PSI - Issue 34

Dario Santonocito et al. / Procedia Structural Integrity 34 (2021) 211–220 D. Santonocito et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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(Cucinotta et al. (2020), (2019); Dapogny et al. (2019)). Several authors have investigated the mechanical properties of such material, both plastics and metals. Berto and coworkers (Berto et al. (2018)) developed a design strategy with advanced numerical simulation to avoiding physical tests. Shanmugam et al. (Shanmugam et al. (2021)) investigated the fatigue properties of 3D printed polymeric cellular matrix obtained by Filament Deposition Moulding (FDM) technique. Several authors made a comparison between FDM and Selective Laser Sintering (SLS) technique (Terekhina et al. (2020)) and between SLS and MultiJet Fusion technique (Rosso et al. (2020)) for Polyamide-12 (PA12) specimens. Usually, the investigation of the fatigue properties requires a large amount of time (even moth) and material to be tested. On the other hand, the development of energy methods allows the fatigue assessment of several kind of material in a rapid way. Santonocito and coworkers, for the first time investigated the fatigue properties of 3D printed polymers and metals, by applying the Static Thermographic Method (STM) and the Thermographic Method (TM) (Santonocito (2020); Santonocito et al. (2021)). Infrared thermography (IR) is a valid aid in the investigation of fatigue properties. It has been applied on several materials under different loading conditions: notched and plain steel specimens under static and fatigue tests (Corigliano et al. (2020), (2019); Foti et al. (2020); Ricotta et al. (2019); Rigon et al. (2019); Antonino Risitano and Risitano (2013)), glass fibre reinforced composites under static and fatigue loading (Crupi et al. (2015b)), steels under high cycle (Amiri and Khonsari (2010); Curà et al. (2005); Meneghetti et al. (2013)) and very high cycle fatigue regimes (Crupi et al. (2015a); Plekhov et al. (2015)), high strength concrete (Cucinotta et al. (2021)). In 2000, La Rosa and Risitano, proposed the Thermographic Method (TM) as an innovative approach based on thermographic analyses of the temperature evolution during the fatigue tests in order to predict the fatigue limit and the S-N curve (Fargione et al. (2002)). In 2013, Risitano and Risitano proposed the Static Thermographic Method (STM) as a rapid procedure to derive the fatigue limit of the material evaluating the temperature evolution during a static tensile test. The aim of this research activity is the application of the STM during static tensile tests on 3D-printed PA12 specimens. Infrared Thermography has been adopted to monitor the temperature evolution during static tensile tests and to assess the limit stress, as the macroscopic stress at which the temperature trend deviates from the linearity. To verify the correlation between the limit stress and the fatigue damage, a fatigue test campaign, with a stepwise increase of the stress level has been carried out, applying the TM. Nomenclature c specific heat capacity of the material [J/kg.K] f test frequency [Hz] k inverse slope of the SN curve K m thermoelastic coefficient [MPa -1 ] R stress ratio t test time [s] T, T i instantaneous value of temperature [K] T 0 initial value of temperature estimated at time zero [K] α thermal diffusivity of the material [m 2 /s] ΔT s absolute surface temperature variation during a static tensile test [K] ΔT st stabilization temperature reached during fatigue test [K] ΔT 1 estimated value of temperature for the first set of temperature data [K] ΔT 2 estimated value of temperature for the second set of temperature data [K] Φ Energy Parameter [Cycles K] ρ density of the material [kg/m 3 ] σ stress level [MPa] σ lim fatigue limit estimated with the Static Thermographic Method [MPa] σ 0 , σ 0 TM fatigue limit, fatigue limit assessed by Thermographic Method [MPa] σ 1 uniaxial stress [MPa]