This study explores the influence of mold temperatures below 60°C on thermoplastic polyurethane (TPU) properties during injection molding, focusing on phase separation and its impact on mechanical, ...thermal, and viscoelastic properties. Using a combination of micro‐indentation, temperature scanning stress relaxation, and conventional characterization methods, the research highlights how increased mold temperatures promote more distinct phase separation, enhancing mechanical stability and physical properties. The novel use of micro‐indentation revealed a gradient in material stiffness from the surface to the core of injection‐molded samples, attributed to differential cooling rates and shear forces, which affect phase separation and crystallinity of the hard domains. These insights are critical for applications requiring specific surface properties and underscore the importance of understanding the interplay between chemical composition and processing conditions for optimizing TPU properties. Furthermore, the paper shows that tensile testing, differential scanning calorimetry, and Shore hardness cannot quantify the effects of mold temperatures below 60°C. The research highlights the influence and importance of chemical composition, rheological history, and thermal history on the properties of TPU.
Micro Indentation, Temperature Scanning Stress Relaxation, and Dynamic Mechanical Analysis, among other techniques, were used to characterize the differences in local and macro properties of TPU injection molded at 20°C and 60°C.
Metal-supported oxide cells (MSCs) are considered as the third-generation solid oxide cells (SOCs) succeeding electrolyte-supported (first generation) and anode-supported (second generation) cells, ...which have gained much attention and progress in the past decade. The use of metal supports and advanced technical methods (such as infiltrated electrodes) has vastly improved cell performance, especially with its rapid startup ability and power density, showing a significant decrease in raw materials cost. However, new degradation mechanisms appeared, limiting the further improvement of the performance and lifetime. This review encapsulates the degradation mechanisms and countermeasures in the field of MSCs, reviewing the challenges and recommendations for future development.
There is a growing interest for integrating additive manufacturing (AM) technology in different manufacturing processes such as injection moulding (IM) due to the possibility of achieving shorter ...manufacturing times and increased cost effectiveness. This paper evaluates IM inserts fabricated by the AM vat photopolymerisation method. The inserts are directly manufactured with a photopolymer material, integrated on an injection moulding tool and subsequently used for IM. Therefore, particular attention has to be paid in order to develop the soft tooling process chain and the IM experimental procedure as detailed in this study. Different combinations of IM parameters are investigated in this work in order to determine the influence of the various process settings on the inserts’ performance (lifetime, crack propagation, consistency of the mould surface features). The mould inserts were analysed by three-dimensional optical metrology and evaluated with regard to the different surface features that were affected by the IM process. A three-dimensional thermo-mechanical with phase change model for the analysis of the effects of the IM process on the additive manufactured tools was accomplished in the FE software COMSOL Multiphysics. The potential causes for the insert failure are identified both by means of the IM experiments and the numerical model. The developed model could also predict the thermally induced deformations produced in the mould and identify where this phenomenon would eventually lead to defects in the shape of the parts. The influence of three different temperatures of the insert at 25 °C, 50 °C and 100 °C on the failure of the insert was investigated. Also a detailed discussion about the solidification and temperature changes is given.
This work presents an Additive Manufacturing (AM) based method for production of components with micro-structured surfaces. Vat photopolymerization was used for the experiments by an AM custom-build ...machine at the Technical University of Denmark (DTU). Components with micro holes were printed in different sizes and the uniformity of them analyzed. Subsequently, in order to assess the functionality of the surface, the water droplet contact angle was measured to evaluate the wettability of the different components with micro holes. It was found that it was possible to fabricate the components with micro holes using precision AM process. The printed substrate exhibited hydrophobicity as a hydrophilic material (intrinsic contact angle of 65°). A hydrophobic surface was achieved with the printed features exhibiting a maximum contact angle of 113°. Additionally, the volume of fluid (VOF) method was employed to predict the surface contact angle. The predicted results were validated by comparison against the experiments. The average value from experiments was predicted by the model. However, it was noted that the cross-sectional height profile of the structures and the surface roughness of the printed samples, were not precisely replicated as designed, which slightly affects the prediction results, though, similar prediction trend was observed.
