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In this study, we introduce progress in intelligent control for reducing structural vibrations. The field of intelligent control for dampening structural vibrations is evolving rapidly, driven by advancements in materials science, AI, and actuator technology. These innovations have led to more efficient, reliable, and adaptable vibration-control systems with applications ranging from civil engineering to aerospace. The use of smart materials has opened new avenues for vibration control of piezoelectric materials. When mechanical stress is applied to these materials, an electric charge response is formed, allowing for precise control over the vibrations. Improved computational models and simulations play crucial roles in the design and testing of vibration-control systems. Finite element analysis helps in accurately predicting the behavior of structures under various loads, thereby aiding in the design of effective vibration-control systems. In our work, we use intelligent control theory to dampen structural vibrations in engineering structures.

In this study, we investigated the performance improvement caused by the addition of copper (Cu) nanoparticles to high-density polyethylene (HDPE) matrix material. Composite materials, with filler percentages of 0.0, 2.0, 4.0, 6.0, 8.0, and 10.0 wt% were synthesized through the material extrusion (MEX) 3D printing technique. The synthesized nanocomposite filaments were utilized for the manufacturing of specimens suitable for the experimental procedure that followed. Hence, we were able to systematically investigate their tensile, flexural, impact, and microhardness properties through various mechanical tests that were conducted according to the corresponding standards. Broadband Dielectric Spectroscopy was used to investigate the electrical/dielectric properties of the composites. Moreover, by employing means of Raman spectroscopy and thermogravimetric analysis (TGA) we were also able to further investigate their vibrational, structural, and thermal properties. Concomitantly, means of scanning electron microscopy (SEM), as well as atomic force microscopy (AFM), were used for the examination of the morphological and structural characteristics of the synthesized specimens, while energy-dispersive X-ray spectroscopy (EDS) was also performed in order to receive a more detailed picture on the structural characteristics of the various synthesized composites. The corresponding nanomaterials were also assessed for their antibacterial properties regarding Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) with the assistance of a method named screening agar well diffusion. The results showed that the mechanical properties of HDPE benefited from the utilization of Cu as a filler, as they showed a notable improvement. The specimen of HDPE/Cu 4.0 wt% was the one that presented the highest levels of reinforcement in four out of the seven tested mechanical properties (for example, it exhibited a 36.7% improvement in the flexural strength, compared to the pure matrix). At the same time, the nanocomposites were efficient against the S. aureus bacterium and less efficient against the E. coli bacterium. The use of such multi-functional, robust nanocomposites in MEX 3D printing is positively impacting applications in various fields, most notably in the defense and security sectors. The latter becomes increasingly important if one takes into account that most firearms encompass various polymeric parts that require robustness and improved mechanical properties, while at the same time keeping the risk of spreading various infectious microorganisms at a bare minimum.

This study outlines a comprehensive strategy for designing and implementing robust controllers tailored for intelligent structures. This study presents a robust control-based structural identification technique that uses the input/output data of the system to construct a state-space mode and frequency domain. To reduce vibrations, a robust controller is created using the control Simulink model. The identification and robust control of smart structures using Simulink involve a combination of system identification techniques and control design within the MATLAB Simulink environment. The key challenge is dealing with uncertainties and variations in system dynamics. Robust control methods have been employed to suppress the vibrations during dynamic disturbances. These methods are important for mechanical systems operating under stochastic loading conditions.

Abstract The development of efficient and sustainable composites remains a primary objective of both research and industry. In this study, the use of biochar, an eco-friendly reinforcing material, in additive manufacturing (AM) is investigated. A high-density Polyethylene (HDPE) thermoplastic was used as the matrix, and the material extrusion (MEX) technique was applied for composite production. Biochar was produced from olive tree prunings via conventional pyrolysis at 500 °C. Composite samples were created using biochar loadings in the range of 2.0–10.0 wt. %. The 3D-printed samples were mechanically tested in accordance with international standards. Thermogravimetric analysis (TGA) and Raman spectroscopy were used to evaluate the thermal and structural properties of the composites. Scanning electron microscopy was used to examine the fractographic and morphological characteristics of the materials. The electrical/dielectric properties of HDPE/biochar composites were studied over a broad frequency range (10–2 Hz–4 MHz) at room temperature. Overall, a laborious effort with 12 different tests was implemented to fully characterize the developed composites and investigate the correlations between the different qualities. This investigation demonstrated that biochar in the MEX process can be a satisfactory reinforcement agent. Notably, compared to the control samples of pure HDPE, biochar increased the tensile strength by over 20% and flexural strength by 35.9% when added at a loading of 4.0 wt. %. The impact strength and microhardness were also significantly improved. Furthermore, the Direct current (DC) conductivity of insulating HDPE increased by five orders of magnitude at 8.0 wt. % of biochar content, suggesting a percolation threshold. These results highlight the potential of C-based composites for the use in additive manufacturing to further exploit their applicability by providing parts with improved mechanical performance and eco-friendly profiles. Graphical Abstract

A cyclic economy and sustainability-driven production are key aspects of the industry. Recycled feedstocks are steadily replacing virgin materials to produce parts and as sustainable additives to develop eco-friendly composites. The reinforcing potential of recycled fine powder glass (FPG) on terephthalate glycol (PETG) is investigated. The performances of six different compounds (with FPG loadings of 2.0, 4.0, 6.0, 8.0, 10.0, and 12.0 wt%) in filament and three-dimensional (3D) specimens form (manufactured with the material extrusion – MEX method) were compared with PETG pure. This research included thermal and rheological analyses, mechanical tests, and morphological and structural investigations. According to these findings, the PETG/RFPG 8.0 wt% composite presented remarkable results in the tensile and flexural (16.3 % and 16.9 % strength increase, respectively) tests, while PETG/RFPG 10.0 wt% had the greatest performance concerning microhardness. Both the dimensional deviation and porosity results show excellent performance in the case of PETG/RFPG 6.0 wt%, by being 67.3 % and 87.1 % improved vs. the PETG pure. These results indicate that RFPG is a promising reinforcement additive for MEX 3D printing that can replace the commonly used inorganic fillers and promote the sustainability of 3D printing.

AbstractHerein, a new generation of printable bio-composite nanofilaments is explored. The aim was to explore the efficiency of Titanium nitride (TiN) as a reinforcing agent for the Fused Filament Fabrication (FFF) 3D printing technique. TiN, a common ceramic in medical devices, in nanopowder form, was used as a polymer enhancer for the also popular medical devices polypropylene thermoplastic. Such filaments with superior performance are needed for demanding app­lications, in which common polymers do not meet the specifications. To fully comprehend the material qualities and behaviour, a variety of tests, including mechanical testing, thermal and rheological investigation, and spectroscopic analysis, were carried out following standards. The effect of the filler percentage was also considered. The morphological properties of the materials were also assessed. The mechanical response of the nanocomposite with a ‑2.0 wt. % filler concentration showed the best improvements in all experiments conducted, including tensile (41.5%), flexural (33.7%), and impact (18.0%) strength. The microhardness was improved 44.8% by the 2.0 wt. % filler concentration nanocomposite. Overall, the efficiency of TiN as a reinforcement agent in FFF 3D printing was proven, making the proposed nanocomposites a sufficient solution when improved performance is required.

