In this study, a computational fatigue analysis of topology optimised auxetic cellular structures made of Selective Laser Melting (SLM) AlSi10Mg alloy is presented. Structures were selected from the Pareto front obtained by the multi-objective optimisation. The fatigue life of the analysed structures was determined by the strain–life approach using the Universal Slope method, where the needed material parameters were determined according to the experimental results obtained by quasi-static unidirectional tensile tests. The obtained computational results have shown that generally less auxetic structures tend to have a better fatigue life expectancy. Furthermore, the fillet radius has a significant impact on fatigue life. In general, the fatigue life decreases for smaller fillet radiuses (less than 0.3 mm) as a consequence of the high-stress concentrations, and also for larger fillet radiuses (more than 0.6 mm) due to the moving of the plastic zone away from the edge of the cell connections. The obtained computational results serve as a basis for further investigation, which should be focused on the experimental testing of the fabricated auxetic cellular structures made of SLM AlSi10Mg alloy under cyclic loading conditions.
COBISS.SI-ID: 22684675
The static and low-cycle durability of three planar cellular structures, hexagonal, auxetic and auxetic-chiral, have been compared. The three structures have the same critical cross-section and are made from an aluminium alloy Al7075-T651. The reference region of each structure is represented by a matrix of nine elementary shaped cells (3 rows by 3 columns). For each structure static and low-cycle fatigue experiments at different loading amplitudes were made. Numerical simulations were then performed for the same boundary conditions to predict the static and low-cycle fatigue durability. For this purpose a continuum damage mechanics approach with element removal was used in explicit dynamic simulations. The results of static simulations were also checked using the eXtended Finite Element Method (XFEM). All the numerical simulations were carried out using Abaqus. Good agreement was observed between the simulated and measured results for each of the three cellular structures.
COBISS.SI-ID: 22988310
The behaviour of the auxetic structure under external load was regarded as the behaviour of the compliant (flexible) mechanism. The multi-objective topological optimization, based on genetic algorithms and the finite element method, was used to find the optimal shape of such two-dimensional compliant mechanism in this study. The optimization was performed on a quarter of a double-symmetric representative unit cell, which is a building block of the symmetrical auxetic structure. Static linear computational simulations were performed to determine the mechanical response of cell topologies. The proposed method leads to a set of best solutions positioned on the Pareto front with different topologies and gives a broad overview of possible designs of new auxetic structures. The method is highly effective and can be easily extended to large deformation formulations, nonlinear elasticity or elasto-plasticity.
COBISS.SI-ID: 25011971
A 3D numerical simulation of the mechanical behaviour of a chiral auxetic cellular structure subjected to multiaxial loading conditions is presented in this paper. The proposed computational models are used to study the geometry effect of the unit cell on the Poisson’s ratio and deformation behaviour of the analysed chiral auxetic structure. A 3D computational model of a chiral auxetic structure is built using beam finite elements in the framework of LS DYNA software. Here, the lattice model is positioned between rigid plates and assembled in a way to simulate hydro-compression loading conditions. Between the contacting surfaces, interactions in normal (contact) and tangential (friction) directions are prescribed, with the node-to-surface approach. The developed computational model offers insight into the deformation (damage) behaviour of the analysed chiral auxetic cellular structure, and enables better understanding of its crushing behaviour under multiaxial loading.
COBISS.SI-ID: 22996246
Auxetic cellular structures build from inverted tetrapods were experimentally tested at high strain rate compression loading for the first time. The strain rates up to 10,000 /s were achieved with gas powder gun, where the shock deformation mode is predominant. The deformation localizes in the deformation front between the impacting specimen and the fixed plate. This deformation mode results in stiffness increases in comparison to the quasi-static response. The results from experimental testing were used for validation of developed computational models in finite element explicit code LS-DYNA. Furthermore, the validated computational models were used for critical strain rate analysis, determination of critical loading velocities and analysis of deformation modes together with analytical constitutive crushing models of cellular structures.
COBISS.SI-ID: 21653270