A NEW MICROCOMPUTER-AIDED SYSTEM FOR MEASURING FATIGUE-CRACK PROPAGATION THRESHOLD AND SELECTING TESTING PARAMETERS

A new mathematical model is proposed for measuring fatigue crack propa gation (FCP) threshold by using K-decreasing and K-increasing method. The formulae for efficiently selecting load-variation coefficients C(D ), C(I) and crack growth increments (DELTAa)D, (DELTAa)I in the case o f K-decreasing and K-increasing tests are given and a correct method f or determining FCP rate in the near-threshold region is recommended. O n the basis of the above-mentioned work, a personal microcomputer-aide d system is set up and successfully used for the FCP rate measurement in Lc9 aluminum alloy in 3.5% NaCl salt water environment. Compared wi th other systems, this system can increase the measurement accuracy, s horten testing time and obtain more information. Furthermore, the hard ware is inexpensive.