Acrylonitrile butadiene styrene (ABS) composites were prepared in filament form compatible with the material extrusion (MEX) 3D printing method, using biochar as a filler at various loadings of up to 10.0 wt %. Samples were fabricated to experimentally investigate their mechanical performance. The ABS/biochar composites were characterized using thermogravimetric analysis, differential scanning calorimetry, Raman spectroscopy, and rheological tests. The electrical properties of the composites were investigated using broadband dielectric spectroscopy. Scanning electron microscopy was utilized to analyze the morphological features of the fabricated specimens by examining their side and fracture surfaces. The results indicate that the composite with 4.0 wt % biochar content compared to pure ABS showed the highest mechanical response between the prepared composites (24.9 % and 21 % higher than the pure ABS tensile and flexural strength respectively). The composites retained their insulating behavior. These findings contribute to expanding the utilization of the material extrusion (MEX) 3D printing method while also unlocking prospects for potential applications in microelectronics, apart from mechanical reinforcement.

This research focused on developing medical-grade polypropylene (PP)/silver (Ag) nanocomposites for the production of components through material extrusion (MEX) three-dimensional printing (3DP). The objective was to improve the performance of PP by enhancing its mechanical properties and imparting antibacterial characteristics. An industrially scalable process was utilized to fabricate PP/Ag nanocomposites through the reactive melt mixing technique. Polyethylene glycol (PEG) served as the reduction agent, and silver nitrate (AgNO3) was incorporated as the additive. During the extrusion of the three-dimensional printing (3DP) filaments, reactive melt mixing occurred, resulting in the production of specimens for various standard tests. The addition of 5.0 wt% AgNO3 and 2.5 wt% PEG in the PP thermoplastic led to a slight improvement in mechanical performance, with a 9.9 % increase in tensile strength observed. The antibacterial properties of the composites were assessed through agar well diffusion tests against Escherichia coli (E-coli) and Staphylococcus aureus (S. aureus). A more significant biocidal effect was observed for S. aureus compared to E-coli. These composites have the potential to be utilized in industrial applications that require enhanced mechanical properties and durability, as well as important biocidal properties, such as in the medical equipment industry or the defense sector.

Herein, silicon nitride (Si3N4) was the selected additive to be examined for its reinforcing properties on high-density polyethylene (HDPE) by exploiting techniques of the popular material extrusion (MEX) 3D printing method. Six different HDPE/Si3N4 composites with filler percentages ranging between 0.0–10.0 wt. %, having a 2.0 step, were produced initially in compounds, then in filaments, and later in the form of specimens, to be examined by a series of tests. Thermal, rheological, mechanical, structural, and morphological analyses were also performed. For comprehensive mechanical characterization, tensile, flexural, microhardness (M-H), and Charpy impacts were included. Scanning electron microscopy (SME) was used for morphological assessments and microcomputed tomography (μ-CT). Raman spectroscopy was conducted, and the elemental composition was assessed using energy-dispersive spectroscopy (EDS). The HDPE/Si3N4 composite with 6.0 wt. % was the one with an enhancing performance higher than the rest of the composites, in the majority of the mechanical metrics (more than 20% in the tensile and flexural experiment), showing a strong potential for Si3N4 as a reinforcement additive in 3D printing. This method can be easily industrialized by further exploiting the MEX 3D printing method.

To simulate a lightweight structure with integrated actuators and sensors, two-dimensional finite elements are utilized. The study looks at the optimal location and active vibration control for a piezoelectric smart flexible structure. Intelligent applications are commonly used in engineering applications. In computational mechanics, selecting the ideal position for actuators to suppress oscillations is crucial. The structure oscillates due to dynamic disturbance, and active control is used to try to reduce the oscillation. Utilizing an LQR and Hinfinity controller, optimization is carried out to determine the best controller weights, which will dampen the oscillation. Challenging issues arise in the design of control techniques for piezoelectric smart structures. Piezoelectric materials have been investigated for use in distributed parameter systems (for example airplane wings, intelligent bridges, etc.) to provide active control efficiently and affordably. Still, no full suppression of the oscillation with this approach has been achieved so far. The controller’s order is then decreased using optimization techniques. Piezoelectric actuators are positioned optimally according to an enhanced optimization method. The outcomes demonstrate that the actuator optimization strategies used in the piezoelectric smart single flexible manipulator system have increased observability in addition to good vibration suppression results.

Robust materials in medical applications are sought after and researched, especially for 3D printing in bone tissue engineering. Poly[ε-caprolactone] (PCL) is a commonly used polymer for scaffolding and other medical uses. Its strength is a drawback compared to other polymers. Herein, PCL was mixed with hydroxyapatite (HAp). Composites were developed at various concentrations (0.0–8.0 wt. %, 2.0 step), aiming to enhance the strength of PCL with a biocompatible additive in bioplotting. Initially, pellets were derived from the shredding of filaments extruded after mixing PCL and HAp at predetermined quantities for each composite. Specimens were then manufactured by bioplotting 3D printing. The samples were tested for their thermal and rheological properties and were also mechanically, morphologically, and chemically examined. The mechanical properties included tensile and flexural investigations, while morphological and chemical examinations were carried out employing scanning electron microscopy and energy dispersive spectroscopy, respectively. The structure of the manufactured specimens was analyzed using micro-computed tomography with regard to both their dimensional deviations and voids. PCL/HAp 6.0 wt. % was the composite that showed the most enhanced mechanical (14.6% strength improvement) and structural properties, proving the efficiency of HAp as a reinforcement filler in medical applications.

This study aimed to investigate the potential of antimony-doped tin oxide (ATO) as a reinforcing agent for polyamide 12 (PA12) in 3D printing by examining four mixtures with varying ATO concentrations (2.0 to 8.0 wt.%, with a 2.0 wt.% interval). These mixtures were used to fabricate filaments for the manufacturing of specimens through the material extrusion method. The mechanical properties of the resulting PA12/ATO composites and PA12 pure samples were evaluated through tensile, Charpy impact, flexural, and microhardness tests. Additionally, rheology, structure, morphology, thermal properties, pore size, and consistency in the dimensions of the samples were evaluated. Thermogravimetric analysis, along with differential scanning calorimetry, scanning electron microscopy, energy-dispersive and Raman spectroscopy, and micro-computed tomography, were conducted. The results were correlated and interpreted. The greatest reinforcement was achieved with the PA12/ATO 4.0 wt.% mixture, which exhibited a 19.3% increase in tensile strength and an 18.6% increase in flexural strength compared with pure PA12 (the control samples). The Charpy impact strength and microhardness were also improved by more than 10%. These findings indicate the merit of composites with ATO in additive manufacturing, particularly in the production of components with improved mechanical performance.

