Question

Q-1. You are testing a circular beam of two metals, 1045 steel and 2014-T6 aluminum, in a rotating-cantilever beam fatigue test. If you need to choose one of these metals so that you can essentially design a part made of that metal, and subject the part to a repetitive stress- amplitude without ever failing due to fatigue, which one would you choose. (See the attached figure) 700 600 Ti-5Al-2.5Sn titanium alloy 4340 steel 500 400 Maximum stress, S (MPa) 1045 steel 300 Ductile cast iron 200 70Cu-30Zn brass 2014-T6 Al alloy 100 EQ21A-T6 Mg alloy 0 104 10 108 10° 106 107 Cycles to failure, N Q-2. What is the fatigue strength for the 1045 steel alloy, if you expect to survive 100,000 cycles of repetitive stress? Answer: Q-3. What is the stress below which you could essentially claim that a part made of 4340 steel alloy would not fail due to fatigue? Answer: Q-4. What is the stress below which you could essentially claim that a part made of 2014-T6 Al alloy would not fail due to fatigue? Answer:

Answer 1

1) For same cycles ie 10^5, 1045 steel has more maximum stress compared with 2014-T6 aluminium, so 1045 steel selected

2) 395 MPa for 1045 steel

3) 485 MPa for 4340 steel

4) there is no specific stress for 2014-T6 aluminium

1045 steel metal I need to choose 1045 sheet metal so that I can essentially design e part of that mehal and subject repetitive einers-amplitude without failing to a the pad due do fatique. Reason The fatigue abrength of 10th areel metal for infinite life is 310 MPa But Aluminimum does not have a fatigue limit, in that the sN curre continues its down mard trend at increasingly greater N values. Thus, the fatigue ultimately occups rezarallers of The magnitude og the atress. The faſique response is specified fatigue estrength which is defined as the atress level at which foilue usill occur for grecified members of cycles. That's why 1045 sheel is delected because as Some. maximum ata there is no life time indicated and from fuse the of 1045 sheel is greater than for same cycles to failure than 2014-16 aluminium which indicated that can carry more repetitive stress amplitinde than Q2) 395 MPa (aproximately) is the fatigue extrength for the 1045 sheel alloy, if you expect to aurrine 100,000 cycles 1045 steel 2014 -T6 aluminium of repetitive stren

made QI. 485 MPa (approximately) is the stones below which could essentially claim that a paet 4340 heel alloy would not fail due to fatigue OG 2014-76 Aluminum donot have specific amess below which I could easentially clain that 2014 -T6 Al alloy would fail due to fatigue. a part made of hot from figure SN curre continues can know that occurs 108 (e.g. of cycles its downward treat of increasingly greater N values. Thus, fatigue ultimately regardless of the magnitude of the estren. The the strens. The fatigue reaponse fatigue reaponse in specified falique atrength, which is defined as the others level at which failure will occur for esome specified number cycles) Eg. ofailure - 270 MPa (oppooni mahely) - 815 mia Capporoximately) - 175 MPa (approximately) cycles to failure los egles to failem - 140 MPa (apporoximately The below fatigue antrength does not failure occurs due to fatigue corresponding cycles to failure Fatigue atrength cycles to 105 106 cycles to failure jo? e