Crack size, hammer stroke frequency and rotary speed influence the drilling string fatigue life involve, in which the crack size and stroke frequency were two major factors.

The theory and test proved that the impacting frequency of hydraulic rammer can be adjusted by pipe hammer stroke. The influences of stroke on characteristics of hammer are discussed.

They thought the moment of their deliverance was come, but no stroke of the hammer was heard, no stone fell out of the wall, and it seemed to Maid Maleen that her father had forgotten her.