In this study, titanium nitride (TiN) was selected as an additive to a high-density polyethylene (HDPE) matrix material, and four different nanocomposites were created with TiN loadings of 2.0–8.0 wt. % and a 2 wt. % increase step between them. The mixtures were made, followed by the fabrication of the respective filaments (through a thermomechanical extrusion process) and 3D-printed specimens (using the material extrusion (MEX) technique). The manufactured specimens were subjected to mechanical, thermal, rheological, structural, and morphological testing. Their results were compared with those obtained after conducting the same assessments on unfilled HDPE samples, which were used as the control samples. The mechanical response of the samples improved when correlated with that of the unfilled HDPE. The tensile strength improved by 24.3%, and the flexural strength improved by 26.5% (composite with 6.0 wt. % TiN content). The dimensional deviation and porosity of the samples were assessed with micro-computed tomography and indicated great results for porosity improvement, achieved with 6.0 wt. % TiN content in the composite. TiN has proven to be an effective filler for HDPE polymers, enabling the manufacture of parts with improved mechanical properties and quality.

This study’s goal is to utilize robust control theory to effectively mitigate structural oscillations in smart structures. While modeling the structures, two-dimensional finite elements are used to account for system uncertainty. Advanced control methods are used to completely reduce vibration. Complete vibration suppression is achieved using advanced control techniques. In comparison to traditional control approaches, Hinfinity techniques offer the benefit of being easily adaptable to issues with multivariate systems. It is challenging to simultaneously optimize robust performance and robust stabilization. One technique that approaches the goal of achieving robust performance in mitigating structural oscillations in smart structures is H-infinity control. H-infinity control empowers control designers by enabling them to utilize traditional loop-shaping techniques on the multi-variable frequency response. This approach enhances the robustness of the control system, allowing it to better handle uncertainties and disturbances while achieving desired performance objectives. By leveraging H-infinity control, control designers can effectively shape the system’s frequency response to enhance stability, tracking performance, disturbance rejection, and overall robustness.

Abstract The development of sustainable and functional biocomposites remains a robust research and industrial claim. Herein, the efficiency of using eco-friendly biochar as reinforcement in Additive Manufacturing (AM) was investigated. Two AM technologies were applied, i.e., vat photopolymerization (VPP) and material extrusion (MEX). A standard-grade resin in VPP and the also eco-friendly biodegradable Polylactic Acid (PLA) in the MEX process were selected as polymeric matrices. Biochar was prepared in the study from olive trees. Composites were developed for both 3D printing processes at different biochar loadings. Samples were 3D-printed and mechanically tested after international test standards. Thermogravimetric Analysis and Raman revealed the thermal and structural characteristics of the composites. Morphological and fractographic features were derived, among others, with Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Biochar was proven to be sufficient reinforcement agent, especially in the filament MEX process, reaching more than 20% improvement at 4 wt.% loading in tensile strength compared to the pure PLA control samples. In the VPP process, results were not as satisfactory, still, a 5% improvement was achieved in the flexural strength with 0.5 wt.% biochar loading. The findings prove the strong potential of biochar-based composites in AM applications, too. Graphical Abstract

Polypropylene (PP) composites reinforced with hexagonal boron carbide (B4C) nanoparticles were constructed using a Material Extrusion (MEX) 3D printing method. The goal was to provide nanocomposites for MEX 3D printing with enhanced mechanical properties by exploiting the superior properties of the B4C additive. The fabricated 3D-printed specimens were subjected to standard evaluation tests to determine the effect of the B4C nanofiller level inside the polymer framework on their mechanical, thermal, and rheological properties. The structures and fracture patterns of the filaments and specimens were inspected by electron microscopy. Raman spectroscopy and energy-dispersive spectroscopy were used to determine the chemical compositions of the nanocomposites. Comparing the unfilled polymeric matrix to the B4C-filled nanocomposites reveals that the mechanical strength of the novel nanocomposite material was substantially increased. The optimum nanocomposite concentration of PP/ B4C 6.0 wt% outperformed reference PP by 18.3%, 10.8%, 11.8%, and 15.6% in terms of flexural and impact strength, as well as tensile and flexural toughness, respectively, while having notably improved performance in the remaining mechanical properties. The nanocomposites presented herein can support applications that require polymeric materials with advanced mechanical properties.

In this study, piezoelectric patches are used as actuators to dampen structural oscillations. Damping oscillations is a significant engineering challenge, and the use of piezoelectric patches in smart structures allows for a reduction in oscillations through sophisticated control methods. This analysis involved H-infinity (H∞) robust analysis. H∞ (H-infinity) control formulation is a robust control design method used to ensure system stability and performance under disturbances. When applied to piezoelectric actuators in smart structures, H∞ control aims to design controllers that are robust to variations in system dynamics, external disturbances, and modeling uncertainties, while meeting specified performance criteria. This study outlines the piezoelectric effects and advanced control strategies. A structural model was created using finite elements, and a smart structural model was analyzed. Subsequently, dynamic loads were applied and oscillation damping was successfully achieved by employing advanced control techniques.

In this study, poly (ethylene terephthalate) (PETG) was combined with Antimony-doped Tin Oxide (ATO) to create five different composites (2.0–10.0 wt.% ATO). The PETG/ATO filaments were extruded and supplied to a material extrusion (MEX) 3D printer to fabricate the specimens following international standards. Various tests were conducted on thermal, rheological, mechanical, and morphological properties. The mechanical performance of the prepared nanocomposites was evaluated using flexural, tensile, microhardness, and Charpy impact tests. The dielectric and electrical properties of the prepared composites were evaluated over a broad frequency range. The dimensional accuracy and porosity of the 3D printed structure were assessed using micro-computed tomography. Other investigations include scanning electron microscopy and energy-dispersive X-ray spectroscopy, which were performed to investigate the structures and morphologies of the samples. The PETG/6.0 wt.% ATO composite presented the highest mechanical performance (21% increase over the pure polymer in tensile strength). The results show the potential of such nanocomposites when enhanced mechanical performance is required in MEX 3D printing applications, in which PETG is the most commonly used polymer.

