Effect of loading rate on crack resistance of hardened steel

Crack resistance of hardened steel 40Kh (HRC 46-50) is studied at the moment of crack growth onset in the range of loading rates of 2.1x106 MPaxmsup(1/2) s-1 <= Ksub(I) <3x107 MPa msup(1/2)sSup(-1). It is established that fracture toughness in the hardened steel becomes five times as high with the rise of loading rate from 6x106 to 6x107 MPa msup(1/2) s-1. When analysing the results of studies an attempt is made to establish the connection between the loading rate dependence of crack resistance and deformation rate dependence of the strain resistance