Fundametal study on Surface Crack experiencing pseudo-random loading has been carried out by means of unloading elastic compliance technique. As an essential part of the study, some experimental results on crack closure behavior under two kinds of random loading namely, narrow and wide band random loading have been gathered. Also, efforts have been made to see the difference in crack closure behavior with various number of cycles per block ,i.e. 500 and 1000 cycles per block. As a result of comparing surface crack growth behavior under pseudo random loading with that of constant amplitude loading which was acquired by J.H.Kim, we found that somewhat different tendencies lie between two cases. We have reached following conclusions. Definite effects of variation in number of cycles per block and types of rand loading on surface crack growth is not found. Crack growth under random loading is much different from under contant amplitude loading. Using results of surface crack growth unde contant amplitude loading, We tried to predict the surface crack growth under random loading But in vain. This also tells us that surface crack growth under random loading should be m different from that of constand loading. Different "aspect ratio" under random loading has found by experiment. Among other results, this result told us a lot. It told us it is very that surface crack growth under random loading went through different crack growth path.
