الفهرس 
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Abstract
The importance of fatigue proble~ arises from the fact that fatigue is a mtjor fialure ~cde. Unlike most other structural fialure mec~anisms in ~hich failure is the result
of a large scale deformation process, which can be cbserved and used as an inclcator of upcoming failure, fatigue is a highly localized pllenomenon which occurs without warning, it is sudden and potentially dangerous.
The fatig~e life of any structural component due to a fufly reversed load history can be easily evaluated using the ordinary strain or stress-life curves. The problem arises when the 1) 1 d history is random or complicated due to the presence of the interaction effect betwee~ loads of high and low levels.
The purpose of this research is to evaluate fatigue life of a metal subjected to random or stochastic load histories. In this study, two different routes have been followed for this purpose; the modified life curves ccncept and the semi-theoretic method. In the first rcute, the m0dified life curves have been obtained with no need for
carrying out random excperime~ts. The point, at which the ordinary curve changes into a straight line, can be determin¬ed as a general point for all kinds of metals. The results
Of this research have shown that this point may be obtained ways depending en the sensitivity of the ~nary strain-life curve for the interaction effect. This
sensitivity. the degree of flatness. can be measured by a .called the non-conservative factor.
The second route that has been followed in this research
r fatigue life evaluation is the semi-thecretic method. is method is proposed here by the author to deal with the of metal fatigue under random loading taking into
the time factor.
The results of the semi-thecretic method that have bee~
in this research are very encouraging. More
have to be carried out using a variaty of metals
verify the theory.
The study performed in this research is based on the following assumptions:-
The closed hysteresis loops are considered as the events
most representative of the fatigue damage.
The rainflow counting technique is used in this research because of its supriority. This technique cannot be misled by any complex load sequences and always counts correctly assu~ingthe closed hysteresis loops as the most