Abstract
Fatigue crack growth behavior of metallic materials before and after high pressure torsion (HPT) treatment was investigated using RCT-specimen under tension-tension loading. In order to clarify the influence of crystal lattice on fatigue crack propagation process, specimens made of pure Fe (bcc) and 99.9%Ni (fee) were examined. The growth of fatigue crack was observed by optical microscope during fatigue process and the fracture surfaces were observed using scanning electron microscope. From the results, it is found that the relationships between crack growth rates, da / dN, and stress intensity factor range, ΔK, in HPT-processed specimen of the both materials are almost the same at low ΔK region, but in ΔK values is above 30MPam_<1/2>, da / dN of 99.9% Ni increased in comparison with that of Fe-11ppmC. Stripe like pattern was observed in the fracture surface of the both HPT-processed specimens, but not observed in untreated specimen.
