Numerical simulations of gyroid structures under compressive loads

Numerical simulations are essential for predicting the mechanical properties of different structures like gyroids that center this study. Three different methods are explored: shell elements, solid elements, and homogenization. Results reveal that homogenization is only suitable for obtaining the properties in the elastic zone, whereas solid models can determine also the behaviors in the plateau zone and the densification point. In the case of shell elements model, it can predict the elastic behavior model and the levels of stress in the plateau zone but with a lower accuracy than the solid element, but it cannot predict the densification point

Density-based topology optimization for 3D-printable building structures

This paper presents the study of a new penalty method for density-based topology optimization. The focus is on 3D-printable building structures with optimized stiffness and thermal insulation properties. The first part of the paper investigates the homogenized properties of 3D-printed infill patterns and in the second part a new penalty method is proposed and demonstrated. The method presents an alternative way to implement multi-material topology optimization without increasing computational cost. A single interpolation function is created, based on the homogenized properties of a triangular infill pattern. The design variables are linked to the different possible infill densities of the pattern. A high density represents a solid structure with high stiffness, but weak thermal properties, while an intermediate density provides the structure with good insulation qualities. On the other hand, when the air cavities become too large (i.e., low infill densities), the heat flow by convection and radiation again decreases the thermal performances of the material. The optimization study is performed using the GCMMA algorithm combined with a weighted-sum dual objective. One part of the equation aims to maximize stiffness, while the other attempts to minimize the thermal transmittance. Different case studies are presented to demonstrate the effectiveness of this multi-physics optimization strategy. Results show a series of optimized topologies with a perfect trade-off between structural and thermal efficienc

Two-scale topology optimization with heterogeneous mesostructures based on a local volume constraint

A new approach to produce optimal porous mesostructures and at the same time optimizing the macro structure subject to a compliance cost functional is presented. It is based on a phase-field formulation of topology optimization and uses a local volume constraint (LVC). The main novelty is that the radius of the LVC may depend both on space and a local stress measure. This allows for creating optimal topologies with heterogeneous mesostructures enforcing any desired spatial grading and accommodating stress concentrations by stress dependent pore size. The resulting optimal control problem is analysed mathematically, numerical results show its versatility in creating optimal macroscopic designs with tailored mesostructures

Evaluation of Properties of Triply Periodic Minimal Surface Structures Using ANSYS

abstract: The advancements in additive manufacturing have made it possible to bring life to designs that would otherwise exist only on paper. An excellent example of such designs are the Triply Periodic Minimal Surface (TPMS) structures like Schwarz D, Schwarz P, Gyroid, etc. These structures are self-sustaining, i.e. they require minimal supports or no supports at all when 3D printed. These structures exist in stable form in nature, like butterfly wings are made of Gyroids. Automotive and aerospace industry have a growing demand for strong and light structures, which can be solved using TPMS models. In this research we will try and understand some of the properties of these Triply Periodic Minimal Surface (TPMS) structures and see how they perform in comparison to the conventional models. The research was concentrated on the mechanical, thermal and fluid flow properties of the Schwarz D, Gyroid and Spherical Gyroid Triply Periodic Minimal Surface (TPMS) models in particular, other Triply Periodic Minimal Surface (TPMS) models were not considered. A detailed finite element analysis was performed on the mechanical and thermal properties using ANSYS 19.2 and the flow properties were analyzed using ANSYS Fluent under different conditions.Dissertation/ThesisMasters Thesis Mechanical Engineering 201

