In-situ thermal monitoring is a versatile tool in additive manufacturing, enabling real-time process control, recording for process certification and qualification, and the investigation of underlying process mechanisms. However, this field lacks a systematic review, especially in terms of applied technology. This review discusses thermal monitoring techniques in polymeric powder bed fusion, focusing on thermal imagers. Underlying principles of thermal imaging, their limitations and key considerations are presented. Existing academic usage in polymeric powder bed fusion is discussed, and tabulated information of thermal cameras and their specifications are presented. It was found Indium Antimonide medium-wave infrared (3–5 μm) sensors dominate the higher frame rate and resolution models, offering excellent thermal sensitivity (NETD), while cheaper microbolometer long-wavelength infrared (7–14 μm) sensors were more accessible but lower performance. Additionally, temperature-dependent emissivity was found to be highly significant in accurate data collection, however newer, more productive forms of polymeric powder bed fusion such as High-Speed Sintering, Large Area Projection Sintering and Multi Jet Fusion are largely unexplored thermographically. Further investigation of these newer processes thermo-optical properties has promise in better leveraging their high productivity through improved understanding of their underlying behaviour.

Purpose This study aims to introduce an algorithm that can successfully define optimum laser-based powder bed fusion (LB-PBF) processing and post-heat treatment parameters for manufacturing 316L stainless steels with limited energy usage and enhanced properties. Design/methodology/approach Taguchi’s design of the experiment (DoE) was elaborated to define the ideal LB-PBF process and heat treatment parameters. Based on the DoE and experimental results, the LB-PBF energy density between 6.7 J/mm3 and 14.7 J/mm3 produced parts with a volumetric mass density of 98.8% or higher. The authors’ proposed processing window shows 316 L manufactured products can reach the highest mechanical strength reported in literature. Findings The microstructure characteristics of the enhanced 316L builds showed characteristic dislocation density, grain size and texture features. The proposed heat treatments at 650, 870 and 1,150 °C results in preferential grain growth up to approximately 45 µm, reorienting the as-built grain structure from < 100> to < 101> components. This promoted mechanical twinning propensity and the dynamic Hall–Petch effect, resulting in significant improvements in the mechanical properties. Originality/value The manufactured parts in the optimised conditions achieved improvement in ultimate tensile strength (970 MPa) and elongation (32%), representing a noticeable strength–ductility combination for LB-PBF of 316L.

Lunar dust poses persistent operational and health hazards for future missions. This review evaluates 32 passive lunar dust mitigation and tolerance surfaces reported between January 2006 and January 2026. A weighted scoring rubric is applied across five criteria: added build-up (thickness), manufacturability, complexity, environmental durability and dust interaction performance. This framework is used to compare the reported evidence base and to map validation maturity through TRL, without claiming subsystem deployment readiness. Mitigation surfaces can keep residual dust coverage below 10% while adding very little extra material, but they have mostly been tested only on small laboratory samples and not under standardised high-vacuum conditions. By contrast, tolerance surfaces have been tested more thoroughly under thermal cycling, vacuum and ultraviolet exposure, yet there are still very few measurements of how they wear when repeatedly exposed to lunar dust. Critical gaps include the lack of standardised high vacuum dust tests and combined stressor protocols. Within this scoring framework, the two highest scoring technologies are graphene-enhanced perfluorosilane coating (40/50) and graphene/polyamide-imide coatings (38/50). The most promising development path is to pair high-efficacy mitigation surfaces with lightweight, durable tolerance coatings and then evaluate those pairings under combined vacuum, UV, thermal-cycling, and abrasion stressors.

