Engineer

The thickness for the center cracked ferritic-pearlitic specimen in the second problem (labeled #3) is th=0.25"

The lever shown above is subjected to fatigue loads. The lever must not fail over its life of 10 million cycles.

1) Calculate the static safety factor with respect to yielding given that the tube is made out of 1010 CR steel.

2) Sketch the S-N diagram and assume that when all of the correction factors are applied they equal 0.93.

3) Find the Safety Factor at Point A given that the load, F, has the following time-dependent values -50 ≤ F ≤ 50N

a. Draw the Force/Time curve, label the alternating and mean components:

b. Find the stresses at Point A

c. Find the load ratio (R), and the alternating and mean components (if applicable) of the applied stresses at Point A:

d. Find the von Mises alternating and mean components (if applicable):

e. Find the SF for the specific type of loading scenario:

4) Find the Safety Factor at Point A given that the load, F, has the following time-dependent values 0 ≤ F ≤ 50N

a. Draw the Force/Time curve, label the alternating and mean components:

b. Find the stresses at Point A

c. Find the load ratio (R), and the alternating and mean components (if applicable) of the applied stresses at Point A:

d. Find the von Mises alternating and mean components (if applicable):

e. Find the SF for the specific type of loading scenario:

3) You have a plate with a crack in the center, as shown above. The plate is made of Ferritic-Pearlitic steel. The following values are to be used for this problem b=8”, a=0.1”, and the load fluctuates from P=0lbf to P=10,000lbf.

a. Draw the da/dN versus ΔK curve for the entire Paris region. Label the axis correctly, indicate the slope and Y-intercept values on the plot. If you don’t remember log-log rules, look them up.

b. How many cycles are required to grow the crack from the initial length of ai=0.1” to the final length of af=3”? You may assume that β=1 and you MUST use stress in ksi if you intend to use EQ 6.4b

4) The 2” diameter rotating steel shaft (4041 QT 1200F) shown in Figure 1 is subjected to pure torsional loading. The design engineer who will be implementing this steel shaft wants to analyze its Safety Factors under various loading conditions. Assume that the rod is ground, used at room temperature and indoors, and a reliability of 99.9% is required. Any other correction factors must be assumed and justified.

a) What is the safety factor for infinite life for fully reversed loading of +/- 15,000in-lbf (pure torsion)

b) What is the safety factor for 10,000 cycles given the fully reversed loading of part a?

c) If the loading changes to (R=0) 0 ≤ F ≤ 15,000 in-lbf, what is the safety factor for infinite life?

d) If the loading changes to (R=0.25) 5,000 ≤ F ≤ 20,000 in-lbf, what is the safety factor for infinite life?

e) Draw the S-N diagram for fully reversed loading

f) What if the design engineer wanted to use Aluminum 6061 HT (only analyze the Safety Factor for the fully reversed case)

g) Discuss your thoughts as to what the safety factors in a, c and d may be different (less than 100 words)./

Figure: 2” diameter rotating steel shaft in pure torsion