Abstract: | The increase with increasing temperature of KIc, measured with 2CT and 1'CT specimens, from about 103N mm
at 77 K to about 2.103 N mm
at about 170 K is attributed to the increasing proportion of dimple to cleavage fracture as revealed by scanning electron microscope investigation. The specimens were prestrained to different partial scale yielding states by the same kind of loading, performed at 298 K, as in the later KIctests, performed at 77 K. After pretension KIc = K*Ic is increased by a maximum amount of about half of the value K0Icof nonprestrained specimens, after precompression it is reduced by the same amount if this value is evaluated from the load at which a pop-in occurs. The value KIc = K**Ic for the final fracture lies between K*Ic and K0Ic. These results are interpretated in terms of the residual stress states due to prestraining. |