Polyethylene terephthalate glycol (PETG) and silicon nitride (Si3N4) were combined to create five composite materials with Si3N4 loadings ranging from 2.0 wt.% to 10.0 wt.%. The goal was to improve the mechanical properties of PETG in material extrusion (MEX) additive manufacturing (AM) and assess the effectiveness of Si3N4 as a reinforcing agent for this particular polymer. The process began with the production of filaments, which were subsequently fed into a 3D printer to create various specimens. The specimens were manufactured according to international standards to ensure their suitability for various tests. The thermal, rheological, mechanical, electrical, and morphological properties of the prepared samples were evaluated. The mechanical performance investigations performed included tensile, flexural, Charpy impact, and microhardness tests. Scanning electron microscopy and energy-dispersive X-ray spectroscopy mapping were performed to investigate the structures and morphologies of the samples, respectively. Among all the composites tested, the PETG/6.0 wt.% Si3N4 showed the greatest improvement in mechanical properties (with a 24.5% increase in tensile strength compared to unfilled PETG polymer), indicating its potential for use in MEX 3D printing when enhanced mechanical performance is required from the PETG polymer.

Silicon nitride (Si3N4) is a well-known bio-ceramic that is widely used for medical and healthcare purposes, due to its biocompatibility and superior chemical, physical and mechanical properties, which make it suitable for implants. Due to its unique features, examining its efficiency as a cost-effective reinforcement agent for thermoplastics in material extrusion (MEX) Additive Manufacturing (AM) seems promising for the development of composites for biomedical applications. The mainstream thermoplastic in MEX AM is the biodegradable and biocompatible Polylactic Acid (PLA). Herein, a biomedical grade PLA was used as a matrix for Si3N4 nanopowder in various filler loadings. Filaments were prepared with melt extrusion, whereas MEX 3D printing was engaged to prepare specimens for mechanical evaluation, according to standardized tests. The effect of the Si3N4 nanoparticles loading and its optimization was carried out by means of fifteen (15) different tests. The nanocomposites were fully characterized with Raman, Thermogravimetric Analysis, and Scanning Electron Microscopy, among others. Aspects of the process, such as rheology and processability, were also assessed and quantified. A more than 40% increase in both flexural and tensile strength of the samples was found, proving the hypothesis for the effectiveness of Si3N4 nanoparticles as a compelling alternative reinforcement agent in MEX AM of biomedical PLA-based parts.

Loss of eyesight inflicts multiple difficulties in everyday lives’ tasks affecting not just the visually impaired but also their loved ones. The sense of being depleted by the otherwise visually perceived satisfaction from attending various events becomes a burden not just in terms of joy but also in relation to accompanying parties. The aim of this research work was to provide a worthy perceived experience of attending a soccer match with the company of a friend, centered at the visually impaired person’s needs and perspective. The methodology developed was based on a holistic approach combining a number of creative tools, in order to explore, visualize and evaluate the proposed solutions, with advanced CAD modeling, rendering techniques and 3D printing technology for improved representation and prototyping of the final product. Evaluation via multi-criteria decision-making casted the developed system as quite usable, suitable for assisting the visually impaired users in absorbing valuable information regarding the real time progress of a live soccer event using the selves-developed tactile interface. That way, visually impaired people are able to use the final product with a great deal of success and “feel the view” and the “time” in a variety of cases, allowing them to better enjoy attending an entertainment event, such as soccer, with the interactive company of a friend.

Currently, energy efficiency and saving in production engineering, including Material Extrusion (MEX) Additive Manufacturing, are of key importance to ensure process sustainability and cost-effectiveness. The functionality of parts made with MEX 3D-printing remains solid, especially for expensive high-performance polymers, for biomedical, automotive, and aerospace industries. Herein, the energy and tensile strength metrics are investigated over three key process control parameters (Nozzle Temperature, Layer Thickness, and Printing Speed), with the aid of laboratory-scale PEEK filaments fabricated with melt extrusion. A double optimization is attempted for the production by consuming minimum energy, of PEEK parts with improved strength. A three-level Box-Behnken design with five replicas for each experimental run was employed. Statistical analysis of the experimental findings proved that LT is the most decisive control setting for mechanical strength. An LT of 0.1 mm maximized the tensile endurance (∼74 MPa), but at the same time, it was responsible for the worst energy (∼0.58 MJ) and printing time (∼900 s) expenditure. The experimental and statistical findings are further discussed and interpreted using fractographic SEM and optical microscopy, revealing the 3D printing quality and the fracture mechanisms in the samples. Thermogravimetric analysis (TGA) was performed. The findings hold measurable engineering and industrial merit, since they may be utilized to achieve an optimum case-dependent compromise between the usually contradictory goals of productivity, energy performance, and mechanical functionality.

Herein, a blend of nanoparticle (NP) inclusions has been arranged at various loadings into a photosensitive resin, while bi-functional three-dimensional (3D) printed specimens were fabricated through a vat photopolymerization process, to elucidate physicochemical mechanisms and synergistic effects, over the filler loading. Energy-dispersive X-ray spectroscopy (EDS), Raman, and thermogravimetric analysis (TGA) revealed the chemical/spectroscopic and thermal properties of the fabricated specimens. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) depicted the surface morphology, while SEM fractography demonstrated the morphology of tensile test specimens’ fractured surfaces. Mechanical tests exhibited a strong reinforcement mechanism. The highest reinforcement of 20.8% in the tensile strength is reported for the 2 wt.% nanocomposite. All the prepared recipes exhibited a boosted antibacterial performance, as was documented via a screening agar well diffusion method. The research herein leads towards a novel generation of low-cost bi-functional materials for 3D printing bioactive applications, where mechanical reinforcement and antibacterial performance are required in the operational environment.

In this study, we created an accurate model for a homogenous smart structure. After modeling multiplicative uncertainty, an ideal robust controller was designed using μ-synthesis and a reduced-order H-infinity Feedback Optimal Output (Hifoo) controller, leading to the creation of an improved uncertain plant. A powerful controller was built using a larger plant that included the nominal model and corresponding uncertainty. The designed controllers demonstrated robust and nominal performance when handling agitated plants. A comparison of the results was conducted. As an example of a general smart structure, the vibration of a collocated piezoelectric actuator and sensor was controlled using two different approaches with strong controller designs. This study presents a comprehensive simulation of the oscillation suppression problem for smart beams. They provide an analytical demonstration of how uncertainty is introduced into the model. The desired outcomes were achieved by utilizing Simulink and MATLAB (v. 8.0) programming tools.

High-density polyethylene polymer (HDPE) and carbon black (CB) were utilized to create HDPE/CB composites with different filler concentrations (0.0, 2.0, 4.0, 6.0, 8.0, 10.0, 16.0, 20.0, and 24.0 wt.%). The composites were extruded into filaments, which were then utilized to fabricate 3D-printed specimens with the material extrusion (MEX) method, suitable for a variety of standard mechanical tests. The electrical conductivity was investigated. Furthermore, thermogravimetric analysis and differential scanning calorimetry were carried out for all the HDPE/CB composites and pure HDPE. Scanning electron microscopy in different magnifications was performed on the specimens’ fracture and side surfaces to investigate the morphological characteristics. Rheological tests and Raman spectroscopy were also performed. Eleven different tests in total were performed to fully characterize the composites and reveal connections between their various properties. HDPE/CB 20.0 wt.% showed the greatest reinforcement results in relation to pure HDPE. Such composites are novel in the MEX 3D printing method. The addition of the CB filler greatly enhanced the performance of the popular HDPE polymer, expanding its applications.

