PSI - Issue 41

Danilo D’Andrea et al. / Procedia Structural Integrity 41 (2022) 199–207 D’Andrea et al./ Structural Integrity Procedia 00 (2019) 000–000

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biomedical (Chen et al. (2016); Tilton et al. (2020)), thanks to its good weldability, machinability, and corrosion resistance (M. Godec et al. (2020); Kurgan and Varol (2010)). In recent decades, with the spread of additive manufacturing (AM), many studies have focused on the printability of the SS316L (Matjaž Godec et al. (2020); Liverani et al. (2017); Saboori et al. (2020)). AM presents several advantages over to the traditional production methods, as it allows to obtain components with complex geometries (G. Epasto et al. (2019)), which with conventional techniques would entail high costs (Yang et al. (2017)). Furthermore, many manufacturers have approached this technique, thanks to the possibility of optimizing components, reducing manufacturing times and waste of material. Another fundamental aspect, especially in the prosthetic and jewels industry, is the possibility to customize the products according to specific cases (DebRoy et al. (2018)). Many AM techniques have been developed in recent years, such as selective laser melting (SLM) (Simson et al. (2017)), electron beam melting (EBM) (Gabriella Epasto et al. (2019)), Direct energy deposition (DED) (Saboori et al. (2019)) and so on. However, the AM of metal powder has characteristic defects due to porosity induced by incorrect fusion of the powders, or the formation of residual stress and large grain growth caused by the different heat treatment, caused by the method of printing. These issues affect the mechanical properties and corrosion resistance of the SS316L (Du Plessis et al. (2020); Malekipour and El-Mounayri (2018)). As the printing parameter significantly affect the mechanical properties of the obtained material, it is necessary to perform several tests to retrieve such properties performing a huge number of tests with a high material consumption. However, the adoption of infrared thermography can severally shorten the required time to obtain such information. The development of the Thermographic Method (TM or Risitano TM) (La Rosa and Risitano (2000)) leads to a rapid assessment of the fatigue limit of the material and of the SN curve (Fargione et al. (2002)) adopting few specimens and performing on it a stepwise fatigue test. Other researcher also adopted thermography and other energy-based techniques to assess the fatigue properties of a wide class of materials. In 2013, Risitano and Risitano proposed a rapid test procedure to assess the beginning of damage within the material monitoring the superficial temperature during a static tensile test (Risitano and Risitano (2013)), i.e. the Static Thermographic Method (STM). A limit stress could be identified when a deviation from the linear thermoelastic trend of the temperature signal is noticed. The Static Thermographic Method has been applied to several kind of materials and compared both with traditional fatigue test and TM, showing good agreement (Corigliano et al. (2020); Crupi et al. (2015); Cucinotta et al. (2021); Risitano et al. (2018)). Santonocito, for the first time applied the STM to 3D-printed PA12 (Santonocito (2020)) and monitored the temperature trend of AISI 316L specimens obtained by SLM (Santonocito et al. (2021)). The aim of this work is the comparison between traditional AISI 316L specimens and AM specimens of the same material, monitoring the energy release during static tests. Furthermore, to correlate the mechanical behaviour of the material with the microstructural characteristics of the alloy, the failure analysis was performed on the fracture surfaces with the aid of optical and scanning electron microscopes (SEM).

Nomenclature c

specific heat capacity of the material [J/kg.K]

K m

thermoelastic coefficient [MPa -1 ]

t

test time [s]

T, T i

instantaneous value of temperature [K]

T 0

initial value of temperature estimated at time zero [K] thermal diffusivity of the material [m 2 /s] absolute surface temperature variation during a static tensile test [K] estimated value of temperature for the first set of temperature data [K] estimated value of temperature for the second set of temperature data [K]

α

ΔT s ΔT 1 ΔT 2

ρ σ

density of the material [kg/m 3 ]

stress level [MPa]

σ lim

fatigue limit estimated with the Static Thermographic Method [MPa]

σ U

ultimate tensile strength [MPa]