MAE 342 Mechanical Design II Spring 2007 Exam 2

Name:______

Instructions: Exam is closed book, closed notes, one 8x11 cheat sheet is allowed. Try to use front and back of the paper.

1. The figure shows a specimen subject to bending, axial, and torsional loads. Calculate the following:

a)  Find the safety factors for the stress elements A and B for the two given materials based in either the Distortion Energy Theory or Modified Mohr, whichever applies based on whether the material is ductile or brittle.

b)  Draw the failure diagram for all the cases (only one diagram). Make sure you draw the yield and failure boundaries, and plot and clearly label all the load cases.

c)  Place the calculated safety factors in the provided table and answer the question below the table.

Loading: F = 4.1 kN ; T = 650 N-m ; P = –8 kN

Material 1:

Gray Cast Iron ASTM A48 Grade G2

Elongation at Fracture: 1%

Ultimate Tensile Strength: 276 MPa

Ultimate Compressive Strength: 827 MPa

Material 2:

Titanium Ti-5Al-2.5Sn

Elongation at Fracture: 15%

Tensile Yield Strength: 830 MPa

Compressive Yield Strength: 830 MPa

Stress Element A / Stress Element B
Material 1
Material 2

Place the Safety Factors in this table:

Stress Element A / Stress Element B
Material 1
Material 2

Fill in whether the part will fail or not for each case (Y/N in each cell)

Draw your Failure Diagram here:

Problem 1 Calculations (use the back of the page if necessary)

2. Draw the Stress-Life Diagram for a rotating steel bar subject to a fully reversed loading in bending. The bar is 2.75 in square and has a machined surface. The material’s Ultimate Strength is 200 kpsi. Assume that a reliability factor 99.9% is necessary and that the bar will operate at room temperature.

Q. How many cycles of life can be expected if the alternating stress is 80 kpsi? (Show calculations)

Ans. N = ______

Problem 2 Calculations (use the back of the page if necessary)

Here are some figures and tables which might be useful.