PARTICULATE-BASED MODELING AND EXPERIMENTAL STUDY OF CHARPY IMPACT TEST OF A36 STEEL AND 3D PRINTED 316L STAINLESS STEEL

The impact properties of steel are critical determinants of its suitability for structural applications. With the rapid advancement of additive manufacturing (AM) technologies, understanding the mechanical behavior differences between conventionally wrought and additively manufactured steels has become increasingly important. This thesis is aimed at investigating the impact behavior of AM-produced steels through a combined approach combining computational modeling and experimental studies. The research focuses on two widely used steel alloys: A36 carbon steel and 316L stainless steel. Their Charpy impact responses are systematically analyzed using two complementary particle-based simulation methods: Smoothed Particle Hydrodynamics (SPH) and the Discrete Element Method (DEM).

For A36 steel, the SPH model incorporates the Johnson-Cook material constitutive model and undergoes validation against uniaxial tensile test data from established literature. Following validation, Charpy impact simulations reveal a correlation between temperature and impact energy. The experimental Charpy impact energy for testing temperatures 77 K, 298 K, 373 K, 503 K, 623 K and 723 K is 1  0.0 J/cm2, 141  7.0 J/cm2, 161  11.0 J/cm2, 105  5.9 J/cm2, 98  2.9 J/cm2 and 95  2.0 J/cm2 , respectively. The SPH-simulated Charpy impact energy at 298 K, 373 K, 503 K, 623 K and 723 K is 142 J/cm2, 161 J/cm2, 105 J/cm2, 98 J/cm2 and 95 J/cm2, respectively, suggesting reasonable agreement with experimental. The decrease in impact energy between 503 K and 723 K is likely due to the interaction between carbon and nitrogen atoms and dislocations.

For 316L stainless steel, the DEM model employs the soft bond approach and is validated through uniaxial compression testing at multiple strain rates. Charpy impact simulations similarly demonstrate increased energy absorption with rising temperature, aligning with experimental findings. For testing temperatures of 77 K, 298 K and 373 K, the experimental Charpy impact energy for AM’ed 316L is 55  1.0 J/cm2 , 95  0.5 J/cm2 and 112  2.0 J/cm2, respectively. The DEM simulated Charpy impact energy at 77 K, 298 K and 373 K is 38.6 J/cm2, 72.7 J/cm2 and 87.0 J/cm2 respectively. Detailed microstructural analysis reveals increasingly ductile fracture surfaces at elevated temperatures. Notably, wrought samples consistently exhibit higher impact energy and lower Vickers hardness values compared to their AM counterparts, attributed to fundamental differences in grain structure and morphology.