Fatigue Damage Assessment of Materials Under Uniaxial Variable Amplitude Loading Conditions

This  thesis  intends  to  further  apply  an  earlier  developed  energy  based-critical  fatigue damage  parameter  to  assess  the  fatigue  damage  of  different  materials  subjected  to repeated  random  block  histories.  In  fatigue  damage  assessment  under variable  loading conditions, further phenomenological factors of: (i) sequence loading effect, (ii) memory effect, and (iii) the effect of small  amplitude cycles below the material endurance limit have been introduced.The effect due to sequence loading is studied for variable amplitude loading conditions. It is  found  that  the  loading  sequence  has  a  great  influence  on  the  cyclic  stress-strain hysteresis loops and therefore on fatigue damage of materials. Memory effect concept has been carefully monitored and programmed to correspond to the closed hysteresis loops in each  block  loading  history.  The  small  cycles  exceeding  50%  of the  fatigue  endurance limit contributed to the accumulated damage.A  comparison  of  the  predicted  fatigue  life  results  based  on  energy  based-critical parameter  including  the  phenomenological  factors  with  the  experimental  live  data reported in the literature has shown a good agreement.