The cost-effectiveness and the environmental impact of Additive Manufacturing (AM) are nowadays two of the hottest process-related industrial and research topics. Energy efficiency is a strong claim, and so is the demand for durable and functional 3D-printed workpieces. These contradictory aspects usually require flexibility and compromises. Especially for Material Extrusion (MEX) 3D printing, the plurality of the control parameters makes such optimizations complicated. This research explores the effect of seven generic and machine-independent control factors (e.g., Raster Deposition Angle; Orientation Angle; Layer Thickness; Infill Density; Nozzle Temperature; Bed Temperature, and Printing Speed) on energy consumption of Polylactic Acid over the compressive response of MEX 3D printed specimens. To make it possible, a three-level L27 orthogonal array was compiled. Each experimental run included five specimen replicas (after the ASTM D695-02a standard) summing up 135 experiments. The fabrication time and the energy consumption were determined by the stopwatch method, whereas the compressive strength, elasticity modulus, and toughness were derived with compressive tests. The Taguchi analysis ranked the impact of each control parameter on each response metric. The printing speed and the layer thickness were the most influential control parameters on energy consumption. Furthermore, the infill density and the orientation angle were found as the most dominant factors in the compressive strength. Finally, Quadratic Regression Model (QRM) equations for each response metric over the seven control parameters were compiled and validated. Hereto, the best settlement between energy efficiency and mechanical strength is now possible, an option with great technological and industrial merit.

In this paper, our strategy is to look for locally optimum answers to a non-smooth optimization problem that has been constructed to include minimization goals and restrictions for smart structures’ vibration suppression. In both theoretical analysis and practical implementation, it is widely recognized that designing multi-objective control systems poses a considerable challenge. In this study, we assess the effectiveness of this method by employing the open-source Matlab toolbox Hifoo 2.0 and juxtapose our findings with established industry standards. We start by framing the control problem as a mathematical optimization issue and proceed to identify the controller that effectively addresses this optimization. This approach introduces the potential application of intelligent structures in tackling the challenge of vibration suppression. This study makes use of the most recent version of the freely available application Hifoo which tries to study vibration suppression with the limits outlined above in the context of multi-objective controller design. A controller directive is initially set, allowing for a lower order.

During the past few years, there has been a notable surge of interest in the field of smart structures. An intelligent structure is one that automatically responds to mechanical disturbances by minimizing oscillations after intelligently detecting them. In this study, a smart design that contains integrated actuators and sensors that can dampen oscillations is shown. A finite element analysis is used in conjunction with the application of dynamic loads such as wind force. The dynamic-loading-induced vibration of the intelligent piezoelectric structure is aimed to be mitigated using a μ-controller. The controller’s robustness against uncertainties in the parameters to address vibration-related concerns is showcased. This article offers a thorough depiction of the benefits stemming from μ-analysis and active vibration control in the behavior of intelligent structures. The gradual surmounting of these challenges is attributed to the increasing affordability and enhanced capability of electronic components used for control implementation. The advancement of μ-analysis and robust control for vibration reduction in intelligent structures is amply demonstrated in this study.

The goal of this paper is to investigate tungsten carbide (WC) as a reinforcement in the popular material extrusion (MEX) additive manufacturing (AM) procedure. The impressive characteristics of WC demonstrate its potential as a valuable additive for commonly used polymeric matrices in MEX 3D printing, offering reinforcement and stabilization properties. The mechanical properties of hybrid polymer/ceramic nanocomposites made up of various filler loadings (0–10 wt. %) of medical-grade polylactic acid (PLA) and WC were studied. The mechanical characteristics, structure, and thermomechanical properties of the resulting compounds were fully characterized following the respective standards. The fracture mechanisms were revealed with Scanning Electron Microscopy. Overall, a laborious effort was implemented with fifteen different tests to fully characterize the nanocomposites prepared. In comparison to the raw PLA material, the tensile strength of the 4.0 wt. % WC PLA/WC nanocomposite was improved by 42.5% and the flexural strength by 41.9%. In the microhardness test, a 120.4% improvement was achieved, justifying the properties of WC ceramic. According to these findings, PLA nanocomposites reach high-performance polymer specifications, expanding their potential use, especially in wear-related applications.

In this study, we successfully address a significant research and engineering gap by quantitatively assessing the impact of varying compressive loading rates on the mechanical behavior of four popular thermoplastic polymers in material-extrusion-based (MEX) 3D printing. Raw powders of polycarbonate (PC), polyethylene terephthalate glycol (PETG), polymethyl methacrylate (PMMA), and thermoplastic polyurethane (TPU) were processed through melt extrusion, and the filaments were used to 3D-print the test samples. For completeness, thermogravimetric analysis and a compressive test following the ASTM-D695 standard were conducted. Ultimately, the compressive strength and yield stress, the compressive modulus of elasticity and toughness, and the maximum compressive sensitivity index were thoroughly documented. Specimens were tested in strain rates from 1.3 mm/min to 200 mm/min. The compressive strength (40% for the PMMA) and stiffness (29% for the TPU) increased with the increase in the strain rate in all polymers tested. PC had the highest strain rate sensitivity. Significant variations in deformation and fracture modes were observed and thoroughly documented throughout this study. Our findings can be useful in industrial engineering as valued design optimization input parameters in various applications involving the above-mentioned polymeric materials.

In this study, innovative nanocomposite materials for material extrusion (MEX) 3D printing were developed using a polypropylene (PP) polymer with tungsten carbide (WC) nanopowder. The raw materials were converted into filaments using thermomechanical extrusion. The samples were then fabricated for testing according to the international standards. Extensive mechanical testing was performed on the 3D-printed specimens, including tensile, impact, flexural, and microhardness assessments. In addition, the impact of ceramic additive loading was examined. The thermal and stoichiometric characteristics of the nanocomposites were examined using thermogravimetric analysis, energy-dispersive X-ray spectroscopy, differential scanning calorimetry, and Raman spectroscopy. The 3D-printed shape, quality, and fracture process of the specimens were examined using scanning electron microscopy. The results showed that the filler significantly enhanced the mechanical characteristics of the matrix polymer without reducing its thermal stability or processability. Notably, the highest level of nanocomposite mechanical responsiveness was achieved through the inclusion of 6.0 and 8.0 wt. % fillers. The 10.0 wt. % loading nanocomposite showed significantly increased microhardness, indicating a possible high resistance to wear.