Understanding how molecular weight distribution (MWD) influences the mechanical and fracture behaviour of additively manufactured PA12 is essential for establishing reliable process–structure–property relationships. An approach to minimize anisotropy has been to specifically target the feedstock materials with the goal of enhancing interlayer adhesion. In this study, polyamide 12 (PA12) grades of MWD were investigated to determine the effect of MWD on the interlayer bond formation and anisotropy of the printed samples. Three different grades of PA12 were printed into tensile coupons and double cantilever beam (DCB) specimens and the mechanical properties were assessed to study interlayer bond strength using standard fracture toughness technique. A significant improvement in mechanical properties and fracture toughness were observed with higher print temperatures attributed to strong interlayer adhesion owing to longer interlayer bonding times (verified through the Lumped Capacity model and thermocouple data). Fracture toughness assessment also demonstrated that amongst samples printed at the same temperature, PA12 with a lower average MWD provided the highest fracture toughness (G1C) values, attributed to the faster diffusion of short polymer chains across the interlayer interface. Tailoring the MWD of feedstock polymers utilized in 3D printing as a strategy to optimize performance and lower anisotropy was demonstrated to be a feasible pathway. These findings were utilized by developing a PA12 blend of broad MWD which provided the highest overall mechanical properties and G1c, demonstrating the usefulness of incorporating a high proportion of fast diffusing short polymer chains in the development of polymeric feedstock materials. Additionally, for large scale 3D printing applications, where maintaining high chamber temperatures is impractical, these results suggest that optimizing MWD can be an alternative strategy to improve interlayer adhesion and mechanical properties without relying solely on elevated print temperatures.

Abstract This paper presents an iterative, research-through-design methodology for advancing joint design in multi-material additively manufactured fibre composite systems. The research responds to a condition inherent to large-scale additive manufacturing and composite lamination, where robotic reach envelopes, print-bed dimensions and curing protocols impose mandatory divisions on continuous geometries, producing tectonic seams that become structurally critical in multi-material systems where materials are deposited and cured in sequential stages. The methodology combines robotic additive manufacturing of polymer shells with carbon fibre reinforcement through sequential cycles of prototyping, mechanical testing and full-scale application. Seven joint iterations were developed across two experimental stages, the first establishing an embedded spine and plate configuration and the second responding to fabrication and performance observations from Ghost Tectonics, the full-scale architectural demonstrator. Three-point flexural mechanical testing established that configurations with a continuous internal carbon fibre spine substantially outperformed those omitting or interrupting the spine, with the embedded spine and plate configuration achieving the highest flexural performance in the series. The research demonstrates that joint performance is governed by the interaction of reinforcement continuity, fastener integration and interface control. The joint is therefore treated as a tested architectural detail, where structural behaviour and tectonic expression are developed through the same assembly logic. Thus, the research advances frameworks for materially integrated joints that operate across the scales of digital design, composite fabrication, and architectural tectonics.

Metal thin-walled structures (TWS) are critical to all engineering industries, however, their complex manufacture has prevented large-scale adoption. The additive manufacturing process of laser-based powder bed fusion (PBF-LB) can produce high-resolution metal TWS with micro-scale geometries and intricate features. However, the thermal nature of PBF-LB increases the likelihood of defect formation. By modeling the manufacturability of metal TWS using a digitally reconstructed model guided by Multi-Layer Perceptron (MLP) Artificial Neural Networks (ANN) and Computational Fluid Dynamics (CFD), this problem can be predicted and then resolved. This research presents the first experimentally validated digital reconstructions guided by ANN-CFD as a predictive tool for PBF-LB manufacturability of metal TWS. This work contributes to the body of knowledge by introducing a new AI-based model to predict TWS porosity, dimensional deviations and distortion. To generate the MLP-ANN model, three control factors were selected: inclination angle, laser power, and the number of laser scan passes. To train the ANN, a full factorial dataset of AlSi10Mg samples was produced. Results show the MLP-ANN model as a precise tool to predict the manufacturability of TWS produced by PBF-LB with accuracy exceeding 90%. The most effective factor for the thickness, dimensional deviations and distortion was found to be the number of laser passes. The results also showed inclination angle was the main driving factor for the porosity of the TWS. The outcomes from this study highlight the value of ANN networks in the prediction and eventual certification of AM processes for global engineering interests.

