failure under , diagram.
3. D3/6 is volume of a sphere of diameter D; again diameters are preferred to radii.
13-17) Using the stress/strain properties for a polymer (Figure 13.13 and Table 13.1),
determine whether a sheet of this polymer 0.10 m thick could serve as a micrometeorite
shield, if this time the shield must survive a micrometeorite strike without being
permanently dented or damaged. Assume the properties of the polymer are symmetric to
tension and to compression.
Need: Polymer shield will survive undamaged ___ Yes/No?
Know: KE of micrometeorite = 1.31 10-8 J; impact area = 7.85 10–13 m
13-18) Suppose one was required to use a micrometeorite shield no more than 0.01
meters thick. What would be the required toughness of the material from which that
shield was made, if the shield must survive a micrometeorite strike without being
permanently dented or damaged.
Need: Toughness of micrometeorite shield ___ MPa.
Know: KE of micrometeorite = 1.31 10-8 J; impact volume =
7.85 10–15 m3 (i.e., 7.85 10-13 0.01).
13-19) Suppose a shield exactly 0.01 m
thick of the material in Exercise 18
exactly met the requirement of surviving
without denting or damage at a strain of –
0.10, yet any thinner layer would not
survive. What are the yield stress and the
elastic modulus of the material? (A:
yield = -33.0 MPa, E = 0.33 GPa.).
Need: E = ____ GPa and yield
strength = ___ MPa..
Know: Toughness = 1.67 MPa
and max = -0.10. Also there is no plastic zone in this material.
0,0
= -0.10
Toughness
, yield
0,0
= -0.10
Toughness
, yield
13-20) Your company wants to enter a new market by reverse engineering a popular
folding kitchen step stool whose patent has recently expired. Your analysis shows that by
simplifying the design and making all the components from injection molded PVC plastic
you can product a similar product at a substantially reduced cost.
However, when you make a plastic prototype and test its performance you find that it
is not as strong and does not work as smoothly as your competitor’s original stool. Your
boss is anxious to get your design into production because he has promised the company
president a new high profit item by the end of this quarter. What do you do?
a) Release the design. Nearly everything is made from plastic today, and people
don’t expect plastic items to work well. You get what you pay for in the
commercial market.
b) Release the design, but put a warning label on it limiting its use to people
weighing less than 150 pounds.
c) Quickly try to find a different, stronger plastic that can still be injection molded
and adjust the production cost estimate upward.
d) Tell your boss that your tests show the final product to be substandard and ask if
he wants to put the company’s reputation at risk. If he/she presses you to release
your design, make an appointment to meet with the company president.
1) Apply the Fundamental Canons: Engineers, in the fulfillment of their professional duties,
shall:
6) Conduct themselves honorably, responsibly, ethically, and lawfully so as to
1) Engineering Ethics Matrix:
Options
Canons
a) Release
the design
b) Release
with
warning
c) Try to
find a
stronger
plastic
Hold
paramount
the safety,
health and
welfare of
the public.
Does not
meet canon
Meets canon
Meets canon
Perform
services only
in the area of
your
competence
Does not
apply
Meets canon
Meets canon
only if you
are
competent to
make
materials
switch with
safety
Issue public
statements
only in an
objective and
truthful
manner
Silence here
is an
untruthful
public
statement
Meets canon
Meets canon
Act for each
employer or
client as
faithful
agents or
trustees
Does not
meet canon,
Puts
employer at
risk
Meets canon
Meets canon
Avoid
deceptive
acts
Is deceptive
Meets canon
Meets canon
Conduct
themselves
honorably …
Dishonorable
Meets canon
Meets canon
Solution: An ethical engineer must do option d) or some improvement on
it: halting production and assembling a team to improve the product before
13-21) As quality control engineer for your company you must approve all material
shipments for your suppliers. Part of this job involves testing random samples from each
delivery and make sure they meet your company’s specifications. Your tests of a new
shipment of carbon steel rods produced yield strengths 10% below specification. When
you contact the supplier they claim their tests show the yield strength for this shipment is
within specifications. What do you do?
a) Reject the shipment and get on with your other work.
b) Retest samples of this shipment to see if new data will meet the specifications.
c) Accept the shipment since the supplier probably have better test equipment and
has been reliable in the past.
d) Ask your boss for advice.
1) Apply the Fundamental Canons: Engineers, in the fulfillment of their professional duties,
shall:
2) Engineering Ethics Matrix
Options
Canons
a) Reject the
shipment
b) Retest
c) Accept
Hold
paramount
the safety,
health and
welfare of
the public.
Does not
meet canon
Meets canon
Does not
meets canon
Perform
services only
in the area of
your
competence
Meets canon
if you accept
the
competence
of a superior
Meets canon
Meets canon
Issue public
statements
only in an
objective and
truthful
manner
Silence here
is an
untruthful
public
statement
Meets canon
Meets canon
Act for each
employer or
client as
faithful
agents or
trustees
Meets canon,
Meets canon
Meets canon
Avoid
deceptive
acts
Meets canon
Meets canon
May be
deceptive if
done
without
giving
reasons
Conduct
themselves
honorably …
Meets canon
Meets canon
May be
dishonorable
if it results
in safety
being swept
under the
rug.