Because of the stochastic nature of the damage processes, it is generally inadvisable to formulate a deterministic approach to predict fatigue damage and fatigue life. Thus, many stochastic mathematical expressions for fatigue life and fatigue damage process have been developed. specimens, fatigue data can be described by random variables to study the variability of damage and life and to analyse their average trends [1, 2]. With improvements in crack-size measurements, fatigue crack growth data can be described in a random time-space and state-space to depict local variations within a single specimen analyse. This has been done by a stationary lognormal process-based randomized approach of deterministic crack growth equation in power law and polynomial forms [7][8][9][10]. Under random spectrum loading, a fatigue cumulative process can be described by discrete Markov chain models [3,6] or continuous Markov process methods based on the solution of the Fokker-Planck equation [4,6,11,12]. The appropriateness and accuracy of these categories of stochastic models have been verified by statistically meaningful fatigue crack growth data sets with certain degrees of accuracy [7,8,[13][14][15]. In fact, all above categories of stochastic models have been obtained by randomizing the deterministic fatigue crack growth equation and using large sample numbers of statistically meaningful data sets from which to determine the random coefficients for the models.However, in many circumstances, due to time and resource constraints, it is infeasible to conduct extensive experimental investigations in order to generate the large numbers of data sets required by classical statistical processes. Hence, it is desirable to have a technique to address the paucity of data in assessing the structural probability of fatigue and fracture performance. In the chapter, a series of original and practical approaches of deterministic equation are proposed for the J. J. Xiong and R. A. Shenoi, Fatigue and Fracture Reliability Engineering, Springer Series in Reliability Engineering,