FLatt Pack: A research-focussed lattice design program

Lattice structures are an important aspect of design for additive manufacturing (DfAM). They enable significant component light-weighting and the tailoring of a wide range of physical responses; mechanical, thermal, acoustic, etc. In turn, lattice design relies on fundamental research to uncover useful structure-property relationships, such as the influence of cell geometry and volume fraction. A number of commercial computer-aided-design (CAD) programs exist that offer lattice generation, but these tend to prioritise product design. This paper describes the FLatt Pack program (or Functional Lattice Package), which was created to address the paucity of research-focussed lattice design software. It possesses a number of features with this in mind, including; (i) it is free to use for research, (ii) it is standalone software with minimal, and also free, dependencies, and (iii) it undergoes frequent and rapid development based on state of the art lattice information and modelling methods. FLatt Pack includes twenty-three lattice cell types covering a broad range of pore connectivity, structural anisotropy, and surface area; a clear GUI presenting the lattice design stages in a sequential manner; and the option to export designs in appropriate formats for AM and finite element (FE) simulation. The program also features conformal lattice generation in arbitrary shapes, arbitrary volume fraction grading, and resource-efficient computation through an adaptive spatial resolution based on the user's design choices. The most recent version of FLatt Pack is freely available at: www.github.com/ian27ax/FLatt_Pack_dist

A novel bio-inspired design method for porous structures: Variable-periodic Voronoi tessellation

This paper introduces a novel approach, namely Variable-Periodic Voronoi Tessellation (VPVT), for the bio-inspired design of porous structures. The method utilizes distributed points defined by a variable-periodic function to generate Voronoi tessellation patterns, aligning with a wide diversity of artificial or natural cellular structures. In this VPVT design method, the truss-based architecture can be fully characterized by design variables, such as frequency factors, thickness factors. This approach enables the optimal design of porous structures for both mechanical performance and functionality. The varied, anisotropic cell shapes and sizes of VPVT porous structures provide significantly greater design flexibility compared to typical isotropic porous structures. In addition, the VPVT method not only can design micro-macro multiscale materials, but is also applicable for the design of meso-macro scale truss-based porous structures, such as architecture constructions, biomedical implants, and aircraft frameworks. This work employs a Surrogate-assisted Differential Evolution (SaDE) method to perform the optimization process. Numerical examples and experiments validate that the proposed design achieves about 51.1% and 47.8% improvement in compliance performance and damage strength, respectively, than existing studies

Optimal design and modeling of gyroid-based functionally graded cellular structures for additive manufacturing

Lightweight cellular structure generation and topology optimization are common design methodologies in additive manufacturing. In this work, we present a novel optimization strategy for designing functionally graded cellular structures with desired mechanical properties. This approach is mainly by generating variable-density gyroid structure and then performing graded structure optimization. Firstly, the geometric properties of the original gyroid structures are analyzed, and the continuity and connectivity of the structures are optimized by adding a penalty function. Then, a homogenization method is used to obtain mechanical properties of gyroid-based cellular structures through a scaling law as a function of their relative densities. Secondly, the scaling law is added directly into the structure optimization algorithm to compute the optimal density distribution in part being optimized. Thirdly, the density mapping and interpolation approach are used to map the output of structure optimization into the parametric gyroid structure which results in an optimum lightweight lattice structure with uniformly varying densities across the design space. Lastly, the effectiveness and robustness of the optimized results are analyzed through finite element analysis and experiments

Substitutos ósseos baseados em compósitos auxéticos com gradientes de funcionalidade