High performance polymers (HPPs), particularly polyimides (PIs), including both thermosetting and thermoplastic types, exhibit remarkable properties such as exceptional mechanical properties, outstanding thermal stability, and inherent flame retardancy. PIs are lightweight and potentially economical alternatives to metal based materials used in demanding applications, such as aerospace, transportation, and defense. However, processing PIs into the desired complex shapes is a significant challenge owing to their high melting temperature, high melt flow viscosity, and very narrow processing temperature window. Additive manufacturing (AM) techniques present an important avenue for processing such materials and emerged as a revolutionary approach to overcome these limitations, offering unprecedented design flexibility, reduced material waste, and the capability for rapid prototyping and production. Despite these advantages, AM of PIs has received considerably less attention, primarily due to significant processing challenges including material printability, thermal management complexities, and dimensional accuracy challenges that have hindered further advancements in this field. This comprehensive review explores the evolution and current status of polyimides additive manufacturing, providing insights into their chemistry, structural modifications, and detailed structure-property relationships. Various AM techniques including vat photopolymerization, material extrusion, direct ink writing, material jetting along with hybrid and emerging approaches are critically discussed, highlighting recent innovations, key challenges, and strategic solutions to enhance processing capabilities. Furthermore, the review identifies prospective research directions, emphasizing the potential for multifunctional and stimuli-responsive polyimides that could revolutionize next-generation applications. Overall, this review aims to stimulate further advancements in polyimide based additive manufacturing, fostering its broader industrial adoption and facilitating significant developments in high performance polymer technology.

Additive manufacturing (AM) has progressed from rapid prototyping to rapid manufacturing of equipment for various industries, including the space industry, where polymer-based techniques like Material extrusion (MEX) are particularly interesting. Polyetherimide (PEI), Poly ether ether ketone (PEEK) and Poly ether ketone ketone (PEKK) are frequently chosen to manufacture end use equipment in MEX due to their desirable properties. Although some previous studies analysed the effects of protons, electrons, and UV, less is known about the effects of heavy ions from galactic cosmic rays (GCR) and solar particle events (SPE) on these polymers. This study investigated the effects of heavy ions from GCR and SPE on chemical (X-Ray photoelectron spectroscopy and FT-IR spectroscopy), surface (SEM-EDS), and micromechanical (nanoindentation) properties of PEKK. To achieve this, SPENVIS simulations were performed to quantify the fluences of protons and heavy ions experienced by satellites on orbit and the calculated fluences of ions were then implanted on PEKK to emulate space-like conditions for the first time in literature. MEX printed PEKK samples were irradiated with 57 MeV 56Fe ions to achieve absorbed doses up to of 80 Gy, representative of the total dose to which satellites are exposed throughout their transport and time in orbit and up to 200 times more. The chemical, surface, and mechanical properties of the PEKK samples were analysed both before and after irradiation. Results showed no significant changes in properties, indicating that PEKK has potential structural applications in long-duration space missions. This suggests that PEKK can withstand the harsh conditions in space and may offer a viable alternative to traditional metals.

Despite the widespread use of fused filament fabrication (FFF) (an extrusion-based additive manufacturing process) to manufacture end-use parts for the aerospace industry, limited materials are available within this process that can be used for structural applications in the harsh space environment. Currently available high-performance polymers need to be improved by incorporating additives within the polymer matrix to achieve multi-functional properties. Additives such as graphene, graphene oxide, carbon nanotubes and boron carbide are known to improve mechanical and thermal properties and radiation shielding. This study aims to understand if these additives can be successfully incorporated into PEKK matrix to manufacture printable filaments for FFF. Graphene, graphene oxide (GO) and boron carbide (B 4 C) were compatibilised with PEKK matrix, and their mechanical, thermal and rheological properties were analysed and compared with commercially available carbon fibre and carbon nanotube-reinforced PEKK where appropriate. As rheological properties of the formulations confirmed that they were printable, filaments for FFF were then manufactured. Graphene–PEKK was the most printable filament followed by GO–PEKK while B 4 C–PEKK was not printable. TEM images of filament cross-section showed good dispersion of graphene and graphene oxide, while boron carbide formed large agglomerates; B 4 C also presented feeding issues due to its hardness which affected its printability. Dispersion of the additives was also confirmed by studying their X-ray diffraction (XRD) patterns, and chemical structures were assessed using FT-IR spectroscopy. Finally, parts were printed using selected composite filaments, and their porosity and surface roughness were compared with neat PEKK and commercial CNT-reinforced PEKK to develop an understanding of metrology and bulk material properties of the composites.

