Enhancement and Retardation of Crack Initiation and Growth Due to Thermomechanical Stresses.

A thermomechanical energy density factor S is derived in terms of the mechanical and thermal stress intensity factors [image omitted] and [image omitted], respectively. While both [image omitted] and [image omitted] can change sign depending on the directions of the applied mechanical stress and thermal gradient, the quadratic form [image omitted], however, is positive definite. The mixed term with A12 can be either positive or negative depending on the sign of [image omitted] and [image omitted]. Hence, S can increase or decrease with the crack length that is contained in the expressions for the intensity factors. Based on the criterion of crack growth similarity with the proportion S/r being equal to the area under the true stress and true strain curve, it is found that crack growth initiation can be enhanced or retarded. If the mechanical stress is fixed in tension, crack growth is enhanced when the thermal gradient is in the direction of crack initiation while the opposite prevails when the direction of thermal gradient is against the direction of crack initiation induced by the mechanical tension. The formulation provides a clear interaction of how the mechanical and thermal effects would compete. Results are obtained for 38Cr2Mo2VA steel, LY12 aluminum and TC6 titanium alloys which are the sequential order of crack growth enhancement and retardation. Such information can assist the correlation of crack growth data when comparing the results for different materials. [ABSTRACT FROM AUTHOR]