Determination of ΔK_(th) by Compression Pre-Cracking in a Structural Steel

摘要

The traditional experimental procedures used to generate thresholds (known as "AK-decreasing" and "constant K"_(max)") have been challenged because it seems they affect the experimental results, sometimes in a non conservative way. In order to fix this problem, different experimental procedures ("compression pre-cracking constant amplitude" and "compression pre-cracking load reduction" (CPLR)) based on a compression-compression pre-cracking of fracture mechanics specimens have been proposed. Up till now, such procedures are not yet wide-spread between fracture mechanics experimentalists. In particular, due to the recent introduction, CPLR has been applied only to few cases: Al alloys, Ti alloys, and high strength steels (ultimate tensile strengths-1300 MPa), all in the shape of M(T) or C(T) specimens subjected to positive stress ratios. The present paper deals with the application of these novel "compression pre-cracking" procedures, with particular attention to CPLR, to the unexplored and technically very important case of the structurally mild A1N steel grade (very commonly used to produce European railway axles) in the shape of SE(6) specimens subjected to stress ratios varying between -2 and 0.85.