Three models of crack growth under constant load in VT6 alloy

Subcritical crack growth in VT6 alloy is studied using notched samples with hydrogen content in them 0.002, 0.006 and 0.017 mass %. Three types of crack development are detected. A decrease in the crack growth rate with time is characteristic of one of them, spasmodic crack development - of the second one, and crack growth with a constant rate at the constant stress intensity factor (SIF) - of the third one. Experimental and calculated dependences of crack growth rate on SIF are plotted. The mechanism of crack growth is described as destruction of certain structural elements located prior to the crack vertex and subsequent merging of the destructed elements with manifold crack. The frequency of the element destruction is determined by dislocation and hydrogen accumulation rates