Issue 41

G. Meneghetti et alii, Frattura ed Integrità Strutturale, 41 (2017) 299-306; DOI: 10.3221/IGF-ESIS.41.40 299 Focused on Crack Tip Fields The heat energy dissipated in a control volume to correlate the crack propagation rate in stainless steel specimens G. Meneghetti, M. Ricotta University of Padova, Italy giovanni.meneghetti@unipd.it , http://orcid.org/0000-0002-4212-2618 mauro.ricotta@unipd.it, http://orcid.org/0000-0002-3517-9464 A BSTRACT . Metallic materials dissipate thermal energy when subjected to fatigue. Some of them, due a favorable combination of thermo-physical material properties, exhibit a significant temperature rise, which can be easily measured in-situ by means of thermocouples or infrared cameras. The heat energy dissipated in a unit volume of material per cycle (the Q parameter) has proven to be effective as a fatigue damage index in case of AISI 304L plain and notched specimens. Originally conceived and applied as a point-related quantity, recently Q has been averaged at the tip of propagating fatigue cracks (the Q* parameter) in order to correlate crack growth data gathered from fracture mechanics tests. The use of Q* seems interesting because (i) it can be evaluated in-situ from infrared temperature maps and (ii) crack acceleration due to excessive plasticity is likely to be accounted for. K EYWORDS . Fracture Mechanics; Crack tip plasticity; Energy methods; Fatigue; Temperature. Citation: Meneghetti, G., Ricotta, M., The heat energy dissipated in a control volume to correlate the crack propagation rate in stainless steel specimens, Frattura ed Integrità Strutturale, 41 (2017) 299-306. Received: 28.02.2017 Accepted: 03.05.2017 Published: 01.07.2017 Copyright: © 2017 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION n the last years the authors proposed [1] to use the heat energy to rationalise the fatigue behaviour of plain and bluntly notched specimens made of AISI 304L stainless steel subjected to push-pull, constant amplitude [2,3] and two load level [4] fatigue tests. The mean stress influence in fatigue has also been taken into account [5]. The proposed approach assumes the heat energy dissipated in a unit volume of material per cycle, Q, as a fatigue damage index, that can be readily evaluated by means of temperature measurements performed at the crack initiation point. Originally conceived and applied as a point-related quantity, Q can hardly correlate fatigue test results generated from cracked specimens. Rather, it should be averaged inside a material dependent structural volume V c [6]. The approach is sketched in Fig. 1a. In a previous paper it was demonstrated that the specific energy per cycle dissipated as heat is approximately equal to the plastic strain hysteresis energy, which drives fatigue crack propagation according to ref. [7]. I