Zaki Alomar received his M.Sc. degree in mechanical engineering from the University of Balamand. He is currently pursuing a Ph.D. in advanced systems engineering at the Free University of Bolzano/Bozen under the supervision of Dr. Franco Concli. His work involves the dynamics and design optimization of lattice structures.
With the recent development of metal additive manufacturing processes, the fabrication of lattice structures became more feasible. Mainly, with the selective laser melting process, lattices of various topologies have been designed and manufactured with superior properties. Their excellent characteristics have drawn the attention of major leading industrial sectors. Nevertheless, their full-scale adoption is still limited, owing to the lack of a standard numerical model that can accurately represent the lattices’ mechanical and failure response. The main challenge in developing such a model is the high computational cost associated with the fine three-dimensional meshes of the struts. Besides, the need to incorporate the struts’ defects into the finite element model while also accounting for the material behavior significantly increases the complexity of the model. In this context, this paper presents a review of the numerical models explicitly developed to simulate the lattices’ behavior. The potential of modeling lattices at the macro-scale level using reduce order elements will also be discussed. Overall, the aim of this paper is first to identify the important numerical parameters needed to construct the optimum numerical setup, and second to pinpoint the gaps that can be worked upon to develop a more reliable and computationally effective model.
An accurate fracture simulation is often associated with how reliably the material model is represented. Hence, many models dealing with the calibration of ductile damage of materials have already been developed to predict failure initiation. Nevertheless, the challenge remains in obtaining an accurate representation of the fracture growth. Herein, an element deletion algorithm is developed and implemented into finite element open-source software. The deleted elements are replaced by new cells made of a virtual low-stiffness material. To better visualize the failure progression, the final model excludes these virtual cells from the representation. The functionality of the algorithm is tested through a series of two-dimensional simulations on three different geometries with a well-known behavior under uniaxial tension. Moreover, the failure response of a three-dimensional lattice structure is numerically investigated and compared against experimental data. The results of the two-dimensional simulations showed the capability of the algorithm to predict the onset of failure, crack nucleation, and fracture growth. Similarly, the onset and the initial fracture region were accurately captured in the three-dimensional case, with some convergence issues that prevent the visualization of the fracture growth. Overall, the results are encouraging, and the algorithm can be improved to introduce other computational functionalities.
A new phenomenological model for lattice structures that exhibit crushing‐like failure mechanisms is presented. The model estimates the compressive stress–strain curves of such lattices based on their relative density. The model is derived from the underdamped oscillator's general equation and the rheological model's properties. The model applicability is tested on five circular cell lattice structures having various relative densities, as well as a body‐centered‐cubic and a square cell lattice, for further validation. The model accurately captures the curves’ profile qualitatively and quantitatively compared with the experimental data. A relationship between each parameter and the relative density is established to extend the model's functionality as fourth‐order polynomial equations. Additionally, the energy absorption values between the measured data and the model up to the crushing of the first layer are in relatively good agreement ranging between 2.68% and 25.3%, proving the model's effectiveness. Overall, the new phenomenological model can estimate essential features of the lattice structures based solely on the relative density while reducing the time and the cost needed during the design phase.
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