A small-sized bending fatigue testing machine of electro-dynamic type was constructed. The capacity of the testing machine is 10kgf. All the parts used were obtained in domestic markets. Particularly, the field magnet and the moving coil taken from a home-made audio-speaker were successfully utilized as the components of the force exciter.
Using this machine, small surface fatigue crack growth tests were performed on 7075-T6 Aluminum alloy. Crack length and crack closure are measured by unloading elastic compliance technique using back face strain gage. The growth rates of small surface fatigue crack, of 0.5-1㎜ depth can be explained in terms of the effective stress intensity range accounting for crack closure.
