Description

Time limit 1 hour 1 que

Show all work, including relevant equations, sketches, free body diagrams, shear force diagrams and bending moment diagrams.

Name _______________________________ CHE 3260

3rd Exam, Spring, 2021

Signature ___________________________________

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1) One scenario that has been examined in the failure investigation of the Space Shuttle Columbia is the impact

of a chunk of polyamide foam of mass of 1.211 kg, of dimensions of 0.508 m wide x 0.406 m long x 0.152 m

tall, traveling at 457.3 m/s with a thermal heat-shielding tile, essentially composed of silica (SiO2).

A) (4 pts.) Calculate the kinetic energy with which the polyamide foam hit the silica tile.

B) (7 pts.) Use your textbook to determine silica’s modulus of elasticity (E), the yield stress (YS), the

ultimate tensile strength (UTS), percent elongation (the amount of strain multiplied by 100%) at

failure, the coefficient of thermal expansion (CTE), and the fracture toughness (also known as the

critical stress-intensity factor). Use SI units. Assume the worst case.

C) (6 pts.) Assume the ultimate compressive strength is equal to the ultimate tensile strength. Sketch the

stress-strain curve for silica along with the YS, UCS, MOE, RS, and the strain at the yield stress

and the strain at failure.

D) (7 pts.) Assume that the silica is highly efficient at transferring the load from the point of

impact and distributing the load equally over the whole tile (Cross-sectional area = .005 m2 with a

thickness of 0.05 m). Calculate the amount of energy in Joules that a silica tile would be capable

of absorbing without plastically deforming.

E) (1 pt.) Comparing your results of parts D and A, would the silica tile elastically absorb the impact?

F) (4 pts.) Compute the amount of plastic deformation that the silica tile can absorb.

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Name _______________________________ CHE 3260

3rd Exam, Spring, 2021

Signature ___________________________________

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G) (4 pts.) If the silica has a 1 mm crack from a previous incident, given the numbers from part

B, and assuming Y = 1, calculate the maximum amount of stress that the tile could take now.

Would you be safe using a shuttle tile with a 1 mm crack in it? Provide a brief explanation using

some of the quantities you have either looked up or have calculated.

2) (10 pts.) An ion gauge with a glass/metal interface (see photo) is heated under vacuum. The interface

heats up such that the glass side (Ã¢â‚¬Å“Glass, borosilicate (Pyrex)Ã¢â‚¬Â in the accompanying tables) heats up from

298 K to 340 K, but the annealed Ã¢â‚¬Å“Super InvarÃ¢â‚¬Â (under Miscellaneous Nonferrous AlloysÃ¢â‚¬Â heats up only to

310 K. Using Appendix B, determine a) the strain that the glass experiences, b) the strain that the Super

Invar metal experiences, and c) the difference in strain (the strain across the interface between the two

materials. Do either the glass or the metal experience enough strain to be plastically deformed? Do either

the glass or the metal experience enough strain such that the glass/metal interface breaks?

3) A) (5 pts.) List a set of causes as to why your teeth might fail.

B) (5 pts.) Associate each cause from part A with one or more failure mechanisms in part B.

C) (5 pts.) What might you do to prevent premature tooth failure?

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Name _______________________________ CHE 3260

3rd Exam, Spring, 2021

Signature ___________________________________

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I have neither given nor received help on this exam.

4) You are part of a team designing a process and robots to mine the moon’s soil, do a very preliminary

separation of such soil to separate aluminum-rich particles by size (Assume they will be smaller.) from

other lunar soil, and then use a flying robot to transport the Al-rich particles to an aluminum refinery

elsewhere on the moon’s surface.

A) (5 pts.) List a set of causes as to why your process and robots might fail.

B) (5 pts.) Associate each cause from part A with one or more failure mechanisms in part B.

C) (5 pts.) What might you do to prevent premature failure of any part of the lunar mining and refining?

5) Some fish can live at depths of 5000 meters. Assume gravity is 9.81 m/s2. Assume fish and human

bone have a yield stress of 100 MPa, a modulus of elasticity of 1500 MPa, and a Poisson’s ratio of

0.3. Assume the density of salt water and bone are 1025 kg/m3 and 1900 kg/m3, respectively.

A) (3 pts.) Calculate the bulk modulus of the fish.

B) (3 pts.) Calculate the volumetric strain on the fish at a depth of 5000 meters.

C) (3 pts.) Assuming (incorrectly) that the fish is isotropic, calculate the amount of stress on the fish, and

determine whether or not the fish bone is plastically deformed.

D) (3 pts.) Calculate the shear modulus of the fish bone.

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Name _______________________________ CHE 3260

3rd Exam, Spring, 2021

Signature ___________________________________

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6) (15 pts.) You have prepared a molybdenum nitride by cooling a 6 wt. % N/94% Mo mixture infinitely

slowly. A) Sketch what the material will look like after that infinitely slow cooling. B) What is

undesirable about the material in part A? C) Thoroughly describe a process, being specific about

temperatures and endpoints (but not exact times), to best remediate the problem described in parts A and B.

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Question 1

For the beam shown below, draw the shear force and bending moment diagrams (50 Points Total).

Note – Your solution should include the following:

.

Proper sectioning of the beam; and equations to find the internal shear force and bending moment along the length of the beam.

Appropriate FBDs of sections taken with internal shear forces and moments drawn in the default positive directions.

Ã¢â‚¬Â¢ Shear force and bending moment diagrams for the beam with values marked on the diagrams.

50 kN

10 kN/m

20 kN.m

A

(o=

B

2 m

4 m

2 m

2 m

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