This study investigates reentry conditions for Mars missions, focusing on extreme anaerobic heating. This work studies poly(ether ketone ketone) (PEKK), a high-performance thermoplastics polymer, in both small-scale laboratory and simulated oxyacetylene test bed conditions to eliminate low-performing polymeric materials. Previous research demonstrated PEKK's superior ablation performance compared to poly(ether ether ketone) (PEEK) and polyetherimide. The aerothermal performance of neat PEKK can be further enhanced with reinforcement materials. This work explores PEKK composite materials reinforced with additives such as carbon nanotubes (CNTs), carbon fibers (CFs), and glass fibers (GFs). The CNT-reinforced (10%wt) PEKK exhibited the highest char yield (69%wt) during thermogravimetric analysis (TGA) in nitrogen, superior to the short CF-reinforced PEKK. Various CF and GF loadings (10% and 20%wt) were tested for their thermophysical and aerothermal performance. Oxyacetylene tests (OTBs) under fuel-rich conditions further validated the results. Except for 10% CF PEEK, the mass loss in OTB tests correlated with TGA and thermal diffusivity measurements. The addition of CF/GF in PEKK enhanced thermal effusivity, but it also led to significant swelling due to increased conductive flux and reduced ablated heat flux. Among the tested materials, CNT-reinforced PEKK displayed the highest char yield, lowest mass loss, and minimal swelling. The unique porous structure of CNTs minimized char expansion and erosion during the OTB tests, making a promising material for reentry flights.

Thermoplastic polyimides (TPIs) are promising lightweight materials for replacing metal components in aerospace, rocketry, and automotive industries. Key TPI attributes include low density, thermal stability, mechanical strength, inherent flame retardancy, and intrinsic fluorescence under UV light. The application of advanced manufacturing techniques, especially 3D printing, could significantly broaden the use of TPIs; however, challenges in melt-processing this class of polymer represent a barrier. This study explored the processability, 3D-printing and hence mechanical, and fluorescence properties of TPI coupons, demonstrating their suitability for advanced 3D-printing applications. Moreover, the study successfully 3D-printed a functional impeller for an overhead stirrer, effectively replacing its metallic counterpart. Defects were shown to be readily detectable under UV light. A thorough analysis of TPI processing examining its rheological, morphological, and thermal properties is presented. Extruded TPI filaments were 3D-printed into test coupons with different infill geometries to examine the effect of tool path on mechanical performance. The fluorescence properties of the 3D-printed TPI coupons were evaluated to highlight their potential to produce intricately shaped thermally stable, fluorescence-based sensors.

For the first time in the literature, this study validates the absorption phenomena in Multi-Jet Fusion (MJF) printed polypropylene (PP) structures through Laser Flash (LFA) and Corrected Porosity (CP) methods. The influence of process parameters such as build height and build orientation was investigated on tensile properties, crystallinity, porosity and thermophysical attributes in MJF printed PP coupons. Results showed that both crystallinity and tensile performance did not significantly vary with either location or build orientation. Interestingly, samples printed in the Z orientation showed a 35% decrease in strain, indicating that Z-oriented MJF coupons were more brittle than the flat samples (XY). Samples printed in Z orientation also possessed higher porosity and relatively lower crystallinity than the XY orientation. However, large deviations within porosity values were an obstacle to determining a suitable build chamber location for manufacturing dense samples. Therefore, a detailed investigation on porosity of printed samples using micro-CT scans and CT image analysis was necessary. Initially, poor contrast was obvious when MJF printed samples were positioned vertically in the micro-CT chamber which was mainly due to high value of horizontal intensity profile (HIP ~ 70%). Contrast in MJF samples improved significantly in the horizontal orientation (HIP ~ 40%). In parallel, the half-time and heat loss were measured in LFA to understand changes in absorption phenomena with height and orientation of the build. A direct correlation was found between LFA half-time and porosity only when the porosity correction method was implemented. Corrected porosity value was found to be inversely proportional to the heat loss of printed PP samples which indicated higher absorption for samples printed in the bottom of build chamber, XY12, whereas lower absorption was observed for less dense Z samples. Finally, heat loss phenomenon was verified using dense reference Pyroceram samples as they possess high diffusivity and low half-time and porosity compared to MJF printed samples. There is a science behind understanding the absorptivity of the MJF process which is related to the complexity of the process and is challenging to address in MJF PP samples when mixed with carbon black. The study showed that accurately determining the level of porosity is the key to validate absorption phenomena within MJF printed coupons. The contributions of this work are the investigation of the light absorption phenomena in MJF printed PP structures, and the establishment of the absorption-porosity correlation. These contributions help to predict the mechanical properties and subsequently the overall quality of the produced parts which can save cost and time in effectively utilising the MJF process.

