Issue 47

D. Rigon et alii, Frattura ed Integrità Strutturale, 47 (2019) 334-347; DOI: 10.3221/IGF-ESIS.47.25 335 Figure 1 : Fatigue test results of plain and notched AISI 304L in term of net-section stress amplitude (a) and re-elaborated in terms of specific heat loss Q (b). Data are extrapolated from Ref. [22]. In [14], a simple experimental technique was proposed to evaluate the Q parameter at a point of a component, starting from the cooling gradient measured at that point immediately after the fatigue test has been stopped, according to Eqn. (1): L T c t Q f       (1) where T(t) is the time-variant temperature at the point, ρ is the material density, c is the material specific heat and f L is the load test frequency. Figure 2 : Specimen’s geometry (a) and experimental setup of the fatigue tests carried out in Ref. [22] and analysed in the present contribution (b). In [16–19], the Q parameter was adopted to synthesize 140 experimental results obtained from constant amplitude, push- pull, stress- or strain-controlled fatigue tests carried out on plain and notched hot rolled AISI 304L stainless steel specimens as well as from cold drawn un-notched bars of the same steel, under fully reversed axial or torsional fatigue loadings. The fatigue test results synthesized in term of Q fall in a single energy-based scatter band, which was fitted only on the fatigue test results relevant to plain material, hole specimens (r n =8 mm), U (r n =5 mm), and bluntly V (r n =3 mm) notched specimens a) b) 10 100 1.E+3 1.E+4 1.E+5 1.E+6 1.E+7 1.E+8  an [MPa] N f , number of cycles to failure Scatter band: 10-90% survival probabilities, from Ref [16] k=5.8, T  =1.30, T N =4.60 from Ref [22] r n =3mm, K tn = 3.41 r n =1mm, K tn = 4.85 r n =0.5mm, K tn = 6.10 AISI 304L R=-1 500   = 202 MPa Short stair-case unbroken, broken V-notch 2  =135° plain material from Ref. [19], k=17.2 k 1 0.1 1 10 1.E+3 1.E+4 1.E+5 1.E+6 Q [MJ/(m 3 ꞏcycle)] N f , number of cycles to failure Dara from Ref. [22] r n =3mm r n =1mm r n =0.5mm Scatter band: 10-90% survival probabilities, from [16] k=2.11, T Q =2.04, T N =4.50 Q A,50% =0.133 MJ/(m 3 cycle) (N A =2ꞏ10 6 cycles) R=-1 AISI 304L Data from Ref. [19] Plain material V-notch 2  =135°