The Influence of Specimen Geometry on Near Threshold Fatigue Crack Growth

Abstract

The near threshold fatigue behavior of a nickel base superalloy and a wrought 2024 aluminum alloy is examined as a function of specimen geometry. Experimental results revealed that for a given value of AK in Region I, crack growth rates were observed to increase as the specimen loading became more symmetric with respect to the load line. Compact tension type specimens exhibited lower crack growth rates than the more symmetrically loaded center cracked tension specimens. Consideration of the observed discrepancies is given in terms of the near field crack tip stress distribution and deformation behavior of the material affecting crack advance.

Fatigue crack growth and damage tolerance

“…As a result, different specimen geometries loaded such that they experience the same K can have different T ‐stresses. This can result in different thresholds and different d a /d N versus Δ K curves . Hutar et al .…”

Damage tolerance of railway axles – The issue of transferability revisited

“…It has been sought to explain the geometry influence by the so-called constraint effect, i.e. by different stress states near the crack tip in specimens of different geometry [9,[20][21][22][23]. The authors of [20,22,23] argue the constraint effects by the T-stress, which shows a large variation in specimens tested in the respective studies.…”

Fatigue crack growth testing at negative stress ratios: discussion on the comparability of testing results

“…In literature, the investigations of the specimen influence consider the case of a crack in tension. Aspects of research are the constraint effect due to thickness [23][24][25] and differences in stress triaxiality [26][27][28] influencing the crack tip plasticity in tension.…”