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•Direct fabrication of the components with micro structured surfaces by digital light processing method.•Digital Light Processing method was pushed to its limit for fabrication of the components with micro holes.•Measurement of the components with micro holes present uniformity of the print in different areas of the structure.•The printed substrate realized hydrophobicity on the hydrophilic materials (intrinsic contact angle of 65°).•3D dynamic impact behavior simulation for contact angle prediction was used to estimate wettability of the surface.
Selective laser sintering (SLS) is a well-established technology that is used for additive manufacturing. Significant efforts have been made to improve SLS by optimizing the powder deposition, laser ...beam parameters, and temperature settings. The purpose is to ensure homogeneous sintering and prevent geometric and appearance inaccuracies in the manufactured objects. We evaluated the differences in the surface roughness and grain size of curved objects manufactured by using upcoming SLS technology that features two CO laser sources. Our analysis was carried out on polyamide 11 (PA11), which is a sustainable biobased polymer that has been gaining popularity due to its high-performance properties: its low melting point, high viscosity, and excellent mechanical properties. By using a Taguchi experimental design and analysis of variance (ANOVA), we examined the influence on the surface roughness and grain size of the build setup, the presence of thin walls, and the position of the sample on the powder bed. We found significant differences in some surface roughness and grain size measurements when these parameters were changed.
Purpose
The purpose of this paper is to evaluate the influence of layer thickness and post-curing temperature on shape memory properties in components manufactured by stereolithography.
...Design/methodology/approach
Layer thicknesses of 20 and 100 µm and 22 and 45°C for post-curing temperature were selected following the design of experiments approach. Tensile and bending tests were applied for quantitative evaluation of the shape memory effect (SME). Qualitative analysis was performed using complex geometries and computed tomography as a measurement tool. Additionally, the degree of photopolymerization and glass transition temperature (Tg) were evaluated.
Findings
The tensile test resulted in fixity and recovery ratio values close to 100%. In bending, they varied between 97%–111% for fixity and 88%–95% for recovery. The layer thickness was found to have a higher influence on the SME. In complex structures, SME was dependent on geometry and less sensitive to variation in process parameters. The post-curing temperature had a higher influence on the photopolymerization and Tg. Average Tg of 77.5°C was achieved at 45°C, compared to 73.1°C at 22°C.
Originality/value
In the current state of the art in the processing of shape memory polymers with vat photopolymerization typically, the chemical composition or the thermal and deformation patterns are studied. The effect of the processing parameters is, however, not explored. This paper aims to close the research gap and facilitate the process optimization towards high fixing and recovery characteristics.
Herein, 440C martensitic stainless steel (440C MSS) is manufactured by spray forming (SF) technology. Microstructural and mechanical properties such as strength, ductility, and toughness are ...evaluated after quenching and tempering–partitioning (Q–TP) and quenching–intercritical–quenching–tempering (Q–IQ–T) heat treatments. The microstructural features that control the deformation and fracture behavior of the heat‐treated specimens are discussed. The experimental results show that after austenitizing at 1050 °C, the material exhibits no apparent plastic deformation before fracture. However, specimens austenitized above 1050 °C and the specimen subjected to Q–IQ–T exhibit an improvement in the tensile properties by showing an elastic–plastic transition that is related to the strain‐induced martensitic transformation of retained austenite formed during the Q–TP process and to a decrease in the volume fraction of martensite with increasing austenitizing temperature. Also, it is observed that the strain hardening rate decreases with increasing austenitizing temperature. Furthermore, the stress–strain data suggest that the Q–IQ–T heat treatment effectively improves the toughness and ductility of the steel without compromising strength. The results indicate that the mechanical response of the SF‐440C MSS can be tailored by adjusting the heat treatment parameters to enable better design for industrial applications.