The development of structural epoxy adhesives with the capacity to bond and de-bond on-demand would open many opportunities for the assembly, inspection, repair, and end of life disposal of structural bonded assemblies. Herein, a reversible cross-linking mechanism enabling bonding and debonding of an epoxy adhesive based on Diels-Alder (DA) chemistry is investigated and demonstrated. The Diels-Alder incorporated multifunctional diamine cross-linker was initially synthesised, followed by forming a covalently cross-linked network with DGEBA epoxy at low temperature (80 degrees C) that breaks via cleavage of DA adducts at elevated temperature (150 degrees C). Upon cooling the covalent cross-links reform enabling the epoxy to retain adhesive properties, and the bonding/de-bonding effect was performed over two complete cycles advancing a thermally reversible adhesive based on the retro-DA mechanism. The viscoelastic properties of the prototype adhesive including viscosity, storage and loss modulus were retained after bonding and de-bonding cycles, affirming retro-DA reaction occurs at about 150 degrees C upon heating cycle and DA reaction upon cooling cycle. Mechanical testing demonstrates maximum of 39.5% reduction in bond strength in debonding cycle, followed by maximum of 100% bond strength in re-bonding cycle with no additional application of the prototype adhesive, revealing excellent adhesive performance.

3D printing of poly(lactic acid) (PLA) blends has been attempted to resolve issues such as inherent brittleness and slow crystallization rate of PLA. However, a persistent challenge remains in the form of phase separation or gradual migration of the blended soft polymer or plasticizers. To simultaneously enhance the miscibility of the blends and toughness of 3D-printed parts, a triblock copolymer PLA-PEG-PLA was synthesized and blended with PLA in varying proportions (5, 10, 15, and 20 wt %). Blending only 10-20 wt % low molecular weight PLA-PEG-PLA into PLA yielded a miscible blend that showed a 45-fold increase in elongation at break and a 23-fold enhancement in toughness over neat PLA. Scanning electron microscopy (SEM) images of fractured cross sections revealed a brittle to ductile transition in 3D-printed PLA/PLA-PEG-PLA samples. Isothermal crystallization studies and data analysis using the Avrami equation showed an enhancement in the crystal growth rate and overall rate of crystallization. The blends achieved half of their crystallinity in approximately 3 min, a significant improvement over the 9 min required by PLA alone. This underscores the efficiency of our approach. This was also evident in the spherulite growth of 3D-printed PLA and mPLA blends when examined using polarized optical microscopy (POM). To the best of our knowledge, this is the first report exploring the use of blends that include PLA and low molecular weight PLA-PEG-PLA triblock copolymers for 3D printing applications.

Powder bed fusion (PBF) is an important additive manufacturing (AM) technology that is widely implemented to rapidly fabricate high-precision metallic, polymeric, ceramic, and composite components. The build time for PBF-based manufacture, however, remains extensive. To address this issue, recently high-speed sintering PBF processes, such as HP’s Multi-Jet Fusion (MJF™) technology, were developed to produce polymeric components with much higher throughput. The crystallinity and mechanical properties of components fabricated with MJF™ and other PBF technologies will depend on both process parameters and thermoplastic polymer solidification and crystallization properties. In this research, a new mathematical model has been developed to estimate the crystallinity of semicrystalline polypropylene based on MJF™ process parameters. The proposed predictive model for the crystallinity is a function of the temperature of the process and subsequently the process parameters such as tool power, tool speed, and the scanning area. In addition, an empirical model is also described, which links the crystallinity to the tensile properties of the printed structures quantitatively. The model was validated by the experimental results from mechanical testing and differential scanning calorimetry (DSC). The results from this study demonstrate the precision of the proposed model in predicting both the crystallinity and mechanical attributes of MJF™-printed polymeric materials, which can be used to accelerate design and process optimization for AM production and elevate its acceptance and integration in mainstream engineering.

