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Multiscale techniques, namely homogenization, result in significant computational time savings in the analysis of complex structures such as lattice structures, as in many cases it is inefficient to model a periodic structure in full detail in its entire domain. The elastic and plastic properties of two TPMS-based cellular structures, the gyroid, and the primitive surface are studied in this work through numerical homogenization. The study enabled the development of material laws for the homogenized Young's modulus and homogenized yield stress, which correlated well with experimental data from the literature. It is possible to use the developed material laws to run optimization analyses and develop optimized functionally graded structures for structural applications or reduced stress shielding in bio-applications. Thus, this work presents a study case of a functionally graded optimized femoral stem where it was shown that the porous femoral stem built with Ti-6Al-4V can minimize stress shielding while maintaining the necessary load-bearing capacity. It was shown that the stiffness of cementless femoral stem implant with a graded gyroid foam presents stiffness that is comparable to that of trabecular bone. Moreover, the maximum stress in the implant is lower than the maximum stress in trabecular bone. [ABSTRACT FROM AUTHOR]

Weight reduction is one of the main concerns when designing any component as it reduces material cost and green house gas emissions, among other aspects. Several numerical approaches exist in the literature with the objective of having any component with known mechanical loading become optimized in terms of mass minimization and stiffness maximization. Thus, the objective of this work is the development of optimized structures maintaining the same geometry by means of cellular materials, namely the gyroid infill, and generating functionally graded cellular structures with higher stiffness-to-weight ratio. Remodelling algorithms based on biological phenomena, namely bone growth, as well as Bi-evolutionary structural optimization (BESO) were employed to obtain the density map allowing the material functional gradient distribution. Smoothing functions were tested as a possibility of enhancing stiffness as abrupt density changes are avoided. The gyroid infill was characterized in order to create a phenomenological law based on bone remodelling laws. The gyroid law was implemented on the analysis FEMAS (opens-source, academic and educational FEM and meshless method software) software which presented the density map as an output. Each gradient consisted on areas at a similar density being concatenated into one solid. The different solids, at different density levels, are assembled thus creating the material functional gradient. Lastly, simulations consisted on three distinct and benchmark flexural load cases. Specimens were printed using FFF technology in PLA (E = 3145 MPa, ν = 0.3) having then been tested experimentally according to the appropriate load case. Numerical results correlated with the experimental results in terms of accuracy between theoretical and experimental stiffness where there was a greater accuracy for the specimens subject to a Four-Point bending load case, where only a 16% gap was verified between numerical and experimental flexural stiffness. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to evaluate the influence of the parameters of the Fused Filament Fabrication (FFF) process on the mechanical properties and on the mass of parts printed in Polylactic Acid (PLA). In addition, the authors developed predictive models for the analysed responses. Design/methodology/approach: A full Factorial type of experimental planning method was used to define the conditions for manufacturing parts according to the variation of the construction parameters, extrusion temperature and print speed. Samples were printed for tensile, flexion and compression tests. Their mass was measured. Multiple regression methods, based on power equations, were used to build the forecasting models. Findings: It was found that the extrusion temperature was the parameter of greatest influence in the variation of the analysed responses, mainly because it generates behaviour patterns and indirectly demonstrates thermal/rheological characteristics of the material used. Print speed affects responses, however, with variations dependent on part geometry and printer hardware/software. It was possible to establish prediction models with low error rates in relation to the experimental values. Originality/value: The study demonstrates a good relation between the use of a structured experimental planning method as the basis for the development of predictive models based on mathematical equations, the same structure of which can be used to describe different responses. [ABSTRACT FROM AUTHOR]

