During a recent laboratory session, you were able to observe the rotary bending fatigue test where the fatigue test spec

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During A Recent Laboratory Session You Were Able To Observe The Rotary Bending Fatigue Test Where The Fatigue Test Spec 1 (478.34 KiB) Viewed 34 times

During a recent laboratory session, you were able to observe the rotary bending fatigue test where the fatigue test specimen is subjected to a completely reversed bending stress cycle. The data obtained after a large number of tests is used to plot the S-N curve for the material. Write a brief account on: 'Laboratory tests for fatigue and the effect of mean stress on fatigue failure'. [3 Marks] An alloy steel power transmitting shaft of 50 mm diameter, shown in Figure Q5(b), rotating at high speed, is subjected to a steady axial tensile force Fof 150 kN and a bending moment M of 1500 Nm acting on a vertical plane through the shaft axis, simultaneously. P- Figure Q5(b) (0) Sketch the general form of the stress cycle at a point where the vertical plane intersects the shaft surface and determine the mean stress and the stress amplitude. [6 Marks] The ultimate tensile strength of the alloy steel is 580 MNm-2. Calculate the fatigue limit of the steel if the shaft has been designed for 'infinite fatigue life based on the Goodman criterion, with a safety factor of 1.5. [4 Marks] An aluminium alloy to be used in an aircraft was tested for fatigue and its behaviour conformed to the expression 4o. (No)a = b where a and b are constants, Ni is the number of cycles to failure and do is the alternating stress range (for a completely reversed cycle). The following table gives two observed results: 1 2 250 40 (MNm- 2200 NA 2 x 106 1.5 x 10 (0) (ii) Estimate the number of cycles to failure for a component of this alloy subjected to an alternating stress range of 170 MNm . [5 Marks] An aircraft component of this alloy undergoes 106 cycles per year when operated at an alternating stress range of 170 MNm-2 for 10 years. It is desired to use this component for a further 10 years in similar operations by reducing the alternating stress range. Using Miner's Rule, estimate the new stress range required to achieve this additional life. [7 Marks]