When a component subjected to variable load fails at 104 cycles, then such a failure is called as high fatigue cycle failure.  Select one: True False

Fatigue angle Failure (record number of cycles before failure) Large Metal Paperclip in Small Metal Small Plastic Large Plastic Paperclip degrees Paperclip Paperclip 45° 90° 180° 270° Evaluate: 1. Which type of paperclip lasted the largest number of cycles before failure (small metal, large metal, small plastic, or large plastic)? 2. Which paperclip lasted the least number of cycles before failure? 3. Which angle (45°, 90°, 180°, and 270°) was associated with the fewest cycles before failure? 4. Give three reasons why different paperclips may break at different number of bends?

11. For the given fluctuating fatigue load, the values of stress amplitude and stress ratio are respectively MPa 250 200 150 100 50 Time

Q1/ The table below shows the values of stress amplitude and life cycles : Fatigue strength Sf (Mpa) Number of cycles (Nf) 474 111 417 496 352 3002 316 7065 290 21930 262 66075 The test were done, to estimate the failure, on un-notched axially load specimens under zero mean stress. Calculate a and b using the stress -life equation.

Q) A helical compression spring of a mechanism is subjected to Pas =120 N 19ad cycle. The diameter if the wire is 3 mm, with a spring index of € = 7 P, =4N and .The spring is made of oil-hardened and tempered steel, with”« ~ L0t dm Determine the factor of safety in fatigue loading.

True or False a) If an accurate value for the notch sensitivity is hard to find, I should consider the fatigue stress concentration factor higher than the stress concentration factor under static loading condition in design.  b) It is easier to find the asymptotic value of fatigue strength as the endurance limit on the S-N curve for a brass alloy (Cu70Zn30) than that of endurance limit on the S-N curve for an AISI 1045 steel.   a good fatigue design should keep the fatigue design factor of safety at a minimum value of______________

Assume any value if it is not available

T or F Ductile materials have long stress-strain diagrams so they fail suddenly without warning. T or F Connections have 3 modes of failure: shearing of bolts, bearing in plate holes, and tension in plates. T or F Brittle materials are often weak in tension. T or F If a beam fails with vertical cracks (perpendicular to the length), then it is due to shear. T or F The maximum normal stress always occurs on a section plane that is normal to the longitudinal axis.

A bracket shown in Fig.(2) is fastened to the wall by four bolts equispaced on a (10 cm) diameter bolt circle. The bracket is subjected to a fluctuating force (0-50 N) . Find the forces acting on each bolt and then choose a suitable bolt size and a preload that will give minimum safety factor (1.5) for any mode of failure.

2. The rotating shaft shown in the figure is machined from AISI 1020 CD steel. It is subjected to a force of F = 6 kN. Find the minimum factor of safety for fatigue based on infinite life. If the life is not infinite, estimate the number of cycles. Be sure to check for yielding. ent Design 25 D. 20 +20 35 D. -180- Mechanical Engineering 12200 10sm 3RD Class -3 R. -500 F -280 -175- -50 D. 25 D. 20 20