Issue 41

G. Meneghetti et alii, Frattura ed Integrità Strutturale, 41 (2017) 299-306; DOI: 10.3221/IGF-ESIS.41.40 305 hand side of the band included by the vertical lines, crack acceleration occurs, which was interpreted as the effect of the excessive plasticity around the crack tip [18]. S YNTHESIS BASED ON THE AVERAGED DISSIPATED ENERGY Q * he same crack growth data previously plotted in Fig. 7a are shown in Fig. 7b. In this case, Q*, calculated using R c =0.52 mm combined with the spatial gradient technique Eq. (2), was assumed as driving force for crack propagation. Fig. 7b reports the mean curve, the 10%-90% survival probability scatter bands and the scatter index T da/dN . The crack growth rates can be rationalized with a higher level of accuracy using the averaged heat energy Q*, rather than the range of the linear elastic mode I SIF  K. C ONCLUSIONS n this paper, the specific heat energy per cycle averaged in a structural volume surrounding the crack tip, Q*, was used as a fatigue parameter to correlate the crack growth data generated from 4-mm-thick, hot rolled AISI 304L stainless steel specimens, tested in fully reversed tension-compression fatigue . The size of the structural volume was defined by equaling the averaged heat energy in cracked and smooth specimens for the same fatigue life and it was found equal to 0.52 mm. The crack growth data were plotted in terms of range of the linear-elastic Mode I stress intensity factor,  K, as well as Q*. When presented in terms of  K, a 10%-90% survival probability scatter band calibrated on crack growth data complying with the conditions of applicability of the LEFM was determined; however, as it is well known, crack acceleration is observed at progressively higher applied  K values. Conversely, by using the averaged heat energy Q*, all crack growth data (irrespective of the applied  K) fall within a single 10%-90% survival probability scatter band having the same scatter index of the  K-based one. This outcome is interpreted with the intrinsic nature of the energy Q*, which accounts for crack acceleration due to excessive plasticity occurring at increasingly higher applied  K values. A CKNOWLEDGMENTS his work was carried out as a part of the project CODE CPDA145872 of the University of Padova. The Authors would like to express their gratitude for financial support. R EFERENCES [1] Meneghetti, G., Analysis of the fatigue strength of a stainless steel based on the energy dissipation, Int. J. Fatigue, 29 (2007) 81–94. DOI: 10.1016/j.ijfatigue.2006.02.043. [2] Meneghetti, G., Ricotta, M., The use of the specific heat loss to analyse the low- and high-cycle fatigue behaviour of plain and notched specimens made of a stainless steel. Eng. Fract. Mech., 81 (2012) 2–17. DOI: 10.1016/j.engfracmech.2011.06.010. [3] Meneghetti, G., Ricotta, M., Atzori, B., A synthesis of the push-pull fatigue behaviour of plain and notched stainless steel specimens by using the specific heat loss. Fatigue Fract. Eng. Mater. Struct., 36 (2013) 1306-1322. DOI: 10.1111/ffe.12071. [4] Meneghetti, G., Ricotta, M., Atzori, B., Experimental evaluation of fatigue damage in two-stage loading tests based on the energy dissipation. Proc IMechE Part C: J Mechanical Engineering Science, 229 (2015) 1280-1291. DOI: 10.1177/0954406214559112. [5] Meneghetti, G., Ricotta, M., Atzori, B., A two-parameter, heat energy-based approach to analyse the mean stress influence on axial fatigue behaviour of plain steel specimens. Int J Fatigue, 82 (2016) 60-70. DOI: 10.1016/j.ijfatigue.2015.07.028. [6] Neuber, H., Über die Berücksichtigung der spannungskonzentration bei festigkeitsberechnungen. Konstruction 20 (1968) 245-251. I T