Multi Jet Fusion (MJF) is a high-speed Powder Bed Fusion (PBF) process that stands to revolutionize the production rate of polymeric Additive Manufacturing (AM). In this review, MJF operational concepts are explained and powder feedstock features including morphology, flowability, molecular weight and the selectively deposited liquid agents are discussed. The mechanical properties of MJF polymeric parts are compared with those from Partial-Liquid Powder Bed Fusion which has the trademark of Selective Laser Sintering (SLS), which shares common elements with MJF, namely powder bed fusion in the semi-solid state. The manufacturability of MJF with regards to surface quality and dimensional accuracy is presented, and finally, industrial applications are reported to demonstrate the capability of MJF for part production in diverse industrial applications. The discussion highlights the opportunity for MJF to fabricate polymeric components with mechanical properties comparable to SLS, with the additional benefit of one of the highest production rates and lowest energy requirements in the entire AM landscape.

Entropy-Driven Ring-Opening Polymerisation represents an attractive mechanism to produce high-performance polymeric materials as it can be performed using neat, low-viscosity precursors and without the production of by-products or release of volatiles. Macrocyclic oligomers (MCOs) of polyether ketone ketone (PEKK) were synthesised and investigated as an in situ method of forming this high-performance thermoplastic. Cyclic oligomers were successfully synthesised by pseudo-high dilution methods, and the reaction conditions were optimised through careful addition of starting materials and carbonate base selection. These novel compounds were characterised, X-ray crystal structures were obtained, and the synthesis method was extended from the homopolymers to MCOs with the structural isomers predominantly used in industry. PEKK formed from MCOs were characterised by DSC, TGA and GPC and found to have similar glass transitions and molecular weight averages to those of a commercial PEKK polymer.

Polyether ketone ketone (PEKK) is a high-performance thermoplastic used in the fused filament fabrication (FFF) process to manufacture end use parts for the biomedical and aerospace industries. While other high-performance polymers such as polyetherimide (PEI) and polyether ether ketone (PEEK) have been studied extensively in literature, minimal studies have investigated the effects of FFF process parameters on PEKK. Tensile properties of FFF-printed PEKK was most affected by build orientation followed by number of contours in our previous study, although effects of build orientation on various properties of materials have been examined extensively, only few studies focused on number of contours. This study aims to understand if the selected parameters from our previous study affect other properties of PEKK, and if employing more contours can further improve these properties. A Taguchi orthogonal array varying contours in 4 levels and all other factors in 2 levels were used for this study. Optimum process parameters that maximize properties including compressive, flexural, thermomechanical, dynamic mechanical, and surface roughness were determined, and samples were printed using those settings to verify the statistical model. For the first time in literature, analysis was performed to understand if process parameters affected porosity and that, in turn, influenced mechanical properties. Comparison of flexural properties with injection-molded counterparts revealed that through optimization of process parameters, even the cost-effective printers used in this study could produce parts with properties almost equal to injection-molded parts in the direction of measurement. In addition, a coefficient of linear thermal expansion varied significantly with changes in process parameters and the variation was attributed mostly to porosity within samples and alignment of rasters with the direction of measurement. A clear relationship between number of contours, porosity, and mechanical properties was observed for most responses. Overall, number of contours was the most significant process parameter as more contours reduced porosity and improved mechanical and dynamic mechanical properties.

The transition of additive manufacturing (AM) from a technique for rapid prototyping to one for manufacturing of near net or net components has been led by the development of methods that can repeatedly fabricate quality parts. High-speed laser sintering and the recently developed multi-jet fusion (MJF) processes have seen quick adoption from industry due to their ability to produce high-quality components relatively quickly. However, the recommended refresh ratios of new powder led to notable amounts of used powder being discarded. In this research, polyamide-11 powder, typically used in AM, was thermally aged to investigate its properties at extreme levels of reuse. The powder was exposed to 180 °C in air for up to 168 h and its chemical, morphological, thermal, rheological, and mechanical properties were examined. To decouple the thermo-oxidative aging phenomena from AM process related effects, such as porosity, rheological and mechanical properties characterisation was performed on compression-moulded specimens. It was found that exposure notably affected the properties of both the powder and the derived compression-moulded specimens within the first 24 h of exposure; however, consecutive exposure did not have a significant effect.