The microstructure and mechanical properties of spray‐formed 440C steel are analyzed in detail. The results indicate that the martensite–austenite ratio greatly influences the strength–ductility of the steel. Higher austenitizing temperatures promote an increase in the volume fraction of retained austenite, improving the ductility of the steel by promoting the strain‐induced transformation of austenite into martensite.
In-situ co-axial meltpool monitoring has become a popular tool for digitising the laser powder bed fusion (L-PBF) process , providing baseline data for certification. Each layer produces an image ...where the pixel position represents the laser coordinates and the pixel intensity denotes the sensor response. The 3D image stacks represent the infrared emission during the manufacturing of the physical component. However, interpreting monitoring data remains a challenge. To address this issue, this study evaluates the performance of a near-infrared photodiode in detecting typical geometrical features such as porosity and overhanging structures ranging from the micro-to-meso scale. Monitoring data is highly sensitive to heat accumulation around overhanging structures and can quantify dross formation based on hotspots. Cold spots, which represent a lack of fusion porosity at scan track intersections, can indicate a probability of defect formation. However, the sensitivity and predictive value of monitoring data for porosity are low due to the healing of defects in subsequent layers. Local process variables, such as the scan strategy and part orientation, significantly influence dross and hot spot formation. This study shows the potential of NIR photodiodes in deriving metrics for in-line certification of L-PBF components, leading to improved process control and quality assurance.
In extrusion-based additive manufacturing, achieving high surface quality typically involves using small layer heights to reduce the size of grooves between layers. However, this approach can be both ...less effective and time-consuming in big-area additive manufacturing. Therefore, the current focus is on investigating methods for printing with fewer layers without compromising surface quality. In this study, single-strand walls were printed using a two-component thermoset material, where different nozzle designs and printing strategies are explored to achieve the flattest possible surface. The success of each approach was evaluated by measuring the percentage of material that required removal to achieve a perfect vertical flat wall. The results suggested that incorporating vertical wings to contain the material in the desired shape was beneficial. Furthermore, the study introduced the idea of adjustable layer heights to mitigate layer deformation. This deformation is most noticeable in the initial layers but largely affects all subsequent printed layers. Finally, making the wings have an angle with regard to the printing direction or trapezoidal wings, served as a pressure funnel that produced the greatest improvement in surface quality. These changes allowed for a reduction of the amount of material which would need to be removed to achieve a flat wall without grooves from 14.3% for a standard print from a round nozzle, to 2.5% for an optimized strand. The research shows a promising path to producing entirely flat vertical structures, even when printing with still-deformable, thermoset materials in the context of big-area additive manufacturing.
•Wet-on-wet 2-component thermoset big area additive manufacturing.•Achieving vertical flat surfaces without visible grooves between layers.•Effect of nozzle design and optional trowel system on extrudate shape.•Numerical simulations used to predict deformations and effective gap in experiments.•Optimization of printing parameters including extrusion velocity and vertical toolpath.
Additive manufacturing of thermoplastic conductive polymer composites offers interesting opportunities for customizing compliant flexural sensors. The study aimed to show that additive manufacturing ...could be used to fabricate flexural sensors for evaluating the effect of sensor geometry on the sensor output. Prior literature has primarily focused on material optimization rather than geometrical design. The results of this paper show that the signal amplitude between geometrically different flexural sensors with the same footprint can increase ∼28 times. In addition, the bending force is found proportional to the signal amplitude. Thus, concentrating the bending to a small section increases the signal amplitude but also increases the effect of material relaxation broadening the hysteresis loop. This study highlights the importance of considering the geometrical design when fine-tuning additive manufactured flexural sensors. In future work, it is paramount to improve reproducibility, signal linearity, and investigate the effects of geometry on other sensor parameters.
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