Com oaumento de doenças e fraturas ósseascada vez existe mais interesse no desenvolvimento de biomateriais para aplicação em substituição e regeneração óssea. Materiais como a hidroxiapatite e policaprolactona são muito referidos na investigação de novos materiais compósitos biocompatíveis e bioativos para regeneração óssea.Neste trabalho aplica-setecnologia deimpressão 3Dpara fabricar estruturascompósitas com comportamento auxético. Estas estruturas 3D apresentama forma de um giróide, possuindo ainda um gradienteunidirecionalde densidades.A estrutura final foi produzida através de uma mistura sólida de 70% de hidroxiapatite e 30% policaprolactonae ainda uma mistura líquida de um solvente (diclorometano), deum surfactante (2-butoxietanol) e de um plastificante (dibutilftalato).Inicialmente, procedeu-se à otimização dasmisturasde modo a produzir uma estrutura 3Dcoesa e biocompatível. Em seguida, realizaram-se ensaios mecânicos de compressão, os quais demonstraram que as peças produzidas exibem comportamento semelhante ao de uma espuma, commódulo de Young igual a 15.9, 19.9e 15.5MPae tensão de colapsoigual a 0.340, 0.567e 0.891MPa,dependente daespessuradas paredes da estrutura, 0.6, 0.8 e 1.0 milímetros, respetivamente.Posteriormente aos ensaios de compressão, testou-se o compósito através de ensaios de bioatividade. Decorridos estes ensaios, as superfícies das amostras foram caracterizadas por Microscopia Eletrónica de Varrimento com Espectrometria de Energia Dispersiva de raios-X, SEM-EDS, para se avaliar e comparar a deposição de cristais apatíticos. Simultaneamente a estes testes, realizou-se ensaios de citotoxicidade para avaliação da biocompatibilidade. Os resultadosmostraram que os materiais são bioativos e não citotóxicos, mostrando potencial para aplicação como substitutos ósseos.xAbstractWith the intensification in bonediseases and fractures, there is an increasing interest in the development of biomaterials for application in bone replacement and regeneration. Materials such as hydroxyapatite and polycaprolactone are often referred to in the investigation of new biocompatible and bioactive composite materials for bone regeneration.In this work, 3D printing technology is applied to manufacture composite structures with auxetic behaviour. These 3D structures have the shape of a gyroid, and also have a unidirectional density gradient. The final structure was produced through a solid mixture of 70% hydroxyapatite and 30% polycaprolactoneand a liquid mixture of a solvent (dichloromethane), a surfactant (2-butoxyethanol) and a plasticizer (dibutyl phthalate).Initially,the mixtures were optimized in order to produce a cohesive and biocompatible 3D structure. Then, mechanical compression tests were performed, which demonstrated that the parts produced exhibit a behavior similar to that of foam, with Young's modulus equal to 15.9, 19.9and 15.5MPa and collapse stress equal to 0.340, 0.567and 0.891MPa, dependent the thickness of the structure's walls, 0.6, 0.8 and 1.0 millimetres, respectively.After the compression tests, the composite was tested through bioactivity tests. After these tests, the sample surfaces were characterized by Scanning Electron Microscopy with X-ray Dispersive Energy Spectrometry, SEM-EDS, to evaluate and compare the deposition of apatitic crystals. Simultaneously with these tests, cytotoxicity tests were performed to assess biocompatibility. The results showed that the materials are bioactive and non-cytotoxic, showing potential for application as bone substitutes

PIVOT: A Framework for Minimizing Stress Deviations in Structural Form

Design of efficient structural members is certainly an intricate process that requires a sound explanation, an exact fit of art and science perhaps, to harness the ever-increasing range of solutions assisted by computational advancements and manufacturing innovations. Many frameworks have been introduced previously to optimize the structural form, however, obtaining a uniform stress distribution has been neglected in favor of determining the least volume satisfying the objective function. Inadvertently, in the process of changing the volume, there are changes to the underlying geometry as well. Since there have been recent studies documenting the impact of geometry on the mechanical performance, it is crucial to obtain reliable knowledge regarding the impact it can have on strategic redistribution of stresses while keeping the volume constant. This investigation proposed the use of Voronoi tessellation, a bioinspired mathematical approach, to determine the positioning of void spaces. Stress-weighted centroids of Voronoi cells were utilized for selecting Voronoi sites based on two different weights. This technique was tested against the Lloyd’s algorithm that utilizes geometric centroids to select Voronoi sites. The results demonstrate a statistically significant difference between the Lloyd’s algorithm and PIVOT. The proposed approach, with weights inversely proportional to the stresses, showed affirmative signs of convergence while reducing the standard deviation of stress, mean stress and lowering the maximum stress value without making any changes to the volume

