## 1 Introduction  
A critical aspect of standard test methods for fatigue characterization is the lack of any information on heat dissipation in the material and the very expensive experimental campaigns in terms of time and costs. Thermal methods represent valid support to study fatigue behaviour of materials, since they allow both the reduction of time and costs of the experimental campaigns and the possibility to estimate damage phenomena correlated to dissipative heat sources developed during fatigue. The fatigue crack develops with consequent generation of thermal energy, which can be considered as the effect of a plausible activation mechanism of the crack, which is therefore correlated with the fatigue limit. Based on this correlation, [PERSON] proposed an alternative method for the evaluation of the fatigue limit through the use of infrared thermography [1, 2, 3]. [PERSON]'s method has the peculiarity consisting of a rapid estimation of this important material property. The use of this technique, in addition to the advantages of thermography, such as the possibility of providing real-time information on the monitored area temperature, the minimum preparation of the specimen and the possibility of not breaking it, involves, in theory, the use of a single specimen for the evaluation of the fatigue limit, which results in a saving in terms of time and cost of the test. The thermographic technique allows obtaining slightly lower fatigue limit values compared with the Stair-Case method and represents a potential non-destructive characterization technique for prediction of fatigue behaviour even of complex shape and in-service components. A lot of works in scientific literature apply thermal methods for a fast determination of the fatigue limit in metal materials, especially in steels [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]. Among these, only a few papers consider the influence of a notch presence, which is a region with high-stress concentration, in these materials [8, 9]. An automatic thermal data analysis procedure has been proposed for fatigue limit evaluation of martensitic and precipitation hardening stainless steel [4; 5]. The thermal rapid determination of fatigue limit for stainless steel has been achieved, by comparing temperature and energy-based approaches available in the literature [6]. A Quantitative Thermographic Method has also been proposed for residual fatigue life assessment of mild steel for specimens with a central flat-bottom hole [7]. Thermographic method based on an iterative procedure has been applied to Fe 510 standard and notched specimens with semi-circular notch, obtaining the fatigue limit as the intersection of the two straight lines interpolating experimental thermographic data corresponding to stresses below and above the fatigue limit [8]. A large amount of fatigue data, referred to AISI 304L smooth and V-notched specimens, were represented in a single scatter band considering the specific heat loss per cycle as a damage parameter [9]. Thermographic approach to estimate the fatigue limit of 3 stainless steel specimens, exhibiting fully austenitic, fully martensitic and duplex biphasic microstructure, has been proposed [10]. Despite the metallic materials case, a lot of scientific researches consider the fatigue damage monitoring by thermal methods in composite materials [11; 12; 13; 14; 15; 16; 17], but only some of these attempt to evaluate the fatigue limit [13; 16]. The application of IR-thermography to different glass and basalt fibre-reinforced composite materials, to relate their thermal response to the mechanical behaviour, is presented in [11]. An analytical model based on cumulative damage was adopted for predicting the damage evolution in carbon/epoxy composite material obtaining a relation between the heat dissipation and damage [12]. An energy-based approach is proposed to analyse the fatigue strength of plain and notched specimens in short fibre-reinforced plastic.