Machine learning (ML) and deep learning (DL) approaches can solve the same problems as the finite element method (FEM) with a high degree of accuracy in a fraction of the required time, by learning from previously presented data. In this work, the bone remodelling phenomenon was modelled using feed-forward neural networks (NN), by gathering a dataset of density distribution comprising several geometries and load cases. The model should output for some point in the domain the its apparent density, taking into consideration the geometric and loading parameters of the model. After training. the trabecular distribution obtained with the NN was similar to the FEM while the analysis was performed in a fraction of the time, having shown a reduction from 1020 s to 0.064 s. It is expected that the results can be extended to different structures if a different dataset is acquired. In summary, the ML approach allows for significant savings in computational time while presenting accurate results. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to address the development and implementation of "AltPrint," a slicing algorithm based on a new filling process planning from a variation in the deposited material geometry. AltPrint enables changes in the extruded material flow toward local variations in stiffness. The technical feasibility evaluation was conducted experimentally by fused filament fabrication (FFF) process of snap-fit subjected to a mechanical cyclical test. Design/methodology/approach: The methodology is based on the estimation of the parameter E from the mathematical relationships among the variation of the material in the material flow, nozzle geometry and extrusion parameters. Calibration, validation and analysis of the printed specimens were divided into two moments, of which the first refers to the material responses (flexural and dynamic mechanical analysis) and the second involves the analysis of the printed components with localized flow properties (for estimating the response to cyclic loading). Finite element analysis assisted in the comparison of two snap-fit geometries, one traditional and one generated by AltPrint. Finally, three examples of compliant mechanisms were developed to demonstrate the potential of the algorithm in the generation of functional prototypes. Findings: The contribution of AltPrint is the variable fill width integrated with the slicing software that varies the print parameters in different regions of the object. The alternative extrusion method based on material rate variation was conceived as an "open software" available in GitHub platform, hence, open manufacturing with initial focus on desktop 3D printer based on FFF. The slicing method provides deposited variable-width segments in an organized and replicable filling strategy, resulting in mechanical properties variations in specific regions of a part. It was implemented and evaluated experimentally and indicated potential applications in parts manufactured by the additive process based on extrusion, which requires local flexibilities. Originality/value: This paper presents a new alternative method for application in an open additive manufacturing context, specifically for additive extrusion techniques that enable local variations in the material flow. Its potential for manufacturing functional parts, which require flexibility due to cyclic loading, was demonstrated by fabrication and experimental evaluations of parts made in acrylonitrile butadiene styrene filament. The changes proposed by AltPrint enable geometric modifications in the response of the printed parts. The proposed slicing and filling control of parameters is inserted in a context of design for additive manufacturing and shows great potential in the area of product design. [ABSTRACT FROM AUTHOR]

The increase in the reciprocal demand of the packaging and food industries currently promotes a volume of waste that is disproportionate to an efficient management in terms of environmental, socio-ethical, economical and political sustainability. In this context, this research proposes the development of a methodology to define strategies that provide parameters for decisions guided by Design for Sustainability. It is anchored in the principle that the discontinuity of the current patterns of production and consumption is essential to achieve transformations with more promising results. This precept was related to Future Studies and in its premise to establish parameters that configure changes of perspective, as well as a deep awareness of the implications that involve the making of decisions. In this field of research, the recognition and adaptation of the Future Workshop method and the creation of Scenarios were highlighted. In this juncture, the scenarios obtained evidenced the aid they can provide for the elaboration of strategies that better lead to a preferable future. In order to seek a verification of this finding, an experiment was developed resulting in a system-packaging concept complementing the applicability of the proposed methodological structure. [ABSTRACT FROM AUTHOR]

This paper presents a systematic review on extrusion additive manufacturing (EAM), with focus on the technological development of screw-assisted systems that can be fed directly with granulated materials. Screw-assisted EAM has gained importance as an enabling technology to expand the range of 3D printing materials, reduce costs associated with feedstock fabrication, and increase the material deposition rate compared to traditional fused filament fabrication (FFF). Many experimental printheads and commercial systems that use some screw-processing mechanism can be found in the literature, but the design diversity and lack of standard terminology make it difficult to determine the most suitable solutions for a given material or application field. Besides, the few previous reviews have offered only a glimpse into the topic, without an in-depth analysis about the design of the extruders and associated capabilities. A systematic procedure was devised to identify the screw-assisted EAM systems that can print directly from granulated materials, resulting in 61 articles describing different pieces of equipment that were categorized as experimental printheads and commercial systems, for small- and large-scale applications. After describing their main characteristics, the most significant extruder modifications were discussed with reference to the materials processed and performance requirements. In the end, a general workflow for the development of 3D printers based on screw extrusion was proposed. This review intends to provide information about the state-of-the-art screw-assisted EAM and help the academy to identify further research opportunities in the field. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to evaluate and compare the mechanical performance of FFF parts when subjected to post processing thermal treatment. Therefore, a study of the annealing treatment influence on the mechanical properties was performed. For this, two different types of Nylon (PA12) were used, FX256 and CF15, being the second a short fibre reinforcement version of the first one. Design/methodology/approach: In this study, tensile and flexural properties of specimens produced via FFF were determined after being annealed at temperatures of 135°C, 150°C or 165°C during 3, 6, 12 or 18 h and compared with the non-treated conditions. Differential scanning calorimetry (DSC) was performed to determine the degree of crystallinity. To evaluate the annealing parameters' influence on the mechanical properties, a full factorial design of experiments was developed, followed by an analysis of variance, as well as post hoc comparisons, to determine the most significative intervening factors and their effect on the results. Findings: The results indicate that CF15 increased its tensile modulus, strength, flexural modulus and flexural strength around 11%, while FX256 presented similar values for tensile properties, doubling for flexural results. Flexural strain presented an improvement, indicating an increased interlayer behaviour. Concerning to the DSC analysis, an increase in the degree of crystallinity for all the annealed parts. Originality/value: Overall, the annealing treatment process cause a significant improvement in the mechanical performance of the material, with the exception of 165°C annealed specimens, in which a decrease of the mechanical properties was observed, resultant of material degradation. [ABSTRACT FROM AUTHOR]