In the material extrusion (MEX) Additive Manufacturing (AM) technology, the layer-by-layer nature of the fabricated parts, induces specific features which affect their quality and may restrict their operating performance. Critical quality indicators with distinct technological and industrial impact are surface roughness, dimensional accuracy, and porosity, among others. Their achieving scores can be optimized by adjusting the 3D printing process parameters. The effect of six (6) 3D printing control parameters, i.e., raster deposition angle, infill density, nozzle temperature, bed temperature, printing speed, and layer thickness, on the aforementioned quality indicators is investigated herein. Optical Microscopy, Optical Profilometry, and Micro Χ-Ray Computed Tomography were employed to investigate and document these quality characteristics. Experimental data were processed with Robust Design Theory. An L25 Taguchi orthogonal array (twenty-five runs) was compiled, for the six control parameters with five levels for each one of them. The predictive quadratic regression models were then validated with two additional confirmation runs, with five replicas each. For the first time, the surface quality features, as well as the geometrical and structural characteristics were investigated in such depth (>500 GB of raw experimental data were produced and processed). A deep insight into the quality of the MEX 3D printed parts is provided allowing the control parameters’ ranking and optimization. Prediction equations for the quality features as functions of the control parameters are introduced herein, with merit in the market-driven practice.

Both energy efficiency and robustness are popular demands for 3D-printed components nowadays. These opposing factors require compromises. This study examines the effects of seven general control variables on the energy demands and the compressive responses of polyamide (PA6) material extrusion (MEX) 3D printed samples. Nozzle Temperature, Layer Thickness, Orientation Angle, Raster Deposition Angle, Printing Speed, Bed Temperature, and Infill Density were studied. An L27 orthogonal array was compiled with five replicas. A total of 135 trials were conducted, following the ASTM D695-02a specifications. The stopwatch method was used to assess the construction time and energy usage. The compressive strength, toughness, and elasticity modulus were experimentally determined. The Taguchi technique ranks each control parameter’s impact on each response measure. The control parameter that had the greatest impact on both energy use and printing time was layer thickness. Additionally, the infill density had the greatest influence on the compressive strength. Quadratic regression model equations were formed for each of the response measures. The ideal compromise between mechanical strength and energy efficiency is now reported, with merit related to technological and economic benefits.

The influence of nanoparticles (NPs) in zirconium oxide (ZrO2) as a strengthening factor of Polylactic Acid (PLA) and Polyamide 12 (PA12) thermoplastics in material extrusion (MEX) additive manufacturing (AM) is reported herein for the first time. Using a melt-mixing compounding method, zirconium dioxide nanoparticles were added at four distinct filler loadings. Additionally, 3D-printed samples were carefully examined for their material performance in various standardized tests. The unfilled polymers were the control samples. The nature of the materials was demonstrated by Raman spectroscopy and thermogravimetric studies. Atomic Force Microscopy and Scanning Electron Microscopy were used to comprehensively analyze their morphological characteristics. Zirconium dioxide NPs showed an affirmative reinforcement tool at all filler concentrations, while the optimized material was calculated with loading in the range of 1.0–3.0 wt.% (3.0 wt.% for PA12, 47.7% increase in strength; 1.0 wt.% for PLA, 20.1% increase in strength). PA12 and PLA polymers with zirconium dioxide in the form of nanocomposite filaments for 3D printing applications could be used in implementations using thermoplastic materials in engineering structures with improved mechanical behavior.

Herein, polytetrafluoroethylene (PTFE) is evaluated as a reinforcement agent in material extrusion (MEX) additive manufacturing (AM), aiming to develop nanocomposites with enhanced mechanical performance. Loadings up to 4.0 wt.% were introduced as fillers of polylactic acid (PLA) and polyamide 12 (PA12) matrices. Filaments for MEX AM were prepared to produce corresponding 3D-printed samples. For the thorough characterization of the nanocomposites, a series of standardized mechanical tests were followed, along with AFM, TGA, Raman spectroscopy, EDS, and SEM analyses. The results showed an improved mechanical response for filler concentrations between 2.0 and 3.0 wt.%. The enhancement for the PLA/PTFE 2.0 wt.% in the tensile strength reached 21.1% and the modulus of elasticity 25.5%; for the PA12/PTFE 3.0 wt.%, 34.1%, and 41.7%, respectively. For PLA/PTFE 2.0 wt.%, the enhancement in the flexural strength reached 57.6% and the modulus of elasticity 25.5%; for the PA12/PTFE 3.0 wt.%, 14.7%, and 17.2%, respectively. This research enables the ability to deploy PTFE as a reinforcement agent in the PA12 and PLA thermoplastic engineering polymers in the MEX AM process, expanding the potential applications.

The industrial demand for functional filaments made of bio-sourced, biocompatible, biodegradable, and/or recyclable polymers and composites for material extrusion (MEX) 3D printing is continuously growing. Polylactic acid (PLA), the most popular filament, combines such properties, yet its reinforcement with low-cost, inert, and/or recycled fillers remains challenging. Herein, glass in three different micro/nano-forms was the reinforcement agent in PLA. Three different experimental tiers were elaborated by producing composite filaments with glass in powder, beads, and flake forms in various loadings to optimize the concentrations. A thermomechanical process, i.e., melt filament extrusion, was exploited. The composites were evaluated for their thermal degradation stability and composition using thermogravimetric analysis and Raman. MEX 3D printing was used to produce tensile, flexural, impact, and microhardness specimens, to quantitatively evaluate their mechanical response. Field emission scanning electron microscopy evaluation and fractography were carried out to depict fracture patterns of the specimens after their tests. All three glass types induced impressive reinforcement effects (up to 60% in flexural loading), especially in the flake form. The impact of the additional process cost through glass fillers implementation was also assessed, indicating that such composites are cost-effective.

The current research aimed to examine the thermomechanical properties of new nanocomposites in additive manufacturing (AM). Material extrusion (MEX) 3D printing was utilized to evolve acrylonitrile butadiene styrene (ABS) nanocomposites with silicon nitride nano-inclusions. Regarding the mechanical and thermal response, the fabricated 3D-printed samples were subjected to a course of standard tests, in view to evaluate the influence of the Si3N4 nanofiller content in the polymer matrix. The morphology and fractography of the fabricated filaments and samples were examined using scanning electron microscopy and atomic force microscopy. Moreover, Raman and energy dispersive spectroscopy tests were accomplished to evaluate the composition of the matrix polymer and nanomaterials. Silicon nitride nanoparticles were proved to induce a significant mechanical reinforcement in comparison with the polymer matrix without any additives or fillers. The optimal mechanical response was depicted to the grade ABS/Si3N4 4 wt. %. An impressive increase in flexural strength (30.3%) and flexural toughness (47.2%) was found. The results validate that these novel ABS nanocomposites with improved mechanical properties can be promising materials.

