ME 270 – Leon Liebenberg
Quiz 4
Name: ……………Hao Chen……………………………. Net-ID: ………haoc6………
Must be submitted on Compass before Friday 3 April at 1 p.m. (US Central Time)
(Total: 20 points)
1.
[Select one correct answer]: Deciding between recycling of conventional plastics and developing
biodegradable plastics is a complex issue, because (2)
a. recycling is so cheap.
b. the properties of the recycled polymer will likely be inferior to the original virgin polymer.
c. biodegradable plastics are easy to design so that they will degrade in the intended timeframe.
d. biodegradable plastics are so cheap.
2.
[Select one correct answer]: Which one of the listed materials (a – g) is easiest to machine? (2)
Material
Yield Strength
(MPa)
Young’s
Modulus
(GPa)
Strain-toFailure (%)
a.
b.
c.
d.
e.
f.
g.
A
3.
[Select one correct answer]: What is the significance of the glass-transition temperature, Tg, in engineering
applications? (2)
a. Below Tg, thermoplastics become rubbery and leathery.
b. Where thermoplastics must carry a load, the material for the part would need to have a Tg higher
than the maximum temperature to which it would be subjected.
c. Below Tg, thermoplastics begin to lose their load-carrying capacity.
d. All the aforementioned (a, b, and c).
4. Consider the shown digitally enhanced cordless telephone. Its housing consists of
two ABS shells that are joined with snap fits; a third (much smaller) ABS part is the
hatch for the batteries (on the rear, not shown).
4.1.
Assuming Newtonian flow, estimate the minimum injection pressure needed to fill the mold for the
top shell. You may simplify the shape as a flat plate: 160 mm long, 50 mm wide and 2 mm thick, and
assume it is injected over the full width from one end to the other. Injection time tin = 0.1 second,
melt viscosity μ = 40 Pa.s. (6)
4.2.
Estimate the cooling time for the top shell. Clearly state your assumptions. Using the very rough ruleof-thumb that cycle time in injection moulding is approximately 10 seconds per mm part thickness,
comment on the realism of your estimation. (8)
NB: Remember to complete and sign the honor code statement on the next page, and to save your completed
assignment as one PDF file, which must be submitted on Compass.
Honor Code Statement
ME 270Take-home quiz: 28 March – 3 April 2020 (1 p.m. US Central Time)
Being a student of high standards, I pledge to embody
the principles of academic integrity.
This ME 270 take-home quiz is my own work. I did not
seek (or get) outside help or collaboration with any of
the questions and their solutions.
I acknowledge that academic violations will be dealt with
according to the UIUC Student Code, Article 1, Part 4.
ME 270 Student’s
signature:_________Hao Chen___________________________________________________
Student’s Name: _______________Hao Chen________________________________________
Net-ID: ____________haoc6___________________________________
Date: _____________4/1/2020__________________________________