PSI - Issue 76

Davide D’Andrea et al. / Procedia Structural Integrity 76 (2026) 151–158

153

σ u σ y σ 0

ultimate stress [MPa] yield stress [MPa] fatigue limit [MPa]

σ 0, RTM

fatigue limit according to RTM [MPa]

2. Materials and methods Specimens of PA12 were obtained by Selective Laser Sintering (SLS) printing technique, with an EOS Formiga P100 printer. The SLS process consists of depositing PA12 powder in the build chamber, followed by selective sintering using a laser that fuses the targeted areas layer by layer to form the 3D object. The surrounding powder remains unfused and acts as support material. The specimens were produced according to the geometry 1A prescribed by ISO 527-2 standard reported in Figure 1-a, with a nominal cross section of 10 mm x 4 mm, adopting the EOS commercial powder PA2200. The specimens building orientation angle was of 0° respect the X and Y machine direction, allowing a volume internal grid-like structure due to the orthogonal laser beam trajectories oriented in loading direction. Tests were carried out using an Italsigma FPF25, equipped with a 25 kN loading cell. Insights into fatigue life of materials have been estimated through Risitano’s Thermographic Method (RTM) (Fargione et al., (2002); La Rosa and Risitano, (2000)) and Static Thermographic Method (STM)(Risitano and Risitano, (2013)), which consist in monitoring the surface temperature of specimens subjected, respectively, to stepwise fatigue tests and to monotonic quasi-static tensile tests. For a better understanding of these methodologies and their application, reader can refer to Davide D’Andrea et al., (2025) . Six quasi-static monotonic tensile tests were conducted under displacement control at a velocity of 5 mm/min (three on specimens printed in the X direction and three on those printed in the Y direction). Constant-amplitude and stepwise fatigue tests were carried out using a stress ratio of R= 0.1 and a testing frequency of f= 1 Hz. To ensure uniform emissivity, the specimens were spray-painted with a black paint. Measurement of the surface temperature were acquired using a FLIR A40 thermal camera, equipped with an FPA sensor offering a resolution of 320×240 pixels and a thermal sensitivity of 80 mK. The test setup is reported in Figure 1-b and the acquired data were analysed using algorithms developed in Python language.

(a) (b) Figure 1. a) ISO 527-2 type 1A specimen’s d imensions (units expressed in mm); b) Test setup: ItalSigma FPF25 hydraulic testing machine with Flir A40 IR camera. 3. Results and discussion 3.1. Quasi-static tensile tests and Static Thermographic Method (STM) Mechanical properties have been calculated according to ISO 527-2 guidelines, which defines the yield point as the point of the stress vs. strain curve where the gradient is zero, the ultimate values as the stress and strain at the moment of specimen failure and Young’s modulus as the slope of the linear zone between with strain between 0.05% and 0.25%. Stress-strain curves for both specimen’s sets are reported in Figure 2 together with mechanical properties