Abstract: In this paper,the crack growth tests and analyses of CCT specimen made of LY 12CZ al.alloy and 30CrMnSiA high strength steel materials are carried out. The specimens are sub- jected to transport flight-by-flight random spectra of high loads encountered 10 times per one thousand flights.The crack growth life is predicted with an equivalent model.Comparing the spectrum based on one hundred flights with that based on one thousand flights,the famer only requires 10 per cent data for cycles.Experiment results show that the differences between the two spectra are less than 10% for crack growth life,A more simply concentrated spectrurn is derived,retaining ground-to-air cycle during every flight and arranging some constant amplitude cycles according to the equivalent damage rule. The data of this spectrum are 10 per cent less thanb those based on one hundred flights,but the differences of the tow spectra whether predicted or the test results for crack growth life are less than 15 per cent.Accordingly,a complex random spectrum may arbitrarily be changed to a concentrated spectrum with the equivalent damage rule, reducing calculation and test work.

Key words: random leads, spectrum analysis crack propagution