Mechanical behavior of PA12 lattice structures produced by SLS

Dissertação de mestrado integrado em Engenharia de PolímerosTaking into account the rapid technological evolution and the growing demand, for the industrial sector to meet the most diverse needs of the market, Additive Manufacturing (AM) technology appears as a transformative approach to industrial production that enables the creation of lighter, stronger parts and systems. The versatility of this type of technology allows a reduction in production time and energy consumption, as well as, reducing material waste in the production of a product. It is in this last point that the technologies of AM stand out when comparing to the technologies of conventional manufacture. In AM technologies, it is possible to carry out the deposition of material in a controlled manner, where it is really necessary and, at the same time, ensure the necessary mechanical properties to meet the product requirements. Due to its versatility and rapid technological advances, it has become possible to implement typological optimization in AM. In this context, this study aims to investigate the mechanical behavior of lattice structures to support further investigations based on Topology Optimization (TO). The study of the mechanical behavior of these structures allows an intelligent distribution of these structures along a given structure in order to absorb the amount of energy needed for the impact, presenting competitive manufacturing times and costs. In the course of this research, the manufacturing technique to be used will focus on the Powder Bed Fusion (PBF) process, more specifically in the EOS P396 equipment with the polymeric material polyamide 12 (PA12), that will shape the desired lattice structures, which are constituted by different topologies and volume fractions. The purpose of this development is focused on obtaining the experimental mechanical properties of certain types of cellular structures in order to compare them with the properties obtained from the simulations. Thus, strut-based (BCC) and Triply Periodic Minimal Surfaces (Schwarz-P and Neovius) lattice structures were defined based on different independent variables, such as, cell size, strut diameter/ surface thickness and shell thickness. The defined structures were evaluated by compression and impact mechanical tests. It was found that beside geometrical design, the relative densities of the unit cells could also significantly influence the impact energy absorption performance.Tendo em conta a rápida evolução tecnológica e a crescente procura do sector industrial para satisfazer as mais diversas necessidades do mercado, as tecnologias de Fabrico Aditivo (FA) aparece como uma abordagem transformadora da produção industrial que permite a criação de peças e sistemas mais leves e fortes. A versatilidade deste tipo de tecnologia permite uma redução do tempo de produção e do consumo de energia, bem como a eliminação do desperdício de material na produção de um produto. É neste último ponto que as tecnologias de FA se destacam no que diz respeito às tecnologias de fabrico convencional. Nas tecnologias FA, é possível realizar a deposição de material de forma controlada, onde é realmente necessário, e ao mesmo tempo, garantir as propriedades mecânicas necessárias para satisfazer os requisitos do produto. Neste contexto, este estudo destina-se a investigar o comportamento mecânico de lattice structures para apoiar investigações posteriores que têm por base a Otimização Topológica (OT). O estudo do comportamento mecânico destas estruturas permite uma distribuição inteligente destas mesmas ao longo de uma determinada estrutura de forma a absorverem a quantidade de energia necessária ao impacto, apresentando tempos e custos de fabrico competitivos. No decurso desta investigação, a técnica de fabrico a ser utilizada centrou-se no processo de Powder Bed Fusion (PBF), mais especificamente no equipamento EOS P396 com o material polimérico poliamida 12 (PA12), que dará forma às lattice structures, constituídas por diferentes células unitárias e frações de volume. O objetivo deste desenvolvimento focou-se na obtenção das propriedades mecânicas experimentais das estruturas celulares de maneira a compará-las com as propriedades obtidas a partir das simulações. Assim, as lattice structures baseadas em strut-based (BCC) e Triply Periodic Minimal Surface (TPMS) (Schwarz-P e Neovius) foram definidas com base em diferentes variáveis independentes, tais como, tamanho da célula unitária, diâmetro da viga/ espessura da superfície e espessura da casca. As estruturas definidas foram avaliadas mecanicamente através de testes de compressão e impacto. Verificou-se assim que, para além do desenho geométrico, as densidades relativas das células unitárias também podiam influenciar significativamente o desempenho de absorção de energia de impacto