In this work, an industrially scalable method was developed for the preparation of multifunctional nanocomposite filaments. Polylactic Acid (PLA) polymer matrix was enriched with Multi Wall Carbon Nanotubes (MWCNT) at various concentrations, to fabricate 3D-printed parts by the Fused Filament Fabrication (FFF) technology. The effect of the nanofiller loading at the mechanical, thermal, electrical, thermomechanical, and antibacterial performance of the novel nanocomposites fabricated in this work was investigated. The filler loading of 5 wt.% was also tested to reveal its electrothermal Joule heating performance. The antibacterial properties of the nanocomposites were examined through a screening process, against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). For loadings of 1 wt.% and higher the mechanical properties were significantly improved. The 5 wt.% loaning showed measurable antibacterial performance. The nanocomposites prepared herein can be characterized as multifunctional materials, suitable for various industrial applications, such as sensors fabrication, health monitoring devices, etc.

Three-dimensional (3D) printed Polypropylene (PP) reinforced with aluminum oxide (Al2O3) nanoparticles (NPs) were developed and fully characterized in this study. Nanocomposite filaments were produced initially following a melt mixing extrusion process, utillised as feedstock for the Fused Filament Fabrication (FFF) specimen manufacturing. Al2O3 NPs at 0.5, 1.0, 2.0 and 4.0 wt% loadings were melt-mixed with the PP thermoplastic matrix. Specific geometry samples were 3D printed and analysed via tensile, flexural, viscoelastic, impact, microhardness and fractographic investigations. Raman spectroscopy verified the polymeric structure and the incorporated Al2O3 NPs within the polymer matrix. Atomic Force Microscopy (AFM) of the extruded filaments revealed the nanoscale roughness induced by the alumina nanoinclusions. All 3D printed nanocomposite structures exhibited enhanced tensile, flexural and thermomechanical properties. Specifically, the best combination was found for the 1.0 wt% loaded specimen showing a tensile and flexural strength increase by approx. 4% and 19%, respectively, with a concomitant slight increase in impact and microhardness properties compared to unfilled PP. Dynamic Mechanical Analysis (DMA) revealed a stiffening mechanism for the PP/Al2O3 nanocomposites being in good agreement with the quasi-static mechanical tests. It could be envisaged that the 3D printed PP/Al2O3 nanocomposites developed herein could find numerous applications as engineered thermoplastics, where enhanced material's static and dynamic mechanical properties are required.

Process sustainability vs. mechanical strength is a strong market-driven claim in Material Extrusion (MEX) Additive Manufacturing (AM). Especially for the most popular polymer, Polylactic Acid (PLA), the concurrent achievement of these opposing goals may become a puzzle, especially since MEX 3D-printing offers a variety of process parameters. Herein, multi-objective optimization of material deployment, 3D printing flexural response, and energy consumption in MEX AM with PLA is introduced. To evaluate the impact of the most important generic and device-independent control parameters on these responses, the Robust Design theory was employed. Raster Deposition Angle (RDA), Layer Thickness (LT), Infill Density (ID), Nozzle Temperature (NT), Bed Temperature (BT), and Printing Speed (PS) were selected to compile a five-level orthogonal array. A total of 25 experimental runs with five specimen replicas each accumulated 135 experiments. Analysis of variances and reduced quadratic regression models (RQRM) were used to decompose the impact of each parameter on the responses. The ID, RDA, and LT were ranked first in impact on printing time, material weight, flexural strength, and energy consumption, respectively. The RQRM predictive models were experimentally validated and hold significant technological merit, for the proper adjustment of process control parameters per the MEX 3D-printing case.

Challenging issues arise in the design of control strategies for piezoelectric smart structures. Piezoelectric materials have been investigated for use in distributed parameter systems in order to provide active control efficiently and affordably. In the active control of dynamic systems, distributed sensors and actuators can be created using piezoelectric materials. The three fundamental issues that structural control engineers must face when creating robust control laws are structural modeling methodologies, uncertainty modeling, and robustness validation. These issues are reviewed in this article. A smart structure with piezoelectric (PZT) materials is investigated for its active vibration response under dynamic disturbance. Numerical modeling with finite elements is used to achieve that. The vibration for different model values is presented considering the uncertainty of the modeling. A vibration suppression was achieved with a robust controller and with a reduced order controller. Results are presented for the frequency domain and the state space domain. This work cleary demostrated the advantage of robust control in the vibration suppration of smart stuctures.

Sustainability and energy efficiency of additive manufacturing (AM) is an up-to-date industrial request. Likewise, the claim for 3D-printed parts with capable mechanical strength remains robust, especially for polymers that are considered high-performance ones, such as polycarbonates in material extrusion (MEX). This paper explains the impact of seven generic control parameters (raster deposition angle; orientation angle; layer thickness; infill density; nozzle temperature; bed temperature; and printing speed) on the energy consumption and compressive performance of PC in MEX AM. To meet this goal, a three-level L27 Taguchi experimental design was exploited. Each experimental run included five replicas (compressive specimens after the ASTM D695-02a standard), summating 135 experiments. The printing time and the power consumption were stopwatch-derived, whereas the compressive metrics were obtained by compressive tests. Layer thickness and infill density were ranked the first and second most significant factors in energy consumption. Additionally, the infill density and the orientation angle were proved as the most influential factors on the compressive strength. Lastly, quadratic regression model (QRM) equations for each response metric versus the seven control parameters were determined and evaluated. Hereby, the optimum compromise between energy efficiency and compressive strength is attainable, a tool holding excessive scientific and engineering worth.

Acrylonitrile Butadiene Styrene (ABS) nanocomposites were developed using Material Extrusion (MEX) Additive Manufacturing (AM) and Fused Filament Fabrication (FFF) methods. A range of mechanical tests was conducted on the produced 3D-printed structures to investigate the effect of Titanium Nitride (TiN) nanoparticles on the mechanical response of thermoplastic polymers. Detailed morphological characterization of the produced filaments and 3D-printed specimens was carried out using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). High-magnification images revealed a direct impact of the TiN concentration on the surface characteristics of the nanocomposites, indicating a strong correlation with their mechanical performance. The chemical compositions of the raw and nanocomposite materials were thoroughly investigated by conducting Raman and Energy Dispersive Spectroscopy (EDS) measurements. Most of the mechanical properties were improved with the inclusion of TiN nanoparticles with a content of 6 wt. % to reach the optimum mechanical response overall. ABS/TiN 6 wt. % exhibits remarkable increases in flexural modulus of elasticity (42.3%) and toughness (54.0%) in comparison with pure ABS. The development of ABS/TiN nanocomposites with reinforced mechanical properties is a successful example that validates the feasibility and powerful abilities of MEX 3D printing in AM.