Fused filament fabrication (FFF) is an extrusion-based process that allows quick and inexpensive part production, practically without any geometric limitations, offering flexibility, promoting reduction in costs and lead-time in an industrial scenario. Being one of the most widespread additive manufacturing techniques, the process has evolved introducing new and advanced materials (e.g. high-performance polymers and composites). Despite its advantages, the process is vastly overlooked due to its high level of anisotropy, poor surface roughness and lack of geometric accuracy caused by the layer thickness. To reduce this effect, a sequence of laborious manual operations can be performed, which may result in time-consuming and inaccurate results. Therefore, efforts have been made towards the development of hybrid manufacturing technologies by combining FFF process and subtractive equipment, aiming to solve these limitations. In this work, two complementary methodologies analysing the behaviour of FFF PA12 and short fibre–reinforced PA12 printed parts when subjected to a subtractive approach are presented. The first experimental plan took into account the final surface roughness (Ra and Rz) via full factorial design of experiments (DOE) and analysis of variance (ANOVA) considering the influence of distinct printing orientations, two types of cutting tools and machining parameters such as, cutting speed, feed and cutting depth. An analysis on tool wear and SEM microscopy to the machined surface was also performed. The second approach was carried out via Taguchi and ANOVA, considering the first experimental approach results. Thus, milling parameters were the focus, evaluating the final material surface roughness, being now monitored the cutting forces and tool wear analysis in order to understand their influence on the final results. It is shown that it is possible to machine PA12-based FFF printed parts without any major problems such as layer delamination. A decrease in Ra, t of 1931% to 0.99 μ m for PA12CF and 2255% for PA12 to 0.96 μ m was achieved, proving the overall machinability of the materials. It was found that PA12 creates higher levels of cutting loads and increased tool wear, thus indicating that short fibre presence improves the material machinability, while parameters such as building orientation do not possess any influence on the final surface roughness. [ABSTRACT FROM AUTHOR]

Additive manufacturing allows for a great degree of design freedom and is rapidly becoming a mainstream manufacturing process. However, as in all manufacturing processes, it has its limitations and specificities. Equipping engineers with this knowledge allows for a higher degree of optimization, extracting the most out of this technology. Therefore, a specific part design was devised and created via L-PBF (Laser Powder Bed Fusion) using AlSi10Mg powder. Certain parameters were varied to identify the influence on material density, hardness, roughness, residual stress and microstructures. It was found that on heat treated parts laser pattern strategy is one of the most influential aspects, showing that chessboard and stripes 67° improved outcome; average Ra roughness varied between 8–12 µm, residual stress was higher on vertical surfaces than horizontal surfaces, with the combination of support structures and stripes 67° strategies generating the lowest residual stress (205 MPa on a lateral/vertical face), hardness was non-orientation dependent and larger on samples with chessboard fabrication strategies, while microstructures were composed of α–Al dendrites surrounded by Si particles. The distribution and grain size of the microstructure is dependent on location regarding melt pool and HAZ area. Furthermore, Al–Mg oxides were encountered on the surface, along with pores generating from lack of fusion. [ABSTRACT FROM AUTHOR]