Partners

Abstract:
This paper presents a non-linear finite element analysis for the elasto-plastic behaviour of thick/thin shells and plates with large rotations and damage effects. The refined shell theory given by Voyiadjis and Woelke (Int. J. Solids Struct. 2004; 41:3747–3769) provides a set of shell constitutive equations. Numerical implementation of the shell theory leading to the development of the C0 quadrilateral shell element (Woelke and Voyiadjis, Shell element based on the refined theory for thick spherical shells. 2006, submitted) is used here as an effective tool for a linear elastic analysis of shells. The large rotation elasto-plastic model for shells presented by Voyiadjis and Woelke (General non-linear finite element analysis of thick plates and shells. 2006, submitted) is enhanced here to account for the damage effects due to microvoids, formulated within the framework of a micromechanical damage model. The evolution equation of the scalar porosity parameter as given by Duszek-Perzyna and Perzyna (Material Instabilities: Theory and Applications, ASME Congress, Chicago, AMD-Vol. 183/MD-50, 9–11 November 1994; 59–85) is reduced here to describe the most relevant damage effects for isotropic plates and shells, i.e. the growth of voids as a function of the plastic flow. The anisotropic damage effects, the influence of the microcracks and elastic damage are not considered in this paper. The damage modelled through the evolution of porosity is incorporated directly into the yield function, giving a generalized and convenient loading surface expressed in terms of stress resultants and stress couples. A plastic node method (Comput. Methods Appl. Mech. Eng. 1982; 34:1089–1104) is used to derive the large rotation, elasto-plastic-damage tangent stiffness matrix. Some of the important features of this paper are that the elastic stiffness matrix is derived explicitly, with all the integrals calculated analytically (Woelke and Voyiadjis, Shell element based on the refined theory for thick spherical shells. 2006, submitted). In addition, a non-layered model is adopted in which integration through the thickness is not necessary. Consequently, the elasto-plastic-damage stiffness matrix is also given explicitly and numerical integration is not performed. This makes this model consistent mathematically, accurate for a variety of applications and very inexpensive from the point of view of computer power and time.

Abstract:
Additive manufacturing (AM) is revolutionizing production with its ability to rapidly create complex designs while minimizing material waste. The influence of the SLM parameters on mechanical properties of two sets of open cell lattices (Set A and Set B) made of IN718 was investigated. The purpose of using the modified parameters was to reduce the cost/time of manufacturing as well as to reduce microporosity in ligaments by increased exposure time (reduced laser scanning speed) or higher energy density based on increased exposure time. The researchers investigate ligament deformation and collapse in porous lattices, its impact on overall behavior, and how microstructure influences hardening under varying strain rates.

Keywords:
highly porous random open-cell lattice, additive manufacturing, direct impact Hopkinson pressure bar technique, Inconel 718

Abstract:
Nowadays, additive manufacturing (AM) is revolutionizing production, enabling the rapid fabrication of objects in various sizes and shapes, including complex designs such as metallic foam, while significantly reducing material waste. This paper examines the effect of 3D printing parameters (Set A and Set B) on the mechanical behavior of a highly porous random open-cell lattice (HPROCL) in IN718 alloy produced by selective laser melting (PBF-LM). The modified build parameters were applied to reduce manufacturing cost and time while minimizing micro porosity in ligaments by increasing exposure time through reduced laser scanning speed or higher energy density. Furthermore, the researchers investigate ligament deformation, key stages of collapse and stability, its role in impact resistance, and how microstructure influences the hardening behavior of the HPROCL across a wide range of strain rates. The SEM-EDS elemental distribution analysis carried out on the tested specimens enabled to conclude that the foam printed with modified parameters (Set B) contained a lower content of the Laves phase and a higher amount of the δ-phase, which led to an increase in both static and dynamic compressive behavior of HPROCL in IN718 alloy.

Keywords:
Additive manufacturing, Impact resistance, Highly porous random open-cell lattice, Inconel 718