Disclaimer

Images for Problems are taken from Shigley’s (9th edition).

Problem 1 (10 Points)

Two steels are being considered for manufacture of as-forged connecting rods subjected to bending loads. One is AISI 4340 Cr-Mo-Ni steel capable of being heat-treated to a tensile strength of 260 ksi. The other is a plain carbon steel AISI 1040 with a ultimate strength of 113 ksi. Each rod is to have a size giving an equivalent diameter of 0.75 in. Determine the endurance limit for each material. Is there any advantage to using the alloy steel for this fatigue application?

Problem 2 (20 Points)

A 1-in-diameter solid round bar has a groove 0.1-in deep with a 0.1-in radius machined into it. The bar is made of AISI 1020 CD steel and is subjected to a purely reversing torque of 1800 lb-in. For the S-N diagram of this material, let f=0.9.

Problem 3 (20 Points)

The cold-drawn AISI 1040 steel bar shown in the figure is subjected to an axial load fluctuating between 0kN and 28kN. Estimate the fatigue factor of safety based on achieving infinite life using modified Goodman criterion and the yielding factor of safety. If infinite life is not predicted, estimate the number of cycles to failure.

Drawing

Problem 4 (50 Points + up to 100 bonus points)

First, complete this tutorial to get familiar with structure design in ANSYS. For more explanations on ANSYS Optimization, please check this tutorial.

Then choose one of the following structure design problems to solve using ANSYS.

  1. The “Chopsticks” that catch SpaceX BFRs during their landing.
  2. A bridge. To narrow down the design specifications, you could refer to any famous bridges, e.g., the Mathematical Bridge at Cambridge.

For the problem of your choice: