Question

After leaving the university you establish your own consulting company dealing in material testing and tooling processes. A client has brought you samples from a metallic material intended for an application where the applied load will not be constant, but fluctuating. The client is looking for technical guidance on the suitability of this material for the said application. You have, therefore, decided to conduct tests which will establish the relationship (S-N curve) between applied loading (S – stress amplitude) and fatigue life (N – number of cycles to failure).

a) Sketch one sinusoidal fatigue loading cycle with zero mean stress (i.e. ?? = 0) and on it indicate

i. Stress range,

ii. Mean stress and

iii. stress amplitude

b) Repeat question (a) by considering a non-zero mean stress (i.e. ?? > 0).

c) Briefly but clearly describe an experiment to obtain a typical S-N curve.

d) On the obtained S-N curves in (c), indicate how the endurance limit will be obtained.

Answer 1

S-N CURIE 0. Senas cidal fatigue loading cycle with Zeno mean stress m = Tmax tomu 20 10 mpa S - Omax. o Completely reversed cycle Tensilel (t) of stren Umzo 6 Egi max 2 min = lompa N. br comp Stress I load oscellate be about a mean zero load/stron men Tompa Ta= max-min 10-1-10) = lompa 2 Ta=lompa Enample 20 mpa 그 stress range Toz Tmax-nun Strep Amplitude es) Stress ratio - O min -10 2-1 max for Non-Zero mean stren [Omso] Purely Tensile cycle Tn= maxt run St W F 2 mak om Ta= max-min min 2 N Tmax - min R= mui may

SN - is Number of cycle a plot between Alternating stren and SN -Cluwe LLEU) SN Cuue. p Cyclic load Stres I matalcoupon developed by german scientist August wöbler to Investigate train axle crash under repeated how level" cyclic load Eacperiment to create Recent way to predict SN Cuove cis by using metal coupon testing machine cyclic Metal us Subjected strail Upon to a cyclic Stress time history until failure several coupons must be tested at different stren levels to develop a Sin catwe low Fatique Steal, Ti shows fatique Infinite cuci limit o impa shows no logo ve ! Endurance lino fatéque time lot Stew Fame hasong smart Tegelt + J Ali mg, Cu 103 (logn) No of cycle MS S All N