The energy efficiency of material extrusion additive manufacturing has a significant impact on the economics and environmental footprint of the process. Control parameters that ensure 3D-printed functional products of premium quality and mechanical strength are an established market-driven requirement. To accomplish multiple objectives is challenging, especially for multi-purpose industrial polymers, such as the Poly[methyl methacrylate]. The current paper explores the contribution of six generic control factors (infill density, raster deposition angle, nozzle temperature, print speed, layer thickness, and bed temperature) to the energy performance of Poly[methyl methacrylate] over its mechanical performance. A five-level L25 Taguchi orthogonal array was composed, with five replicas, involving 135 experiments. The 3D printing time and the electrical consumption were documented with the stopwatch approach. The tensile strength, modulus, and toughness were experimentally obtained. The raster deposition angle and the printing speed were the first and second most influential control parameters on tensile strength. Layer thickness and printing speed were the corresponding ones for the energy consumption. Quadratic regression model equations for each response metric over the six control parameters were compiled and validated. Thus, the best compromise between energy efficiency and mechanical strength is achievable, and a tool creates significant value for engineering applications.

Polycarbonate-based nanocomposites were developed herein through a material extrusion (MEX) additive manufacturing (AM) process. The fabrication of the final nanocomposite specimens was achieved by implementing the fused filament fabrication (FFF) 3D printing process. The impact of aluminum nitride (AlN) nanoparticles on the thermal and mechanical behavior of the polycarbonate (PC) matrix was investigated thoroughly for the fabricated nanocomposites, carrying out a range of thermomechanical tests. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) provided information about the morphological and surface characteristics of the produced specimens. Using energy dispersive spectroscopy (EDS), the elemental composition of the nanocomposite materials was validated. Raman spectroscopy revealed no chemical interactions between the two material phases. The results showed the reinforcement of most mechanical properties with the addition of the AlN nanoparticles. The nanocomposite with 2 wt.% filler concentration exhibited the best mechanical performance overall, with the highest improvements observed for the tensile strength and toughness of the fabricated specimens, with a percentage of 32.8% and 51.6%, respectively, compared with the pure polymer. The successful AM of PC/AlN nanocomposites with the MEX process is a new paradigm, which expands 3D printing technology and opens a new route for the development of nanocomposite materials with multifunctional properties for industrial applications.

The effect of aluminum oxide (Al2O3) nanoparticles (NPs) as a reinforcing agent of Polyamide 12 (PA12) and Polylactic acid (PLA) in fused filament fabrication (FFF) three-dimensional printing (3DP) is reported herein for the first time. Alumina NPs are incorporated via a melt–mixing compounding process, at four different filler loadings. Neat as well as nanocomposite 3DP filaments are prepared as feedstock for the 3DP manufacturing of specimens which are thoroughly investigated for their mechanical properties. Thermogravimetric analyses (TGA) and Raman spectroscopy (RS) proved the nature of the materials. Their morphological characteristics were thoroughly investigated with scanning electron and atomic force microscopy. Al2O3 NPs exhibited a positive reinforcement mechanism at all filler loadings, while the mechanical percolation threshold with the maximum increase of performance was found between 1.0–2.0 wt.% filler loading (1.0 wt.% for PA12, 41.1%, and 56.4% increase in strength and modulus, respectively; 2.0 wt.% for PLA, 40.2%, and 27.1% increase in strength and modulus, respectively). The combination of 3DP and polymer engineering using nanocomposite PA12 and PLA filaments with low-cost filler additives, e.g., Al2O3 NPs, could open new avenues towards a series of potential applications using thermoplastic engineering polymers in FFF 3DP manufacturing.

Vat photopolymerization (VPP) is an additive manufacturing process commonly used in medical applications. This work aims, for the first time in the literature, to extend and enhance the performance of a commercial medical-grade resin for the VPP process, with the development of nanocomposites, using Copper (Cu) nanoparticles as the additive at two different concentrations. The addition of the Cu nanoparticles was expected to enhance the mechanical properties of the resin and to enable biocidal properties on the nanocomposites since Cu is known for its antibacterial performance. The effect of the Cu concentration was investigated. The nanocomposites were prepared with high-shear stirring. Specimens were 3D printed following international standards for mechanical testing. Their thermal and spectroscopic response was also investigated. The morphological characteristics were examined. The antibacterial performance was evaluated with an agar well diffusion screening process. The experimental results were analyzed with statistical modeling tools with two control parameters (three levels each) and eleven response parameters. Cu enhanced the mechanical properties in all cases studied. 0.5 wt.% Cu nanocomposite showed the highest improvement (approximately 11% in tensile and 10% in flexural strength). The antibacterial performance was sufficient against S. aureus and marginal against E. coli.

Welding tools of different designs have been used to join friction stir welding 2-mm-thick Al 7075 sheets, to investigate the effect of the tool geometry on the weld performance. Five cylindrical tools with different pin geometries were manufactured from heat-treatable low alloy steel WNr 1.6582/DIN 34CrNiMo6. Additionally, the effect of the welding speed was considered in the work, with six different speeds ranging from 80 mm/min to 300 mm/min. The weld tool rotational speed was kept constant at 1000 rpm and all other parameters were also kept constant in the experiments. The tensile strength was measured to investigate the mechanical properties of the weld. Results were processed with statistical analysis tools, which showed that the mechanical strength was affected by tool geometry as well as welding speed. The weld tool with the highest pin diameter achieved the highest tensile strength. The welding speed affected the tensile strength differently in the different weld tool geometries studied. The highest weld efficiency reported in the tests is 72.20%, achieved with a cylindrical pin weld tool at 250 mm/min.

The scope of this work was to develop novel polymer composites via melt extrusion and 3D printing, incorporating High-Density Polyethylene filled with zinc oxide particles in various wt. percentages. For each case scenario, a filament of approximately 1.75 mm in diameter was fabricated. Samples for tensile and flexural testing were fabricated with 3D printing. They were then evaluated for their mechanical response according to ASTM standards. According to the documented testing data, the filler increases the mechanical strength of pure HDPE at specific filler concentrations. The highest values reported were a 54.6% increase in the flexural strength with HDPE/ZnO 0.5 wt.% and a 53.8% increase in the tensile strength with 10 wt.% ZnO loading in the composite. Scanning Electron Microscopy (SEM), Raman, and thermal characterization techniques were used. The experimental findings were evaluated in other research areas where they were applicable.

In this work, for the first time, polyamide 12 (PA12) nanocomposites with binary inclusions in material extrusion (MEX) 3D printing were developed. The aim was to achieve an enhanced mechanical response with the addition of titanium nitride (TiN) and antibacterial performance with the addition of copper (Cu) or cuprous oxide (Cu2O), towards the development of multi-functional nanocomposite materials, exploiting the 3D printing process benefits. The prepared nanocomposites were fully characterized for their mechanical properties. The thermal properties were also investigated. Morphological characterization was performed with atomic force microscopy (AFM) and scanning electron microscopy (SEM). The antibacterial performance was investigated with an agar-well diffusion screening process. Overall, the introduction of these nanofillers induced antibacterial performance in the PA12 matrix materials, while at the same time, the mechanical performance was significantly increased. The results of the study show high potential for expanding the areas in which 3D printing can be used.